U.S. patent application number 17/513398 was filed with the patent office on 2022-02-17 for -led, -led device, display and method for the same.
The applicant listed for this patent is OSRAM Opto Semiconductors GmbH. Invention is credited to Peter BRICK, Jean-Jacques DROLET, Hubert HALBRITTER, Laura KREINER, Thomas SCHWARZ, Julia STOLZ.
Application Number | 20220052027 17/513398 |
Document ID | / |
Family ID | |
Filed Date | 2022-02-17 |
United States Patent
Application |
20220052027 |
Kind Code |
A1 |
BRICK; Peter ; et
al. |
February 17, 2022 |
-LED, -LED DEVICE, DISPLAY AND METHOD FOR THE SAME
Abstract
Disclosed are various aspects of a .mu.-LED or a .mu.-LED array
for augmented reality or lighting applications, in particular in
the automotive field. The .mu.-LED is characterized by particularly
small dimensions in the range of a few .mu.m.
Inventors: |
BRICK; Peter; (Regensburg,
DE) ; DROLET; Jean-Jacques; (Obertraubling, DE)
; HALBRITTER; Hubert; (Dietfurt-Toeging, DE) ;
KREINER; Laura; (Regensburg, DE) ; SCHWARZ;
Thomas; (Regensburg, DE) ; STOLZ; Julia;
(Regensburg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OSRAM Opto Semiconductors GmbH |
Regensburg |
|
DE |
|
|
Appl. No.: |
17/513398 |
Filed: |
October 28, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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17039097 |
Sep 30, 2020 |
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17513398 |
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PCT/EP2020/052191 |
Jan 29, 2020 |
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17039097 |
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International
Class: |
H01L 25/075 20060101
H01L025/075; H01L 33/60 20060101 H01L033/60; H01L 33/50 20060101
H01L033/50; H01L 33/24 20060101 H01L033/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 2019 |
DK |
201970059 |
Apr 23, 2019 |
DE |
10 2019 110 499.8 |
May 14, 2019 |
DE |
10 2019 112 616.9 |
May 14, 2019 |
DE |
10 2019 112 639.8 |
Jun 12, 2019 |
DE |
10 2019 115 991.1 |
Jun 14, 2019 |
DE |
10 2019 116 313.7 |
Jul 5, 2019 |
DE |
10 2019 118 251.4 |
Claims
1. A method for producing a .mu.-LED, comprising: creating an
out-coupling structure in a surface region of a semiconductor body
providing an active layer of the .mu.-LED by structuring a surface
area by generating a random topology at the surface area; and
planarizing the surface area to obtain a planarized surface of the
surface area; wherein generating the random topology comprises
layer-by-layer applying of a transparent second material having a
high refractive index greater than 2 to the surface region and
roughening the transparent second material.
2. The method according to claim 1, wherein structuring the surface
area comprises: roughening a surface of the surface region of the
semiconductor body comprising a first material.
3. The method according to claim 2, wherein the transparent second
material with the high refractive index comprises
Nb.sub.2O.sub.5.
4. The method according to claim 1, wherein planarizing comprises:
applying, layer-by-layer, a transparent third material having a low
refractive index less than 1.5 to the surface region.
5. The method according to claim 4, further comprising: thinning
the transparent third material of the low refractive index until a
surface of the surface region terminates flat and/or smooth with
highest elevations in a first material of the semiconductor body or
in the transparent second material of the high refractive
index.
6. The method according to claim 4, wherein the transparent third
material having the low refractive index comprises SiO.sub.2 and is
applied by TEOS (tetraethylorthosilicate).
7. A .mu.-LED device, comprising: an out-coupling structure formed
in a surface region of a semiconductor body providing the .mu.-LED
device by structuring of the surface region; wherein the surface
region is planarized to obtain a planarized surface of the surface
region; and wherein the out-coupling structure comprises a
transparent third material of low refractive index comprising
SiO.sub.2, on a roughened transparent second material of high
refractive index comprising Nb.sub.2O.sub.5, the roughened
transparent second material being attached to a first material of
the semiconductor body of the .mu.-LED device.
8. The .mu.-LED device according to claim 7, wherein the surface
region comprises a roughness less than 1 nanometre, as a mean
roughness value.
9. The .mu.-LED device according to claim 7, wherein the
out-coupling structure comprises the transparent third material
with the low refractive index comprising SiO.sub.2, on a roughened
first material of the semiconductor body of the .mu.-LED
device.
10. The .mu.-LED device according to claim 7, wherein the
out-coupling structure comprises the transparent third material of
the low refractive index comprising SiO.sub.2, on a transparent
second material of a high refractive index, the transparent second
material being attached to the first material of the semiconductor
body of the .mu.-LED device and comprising periodic photonic
crystals or quasi-periodic or deterministic aperiodic photonic
structures.
11. A .mu.-LED arrangement for generating a pixel of a display,
comprising: a flat carrier substrate; and at least three .mu.-LEDs
arranged on a mounting side of the flat carrier substrate, wherein
the at least three .mu.-LEDs are adapted to emit light of different
color transverse to a carrier substrate plane in a direction away
from the flat carrier substrate; a flat reflector element spatially
arranged on an assembly side relative to the at least three
.mu.-LEDs and configured to reflect light emitted by the at least
three .mu.-LEDs in the direction of the flat carrier substrate;
wherein the flat carrier substrate is at least partially
transparent so that light reflected from the flat reflector element
propagates through the flat carrier substrate and emerges at a
display side of the flat carrier substrate opposite the mounting
side; wherein a photonic structure is incorporated in or on the
flat carrier substrate, with first and second regions with
different refractive indexes, whereas converter material forms one
of the first and second regions and is configured in such a way
that radiation is emitted as a directed beam of rays.
Description
[0001] This patent application is a continuation of U.S.
application Ser. No. 17/039,097 filed Sep. 30, 2020, which claims
the priorities of the German applications DE 10 2019 116 313.7 of
14 Jun. 2019, DE 10 2019 118 251.4 of 5 Jul. 2019, DE 10 2019 112
616.9 of 14 May 2019, DE 10 2019 110 499.8 of 23 Apr. 2019, DE 10
2019 112 639.8 of 14 May 2019, DE 10 2019 115 991.1 of 12 Jun.
2019, as well as the priority of the Danish application DK
PA201970059 of 29 Jan. 2019, the disclosure of which are
incorporated herein by way of reference. Finally, this application
also claims priority from the PCT application PCT/EP2020/052191 of
29 Jan. 2020. The disclosure of PCT/EP2020/052191 is incorporated
herein by reference in its entirety. Additionally, this patent
application is related to the following co-pending patent
applications: U.S. application Ser. No. 17/038,283, entitled
".mu.-LED, .mu.-LED Device, Display and Method for the Same," filed
Sep. 30, 2020; U.S. application Ser. No. 17/039,283, entitled
".mu.-LED, .mu.-LED Device, Display and Method for the Same," filed
Sep. 30, 2020; U.S. application Ser. No. 17/039,482, entitled
".mu.-LED, .mu.-LED Device, Display and Method for the Same," filed
Sep. 30, 2020; U.S. application Ser. No. 17/475,030, entitled
".mu.-LED, .mu.-LED Device, Display and Method for the Same," filed
Sep. 14, 2021; U.S. application Ser. No. 17/474,975, entitled
".mu.-LED, .mu.-LED Device, Display and Method for the Same," filed
Sep. 14, 2021; U.S. application Ser. No. 17/510,907, entitled
".mu.-LED, .mu.-LED Device, Display and Method for the Same," filed
Oct. 26, 2021; U.S. application Ser. No. ______ (Ref.
OS01P201WOC3USC3), entitled ".mu.-LED, .mu.-LED Device, Display and
Method for the Same," filed Oct. 28, 2021; and U.S. application
Ser. No. ______ (Ref. OS01P201WOC3USC2), entitled ".mu.-LED,
.mu.-LED Device, Display and Method for the Same," filed Oct. 28,
2021.
BACKGROUND
[0002] The ongoing current developments within the Internet of
Things and the field of communication have opened the door for
various new applications and concepts. For development, service and
manufacturing purposes, these concepts and applications offer
increased effectiveness and efficiency.
[0003] One aspect of new concepts is based on augmented or virtual
reality. A general definition of "augmented reality" is given by an
"interactive experience of the real environment, whereby the
objects from it, which are in the real world, are augmented by
computer generated perceptible information".
[0004] The information is mostly transported by visualization, but
is not limited to visual perception. Sometimes haptic or other
sensory perceptions can be used to expand reality. In the case of
visualization, the superimposed sensory-visual information can be
constructive, i.e. additional to the natural environment, or it can
be destructive, for example by obscuring parts of the natural
environment. In some applications, it is also possible to interact
with the superimposed sensory information in one way or another. In
this way, augmented reality reinforces the ongoing perception of
the user of the real environment.
[0005] In contrast, "virtual reality" completely replaces the real
environment of the user with an environment that is completely
simulated. In other words, while in an augmented reality
environment the user is able to perceive the real world at least
partially, in a virtual reality the environment is completely
simulated and may differ significantly from reality.
[0006] Augmented Reality can be used to improve natural
environmental situations, enriching the user's experience or
supporting the user in performing certain tasks. For example, a
user may use a display with augmented reality features to assist
him in performing certain tasks. Because information about a real
object is superimposed to provide clues to the user, the user is
supported with additional information, allowing the user to act
more quickly, safely and effectively during manufacturing, repair
or other services. In the medical field, augmented reality can be
used to guide and support the doctor in diagnosing and treating the
patient. In development, an engineer may experience the results of
his experiments directly and can therefore evaluate the results
more easily. In the tourism or event industry, augmented reality
can provide a user with additional information about sights,
history, and the like. Augmented Reality can support the learning
of activities or tasks.
SUMMARY
[0007] In the following summary different aspects for .mu.-displays
in the automotive and augmented reality applications are explained.
This includes devices, displays, controls, process engineering
methods and other aspects suitable for augmented reality and
automotive applications. This includes aspects which are directed
to light generation by means of displays, indicators or similar. In
addition, control circuits, power supplies and aspects of light
extraction, light guidance and focusing as well as applications of
such devices are listed and explained by means of various
examples.
[0008] Because of the various limitations and challenges posed by
the small size of the light-generating components, a combination of
the various aspects is not only advantageous, but often necessary.
For ease of reference, this disclosure is divided into several
sections with similar topics. However, this should explicitly not
be understood to mean that features from one topic can not be
combined with others. Rather, aspects from different topics should
be combined to create a display for augmented reality or other
applications or even in the automotive sector.
[0009] For considerations of the following solutions, some terms
and expressions should be explained in order to define a common and
equal understanding. The terms listed are generally used with this
understanding in this document. In individual cases, however, there
may be deviations from the interpretation, whereby such deviation
will be specifically referred to.
[0010] "Active Matrix Display"
[0011] The term "active matrix display" was originally used for
liquid crystal displays containing a matrix of thin film
transistors that drive LCD pixels. Each individual pixel has a
circuit with active components (usually transistors) and power
supply connections. At present, however, this technology should not
be limited to liquid crystals, but should also be used in
particular for driving .mu.-LEDs or .mu.-displays.
[0012] "Active Matrix Carrier Substrate"
[0013] "Active matrix carrier substrate" or "active matrix
backplane" means a drive for light emitting diodes of a display
with thin-film transistor circuits. The circuits may be integrated
into the backplane or mounted on it. The "active matrix carrier
substrate" has one or more interface contacts, which form an
electrical connection to a .mu.-LED display structure. An
"active-matrix carrier substrate" can thus be part of an
active-matrix display or support it.
[0014] "Active Layer"
[0015] The active layer is referred to as the layer in an
optoelectronic component or light emitting diode in which charge
carriers recombine. In its simplest form, the active layer can be
characterized by a region of two adjacent semiconductor layers of
different conductivity type. More complex active layers comprise
quantum wells (see there), multi-quantum wells or other structures
that have additional properties. Similarly, the structure and
material systems can be used to adjust the band gap (see there) in
the active layer, which determines the wavelength and thus the
color of the light.
[0016] "Alvarez Lens Array"
[0017] With the use of Alvarez lens pairs, a beam path can be
adapted to video eyewear. An adjustment optic comprises an Alvarez
lens arrangement, in particular a rotatable version with a Moire
lens arrangement. Here, the beam deflection is determined by the
first derivative of the respective phase plate relief, which is
approximated, for example, by z=ax2+by2+cx+dy+e for the
transmission direction z and the transverse directions x and y, and
by the offset of the two phase plates arranged in pairs in the
transverse directions x and y. For further design alternatives,
swivelling prisms are provided in the adjustment optics.
[0018] "Augmented Reality (AR)"
[0019] This is an interactive experience of the real environment,
where the subject of the picking up is located in the real world
and is enhanced by computer-generated perceptible information.
Extended reality is the computer-aided extension of the perception
of reality by means of this computer-generated perceptible
information. The information can address all human sensory
modalities. Often, however, augmented reality is only understood to
be the visual representation of information, i.e. the
supplementation of images or videos with computer-generated
additional information or virtual objects by means of
fade-in/overlay. Applications and explanations of the mode of
operation of Augmented Reality can be found in the introduction and
in the following in execution examples.
[0020] "Automotive."
[0021] Automotive generally refers to the motor vehicle or
automobile industry. This term should therefore cover this branch,
but also all other branches of industry which include .mu.-displays
or generally light displays--with very high resolution and
.mu.-LEDs.
[0022] "Bandgap"
[0023] Bandgap, also known as band gap or forbidden zone, is the
energetic distance between the valence band and conduction band of
a solid-state body. Its electrical and optical properties are
largely determined by the size of the band gap. The size of the
band gap is usually specified in electron volts (eV). The band gap
is thus also used to differentiate between metals, semiconductors
and insulators. The band gap can be adapted, i.e. changed, by
various measures such as spatial doping, deforming of the crystal
lattice structure or by changing the material systems. Material
systems with so-called direct band gap, i.e. where the maximum of
the valence band and a minimum of the conduction band in the pulse
space are superimposed, allow a recombination of electron-hole
pairs under emission of light.
[0024] "Bragg Grid"
[0025] Fibre Bragg gratings are special optical interference
filters inscribed in optical fibres. Wavelengths that lie within
the filter bandwidth around AB are reflected. In the fiber core of
an optical waveguide, a periodic modulation of the refractive index
is generated by means of various methods. This creates areas with
high and low refractive indexes that reflect light of a certain
wavelength (bandstop). The center wavelength of the filter
bandwidth in single-mode fibers results from the Bragg
condition.
[0026] "Directionality"
[0027] Directionality is the term used to describe the radiation
pattern of a .mu.-LED or other light-emitting device. A high
directionality corresponds to a high directional radiation, or a
small radiation cone. In general, the aim should be to obtain a
high directional radiation so that crosstalk of light into adjacent
pixels is avoided as far as possible. Accordingly, the
light-emitting component has a different brightness depending on
the viewing angle and thus differs from a Lambert emitter.
[0028] The directionality can be changed by mechanical measures or
other measures, for example on the side intended for the emission.
In addition to lenses and the like, this includes photonic crystals
or pillar structures (columnar structures) arranged on the emitting
surface of a pixelated array or on an arrangement of, in
particular, .mu.-LEDs. These generate a virtual band gap that
reduces or prevents the propagation of a light vector along the
emitting surface.
[0029] "Far Field" The terms near field and far field describe
spatial areas around a component emitting an electromagnetic wave,
which differ in their characterization. Usually the space regions
are divided into three areas: reactive near field, transition field
and far field. In the far field, the electromagnetic wave
propagates as a plane wave independent of the radiating
element.
[0030] "Fly Screen Effect"
[0031] The Screen Door Effect (SDE) is a permanently visible image
artefact in digital video projectors. The term fly screen effect
describes the unwanted black space between the individual pixels or
their projected information, which is caused by technical reasons,
and takes the form of a fly screen. This distance is due to the
construction, because between the individual LCD segments run the
conductor paths for control, where light is swallowed and therefore
cannot hit the screen. If small optoelectronic lighting devices and
especially .mu.-LEDs are used or if the distance between individual
light emitting diodes is too great, the resulting low packing
density leads to possibly visible differences between pointy
illuminated and dark areas when viewing a single pixel area. This
so-called fly screen effect (screen door effect) is particularly
noticeable at a short viewing distance and thus especially in
applications such as VR glasses. Sub-pixel structures are usually
perceived and perceived as disturbing when the illumination
difference within a pixel continues periodically across the matrix
arrangement. Accordingly, the fly screen effect in automotive and
augmented reality applications should be avoided as far as
possible.
[0032] "Flip Chip"
[0033] Flip-chip assembly is a process of assembly and connection
technology for contacting unpackaged semiconductor chips by means
of contact bumps, or short "bumps". In flip-chip mounting, the chip
is mounted directly, without any further connecting wires, with the
active contacting side down--towards the substrate/circuit
carrier--via the bumps. This results in particularly small package
dimensions and short conductor lengths. A flip-chip is thus in
particular an electronic semiconductor component contacted on its
rear side. The mounting may also require special transfer
techniques, for example using an auxiliary carrier. The radiation
direction of a flip chip is then usually the side opposite the
contact surfaces.
[0034] "Flip-Flop"
[0035] A flip-flop, often called a bi-stable flip-flop or bi-stable
flip-flop element, is an electronic circuit that has two stable
states of the output signal. The current state depends not only on
the input signals present at the moment, but also on the state that
existed prior to the time under consideration. A dependence on time
does not exist, but only on events. Due to the bi-stability, the
flip-flop can store a data quantity of a single bit for an
unlimited time. In contrast to other types of storage, however,
power supply must be permanently guaranteed. The flip-flop, as the
basic component of sequential circuits, is an indispensable
component of digital technology and thus a fundamental component of
many electronic circuits, from quartz watches to microprocessors.
In particular, as an elementary one-bit memory, it is the basic
element of static memory components for computers. Some designs can
use different types of flip-flops or other buffer circuits to store
state information. Their respective input and output signals are
digital, i.e. they alternate between logical "false" and logical
"true". These values are also known as "low" 0 and "high" 1.
[0036] "Head-Up Display"
[0037] The head-up display is a display system or projection device
that allows users to maintain their head position or viewing
direction by projecting information into their field of vision. The
Head-up Display is an augmented reality system. In some cases, a
Head-Up Display has a sensor to determine the direction of vision
or orientation in space.
[0038] "Horizontal Light Emitting Diode"
[0039] With horizontal LEDs, the electrical connections are on a
common side of the LED. This is often the back of the LED facing
away from the light emission surface. Horizontal LEDs therefore
have contacts that are only formed on one surface side.
[0040] "Interference Filter"
[0041] Interference filters are optical components that use the
effect of interference to filter light according to frequency, i.e.
color for visible light.
[0042] "Collimation"
[0043] In optics, collimation refers to the parallel direction of
divergent light beams. The corresponding lens is called collimator
or convergent lens. A collimated light beam contains a large
proportion of parallel rays and is therefore minimally spread when
it spreads. A use in this sense refers to the spreading of light
emitted by a source. A collimated beam emitted from a surface has a
strong dependence on the angle of radiation. In other words, the
radiance (power per unit of a fixed angle per unit of projected
source area) of a collimated light source changes with increasing
angle. Light can be collimated by a number of methods, for example
by using a special lens placed in front of the light source.
Consequently, collimated light can also be considered as light with
a very high directional dependence.
[0044] "Converter Material"
[0045] Converter material is a material, which is suitable for
converting light of a first wavelength into a second wavelength.
The first wavelength is shorter than the second wavelength. This
includes various stable inorganic as well as organic dyes and
quantum dots. The converter material can be applied and structured
in various processes.
[0046] "Lambert Lamps"
[0047] For many applications, a so-called Lambertian radiation
pattern is required. This means that a light-emitting surface
ideally has a uniform radiation density over its area, resulting in
a vertically circular distribution of radiant intensity. Since the
human eye only evaluates the luminance (luminance is the
photometric equivalent of radiance), such a Lambertian material
appears to be equally bright regardless of the direction of
observation. Especially for curved and flexible display surfaces,
this uniform, angle-independent brightness can be an important
quality factor that is sometimes difficult to achieve with
currently available displays due to their design and LED
technology.
[0048] LEDs and .mu.-LEDs resemble a Lambert spotlight and emit
light in a large spatial angle. Depending on the application,
further measures are taken to improve the radiation characteristics
or to achieve greater directionality (see there).
[0049] "Conductivity Type"
[0050] The term "conductivity type" refers to the majority of (n-
or p-) charge carriers in a given semiconductor material. In other
words, a semiconductor material that is n-doped is considered to be
of n-type conductivity. Accordingly, if a semiconductor material is
n-type, then it is n-doped. The term "active" region in a
semiconductor refers to a border region in a semiconductor between
an n-doped layer and a p-doped layer. In this region, a radiative
recombination of p- and n-type charge carriers takes place. In some
designs, the active region is still structured and includes, for
example, quantum well or quantum dot structures.
[0051] "Light Field Display"
[0052] Virtual retinal display (VNA) or light field display is
referred to a display technology that draws a raster image directly
onto the retina of the eye. The user gets the impression of a
screen floating in front of him. A light field display can be
provided in the form of glasses, whereby a raster image is
projected directly onto the retina of a user's eye. In the virtual
retina display, a direct retinal projection creates an image within
the user's eye. The light field display is an augmented reality
system.
[0053] "Lithography" or "Photolithography"
[0054] Photolithography is one of the central methods of
semiconductor and microsystem technology for the production of
integrated circuits and other products. The image of a photomask is
transferred onto a photosensitive photoresist by means of exposure.
Afterwards, the exposed areas of the photoresist are dissolved
(alternatively, the unexposed areas can be dissolved if the
photoresist is cured under light). This creates a lithographic mask
that allows further processing by chemical and physical processes,
such as applying material to the open areas or etching depressions
in the open areas. Later, the remaining photoresist can also be
removed.
[0055] ".mu.-LED"
[0056] A .mu.-LED is an optoelectronic component whose edge lengths
are less than 70 .mu.m, especially down to less than 20 .mu.m,
especially in the range of 1 .mu.m to 10 .mu.m. Another range is
between 10 to 30 .mu.m. This results in an area of a few hundred
.mu.m.sup.2 down to several tens of .mu.m.sup.2. For example, a
.mu.-LED can comprise an area of about 60 .mu.m.sup.2 with an edge
length of about 8 .mu.m. In some cases, a .mu.-LED has an edge
length of 5 .mu.m or less, resulting in a size of less than 30
.mu.m.sup.2. Typical heights of such .mu.-LEDs are, for example, in
the range of 1.5 .mu.m to 10 .mu.m.
[0057] In addition to classic lighting applications, displays are
the main applications for .mu.-LEDs. The .mu.-LEDs form pixels or
subpixels and emit light of a defined color. Due to their small
pixel size and high density with a small pitch, .mu.-LEDs are
suitable for small monolithic displays for AR applications, among
other things.
[0058] Due to the above-mentioned very small size of a .mu.-LED,
the production and processing is significantly more difficult
compared to previous larger LEDs. The same applies to additional
elements such as contacts, package, lenses etc. Some aspects that
can be realized with larger optoelectronic components cannot be
produced with .mu.-LEDs or only in a different way. In this
respect, a .mu.-LED is therefore significantly different from a
conventional LED, i.e. a light emitting device with an edge length
of 200 .mu.m or more.
[0059] ".mu.-LED Array"
[0060] See at .mu.-Display
[0061] ".mu.-Display"
[0062] A .mu.-display or .mu.-LED array is a matrix with a
plurality of pixels arranged in defined rows and columns. With
regard to its functionality, a .mu.-LED array often forms a matrix
of .mu.-LEDs of the same type and color. Therefore, it rather
provides a lighting surface. The purpose of a .mu.-display, on the
other hand, is to transmit information, which often results in the
demand for different colors or an addressable control for each
individual pixel or subpixel. A .mu.-display can be made up of
several .mu.-LED arrays, which are arranged together on a backplane
or other carrier. Likewise, a .mu.-LED array can also form a
.mu.-Display.
[0063] The size of each pixel is in the order of a few .mu.m,
similar to .mu.-LEDs. Consequently, the overall dimension of a p
display with 1920*1080 pixels with a .mu.-LED size of 5 .mu.m per
pixel and directly adjacent pixels is in the order of a few 10
mm.sup.2. In other words, a .mu.-display or .mu.-LED array is a
small-sized arrangement, which is realized by means of
.mu.-LEDs.
[0064] .mu.-displays or .mu.-LED arrays can be formed from the
same, i.e. from one work piece. The .mu.-LEDs of the .mu.-LED array
can be monolithic. Such .mu.-displays or .mu.-LED arrays are called
monolithic .mu.-LED arrays or .mu.-displays.
[0065] Alternatively, both assemblies can be formed by growing
.mu.-LEDs individually on a substrate and then arranging them
individually or in groups on a carrier at a desired distance from
each other using a so-called Pick & Place process. Such
.mu.-displays or .mu.-LED arrays are called non-monolithic. For
non-monolithic .mu.-displays or .mu.-LED arrays, other distances
between individual .mu.-LEDs are also possible. These distances can
be chosen flexibly depending on the application and design. Thus,
such .mu.-displays or .mu.-LED arrays can also be called
pitch-expanded. In the case of pitch-expanded .mu.-displays or
.mu.-LED arrays, this means that the .mu.-LEDs are arranged at a
greater distance than on the growth substrate when transferred to a
carrier. In a non-monolithic .mu.-display or .mu.-LED array, each
individual pixel can comprise a blue light-emitting .mu.-LED and a
green light-emitting .mu.-LED as well as a red light-emitting
.mu.-LED.
[0066] To take advantage of different advantages of monolithic
.mu.-LED arrays and non-monolithic .mu.-LED arrays in a single
module, monolithic .mu.-LED arrays can be combined with
non-monolithic .mu.-LED arrays in a .mu.-display. Thus,
.mu.-displays can be used to realize different functions or
applications. Such a display is called a hybrid display.
[0067] ".mu.-LED Nano Column"
[0068] A .mu.-LED nano column is generally a stack of semiconductor
layers with an active layer, thus forming a .mu.-LED. The .mu.-LED
nano column has an edge length smaller than the height of the
column. For example, the edge length of a .mu.-LED nanopillar is
approximately 10 nm to 300 nm, while the height of the device can
be in the range of 200 nm to 1 .mu.m or more.
[0069] ".mu.-Rod"
[0070] .mu.-rod or Rod designates in particular a geometric
structure, in particular a rod or bar or generally a longitudinally
extending, for example cylindrical, structure. .mu.-rods are
produced with spatial dimensions in the .mu.m to nanometer range.
Thus, nanorods are also included here.
[0071] "Nanorods"
[0072] In nanotechnology, nanorods are a design of nanoscale
objects. Each of their dimensions is in the range of about 10 nm to
500 nm. They may be synthesized from metal or semiconducting
materials. Aspect ratios (length divided by width) are 3 to 5.
Nanorods are produced by direct chemical synthesis. A combination
of ligands acts as a shape control agent and attaches to different
facets of the nanorod with different strengths. This allows
different shapes of the nanorod with different growth rates to
produce an elongated object. .mu.LED nanopillars are such
nanorods.
[0073] "Miniature LED"
[0074] Their dimensions range from 100 .mu.m to 750 .mu.m,
especially in the range larger than 150 .mu.m.
[0075] "Moire Effect" and "Moire Lens Arrangement"
[0076] The moire effect refers to an apparent coarse raster that is
created by overlaying regular, finer rasters. The resulting
pattern, whose appearance is similar to patterns resulting from
interference, is a special case of the aliasing effect by
subsampling. In the field of signal analysis, aliasing effects are
errors that occur when the signal to be sampled contains frequency
components that are higher than half the sampling frequency. In
image processing and computer graphics, aliasing effects occur when
images are scanned and result in patterns that are not included in
the original image. A moire lens array is a special case of an
Alvarez lens array.
[0077] "Monolithic Construction Element"
[0078] A monolithic construction element is a construction element
made of one piece. A typical such device is for example a
monolithic pixel array, where the array is made of one piece and
the .mu.-LEDs of the array are manufactured together on one
carrier.
[0079] "Optical Mode"
[0080] A mode is the description of certain temporally stationary
properties of a wave. The wave is described as the sum of different
modes. The modes differ in the spatial distribution of the
intensity. The shape of the modes is determined by the boundary
conditions under which the wave propagates. The analysis according
to vibration modes can be applied to both standing and continuous
waves. For electromagnetic waves, such as light, laser and radio
waves, the following types of modes are distinguished: TEM or
transverse electromagnetic mode, TE or H modes, TM or E modes. TEM
or transverse electromagnetic mode: Both the electric and the
magnetic field components are always perpendicular to the direction
of propagation. This mode is only propagation-capable if either two
conductors (equipotential surfaces) insulated from each other are
available, for example in a coaxial cable, or no electrical
conductor is available, for example in gas lasers or optical
fibers. TE or H modes: Only the electric field component is
perpendicular to the direction of propagation, while the magnetic
field component is in the direction of propagation. TM or E modes:
Only the magnetic field component is perpendicular to the
propagation direction, while the electric field component points in
the propagation direction.
[0081] "Optoelectronic Device"
[0082] An optoelectronic component is a semiconductor body that
generates light by recombination of charge carriers during
operation and emits it. The light generated can range from the
infrared to the ultraviolet range, with the wavelength depending on
various parameters, including the material system used and doping.
An optoelectronic component is also called a light emitting
diode.
[0083] For the purpose of this disclosure, the term optoelectronic
device or also light-emitting device is used synonymously. A PLED
(see there) is thus a special optoelectronic device with regard to
its geometry. In displays, optoelectronic components are usually
monolithic or as individual components placed on a matrix.
[0084] "Passive matrix backplane" or "passive matrix carrier
substrate" A passive matrix display is a matrix display, in which
the individual pixels are driven passively (without additional
electronic components in the individual pixels). A light emitting
diode of a display can be controlled by means of IC circuits. In
contrast, displays with active pixels driven by transistors are
referred to as active matrix displays. A passive matrix carrier
substrate is part of a passive matrix display and carries it.
[0085] "Photonic Crystal" or "Photonic Structure"
[0086] A photonic structure can be a photonic crystal, a
quasi-periodic or deterministically aperiodic photonic structure.
The photonic structure generates a band structure for photons by a
periodic variation of the optical refractive index. This band
structure can comprise a band gap in a certain frequency range. As
a result, photons cannot propagate through the photonic structure
in all spatial directions. In particular, propagation parallel to a
surface is often blocked, but perpendicular to it is possible. In
this way, the photonic structure or the photonic crystal determines
a propagation in a certain direction. It blocks or reduces this in
one direction and thus generates a beam or a bundle of rays of
radiation directed as required into the room or radiation area
provided for this purpose.
[0087] Photonic crystals are photonic structures occurring or
created in transparent solids. Photonic crystals are not
necessarily crystalline--their name derives from analogous
diffraction and reflection effects of X-rays in crystals due to
their lattice constants. The structure dimensions are equal to or
greater than a quarter of the corresponding wavelength of the
photons, i.e. they are in the range of fractions of a .mu.m to
several .mu.m. They are produced by classical lithography or also
by self-organizing processes.
[0088] Similar or the same property of a photonic crystal can
alternatively be produced with non-periodic but nevertheless
ordered structures. Such structures are especially quasiperiodic
structures or deterministically aperiodic structures. These can be
for example spiral photonic arrangements.
[0089] In particular, so-called two-dimensional photonic crystals
are mentioned here as examples, which exhibit a periodic variation
of the optical refractive index in two mutually perpendicular
spatial directions, especially in two spatial directions parallel
to the light-emitting surface and perpendicular to each other.
[0090] However, there are also one-dimensional photonic structures,
especially one-dimensional photonic crystals. A one-dimensional
photonic crystal exhibits a periodic variation of the refractive
index along one direction. This direction can be parallel to the
light exit plane. Due to the one-dimensional structure, a beam can
be formed in a first spatial direction. Thereby a photonic effect
can be achieved already with a few periods in the photonic
structure. For example, the photonic structure can be designed in
such a way that the electromagnetic radiation is at least
approximately collimated with respect to the first spatial
direction. Thus, a collimated beam can be generated at least with
respect to the first direction in space.
[0091] "Pixel"
[0092] Pixel, pixel, image cell or picture element refers to the
individual color values of a digital raster graphic as well as the
area elements required to capture or display a color value in an
image sensor or screen with raster control. A pixel is thus an
addressable element in a display device and comprises at least one
light-emitting device. A pixel has a certain size and adjacent
pixels are separated by a defined distance or pixel space. In
displays, especially .mu.-displays, often three (or in case of
additional redundancy several) subpixels of different color are
combined to one pixel.
[0093] "Planar Array"
[0094] A planar array is an essentially flat surface. It is often
smooth and without protruding structures. Roughness of the surface
is usually not desired and does not have the desired functionality.
A planar array is for example a monolithic, planar array with
several optoelectronic components.
[0095] "Pulse Width Modulation"
[0096] Pulse width modulation or PWM is a type of modulation for
driving a component, in particular a .mu.-LED. Here the PWM signal
controls a switch that is configured to switch a current through
the respective .mu.-LED on and off so that the .mu.-LED either
emits light or does not emit light. With the PWM, the output
provides a square wave signal with a fixed frequency f. The
relative quantity of the switch-on time compared to the switch-off
time during each period T (=1/f) determines the brightness of the
light emitted by the .mu.-LED. The longer the switch-on time, the
brighter the light.
[0097] "Quantum Well"
[0098] A quantum well or quantum well refers to a potential in a
band structure in one or more semiconductor materials that
restricts the freedom of movement of a particle in a spatial
dimension (usually in the z-direction). As a result, only one
planar region (x, y plane) can be occupied by charge carriers. The
width of the quantum well significantly determines the quantum
mechanical states that the particles can assume and leads to the
formation of energy levels (sub-bands), i.e. the particle can only
assume discrete (potential) energy values.
[0099] "Recombination"
[0100] In general, a distinction is made between radiative and
non-radiative recombination. In the latter case, a photon is
generated which can leave a component. A non-radiative
recombination leads to the generation of phonons, which heat a
component. The ratio of radiative to non-radiative recombination is
a relevant parameter and depends, among other things, on the size
of the component. In general, the smaller the component, the
smaller the ratio and non-radiative recombination increases in
relation to radiative recombination.
[0101] "Refresh Time"
[0102] Refresh time is the time after which a cell of a display or
similar must be rewritten so that it either does not lose the
information or the refresh is predetermined by external
circumstances.
[0103] "Die" or "Light-Emitting Body"
[0104] A light-emitting body or also a die is a semiconductor
structure which is separated from a wafer after production on a
wafer and which is suitable for generating light after an
electrical contact during operation. In this context, a die is a
semiconductor structure, which contains an active layer for light
generation. The die is usually separated after contacting, but can
also be processed further in the form of arrays.
[0105] "Slot Antenna"
[0106] A slot antenna is a special type of antenna in which instead
of surrounding a metallic structure in space with air (as a
nonconductor), an interruption of a metallic structure (e.g. a
metal plate, a waveguide, etc.) is provided. This interruption
causes an emission of an electromagnetic wave whose wavelength
depends on the geometry of the interruption. The interruption often
follows the principle of the dipole, but can theoretically have any
other geometry. A slot antenna thus comprises a metallic structure
with a cavity resonator having a length of the order of magnitude
of wavelengths of visible light. The metallic structure can be
located in or surrounded by an insulating material. Usually, the
metallic structure is earthed to set a certain potential.
[0107] "Field of Vision"
[0108] Field of view (FOV) refers to the area in the field of view
of an optical device, a sun sensor, the image area of a camera
(film or picking up sensor) or a transparent display within which
events or changes can be perceived and recorded. In particular, a
field of view is an area that can be seen by a human being without
movement of the eyes. With reference to augmented reality and an
apparent object placed in front of the eye, the field of view
comprises the area indicated as a number of degrees of the angle of
vision during stable fixation of the eye.
[0109] "Subpixels"
[0110] A subpixel (approximately "subpixel") describes the inner
structure of a pixel. In general, the term subpixel is associated
with a higher resolution than can be expected from a single pixel.
A pixel can also consist of several smaller subpixels, each of
which radiates a single color. The overall color impression of a
pixel is created by mixing the individual subpixels. A subpixel is
thus the smallest addressable unit in a display device. A subpixel
also comprises a certain size that is smaller than the size of the
pixel to which the subpixel is assigned.
[0111] "Vertical Light Emitting Diode"
[0112] In contrast to the horizontal LED, a vertical LED comprises
one electrical connection on the front and one on the back of the
LED. One of the two sides also forms the light emission surface.
Vertical LEDs thus comprise contacts that are formed towards two
opposite main surface sides. Accordingly, it is necessary to
deposit an electrically conductive but transparent material so that
on the one hand, electrical contact is ensured and on the other
hand, light can pass through.
[0113] "Virtual Reality"
[0114] Virtual reality, or VR for short, is the representation and
simultaneous perception of reality and its physical properties in a
real-time computer-generated, interactive virtual environment. A
virtual reality can completely replace the real environment of an
operator with a fully simulated environment.
[0115] In addition to the structure of a .mu.-LED and various
methods for its manufacture, the following aspects of light
extraction may be useful for the realization of the various
embodiments and applications concerning augmented reality described
herein and in the PCT application PCT/EP2020/052191 incorporated
herein by reference.
[0116] In one aspect a rear decoupling can be provided. For this
purpose, a semiconductor layer stack with a first doped and a
second doped layer is provided, which is arranged on a substrate.
The area of the substrate facing away from the layer stack is
designed for light extraction. The layer stack comprises an active
region which is arranged between the first doped and the second
doped layer. The layer stack is provided with a reflective contact
on the surface facing away from the substrate. The reflective
contact extends isolated from the doped layers along a side surface
to the substrate surface. The shape of this reflective contact is
spherical or paraboloidal or ellipsoidal to direct the light
generated in the active layer towards the substrate. The substrate
is either very thin or transparent. Further light shaping and/or
outcoupling measures can be provided on the area of the substrate
facing away from the layer stack.
[0117] In the previous aspects of improving light extraction, the
focus was on the directionality of the emitted light, among other
things. For many applications, however, a Lambertian radiation
characteristic is required. This means that a light-emitting
surface ideally has a uniform radiation density over its area,
resulting in a vertically circular distribution of radiant
intensity. For a user, this surface then appears equally bright
from different viewing angles. In addition, such a uniform
distribution can be more easily reshaped by light-shaping elements
arranged downstream.
[0118] It is therefore proposed that an optical pixel element for
generating a pixel of a display should comprise of a flat carrier
substrate and at least one .mu.-LED with rear output. The PLED
forms an optical emitter chip. A flat carrier substrate is
understood to be, for example, a silicon wafer, semiconductor
materials such as LTPS or IGZO, insulation material or similar
suitable flat carrier structure, which can accommodate a large
number of .mu.-LEDs arranged next to each other on its surface.
[0119] The function of such a carrier substrate is, among other
things, the accommodation of functional elements such as ICs,
electronics, power sources for the .mu.-LEDs, electrical contacts,
lines and connections, but also, in particular, the accommodation
of the light-emitting .mu.-LEDs. The carrier substrate can be rigid
or flexible. Typical dimensions of a carrier substrate can, for
example, be 0.5-1.1 mm thick. Polyimide substrates with thicknesses
in the range of 15 .mu.m are also known.
[0120] The at least one .mu.-LED is arranged on one side of the
carrier substrate. In other words, the carrier substrate has two
opposite main surfaces, which are referred to here as the assembly
side and the display side. The assembly side is the surface of the
carrier substrate, often also referred to as the top side, which
accommodates the at least one .mu.-LED and which may further
comprise optical or electrical and mechanical components or
layers.
[0121] The display side should describe the side of the carrier
substrate facing a user and on which the pixels for display should
be perceived. In addition, a carrier substrate plane is described,
which extends parallel to the two main surfaces of the carrier
substrate in the same plane. The at least one .mu.-LED is
configured to emit light transverse to the carrier substrate plane
in a direction away from the carrier substrate. However, this
property should not exclude that light components are also emitted
directly or indirectly in the direction of the mounting side of the
carrier substrate.
[0122] A flat reflector element is provided on the pixel element.
This is based on the idea that a more uniform spatial distribution
of the light over the surface of the pixel element can be achieved
by reflection. For this purpose, the reflector element is spatially
arranged on the assembly side relative to the at least one .mu.-LED
and configured with regard to its shape and composition in such a
way that light emitted by the at least one .mu.-LED is reflected in
the direction of the carrier substrate.
[0123] In other words, the reflector element is placed in an area
around the at least one .mu.-LED through which the emitted light of
the .mu.-LED passes. This reflector element can, according to an
example, be a separate prefabricated microelement that is
separately applied. Typical dimensions of such a reflector element
can range from 10 .mu.m to 300 .mu.m in diameter, depending on the
design variant also in particular between 10 .mu.m and 100 .mu.m.
According to an aspect, the reflector element is configured as a
reflective coating or layer of at least one .mu.-LED. According to
an example, the at least one .mu.-LED can have a transparent or
partially transparent coating such as IGZO on its surface, to which
a reflective layer is then applied.
[0124] The reflective layer can, for example, be metallic or
contain a metal in a mixture of substances. The aim here is that as
much of the light emitted by the at least one .mu.-LED as possible
is reflected in order to achieve a high yield. The carrier
substrate is configured to be at least partially transparent so
that light reflected by the reflector element strikes the surface
of the mounting side of the carrier substrate and propagates
through the carrier substrate. This light emerges at least
partially on the opposite display side of the carrier substrate and
can thus be perceived as a pixel by the viewer.
[0125] In other words, the emitted light is decoupled at the back
or rear of the opposite display side of the carrier substrate. The
reflection effects, refraction effects and, if necessary, damping
effects can thus be used to achieve advantageous more uniform
illumination and a more homogeneous distribution of luminous
intensity. According to an example, the reflector element is
arranged and configured in such a way that a Lambertian radiation
characteristic is achieved.
[0126] In one aspect, the reflector element has a diffuser layer on
its side facing the at least one .mu.-LED. This is intended in
particular to scatter the light reflected by the at least one
.mu.-LED. Alternatively or additionally, a reflector material
comprises diffuser particles. By diffusion is meant here that a
further scattering or distribution of the light in a surrounding
spatial area should be achieved. This can also have a beneficial
effect on the scattering or distribution of light and thus achieve
a more uniform or homogeneous distribution of the light intensity,
especially on the display side of the carrier substrate.
[0127] A diffuser layer can be understood as an additional layer on
the reflector element, which can be either uniform throughout, but
also interrupted or only partially applied. In one aspect, the
diffuser layer and/or the diffuser particles have Al.sub.2O.sub.3
and/or TiO.sub.2. These materials can support a diffusion of the
emitted light due to their structural properties. While a diffuser
layer can only be applied to the surface of the reflector, diffuser
particles can, for example, be part of a mixture of materials of
the entire reflector and thus be easier to manufacture.
[0128] According to an aspect, the reflector element surrounds
roundly, polygon-like or parabolically the at least one .mu.-LED.
The underlying consideration can be seen in the fact that in many
cases the at least one .mu.-LED has a spatially wide radiation
pattern. This means that light is emitted in a wide angular range
starting from a small area. It is desirable that as much of this
emitted light as possible is captured by the reflector element and
deflected or reflected towards the display side of the carrier
substrate. In this context, it may also be provided, for example,
that the at least one .mu.-LED comprises a first and a second
.mu.-LED provided for redundancy. This can take over the function
of the first .mu.-LED in the event of production-related failure of
the first .mu.-LED. Control and manufacturing techniques are
disclosed in this notification. The reflector element, which
surrounds both .mu.-LEDs thus ensures uniform radiation regardless
of which of the two .mu.-LEDs is activated during operation. In
another aspect, the reflector element surrounds at least three
individual .mu.-LEDs, which emit different colors during operation.
This means that a reflector element can be provided for each pixel
of a .mu.-display.
[0129] Depending on the radiation pattern of the at least one
.mu.-LED, according to an example, arc-shaped, round, dome-like,
cap-like or similar shapes of the reflector element are
conceivable. The reflector element can, also according to an
example, be made in one or more parts or be provided with recesses
or interruptions. According to another example, the reflector
element has different reflection properties depending on the
wavelength of the light. This can be achieved, for example, by
microstructures on the reflector element or its structural
composition.
[0130] According to an example, the reflector element is configured
as a flat surface which is arranged perpendicular to the carrier
substrate plane above the at least one .mu.-LED. According to an
aspect, the reflector element forms an electrical contact of the at
least one .mu.-LED. The consideration here is that due to the
metallic design of the reflector element, for example, a
simultaneous use as a connecting contact for the .mu.-LED can be
considered. For this purpose, an electrical contact with one of the
.mu.-LED connections must be provided according to an example.
[0131] According to an aspect, the reflector element is configured
and shaped in such a way that at least 90% of the light emitted by
at least one .mu.-LED impinges on the assembly side of the carrier
substrate at an angle of 45.degree.-90.degree. relative to the
carrier substrate plane. According to an example, this proportion
is at least 95%, according to another example at least 80%. The
underlying idea is the need for the highest possible yield. This
means that as much of the light emitted by at least one .mu.-LED as
possible should be emitted on the display side of the carrier
substrate.
[0132] One effect that can occur with flat transparent or partially
transparent substrates is total reflection. This means that light
hitting the surface of the placement side at an acute angle is
refracted when entering the denser medium of the carrier substrate.
As a result, the light is reflected multiple times within the
carrier substrate between the placement side and the display side
and does not exit the carrier substrate because of the too acute
angles to the interfaces. These proportions are usually to be
considered as losses. In order to avoid these losses, it may be
desirable for the light to strike the surface of the placement side
of the carrier substrate at the greatest possible angle, ideally
perpendicularly. Accordingly, the reflector element is configured
to create these angular relationships and in particular to reduce
crosstalk between the pixel elements. In one aspect, the carrier
substrate comprises polyimide or glass. Polyimide is a material
that can be used especially for flexible displays. Glass can serve
as a mechanically very stable base material for rigid displays.
[0133] According to an aspect, a passivation layer is additionally
provided to attenuate or eliminate reflections at mesa edges of the
at least one .mu.-LED. A mesa edge is defined as a wall or contour
that generally slopes steeply to form the boundary of the at least
one .mu.-LED. This is arranged with its surface transverse to the
carrier substrate plane. To avoid crosstalk, it is desirable that
no light passes over in the direction of the respective adjacent
pixel element. For this purpose, light components that emerge in
this direction should be eliminated or at least attenuated by an
appropriate damping layer or passivation layer. The advantage here
can be better contrast and reduction of optical crosstalk.
[0134] According to an aspect, a light-absorbing coating is
provided on the assembly side and/or the display side of the
carrier substrate outside the reflector element. It can be
considered desirable that the non-active areas between the
.mu.-LEDs, especially between different pixels, are opaque or
attenuate light in order to improve contrast and darker impression.
The light-absorbing coating is therefore placed outside the
reflector element. According to an aspect, the display side of the
carrier substrate has a roughened or uneven and/or roughened
structure. This structure is such that it causes scattering or
diffusion effects for the wavelength of the relevant light
spectrum. This can have the advantage, for example, that a higher
proportion of the light transmitted through the carrier substrate
can be coupled out at the display side. Due to the rough structure,
more favorable microstructural angular relationships are created,
which can allow more effective decoupling.
[0135] According to an aspect, a color filter element is arranged
on the display side of the carrier substrate opposite the reflector
element. This color filter element allows a primary color spectrum
of the least one .mu.-LED to pass and attenuates other color
spectra. An advantage can be a better color rendering and better
contrasts by eliminating light portions of adjacent pixel elements
with different colors.
[0136] Furthermore, a process for the production of an optical
pixel element is proposed. In a first step, at least one .mu.-LED
is attached to a mounting side of a flat carrier substrate. Then a
reflector element is produced, for example as a reflective layer of
the at least one .mu.-LED. According to an example, before
attaching the at least one .mu.-LED to the carrier substrate, a
display side of the carrier substrate is processed for
microstructuring and/or roughening. An advantage can be seen in the
fact that the respective surfaces can be finished before the more
sensitive electronic and optical components are applied to the
assembly side.
[0137] A substantial aspect of light extraction is the ability to
suppress unwanted light components. In some applications, a highly
directional light is also desired. The .mu.-LED or pixel should
therefore not have a Lambertian characteristic but a high
directionality. In some cases, on the other hand, an unconverted
portion of the converted light should be blocked or at least
deflected in such a way that it does not reduce the visual
impression.
[0138] Some of these properties can be achieved by providing a
photonic structure or photonic crystal on the exit side of the
light. In the following, some aspects are described, which
illustrate different measures to collimate generated light to
reduce the emission angle or otherwise shape it. Besides micro
lenses or other measures, these include photonic structures. These
change the emission behaviour by creating a "prohibited" area where
light emission is not allowed. Accordingly, light emission in one
or more directions can be suppressed or promoted.
[0139] In some aspects, an optoelectronic device may have a stack
of layers with an active region for generating electromagnetic
radiation. The device comprises at least one further layer having a
photonic crystal structure. At least some of the layers of the
layer stack are semiconductor layers. The stack of layers may
include a p-doped layer and an n-doped layer, as well as a p-doped
and an n-doped Gallium Nitride (GaN) layer forming the active
region between the two layers. It should be noted that the layer
stack forms a .mu.-LED, which may have one or more features of this
disclosure in terms of geometry, material system, structure or
processing.
[0140] At least one layer on the stack of layers can have a
photonic crystal structure, especially a 2-dimensional structure.
The photonic crystal structure can be arranged at least in a
portion of the layer and can be formed for example by wire-like or
cylindrical structures having a longitudinal direction which is at
least substantially parallel to the growth direction of the layer.
The structure forming the photonic crystal, such as the wires or
cylinders, may comprise a first material, for example the material
of the layer, while the space between the structure may be made of
or filled with a second material having a different refractive
index than the first material. The second material can be air or
another substance, for example a conversion material.
[0141] The photonic crystal structure can be used to manipulate
light generated in the active region as the light passes through
the photonic crystal structure. In particular, the photonic crystal
structure can be arranged so that light passing along the direction
of growth can pass through the photonic crystal structure, while
light passing at an angle close to or at 90 degrees with respect to
the direction of growth cannot pass through the photonic crystal
structure. This is particularly the case for light having
wavelengths, which are within a photonic band gap formed by the
photonic crystal structure.
[0142] In some aspects, the periodicity is at about half of a
specific wavelength. This is the wavelength corresponding to the
wavelength of electromagnetic radiation that must be diffracted by
the photonic crystal structure. Thus, a periodicity in the range of
350 nm to 650 nm is appropriate for operation in the visible region
of the spectrum--or even less, depending on the average refractive
index. The repeating ranges of different dielectric constants in
the photonic crystal structure can therefore be produced in this
order of magnitude. In some aspects, an integer multiple of the
corresponding wavelength can also be used.
[0143] In some embodiments, the layer with the photonic crystal
structure is a dielectric layer, which contains or consists of
silicon dioxide, SiO.sub.2, for example. This can be an additional
layer, which is added to the usual layers of a .mu.-LED. The same
fabrication technology can therefore be used for GaN and GaP
systems. The different manufacturing variants and possibilities can
also be transferred to a converter layer. Thus, a greater bundling
or collimation can be achieved compared to standard LEDs without
such a structure. Also, the extraction efficiency with a photonic
crystal structure applied in one layer is improved compared to a
conventional LED without a photonic crystal structure.
[0144] In some aspects, the optoelectronic device may comprise one
or more mirror layers arranged on top of the layer with the
photonic crystal structure. The mirror layer or layers may be
arranged to form an angle-selective mirror, for example as a cover
layer. The concentration of the emitted light can be further
improved. With beam-shaping structures, as given by using a layer
with a photonic crystal structure, up to 50% more light can be
emitted into a 30 cone or less on the chip plane compared to a
standard chip having a roughened surface. Such beam shaping allows
high efficiency and low cost in projection applications. For
.mu.-LED or monolithic display applications it may even be a
requirement.
[0145] The different photonic decoupling structures create a
certain roughness and surface structures on the surface, depending
on their design. In addition, light emitting diodes often have a
structured surface in the past to improve light outcoupling. In
contrast, the stamping technology currently used to place .mu.-LEDs
on electrical contacts is only possible for .mu.-LEDs with planar
or flat surfaces.
[0146] Therefore a method of making photonic structures on a
.mu.-LED, in which an optical outcoupling structure is created in a
surface region of a semiconductor body providing the .mu.-LED. The
surface area with the outcoupling structure is then further
processed and planarized. In this way, a planar surface is
obtained, but light shaping and outcoupling is still improved by
means of the outcoupling structure.
[0147] Accordingly, a .mu.-LED thus contains a decoupling
structure, which is arranged in a planar surface area. The output
structure can also have light-shaping features, such as the
photonic structures revealed here. This allows light to be emitted
from a surface perpendicular to it.
[0148] In one aspect, the surface region of the semiconductor body
is structured by generating a random topology at the surface
region. A random topology involves directly roughening the surface
of the surface region. Alternatively, a transparent second
material, especially Nb.sub.2O.sub.5 with a high refractive index
can be applied and then roughened.
[0149] In another aspect, the surface area is structured by an
ordered topology and then planarized according to the explanations
revealed here. For this purpose, photonic crystals or non-periodic
photonic structures, especially quasi-periodic or deterministic
aperiodic photonic structures, are introduced into a second
transparent material. Interstitial spaces are filled and then
planarized. Filling is done with a transparent third material with
a low refractive index, especially smaller than 1.5, especially
SiO.sub.2.
[0150] The planarization is done by mechanical or
chemical-mechanical polishing (CMP). This creates a planarized
surface with a roughness in the range of less than 20 nanometers,
in particular less than 1 nanometer, as the mean roughness
value.
[0151] As already mentioned, a photonic crystal or other structure
can be applied to the .mu.-LED or .mu.-LED array to form the beam
of an LED or .mu.-LED. However, in some applications it is common
to use non .mu.-LEDs that emit light of different wavelengths in
one operation. Instead, one type of .mu.-LED is used and its
emitted light is then converted. For this purpose, a converter
material is applied to the surface of the .mu.-LED in the main
radiation direction. The photonic crystal as light-shaping
structure is arranged above the converter material as already
revealed in some examples.
[0152] In the following, further aspects are explained, which are
based on the idea of unification of light shaping and converting
structure so that a particularly space-saving arrangement of the
individual elements and thus a particularly small design of an
optoelectronic component is possible. This achieves that the
radiation emitted by the component is specifically radiated into a
certain area of space, while radiation into other areas is reliably
prevented in a comparatively simple way. In addition, all solutions
with photonic structures presented here are characterized by high
energy efficiency and thus by a comparatively good light yield
compared to the known technical solutions.
[0153] In this context, some aspects first concern a converter
element for a .mu.-LED. The converter element comprises at least
one layer with a converter material which, when excited by an
incident excitation radiation, emits a converted radiation into an
emission area. The converter element is characterized in that the
layer has a photonic structure at least in some areas, on which the
converter material is arranged at least in sections. The photonic
structure is designed in such a way that the radiation is emitted
as a directed beam of rays into the emission area. Thus, a layer is
provided which is structured in a suitable manner, wherein a
converter material is applied in or on the structure, which emits
converted radiation when excited by an excitation or pump
radiation.
[0154] By combining the components converter material on the one
hand and structured layer for targeted beam guidance and/or shaping
on the other hand, an element is created in a particularly
space-saving manner which enables a targeted emission of radiation
into the radiation source's radiation area, limited to a desired
spatial area. In this context, it is conceivable that both the
converted radiation emitted by the converter element and the
excitation radiation are directed in a suitable manner so that
radiation is only emitted in a certain direction, while the
emission of such radiation in other directions and/or areas is
excluded or at least significantly reduced.
[0155] In general, it is conceivable that the photonic structure is
coated with a suitable converter material at least in some areas
and/or at least individual areas, for example depressions in the
structure, are filled with the suitable converter material. The
structure is configured in such a way that the emitted converted
radiation is emitted as a beam of rays in a desired direction of
the radiation area. Thus, light is both converted and shaped by the
photonic structure. In this context, it is conceivable to adapt the
photonic structure in a suitable way so that different areas are
present into which a beam of radiation is emitted. In this way,
converter elements can be provided which adjust the radiation
characteristics of an optoelectronic component or a .mu.-LED in
which they are used as required. In particular, it is possible to
provide a converter element by which the emission profile of an
optoelectronic component for which the converter element is used
can be changed in such a way that the radiation no longer follows
Lambert's law, but instead a beam or bundle of rays is generated
which is directed in a specific direction.
[0156] The converter material may include the materials disclosed
in this application and may be doped with various rare earth
elements. As host material the already mentioned YAG or LuAG can be
used. It is also possible to use the already mentioned quantum dots
as converter material. The photonic structure normally does not
change the spectral properties of a quantum dot. Besides the
adaptation of the photonic structure to the emission spectrum of
the quantum dots, they can also be located in the area of the
structure itself, e.g. in formed trenches
[0157] The regular photonic structure or a regular photonic crystal
offers the advantage that the optical properties of the converter
element can be adjusted particularly reliably, safely and
reproducibly with an appropriate structured layer. The structure is
configured in such a way that radiation of a certain wavelength or
a certain wavelength range can penetrate the layer in a
specifically defined direction, while this radiation cannot
penetrate the layer in other directions. Alternatively or
additionally, the structured layer can be configured in such a way
that it is transparent or non-transparent for radiation of a
specific wavelength over at least a large range.
[0158] Furthermore, it is useful if the photonic structure has at
least one recess in which the converter material is located.
Preferably, in this context it is intended that the photonic
structure has a plurality of elevations and depressions, the
depressions being at least partially filled with the suitable
converter material. In this way, a converter element can be
realized comparatively easily, in which the structure provided
according to the invention is combined with the converter material
in such a way that the converted radiation is emitted only in a
specifically limited radiation range and thus in a particularly
targeted manner. In principle, it is conceivable in this regard
that the converter element is configured in such a way that the
excitation radiation is directed by the photonic structure in a
targeted manner onto areas of the converter material provided for
this purpose and/or that the converted radiation impinges on the
structure and is thus emitted as a targeted beam of radiation into
the desired radiation emission range.
[0159] In some aspects, the layer with the photonic structure is
configured such that the layer comprises at least one optical band
gap. In this context, a band gap is understood to be the energetic
range of the layer that lies between the valence band and the
conduction band. Due to the band gap, the solid used for the layer
and thus the converter element provided with the layer are
transparent to radiation in a certain frequency range. The optical
properties of the converter element can be specifically adjusted by
adjusting the band gap and/or selecting a solid state material. In
particular, it is possible to adapt the layer in such a way that
only a part of the incident radiation passes through the layer and
is emitted into the emission range. In some aspects, it is useful
if the photonic structure of the layer has an average thickness of
at least 500 nm, so that an optical band gap is created.
[0160] In some embodiments, it is provided that the layer with the
photonic structure is configured in such a way that the directed
beam of rays is emitted perpendicular to a plane in which the layer
is arranged. In contrast, radiation components that are emitted
into other spatial areas are reliably suppressed.
[0161] Further aspects concern optical filter elements and other
measures. In one aspect, an optical filter element can be arranged
at least on one side of the layer. In some aspects, such a filter
element is designed as a filter layer, which is applied flat on the
structured layer with the converter material. With the aid of such
a filter element or such a filter layer, it is possible that only a
certain part of a radiation impinges on the layer with the
converter material or that only a certain part of the converted
radiation emitted by the structured layer with the converter
material is emitted into the desired spatial region. The filter
element, in particular the filter layer, is thus adapted in some
aspects in such a way that only that part of a radiation can pass
through the filter element or the filter layer which is required as
excitation radiation or which is to be emitted specifically into
the emission range.
[0162] Furthermore, some aspects concern a radiation source with a
.mu.-LED, which radiates an excitation radiation into a converter
element, which is configured according to at least one of the
previously described embodiments of a converter element. The
converter element in turn has at least one layer with a converter
material which, when excited by the excitation radiation emitted by
the .mu.-LED, is excited to emit a converted radiation into a
radiation emission area. In this context it is conceivable that a
.mu.-LED is combined with a converter element in such a way that
the entire excitation radiation emitted by the LED is converted
into converted radiation or that only a part of the excitation
radiation emitted by the LED is converted into converted radiation.
Again, it is substantial that the radiation emitted into the
radiation source's beam area is only directed into a desired
spatial region. The radiation source thus generates a directed beam
of light or a directed beam of radiation that is emitted in a
specifically selected direction or in a specifically selected
radiation range.
[0163] According to another aspect, the structured layer with the
converter material is part of a semiconductor substrate of the
.mu.-LED. The photonic structure can be formed accordingly in a
semiconductor substrate of the .mu.-LED. In this context, it is
also conceivable that the structure is produced by targeted etching
of the LED semiconductor substrate and the structure is then at
least partially coated with converter material and/or the converter
material is filled into etched-out depressions in the
structure.
[0164] Furthermore, in some aspects it is planned that the
structure with the converter material is configured in such a way
that the converted radiation is emitted perpendicular to a plane in
which the semiconductor substrate is located, into the emission
area. The structure is configured in such a way that converted
radiation is only emitted perpendicular to the surface of the
.mu.-LED chip into the emission area due to a bandgap effect. Due
to this technical solution, a high directionality of the converted
radiation emitted by the converter element is achieved. In this
context, it is also possible that the photonic structure, for
example in the form of a photonic crystal, is arranged only in the
uppermost layer of the semiconductor material of the .mu.-LED or
also at least partially in the active zone. It is again
advantageous if the photonic structure has a layer thickness of at
least 500 nm in order to generate reliably an optical band gap.
[0165] In one embodiment at least one filter layer is provided,
which is arranged on one side of the structured layer. By means of
a filter layer, the excitation radiation generated by the .mu.-LED
is suppressed in certain wavelength ranges. In this way, especially
etendue-limited systems based on full conversion of the excitation
radiation can be made significantly more efficient than known
technical solutions by means of directed radiation generation in
the structured layer of the converter element.
[0166] The radiation source may be configured to emit visible white
light or visible converted light with the colors characteristic of
the RGB color space, namely red, green and blue. According to one
embodiment, the radiation source can be a pixelated array, in
which, for example, individual pixels of a larger component can be
switched on and off individually.
[0167] The use of a photonic structure, as described herein, in
combination with the above-mentioned .mu.-LEDs makes it possible to
do without lenses or similar collimating elements. Furthermore, a
photonic structure can improve the contrast between adjacent pixels
due to the provided directionality.
[0168] In addition, some aspects also concern a process for
manufacturing a radiation source that has at least one of the
special properties described above. The process is characterized by
the fact that the structure is formed by at least one etching step
in a semiconductor substrate of the LED. It is advantageous here if
the structure, in particular specifically selected recesses in the
structure, are at least partially filled with the converter
material.
[0169] Some further aspects deal with a .mu.-display with a
photonic structure for the emission of directed light. Especially
in displays that feature .mu.-LEDs, the dimensions of individual
.mu.-LEDs can be very small, so that when a photonic structure is
formed, only a few periods have space on the surface of a single
.mu.-LED. It is therefore proposed to form a photonic structure
over a large area on an array of several .mu.-LEDs. Such arrays can
be pixelated arrays of .mu.-LEDs, for example, where one pixel
forms a light source. Monolithic pixel arrays also fall under this
category as do assembled LED modules with a smooth surface, for
example the cover electrode disclosed in this application. Another
example is an arrangement of single .mu.-LEDs or smaller modules of
.mu.-LEDs, which can also be provided in the form of an array. Such
.mu.-LED modules are also disclosed in this application.
[0170] .mu.-LEDs are normally Lambertian emitters and therefore
emit light in a large solid angle. For pixelated arrays, and
especially for .mu.-displays, however, as already explained, a
directed emission perpendicular to the light emission surface is
important or desirable for a variety of applications.
[0171] Thus, an optoelectronic device comprises an assembly having
a plurality of light sources for generating light emerging from a
light exit surface from the optoelectronic device, and at least one
photonic structure disposed between the light exit surface and the
plurality of light sources. By means of the at least one photonic
structure, which may be in particular a photonic crystal or pillar
structures, also referred to herein as columnar structures, beam
shaping of the emitted light is effected before the light leaves
the device through the light exit surface.
[0172] The photonic structure may be configured in particular for
beam shaping of the light generated by the light sources. The
photonic structure can in particular be configured in such a way
that the light emerges at least substantially perpendicularly from
the light exit surface. The directionality of the emitted light is
thus considerably improved.
[0173] According to one embodiment, the arrangement is an array
comprising a plurality of light sources, in particular .mu.-LEDs,
arranged in rows and columns. The .mu.-LEDs are organized in pixels
or subpixels and can be controlled separately. In some aspects, the
arrangement is realized as a monolithic array, in other aspects,
the arrangement is equipped with .mu.-LED modules or separate
.mu.-LEDs. The array comprises one containing or contacting the
.mu.-LEDs or light sources at least partially and one photonic
crystal. This is arranged or formed in the layer. The photonic
crystal can thus be arranged directly in the layer in which the
pixels of the array are arranged. Alternatively, the photonic
crystal is arranged in the layer above the light sources, so that
the photonic crystal is still located between the light sources and
the light exit surface.
[0174] The layer may comprise a semiconductor material and the
photonic crystal may be structured in the semiconductor material.
Examples of semiconductor materials are GaN or AlInGaP material
systems. Examples of other possible material systems are AlN, GaP
and InGaAs.
[0175] The photonic crystal can be realised by forming a periodic
variation of the optical refractive index in the semiconductor
material, using a material with a high refractive index, such as
Nb.sub.2O.sub.5 (niobium (V) oxide), and introducing it into the
semiconductor material accordingly to form a periodic or
deterministically aperiodic structure. The photonic structures can
be filled with a material of low refractive index, such as
SiO.sub.2.
[0176] Thus, a refractive index variation between a high and a low
index occurs. The photonic crystal is preferably formed as a
two-dimensional photonic crystal, which exhibits a periodic
variation of the optical refractive index in a plane parallel to
the light exit direction in two mutually perpendicular spatial
directions.
[0177] The photonic crystal can be realized by means of holes or
recesses, which are inserted into a material with a high refractive
index, for example Nb.sub.2O.sub.5. The photonic crystal can thus
be formed or be formed by forming the corresponding structuring in
the material with high refractive index. In contrast, the material
surrounding the holes or recesses has a different refractive
index.
[0178] In a further aspect, the arrangement comprises a plurality
of .mu.-LEDs as light sources, the .mu.-LEDs being arranged in a
first layer and a photonic crystal being arranged or formed in a
further, second layer. The second layer is located between the
first layer and the light emitting surface. In combination with a
particularly array-like arrangement of .mu.-LEDs, a photonic
crystal can be provided in an additional, second layer above the
first layer comprising the .mu.-LEDs. This is preferably designed
as a two-dimensional photonic crystal and is realized in the form
of a periodic variation of the optical refractive index in two
spatial directions running parallel to the light exit surface and
perpendicular to one another. As an example of a material with a
high refractive index of the second layer, Nb.sub.2O.sub.5 can
again be mentioned here, and the photonic crystal can be structured
by means of holes or recesses in the material with the high
refractive index. The photonic structures can be filled with a
material with a lower refractive index, for example SiO.sub.2.
Thus, the second layer has a structure of a material with two
different refractive indices.
[0179] .mu.-LEDs can be differentiated between horizontal and
vertical .mu.-LEDs. With horizontal LEDs, the electrical
connections are located on the back of the LED facing away from the
light emission surface. In contrast, in the case of a vertical LED,
one electrical connection is located on the front and one on the
back of the LED. The front side faces the light emission
surface.
[0180] In pixelated arrays, where the electrical contacts of both
polarities are on the backside, the whole array surface can be
structured, e.g. in form of a photonic crystal, especially without
leaving mesa trenches or contact areas. A similar arrangement
results for arrangements of horizontal .mu.-LEDs under a carrier
substrate. According to an embodiment, in an array or an
arrangement of horizontal .mu.-LEDs for the electrical contacting
of the light sources, both poles can be electrically connected in
each case by means of a contacting layer reflecting the generated
light, the contacting layer lying under the photonic structure and
the light sources, viewed from an upper light exit surface. The
contacting layer can thereby have at least two electrically
separated areas in order to avoid a short circuit between the
poles.
[0181] According to another configuration, in the case of an
arrangement of vertical light emitting diodes for the electrical
contacting of the light sources, a first connecting contact facing
away from the light-emitting surface, in particular a positive one,
can be electrically connected to a contacting layer reflecting the
generated light, the contacting layer lying below the photonic
structure and the light sources as seen from an upper
light-emitting surface. On the other hand, the respective other, in
particular negative, second connecting contact, which faces the
light exit surface, can be electrically connected by means of a
layer of an electrically conductive and optically transparent
material, in particular ITO. A filling material can be arranged
between the layer and the reflective contacting layer. In some
aspects, this electrically conductive layer may itself be
structured to produce photonic properties. In other aspects, the
photonic structure is created over the electrically conductive
layer.
[0182] According to an embodiment, each of the light sources or the
.mu.-LEDs can have a recombination zone and the photonic crystal
can be located so close to the recombination zones that the
photonic structure changes an optical state density present in the
region of the recombination zones, in particular in such a way that
a band gap is generated for at least one optical mode with a
direction of propagation parallel and/or at a small angle to the
light exit surface.
[0183] To effect the optical band gap in the recombination zone, it
is useful if the photonic crystal is very close to the
recombination zone. In addition, to form the band gap, it is useful
if the height of the photonic crystal is large when viewed in a
direction perpendicular to the light-emitting surface, in
particular equal to or above 300 nm. By means of the photonic
structure, directionality can thus be achieved for the emitted
light already in the light generation region, since the emission of
light with a direction of propagation parallel and/or at a small
angle to the light exit surface can be suppressed. Light can then
only be generated in a limited emission cone perpendicular to the
light exit surface. The aperture angle of the emission cone depends
on the photonic crystal and can be a small value, for example,
maximum 20.degree., maximum 15.degree., maximum 10.degree. or
maximum 5.degree..
[0184] The photonic crystal can be arranged in relation to a plane
parallel to the light-emitting surface independently of the
positioning of the light points.
[0185] The photonic structure may comprise a plurality of pillar
structures extending at least partially between the light-emitting
surface and the plurality of light sources, one pillar being
associated with each light source and aligned with the
light-emitting surface when viewed in a direction perpendicular to
the light-emitting surface. The pillars or columns have a
longitudinal axis, which preferably extends perpendicular to the
light-emitting surface. When a pillar and an associated light
source are aligned, the extended longitudinal axis of the pillar
intersects the centre of the light source.
[0186] Viewed transversely to the longitudinal axis, the pillars
can have a circular, square or polygonal cross-section. Pillars
preferably have an aspect ratio height to diameter of at least 3:1,
with the height measured in the direction of the longitudinal axis
of the pillars. In particular, pillars are made of a material with
a high refractive index, such as Nb.sub.2O.sub.5. Due to the higher
refractive index compared to the surrounding material, the light
emission in a direction parallel to the longitudinal axis of the
pillars can be increased compared to other spatial directions. The
pillars act as wave guides. Light is more efficiently coupled out
along the longitudinal axis of the pillars than along other
propagation directions. Directionality in the direction of the
longitudinal axis of light can thus be improved. Since the
longitudinal axis of the light is preferably perpendicular to the
light exit surface, improved light extraction perpendicular to the
light exit surface can also be achieved.
[0187] The arrangement may be an array comprising as light sources
a plurality of .mu.-LEDs arranged in pixels arranged in a first
layer and the pillars may be arranged in a further, second layer,
the second layer being positioned between the first layer and the
light emitting surface. Thus, the pillars can be arranged on the
surface of the pixelated array. The pillar or column structures can
be free-standing and made of a material with a high refractive
index. In addition, the free space between the pillars can be
filled with a filling material, e.g. SiO.sub.2, with a low
refractive index.
[0188] In another aspect, the arrangement can be an array that has
as light sources a plurality of pixels arranged in a first layer,
and the pillars can also be arranged in the first layer. In
particular, the pillars may be arranged in the first layer such
that at least a respective part of a pillar is closer to the light
emitting surface than the light source associated with the pillar.
The pillar can thus act as an optical waveguide between the light
source and the light-emitting surface. The pillars can be formed
from a semiconductor material of the array provided in the first
layer, the semiconductor material having a high refractive index.
In particular, semiconductor material in the first layer can be
removed by etching in such a way that the pillars remain
stationary. The free spaces between the pillars can in turn be
filled with a low refractive material.
[0189] In a further aspect, the arrangement can be an array that
has as light sources a plurality of .mu.-LEDs arranged in pixels,
with the pixels being formed in the pillars. An array can thus be
created in such a way that the individual pixels have the form of
pillars. Each pillar is preferably a .mu.-LED and functions as a
single pixel. Seen in relation to the longitudinal axis of a
pillar, the length of the pillar can correspond to half a
wavelength of the emitted light, and the recombination zone of the
.mu.-LED formed by a pillar is preferably located in the centre of
the pillar. Thus, the recombination zone lies in a local maximum of
the photonic state density. The light emission parallel to the
longitudinal direction of the pillars can thus be significantly
increased. Due to the waveguide effect, the light with propagation
direction parallel to the longitudinal axis is additionally coupled
out more effectively than light of other propagation
directions.
[0190] The aspect ratio of height to diameter of a pillar is
preferably 3:1, and at common emission wavelengths, the pillars
have a height of about 100 nm and a diameter of 30 nm. Also
up-scaled, larger heights and diameters, respectively are possible,
which are easier to manufacture. In such a case, it is useful if
the aspect ratio remains the same, for example the 3:1 mentioned
above, but in a fixed ratio to the wavelength of the light to be
influenced. The space between the pillars containing the light
sources can be filled with material, for example SiO.sub.2, which
has a lower refractive index than the semiconductor material for
the pillars.
[0191] In the case of a pillar with a light source, a p-contact can
be made on the underside of the pillar facing away from the
light-emitting surface. For example, an n-contact can be made at
half the height of the pillars on the top of the pillar. The
n-contact can be produced by a transparent conductive material,
especially as an intermediate layer in the filling material or as
the top layer above the pillars. A possible material for an
n-contact layer is for example ITO (indium tin oxide). An inverse
arrangement of n- and p-contact is also possible.
[0192] In particular, in the case of an arrangement of light
emitting diodes, in particular vertical light emitting diodes in
the form of pillars or columns for electrical contacting, a
respective first pole, in particular a positive pole, may be
electrically connected to a reflective contacting layer which may
be formed on and/or along first longitudinal ends of the light
emitting diodes. The respective other, in particular negative,
second pole can be electrically connected to a further layer of an
electrically conductive and optically transparent material, in
particular ITO. This layer can be arranged as an intermediate layer
in the middle of the pillars or columns or at and/or along second
longitudinal ends of the pillars, the second longitudinal ends
being opposite the first longitudinal ends.
[0193] According to another aspect, an optoelectronic device is
proposed for generating an emission of light directed
perpendicularly to an emitting surface from an, in particular
planar, pixel array or from an array of .mu.-LEDs, whereby
optically acting structures, in particular nanostructures such as a
photonic crystal or a pillar structure, are structured along the
entire emitting surface to the perpendicularly directed emission of
the light. According to a further aspect, a method is proposed for
the manufacture of an optoelectronic device for generating an
emission of light directed perpendicularly to an emitting surface
from an, in particular planar, pixelated array or from an array of
.mu.-LEDs, wherein optically acting structures are structured along
the entire emitting surface to the perpendicularly directed
emission of the light.
[0194] Planar array means in particular plane array. A surface of
an array or field is also preferably smooth. A pixelated array is
especially a monolithic, pixelated array.
[0195] All mentioned materials, especially the materials in a
photonic crystal, a pillar, or the filling materials preferably
have a low absorption coefficient. The absorption coefficient is
here in particular a measure of the reduction in the intensity of
electromagnetic radiation when passing through a given
material.
[0196] The photonic crystal can be produced using a lithography
technique known per se. Possible technologies known per se are, for
example, nanoimprint lithography or immersion EUV stepper, where
EUV stands for extreme ultraviolet radiation.
[0197] Another possible application of photonic crystals is based
on the property of polarizing electromagnetic radiation, especially
visible light, with respect to the direction of oscillation. With
the help of photonic structures for polarization of electromagnetic
radiation, it is especially possible to take special pictures and
show them on suitable displays. To create images, which give the
impression of a three-dimensional image to a user, usually several
complementary polarization, directions are combined in a suitable
way.
[0198] It is therefore regularly a problem that the lighting units,
which can provide polarized light on demand, comprise a number of
additional optical components in addition to the emitter used to
generate light. This makes the construction of corresponding
lighting units comparatively complex and increases the costs of
production. Furthermore, the different components require a not
inconsiderable amount of installation space, so that efforts to
miniaturize the lighting units required for augmented reality
applications or in the field of consumer electronics, often reach
their limits. More recent requirements in the automotive sector
also point to the desire to create images that create a
three-dimensional effect on the user.
[0199] To solve this and other problems, an arrangement or an
optoelectronic component is proposed with at least one emitter
unit, in particular a .mu.-LED, which emits radiation via a light
exit surface. The component also comprises a polarization element,
which is connected at least in sections to the light-emitting
surface and changes a polarization and/or an intensity of the
radiation emitted by the emitter unit when the radiation passes
through the polarization element. The arrangement is characterized
in that the polarizing element comprises a three-dimensional
photonic structure.
[0200] The device or optoelectronic component can be a pixel
element of a .mu.-display or a .mu.-display module. The emitter
unit can be formed by a .mu.-LED. One or more such modules, in
which several pixels are arranged in rows and columns, can thus
generate one or more images, which may give the user the impression
of a three-dimensional image.
[0201] The formulation that the polarizing element changes a
polarization also includes the generation of polarized radiation
from non-polarized radiation. The polarizing element can also only
change the intensity of the radiation, possibly depending on the
wavelength, without producing or changing a polarization. The term
"polarizing element" is therefore not to be interpreted narrowly in
the sense that a change or generation of polarization must be
provided for in all configurations.
[0202] The proposed solution provides an optoelectronic component
in which the radiation generated by the emitter, for example a
.mu.-LED, passes directly into the polarizing element, so that a
particularly compact unit for providing demand-polarized radiation
is realized, which in turn can be combined with further such
components and/or a polarizing element, preferably with at least
one polarizing element that has complementary properties.
[0203] The substantial advantage of using a three-dimensional
photonic structure, in particular a photonic crystal, for
polarizing electromagnetic radiation, whereby preferably visible
light is polarized, is that a particularly compact, space-saving
solution is provided by the arrangement of the photonic structure
in the area of the light exit surface of the emitter. With the aid
of the specially configured polarizing element adjacent to the
light-emitting surface, it is possible to polarize electromagnetic
radiation in a targeted manner and still minimize the losses of
radiation whose polarization does not correspond to the
polarization direction of the polarizing element. In general, it is
conceivable that the photonic structure is arranged on the
light-emitting surface, or that a photonic structure is formed in a
suitable manner in a semiconductor layer on which the
light-emitting surface is located or to which the light-emitting
surface is adjacent in the direction of the beam.
[0204] Here it is of particular advantage that the
three-dimensional structures used as polarization elements can be
used to change the radiation characteristics of an illumination
unit with regard to its polarization properties in a particularly
effective way, thus enabling discrimination of different
wavelengths by different polarization properties or radiation
directions.
[0205] According to an aspect, the emitter unit has at least one
.mu.-LED. In this context, it is conceivable that the .mu.-LED
emits preferably white, red, green or blue light, which is
irradiated into the polarizing element and by means of the
polarizing element the radiation is polarized in an oscillation
direction. In this context, the .mu.-LED may also comprise a
converter material so that the light emitted by the .mu.-LED is
converted by the converter material into a desired wavelength and
thus color.
[0206] Furthermore, according to another aspect, the emitter unit,
in particular a .mu.-LED, as well as the polarization element are
to be formed from different layers, which are arranged in a layer
stack one above the other. Again, it is substantial that the
radiation generated in at least one layer of the emitter reaches
the likewise layer-shaped polarizing element before the radiation
from the layer stack is emitted into the environment. In this
context, it is advantageous that the three-dimensional structure
used as a polarization element is located on or in the same
semiconductor chip as the emitter unit.
[0207] When using an emitter unit with a .mu.-LED, it is also
conceivable that the photonic structure is applied to the .mu.-LED
chip or at least is part of the .mu.-LED chip. Various designs of
such a .mu.-LED are disclosed in this application. The .mu.-LED may
be monolithically manufactured and may be part of a larger array of
.mu.-LEDs arranged in rows and columns. These can be processed and
manufactured together. The .mu.-LEDs for individual colors can be
combined into a pixel and surrounded with a structure to improve
light guidance, especially to the main beam direction.
[0208] Such an embodiment provides a particularly space-saving and
energy-efficient optoelectronic component with which polarized
radiation is already generated directly at chip level without the
need for additional optical elements in the downstream beam
path.
[0209] In other aspects, the polarization element has spiral and/or
rod-shaped structural elements. In this case, the three-dimensional
photonic structure is adapted in such a way that light emitted by
the emitter unit or the .mu.-LED only leaves the photonic structure
with a certain polarization. A corresponding three-dimensional
photonic structure with spiral and/or rod-shaped structural
elements in the area of the light exit surface is only irradiated
by radiation with a specific polarization direction. The design and
dimensioning of the structure is preferably adapted to the
radiation emitted by the emitter unit. A spiral structure achieves
a circular polarization, while a rod-shaped structure causes a
linear polarization of the radiation passing through the
structure.
[0210] According to further aspects, it is also conceivable that
when using a converter material, the three-dimensional photonic
structure is located in the beam path between the .mu.-LED and the
converter element or behind the converter element, by which the
excitation radiation and/or the converted radiation is polarized in
a suitable way. The combination of converter element and
three-dimensional photonic structure in the same layer can also be
realized. Thus, directly polarized, converted light can be
generated.
[0211] For example, converter material can be filled into the
three-dimensional photonic structure. The converter material can be
doped with Ce.sup.3+ (Ce for cerium), Eu.sup.2+ (Eu for europium),
Mn.sup.4+ (Mn for manganese) or neodymium ions. As host material,
for example YAG or LuAG can be used. YAG stands for
Yttrium-Aluminium-Garnet. LuAG stands for lutetium aluminum
garnet.
[0212] Quantum dots can also be filled into the three-dimensional
photonic structure as converter material. Quantum dots can be very
small, for example in the range of 10 nm. They are therefore
particularly suitable for filling the three-dimensional photonic
structure. In general, it is conceivable that the structure is
produced by etching material out of the layer, in which the
structure is to be formed. The recesses thus formed can then be
filled with converter material containing, for example, quantum
dots. The quantum dots can, for example, be introduced into a
liquid material with which the recesses are filled. The liquid
material can be at least partially vaporized so that the quantum
dots remain in the recesses. In the process, part of the liquid
material can solidify. The quantum dots can therefore be embedded
in a matrix.
[0213] The photonic structure normally does not change the spectral
properties of a quantum dot. However, a quantum dot has a
narrow-band emission spectrum. The photonic structure can be
adapted to this narrowband emission spectrum, which can improve the
directional selectivity caused by the photonic structure.
[0214] By means of a photonic structure, the radiation
characteristics of quantum dots can thus be influenced very
efficiently as converters.
[0215] In other aspects, the polarizing element has at least one
three-dimensional photonic crystal. It is also conceivable that the
polarizing element comprises at least two two-dimensional photonic
crystals, which are arranged one behind the other along a beam path
of the radiation penetrating the polarizing element.
[0216] It is useful to use one three-dimensional photonic crystal
or at least two two-dimensional photonic crystals arranged one
behind the other in the optical path so that the structure on which
the radiation impinges is transparent to radiation of a specific
wavelength or several specific wavelengths and/or only transmits it
in a specific direction. In this way, the desired polarization of
the radiation impinging on the polarizing element can also be
adjusted. In this context, it is conceivable to produce the
structure directly in the converter material or to insert it into
an additional layer of another material. The property of the
three-dimensional photonic structure is preferably designed such
that the transmission conditions are different for different
wavelengths. In this way it is possible, for example, that
converted radiation can pass the polarizing element unhindered
while the excitation radiation is deflected. It is also conceivable
that at least one of the radiations, namely excitation radiation on
the one hand and converted radiation on the other hand, only passes
through the polarizing element with a certain polarization.
[0217] In some embodiments, it may also be provided that the
polarizing element has at least two different transmittances
depending on a wavelength of the radiation passing through the
polarizing element. In this context, a further embodiment provides
that the emitter unit comprises a .mu.-LED and a converter element
with a converter material which, excited by excitation radiation
emitted by the .mu.-LED, emits converted radiation, and that
excitation radiation incident on the polarizing element is
polarized and/or absorbed differently when passing through the
polarizing element compared to the converted radiation passing
through.
[0218] The properties of the three-dimensional photonic structure
are thus such that the transmission conditions are different for
different wavelengths. In this case, it is conceivable, for
example, that converted light can pass unhindered through the
three-dimensional photonic structure while the excitation radiation
is deflected. It is also conceivable that converted radiation only
leaves the three-dimensional photonic structure with a certain
polarization.
[0219] Furthermore, for some aspects it is conceivable that one of
the two radiations, which have different wavelengths, is
discriminated against by the different properties of the polarizing
element in terms of polarization and direction of propagation. It
is therefore preferable that in a combination of a .mu.-LED and a
converter element, by which a full conversion is realized, a part
of the excitation radiation is filtered out except for a
comparatively small radiation portion with a special wavelength,
which leads to the fact that a thinner layer of the converter
material can be used.
[0220] The structure described herein can be produced in a
particularly small way. In some aspects, for example, an emitter
unit with a .mu.-LED is provided, and the three-dimensional
structure of the polarization element is applied directly on the
.mu.-LED chip, preferably on the semiconductor layer of the
.mu.-LED, through which the generated radiation reaches the light
emission surface. According to such embodiment, the
three-dimensional photonic structure is located directly on or in
the .mu.-LED chip.
[0221] With such a technical solution, the polarized radiation
emission can be used to improve the resolution for the generation
of images, and components for beam generation can be made
comparatively small. This can be achieved, for example, by imaging
the radiation emitted by several components or by several
illumination units with complementary properties via common optics.
Optics that are suitable for this purpose are disclosed in this
application. Illumination units adapted in this way are thus
particularly suitable for augmented reality applications and/or in
the field of consumer electronics.
[0222] Another aspect relates to a method of manufacturing an
optoelectronic component having at least one emitter unit which
emits radiation via a light-emitting surface, and having a
polarizing element, which adjoins the light-emitting surface at
least in sections and changes a polarization and/or an intensity of
a radiation emanating from the emitter unit when the radiation
passes through the polarizing element.
[0223] This method can be further developed by using a .mu.-LED, or
an array of .mu.-LEDs, as emitter unit, on whose light-emitting
surface a three-dimensional photonic structure is applied as
polarization element, for example by two-photon lithography or
glancing angle deposition, and/or the photonic structure is
introduced into a semiconductor layer of the .mu.-LED adjacent to
the light-emitting surface. The three-dimensional structure can be
dimensioned depending on the wavelength of the radiation emitted by
the .mu.-LED.
[0224] Thus, an optoelectronic device based on the principles and
structures or objects disclosed in this application may be used in
a device for the production of three-dimensional images, in
particular for presentation on a display, monitor or screen. In
some aspects, the three-dimensional impression in a user is based
on the fact that light of different polarity is directed to the two
eyes, the respective light, or the generated image or represented
objects, being displayed at slightly different positions.
[0225] In particular, based on the techniques presented here,
three-dimensional images can be generated computer-aided for
augmented reality applications or in the automotive sector. It is
an advantage here that the optoelectronic components disclosed in
this application with a three-dimensional photonic structure as
polarization element change the radiation characteristic of
.mu.-LEDs with respect to the polarization properties and thus a
discrimination of different wavelengths due to different,
wavelength-specific polarization properties or radiation directions
can be achieved.
[0226] The polarized radiation can be generated directly on the
substrate with the emitter unit, in particular at the level of a
.mu.-LED chip, or the selectivity can be improved with full
conversion. This eliminates the need for separate elements, which
could lead to positioning errors or deviations. Due to the emission
of specifically polarized radiation, the resolution of
three-dimensional representations can be improved and at the same
time, the components or illumination units required for image
generation can be reduced in size. This can be achieved, for
example, by imaging the light of several components with
complementary properties via common optics on a display, a screen
or even directly on the retina of a user. Particularly for
augmented reality applications and in the field of consumer
electronics, three-dimensional images can be created by combining
complementary polarization elements.
[0227] In some other aspects, a photonic structure or a photonic
crystal can be used to far-field characteristics of an
optoelectronic component can be specifically altered. Therefore,
among other things, an arrangement is proposed which comprises at
least one optoelectronic emitter unit, which emits electromagnetic
radiation via a light exit surface. In addition, a photonic
structure is provided for beam shaping of the electromagnetic
radiation before it exits via the light exit surface, wherein the
photonic structure shapes the electromagnetic radiation in such a
way that the electromagnetic radiation has a certain and defined
far field.
[0228] The optoelectronic emitter unit is adapted as a .mu.-LED.
The optoelectronic emitter unit can also have an array with several
.mu.-LEDs. This provides a photonic structure over a plurality of
such .mu.-LEDs.
[0229] Due to the photonic structure, the radiation characteristic
of the optoelectronic emitter unit of the arrangement changes from
a Lambertian radiator to a defined radiation characteristic in the
far field. The formulation that the electromagnetic radiation has a
certain far field thus means in particular that the radiation
characteristic is defined in the far field and differs from the
radiation characteristic of a Lambert emitter. The far field refers
to a region, which, depending on the application, is at least a few
centimetres or even a few metres away from the lighting unit so
that the magnetic and electronic fields are perpendicular to each
other.
[0230] The photonic structure may be located, especially in a
layer, below the light-emitting surface and/or between the
optoelectronic emitter unit and the light-emitting surface. Thus,
the light must pass through it before finally leaving the
component. The photonic structure can thus be integrated into the
arrangement, making it compact. The photonic structure can also be
integrated into the light-emitting surface, or an end face of the
photonic structure can form the light-emitting surface.
[0231] In some aspects, the photonic structure is a one-dimensional
photonic structure, especially a one-dimensional photonic crystal.
For example, the photonic structure may be configured such that the
electromagnetic radiation is at least approximately collimated with
respect to a first spatial direction. Thus, a collimated beam can
be generated at least with respect to the first direction in
space.
[0232] A collimating optical system can be arranged downstream of
the light exit surface, viewed in the direction of emission, the
optical system being designed to collimate the electromagnetic
radiation in a further, second spatial direction which is
orthogonal to the first spatial direction. The first direction and
the second direction can be mutually orthogonal directions, which
are parallel to the plane light-emitting surface. Thus, a beam
collimated in both directions can be produced, which is directed
along the main radiation direction away from the light-emitting
surface and orthogonal to both the first and second directions.
[0233] According to an embodiment of the invention, the photonic
structure, in particular formed as a one-dimensional photonic
crystal, can be configured in such a way that a main radiation
direction of the electromagnetic radiation runs at an angle to the
normal of the light-emitting surface, the angle being not equal to
zero degrees. The main radiation direction can thus be inclined to
the normal of the light-emitting surface. A beam collimated in at
least one direction can thus, for example, emerge from the
light-emitting surface at an angle.
[0234] The photonic structure formed as a one-dimensional photonic
crystal can be arranged in a layer below the light-emitting
surface, in particular directly below. The one-dimensional photonic
crystal can thereby have a periodically repeating sequence of two
materials with different optical refractive indexes extending in
one direction. The materials can each have a rectangular or
parallelogram-shaped cross-section. The abutting interfaces of the
materials can be inclined to the light-emitting surface.
[0235] Such a structure can be formed, for example, by etching
trenches running parallel to each other at an angle to the
light-emitting surface into the substrate having the light-emitting
surface. The trenches can be filled with a material having a
different optical refractive index than the substrate material
etched away. The angle may depend on the inclination of the
trenches to the light-emitting surface, and the width of the
trenches or the width of the substrate material remaining between
the trenches influences the wavelengths at which the photonic
structure is effective. Typically, the width of the trenches and
the width of the substrate material remaining between the trenches
are adapted to the wavelength of the electromagnetic radiation.
[0236] In some aspects, the photonic structure can also be a
two-dimensional photonic structure, in particular a two-dimensional
photonic crystal. One end face of the two-dimensional photonic
structure may form the light-emitting surface of the illumination
unit, or the two-dimensional photonic structure may be arranged in
a layer below the light-emitting surface.
[0237] The two-dimensional structure, in particular a
two-dimensional photonic crystal, can be designed in such a way
that it influences the electromagnetic radiation in such a way that
the electromagnetic radiation in the far field forms a defined, in
particular a discrete, pattern. The illumination unit can thus be
used in surface topography systems, for example for face
recognition.
[0238] As mentioned above, the photonic structure may be located in
a layer below the light-emitting surface, or an end face of the
photonic structure may form the light-emitting surface so that the
photonic structure is located directly below the light-emitting
surface and encloses it.
[0239] The photonic structure can also be formed in a semiconductor
layer of the optoelectronic emitter unit.
[0240] The optoelectronic emitter unit may comprise a layer of
converter material and the photonic structure may be formed in the
layer of converter material or in a layer between the layer of
converter material and the light-emitting surface.
[0241] The optoelectronic emitter unit can have at least one
optoelectronic laser, such as a VCSEL (vertical-cavity
surface-emitting laser). A field of several lasers is also
conceivable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0242] In the following section, some of the above-mentioned and
summarized aspects are explained in more detail using various
explanations and examples.
[0243] FIG. 1A shows a diagram illustrating some requirements for
so-called .mu.-displays or micro-displays of different sizes with
respect to the field of view and pixel pitch of the
.mu.-display;
[0244] FIG. 1B shows a diagram of the spatial distribution of rods
and cones in the human eye;
[0245] FIG. 1C shows a diagram of the perceptual capacity of the
human eye with assigned projection areas;
[0246] FIG. 1D is a figure showing the sensitivity of the rods and
cones over the wavelength;
[0247] FIG. 2A is a diagram illustrating some requirements for
micro-displays of different sizes in terms of the field of view and
the angle of collimation of a pixel of the .mu.-display;
[0248] FIG. 2B illustrates an exemplary execution of a pixel
arrangement to illustrate the parameters used in FIGS. 1A and
2A;
[0249] FIG. 3A shows a diagram illustrating the number of pixels
required depending on the field of view for a specific
resolution;
[0250] FIGS. 3B-1 and 3B-2 are a table of preferred applications
for .mu.-LED arrays;
[0251] FIG. 4A shows a principle representation of a .mu.-LED
display with essential elements for light generation and light
guidance;
[0252] FIG. 4B shows a schematic representation of a .mu.-LED array
with similar .mu.-LEDs;
[0253] FIG. 4C is a schematic representation of a .mu.-LED array
with .mu.-LEDs of different light colors;
[0254] FIG. 5A and FIG. 5B show two examples of a structure or
beamline and collimation;
[0255] FIG. 6 shows a .mu.-LED pixel where the light emission is
already directed by a specially formed reflector material;
[0256] FIG. 7 shows an optical pixel element with a spherical
reflector element and control electronics according to some aspects
of the proposed concept;
[0257] FIG. 8 shows a second embodiment of a pixel element with a
reflector element designed as a layer and a passivation layer
according to some aspects of the proposed concept;
[0258] FIG. 9 shows a third embodiment of a pixel element with
light-absorbing coatings on a display side and an assembly side of
the carrier substrate according to some aspects of the proposed
concept;
[0259] FIG. 10 forms a pixel element with a roughened display side
of the carrier substrate;
[0260] FIGS. 11A and 11B are embodiments based on some of the
aspects revealed here, with light absorbing layers to minimize
crosstalk and a color filter element on the display side of the
carrier substrate;
[0261] FIGS. 12A and 12B show embodiments of a pixel element with
IGZO- or LIPS-based drive electronics on the assembly side of the
carrier substrate and optional diffuser layer according to some
aspects of the proposed concept;
[0262] FIG. 13 shows a cross-section and top view of a pixel cell
with three .mu.-LEDs of different colors and a reflector
element;
[0263] FIG. 14 shows a method for manufacturing an optical pixel
element as described above;
[0264] FIG. 15A shows on the top a cross-sectional view of an
exemplary .mu.-LED and on the bottom a perspective view of the
optoelectronic device with a photonic structure;
[0265] FIG. 15B shows a cross-sectional view of another .mu.-LED
with photonic structure according to some suggested aspects;
[0266] FIG. 15C shows on the left side a more detailed
cross-sectional view of another optoelectronic device and on the
right side a more schematic cross-sectional view of the
optoelectronic device;
[0267] FIG. 15D is a cross-sectional view of a .mu.-LED with planar
surface and photonic structure;
[0268] FIG. 15E shows another embodiment of a .mu.-LED with
photonic structure in cross-sectional view;
[0269] FIG. 15F illustrates another embodiment of a .mu.-LED with
photonic structure in cross-sectional view according to some
aspects of the proposed concept;
[0270] FIG. 16 shows an embodiment of a method for producing one of
the structures shown in FIGS. 15D to 15E;
[0271] FIG. 17 illustrates a top view and sectional view of an
optoelectronic device with a .mu.-LED and a converter element
according to some aspects of simultaneous light shaping and light
conversion;
[0272] FIG. 18 shows a cross-section through an optoelectronic
component in a further version according to some aspects of the
proposed concept;
[0273] FIG. 19 is a top view and sectional view of another
component;
[0274] FIG. 20 shows a cross-section through a component with a
.mu.-LED and a converter element according to some aspects of light
shaping and light conversion;
[0275] FIGS. 21A and 21B show a .mu.-display with several
light-emitting units and a photonic structure in a top view and
cross section according to some aspects of the concept
presented;
[0276] FIGS. 22A and 22B represent a second embodiment of a
.mu.-display with a photonic structure in a top view and
cross-section according to some aspects of the presented
concept;
[0277] FIGS. 23A and 23B show a third embodiment of a .mu.-display
with several .mu.-LEDs of a photonic structure in a top view and as
a cross-section according to some aspects of the presented
concept;
[0278] FIGS. 24A and 24B are part of a fourth embodiment of a
.mu.-display with a photonic structure in a top view and as a
cross-section according to some aspects of the concept
presented;
[0279] FIGS. 25A and 25B show a fifth embodiment of a .mu.-display
with a photonic structure in a top view and as a cross-section
according to some aspects of the presented concept;
[0280] FIGS. 26A and 26B illustrate a sixth embodiment of a
.mu.-display with a photonic structure in a top view and as a
cross-section according to some aspects of the concept
presented;
[0281] FIGS. 27A and 27B show a seventh embodiment of a
.mu.-display with a photonic structure in a top view and as a cross
section according to some aspects of the presented concept;
[0282] FIGS. 28A and 28B illustrate an eighth embodiment of a
.mu.-display of a photonic structure in a top view and as a
cross-section;
[0283] FIGS. 29A and 29B show a ninth embodiment of a .mu.-display
of a photonic structure in a top view and as a cross-section
according to some aspects of the presented concept;
[0284] FIG. 30 shows a cross-sectional view of another variant of a
device according to the invention;
[0285] FIG. 31 shows an arrangement of an optoelectronic component
with an emitter unit having a light-emitting surface to which a
polarizing element with a three-dimensional photonic structure is
applied;
[0286] FIG. 32 illustrates a representation of a three-dimensional
photonic structure with a large number of spiral-shaped structural
elements;
[0287] FIG. 33 shows another embodiment of an optoelectronic device
with an emitter unit and a polarization element with a
three-dimensional photonic structure;
[0288] FIG. 34 shows an optoelectronic device with an emitter unit
and a three-dimensional photonic structure into which converter
material is filled;
[0289] FIG. 35 illustrates a perspective view of a first variant of
an arrangement with an emitter unit, which has a photonic structure
for generating a specific far field;
[0290] FIG. 36 shows a sectional view of a second variant of an
arrangement with an emitter unit to illustrate further aspects of
the proposed principle;
[0291] FIG. 37 shows an arrangement of a plurality of arrangements
according to the two preceding figures;
[0292] FIG. 38 shows a perspective view of a third variant of an
arrangement with an emitter unit, which has a photonic structure to
generate a defined far field;
[0293] FIG. 39 illustrates a block diagram of a surface topography
detection system with an arrangement according to one of the
preceding figures;
DETAILED DESCRIPTION
[0294] Augmented reality is usually generated by a dedicated
display whose image is superimposed on reality. Such device can be
positioned directly in the user's line of sight, i.e. directly in
front of it. Alternatively, optical beam guidance elements can be
used to guide the light from a display to the user's eye. In both
cases, the display may be implemented and be part of the glasses or
other visually enhancing devices worn by the user. Googles.TM.
Glasses is an example of such a visually augmenting device that
allows the user to overlay certain information about real world
objects. For the Google.TM. glasses, the information was displayed
on a small screen placed in front of one of the lenses. In this
respect, the appearance of such an additional device is a key
characteristic of eyeglasses, combining technical functionality
with a design aspect when wearing glasses. In the meantime, users
require glasses without such bulky or easily damaged devices to
provide advanced reality functionality. One idea, therefore, is
that the glasses themselves become a display or at least a screen
on or into which the information is projected.
[0295] In such cases, the field of vision for the user is limited
to the dimension of the glasses. Accordingly, the area onto which
extended reality functionality can be projected is approximately
the size of a pair of spectacles. Here, the same, but also
different information can be projected on, into or onto the two
lenses of a pair of spectacles.
[0296] In addition, the image that the user experiences when
wearing glasses with augmented reality functionality should have a
resolution that creates a seamless impression to the user, so that
the user does not perceive the augmented reality as a pixelated
object or as a low-resolution element. Straight bevelled edges,
arrows or similar elements show a staircase shape that is
disturbing for the user at low resolutions.
[0297] In order to achieve the desired impression, two display
parameters are considered important, which have an influence on the
visual impression for a given or known human sight. One is the
pixel size itself, i.e. the geometric shape and dimension of a
single pixel or the area of 3 subpixels representing the pixel. The
second parameter is the pixel pitch, i.e. the distance between two
adjacent pixels or, if necessary, subpixels. Sometimes the pixel
pitch is also called pixel gap. A larger pixel pitch can be
detected by a user and is perceived as a gap between the pixels and
in some cases causes the so-called fly screen effect. The gap
should therefore not exceed a certain limit.
[0298] The maximum angular resolution of the human eye is typically
between 0.02 and 0.03 angular degrees, which roughly corresponds to
1.2 to 1.8 arc minutes per line pair. This results in a pixel gap
of 0.6-0.9 arc minutes. Some current mobile phone displays have
about 400 pixels/inch, resulting in a viewing angle of
approximately 2.9.degree. at a distance of 25 cm from a user's eye
or approximately 70 pixels/.degree. viewing angle and cm. The
distance between two pixels in such displays is therefore in the
range of the maximum angular resolution. Furthermore, the pixel
size itself is about 56 .mu.m.
[0299] FIG. 1A illustrates the pixel pitch, i.e. the distance
between two adjacent pixels as a function of the field of view in
angular degrees. In this respect, the field of view is the
extension of the observable world seen at a given moment. This is
because human vision is defined as the number of degrees of the
angle of view during stable fixation of the eye.
[0300] In particular, humans have a forward horizontal arc of their
field of vision for both eyes of slightly more than 210.degree.,
while the vertical arc of their field of vision for humans is
around 135.degree.. However, the range of visual abilities is not
uniform across the field of vision and can vary from person to
person.
[0301] The binocular vision of humans covers approximately
114.degree. horizontally (peripheral vision), and about 90.degree.
vertically. The remaining degrees on both sides have no binocular
area but can be considered part of the field of vision.
[0302] Furthermore, color vision and the ability to perceive shapes
and movement can further limit the horizontal and vertical field of
vision. The rods and cones responsible for color vision are not
evenly distributed.
[0303] This point of view is shown in more detail in FIGS. 1B to
1D. In the area of central vision, i.e. directly in front of the
eye, as required for Augmented Reality applications and partly also
in the automotive sector, the sensitivity of the eye is very high
both in terms of spatial resolution and in terms of color
perception.
[0304] FIG. 1B shows the spatial density of rods and cones per
mm.sup.2 as a function of the fovea angle. FIG. 1C describes the
color sensitivity of cones and rods as a function of wavelength. In
the central area of the fovea, the increased density of cones (L, S
and M) means that better color vision predominates. At a distance
of about 25.degree. around the fovea, the sensitivity begins to
decrease and the density of the visual cells decreases. Towards the
edge, the sensitivity of color vision decreases, but at the same
time contrast vision by means of the rods remains over a larger
angular range. Overall, the eye develops a radially symmetrical
visual pattern rather than a Cartesian visual pattern. A high
resolution for all primary colors is therefore required, especially
in the center. At the edge it may be sufficient to work with an
emitter adapted to the spectral sensitivity of the rods (max.
sensitivity at 498 nm, see FIG. 1D and the sensitivity of the
eye).
[0305] FIG. 1C shows the different perceptual capacity of the human
eye by means of a graph of the angular resolution A relative to the
angular deviation a from the optical axis of the eye. It can be
seen that the highest angular resolution A is in an interval of the
angular deviation a of +/-2.5.degree., in which the fovea centralis
7 with a diameter of 1.5 mm is located on the retina 19. In
addition, the position of the blind spot 22 on the retina 19 is
sketched, which is located in the area of the optic nerve papilla
23, which has a position with an angular deviation a of about
15.degree..
[0306] The eye compensates this non-constant density and also the
so-called blind spot by small movements of the eye. Such changes in
the direction of vision or focus can be counteracted by suitable
optics and tracking of the eye.
[0307] Furthermore, even with glasses, the field of vision is
further restricted and, for example, can be approximately in the
range of 80.degree. for each lens.
[0308] The pixel pitch in FIG. 1A on the Y-axis is given in .mu.m
and defines the distance between two adjacent pixels. The various
curves C1 to C7 define the diagonal dimension of a corresponding
display from 5 mm to approximately 35 mm. For example, curve C1
corresponds to a display with the diagonal size of 5 mm, i.e. a
side length of approximately 2.25 mm. For a field of view of
approximately 80.degree., the pixel pitch of a display with a
diagonal size of 5 mm is in the range of 1 .mu.m. For larger
displays like curve C7 and 35 mm diagonal size, the same field of
view can be implemented with a pixel pitch of approximately 5
.mu.m.
[0309] Nevertheless, the curves in FIG. 1A illustrate that for
larger fields of view, which are preferred for extended reality
applications, very high pixel densities with small pixel pitch are
required if the well-known fly screen effect is to be avoided. One
can now calculate the size of the pixel for a given number of
pixels, a given field of view and a given diagonal size of a
.mu.-display.
[0310] Equation 1 shows the relationship between dimension D of a
pixel, pixel pitch pp, number N of pixels and the edge length d of
the display. The distance r between two adjacent pixels calculated
from their respective centers is given by
r=d/2+pp+d/2.
D=d/N-pp
N=d/(D+pp) (1)
[0311] Assuming that the display (e.g. glasses) is at a distance of
2.54 cm (1 inch) from the eye, the distance r between two adjacent
pixels for an angular resolution of 1 arcminute as roughly
estimated above is given by
r=tan( 1/60.degree.)*30 mm
r=8.7 .mu.m
[0312] The size of a pixel is therefore smaller than 10 .mu.m,
especially if some space is required between two different pixels.
With a distance, r between two pixels and a display with the size
of 15 mm.times.10 mm, 1720.times.1150 pixels can be arranged on the
surface.
[0313] FIG. 2B shows an arrangement, which has a carrier 21 on
which a large number of pixels, 20 and 20a to 20c are arranged.
Pixels 20 arranged side by side have the pixel pitch pp, while
pixels 20a to 20c are placed on carrier 21 with a larger pixel
pitch pp. The distance between two pixels is given by the sum of
the pixel pitch and half the size for each adjacent pixel. Each of
the pixels 20 is configured so that its illumination characteristic
or its emission vector 22 is substantially perpendicular to the
emission surface of the corresponding LED.
[0314] The angle between the perpendicular axes to the emission
surface of the LED and the beam vector is defined as the
collimation angle. In the example of emission vector 22, the
collimation angle of LEDs 20 is approximately zero. LED 20 emits
light that is collinear and does not widen significantly.
[0315] In contrast, the collimation angle of the emission vector 23
of the LED pixels 20a to 20c is quite large and in the range of
approximately 45.degree.. As a result, part of the light emitted by
LED 20a overlaps with the emission of an adjacent LED 20b.
[0316] The emission of the LEDs 20a to 20c is partially
overlapping, so that its superposition of the corresponding light
emission occurs. In case the LEDs emit light of different colors,
the result will be a color mixture or a combined color. A similar
effect occurs between areas of high contrast, i.e. when LED 20a is
dark while LED 20b emits a certain light. Because of the overlap,
the contrast is reduced and information about each individual
position corresponding to a pixel position is reduced.
[0317] In displays where the distance to the user's eye is only
small, as in the applications mentioned above, a larger collimation
angle is rather annoying due to the effects mentioned above and
other disadvantages. A user is able to see a wide collimation angle
and may perceive displayed objects in slightly different colors
blurred or with reduced contrast.
[0318] FIG. 2A illustrates in this respect the requirement for the
collimation angle in degrees against the field of view in degrees,
independent of specific display sizes. For smaller display sizes
such as the one in curve C1 (approx. 5 mm diagonal), the
collimation angle increases significantly depending on the field of
view.
[0319] As the size of the display increases, the collimation angle
requirements change drastically, so that even for large display
geometries such as those illustrated in curve C7, the collimation
angle reaches about 10.degree. for a field of view of 100.degree..
In other words, the collimation angle requirements for larger
displays and larger fields of view are increasing. In such
displays, light emitted by a pixel must be highly collimated to
avoid or reduce the effects mentioned above. Consequently, strong
collimation is required when displays with a large field of view
are to be made available to a user, even if the display geometry is
relatively large.
[0320] As a result of the above diagrams and equations, one can
deduce that the requirements regarding pixel pitch and collimation
angle become increasingly challenging as the display geometry and
field of view grow. As already indicated by equation 1, the
dimension of the display increases strongly with a larger number of
pixels. Conversely, a large number of pixels is required for large
fields of view if sufficient resolution is to be achieved and fly
screens or other disturbing effects are to be avoided.
[0321] FIG. 3A shows a diagram of the number of pixels required to
achieve an angular resolution of 1.3 arc minutes. For a field of
view of approximately 80.degree., the number of pixels exceeds 5
million. It is easy to estimate that the size of the pixels for a
QHD resolution is well below 10 .mu.m, even if the display is 15
mm.times.10 mm. In summary, advanced reality displays with
resolutions in the HD range, i.e. 1080p, require a total of 2.0736
million pixels. This allows a field of view of approximately
50.degree. to be covered. Such a quantity of pixels arranged on a
display size of 10.times.10 mm with a distance between the pixels
of 1 .mu.m results in a pixel size of about 4 .mu.m.
[0322] In contrast, the table in FIG. 3B shows several application
areas in which .mu.-LED arrays can be used. The table shows
applications (use case) of .mu.-LED arrays in vehicles (Auto) or
for multimedia (MM), such as automotive displays and exemplary
values regarding the minimum and maximum display size (min. and
max. size X Y [cm]), the pixel density (PPI) and the pixel pitch
(PP [.mu.m]) as well as the resolution (Res.-Type) and the distance
of the viewer (Viewing Distance [cm]) to the lighting device or
display. In this context, the abbreviations "very low res", "low
res", "mid res" and "high res" have the following meaning:
TABLE-US-00001 very low res pixel pitch approx. 0.8 - 3 mm low res
Pixel pitch approx. 0.5 - 0.8 mm mid res Pixel pitch approx. 0.1 -
0.5 mm high res Pixel pitch less than 0.1 mm
[0323] The upper part of the table, entitled "Direct Emitter
Displays", shows inventive applications of .mu.-LED arrays in
displays and lighting devices in vehicles and for the multimedia
sector. The lower part of the table, titled "Transparent Direct
Emitter Displays", names various applications of .mu.-LED arrays in
transparent displays and transparent lighting devices. Some of the
applications of .mu.-displays listed in the table are explained in
more detail below in the form of embodiments.
[0324] The above considerations make it clear that challenges are
considerable in terms of resolution, collimation and field of view
suitable for extended reality applications. Accordingly, very high
demands are placed on the technical implementation of such
displays.
[0325] Conventional techniques are configured for the production of
displays that have LEDs with edge lengths in the range of 100 .mu.m
or even more. However, they cannot be automatically scaled to the
sizes of 70 .mu.m and below required here. Pixel sizes of a few
.mu.m as well as distances of a few .mu.m or even less come closer
to the order of magnitude of the wavelength of the generated light
and make novel technologies in processing necessary.
[0326] In addition, new challenges in light collimation and light
direction are emerging. Optical lenses, for example, which can be
easily structured for larger LEDs and can also be calculated using
classical optics, cannot be reduced to such a small size without
the Maxwell equations. Apart from this, the production of such
small lenses is hardly possible without large errors or deviations.
In some variants, quantum effects can influence the behaviour of
pixels of the above-mentioned size and have to be considered.
Tolerances in manufacturing or transfer techniques from pixels to
sub mounts or matrix structures are becoming increasingly
demanding. Likewise, the pixels must be contacted and individually
controllable. Conventional circuits have a space requirement, which
in some cases exceeds the pixel area, resulting in an arrangement
and space problem.
[0327] Accordingly, new concepts for the control and accessibility
of pixels of this size can be quite different from conventional
technologies. Finally, a focus is on the power consumption of such
displays and controllers. Especially for mobile applications, a low
power consumption is desirable.
[0328] In summary, for many concepts that work for larger pixel
sizes, extensive changes must be made before a reduction can be
successful. While concepts that can be easily up scaled to LEDs at
2000 .mu.m for the production of LEDs in the 200 .mu.m range,
downscaling to 20 .mu.m is much more difficult. Many documents and
literature that disclose such concepts have not taken into account
the various effects and increased demands on the very small
dimensions and are therefore not directly suitable or limited to
pixel sizes well above 70 .mu.m.
[0329] In the following, various aspects of the structure and
design of .mu.-LED semiconductors, aspects of processing, light
extraction and light guidance, display and control are presented.
These are suitable and designed to realize displays with pixel
sizes in the range of 70 .mu.m and below. Some concepts are
specifically designed for the production, light extraction and
control of .mu.-LEDs with an edge length of less than 20 .mu.m and
especially less than 10 .mu.m. It goes without saying, and is even
desired, that the concepts presented here can and should be
combined with each other for the different aspects. This concerns
for example a concept for the production of a .mu.-LED with a
concept for light extraction. In concrete terms, a .mu.-LED
implemented by means of methods to avoid defects at edges or
methods for current conduction or current constriction can be
provided with light extraction structures based on photonic crystal
structures. Likewise, a special drive can also be realized for
displays whose pixel size is variable. Light guidance with
piezoelectric mirrors can be realized for .mu.-LEDs displays based
on the slot antenna aspect or on conventional monolithic pixel
matrices.
[0330] In some of the following embodiments and described aspects,
additional examples of a combination of the different embodiments
or individual aspects thereof are suggested. These are intended to
illustrate that the various aspects, embodiments or parts thereof
can be combined with each other by the skilled person. Some
applications require specially adapted concepts; in other
applications, the requirements for the technology are somewhat
lower. Automotive applications and displays, for example, may have
a longer pixel edge length due to the generally somewhat greater
distance to a user. Especially there, besides applications of
extended reality, classical pixel applications or virtual reality
applications exist. This is in the context of this disclosure for
the realization of .mu.-LED displays, whose pixel edge length is in
the range of 70 .mu.m and below, also explicitly desired.
[0331] A general illustration of the main components of a pixel in
a .mu.-display is shown schematically in FIG. 4A. It shows an
element 60 as a light generating and light emitting device. Various
aspects of this are described in more detail below in the section
on light generation and processing. Element 60 also includes basic
circuits, interconnects, and such to control the illumination,
intensity, and, when applicable, color of the pixel. Aspects of
this are described in more detail in the section on light control.
Apart from light generation, the emitted light must be collimated.
For this purpose, many pixels in microdisplays have such
collimation functionality in element 60. The parallel light in
element 63 is then fed for light guidance into some optics 64, for
further shaping and the like. Light collimation and optics suitable
for implementing pixels for microdisplays are described in the
section on light extraction and light guidance.
[0332] The pixel device of FIG. 4A illustrates the different
components and aspects as separate elements. An expert will
recognize that many components can be integrated into a single
device. In practice, the height of a .mu.-display is also limited,
resulting in a desired flat arrangement.
[0333] After light has been generated, it must be collimated and
directionally coupled out as far as possible. Therefore the
following explanations concern different aspects of light
extraction.
[0334] FIGS. 5A and 5B disclose some principles regarding the
collimation and direction of light emitted by individual pixels.
FIG. 5A shows a carrier 50, which also acts as a mirror by
reflecting all light emitted by the LED 51 arranged on the carrier.
Two adjacent LEDs are about 6 .mu.m apart and about 3 .mu.m high.
Their diameter is in the range of 6 .mu.m. Each individual pixel
emits light similar to a Lambert spotlight. Consequently, they are
completely covered with a transparent material with a refractive
index of about n=1.5.
[0335] A hemisphere 53 of the same material with a radius of
approximately 10 .mu.m is arranged on each micropixel. Each
hemisphere 53 covers the area of the underlying pixel 51 and
extends to about half the distance to the next pixel. Because of
the refractive index and geometry, the hemispheres are configured
to collimate the light emitted by the individual pixels.
[0336] FIG. 5B shows an alternative concept for collimating the
light emitted by the pixels. Similar to the above, the micropixels
are arranged at equal distances from each other. Between each
pixel, a pyramid 52 is placed on the support 50. The pyramids 52
are formed of highly refractive material and have distance D
between their tips. The height of the apex of each pyramid is
chosen so that light emitted at an angle less than 45.degree. from
the light-emitting surface is reflected on the sidewalls of the
pyramid as indicated. By using the elements shown in FIG. 5B, light
emitted by micropixels 51 can be parallelized to a certain extent,
which improves its collimation. However, as the size decreases, it
becomes increasingly difficult to shape elements 52 and 53 and to
place them directly above the micropixels.
[0337] FIG. 6 illustrates an example of a pixel for which, in one
aspect, a rear decoupling is provided by shaping the pixel as a
hemisphere and surrounding it with reflective material to shape the
emitted light. The pixel is shaped as a half-dome within an n-doped
first semiconductor material 800. A first contact 801 on a first
side of material 800 serves as the n-contact for the corresponding
pixel. A second contact 802 can be used for a variety of
pixels.
[0338] Thus, it is possible to arrange the plurality of pixels next
to each other to form a .mu.-display. Within the half-dome area of
the pixel, an active layer 803 is arranged. The active layer is
located in the upper third of the half-dome forming the pixel and
is formed by a p-doped layer 804 deposited on the n-doped material
in the half-dome. Other active layers such as quantum wells or
structures mentioned in this disclosure are possible. In order to
form the smallest possible region where recombination occurs, a
current confinement process can be used. This keeps charge carriers
away from the edge and the recombination area becomes smaller.
[0339] A reflective layer 805 is applied to the sidewalls and also
to the upper surface of the material 800. The p-contact 801 is
applied to the reflective layer 805. The reflective layer 805 also
includes an insulating layer (not shown) to prevent a short circuit
between the p-contact and the material 800. P-contact material 801
is in direct contact with the p-doped layer 804 through a gap in
the reflective layer on the half-dome forming the pixel. As a
result, the insulating layer on the reflective layer and the gap in
the reflective layer causes carrier injection only at the tip of
the half-dome. A current broadening layer can also be applied
within the p-doped layer 804.
[0340] Recombination of charge carriers occurs in the active region
803 Light emitted from the active region towards the side is
reflected at the reflective layer towards the output surface TA.
The shape of the half-dome is parabolic in some examples. The shape
should be chosen to support collinearity for light generated within
the active region. In some applications, other elements for guiding
light, such as photonic crystal structures or similar are then
arranged on the exit surface.
[0341] The following aspects deal with a different point of view in
contrast to a direct improvement of the directionality of the
emitted light. The following examples are intended for the creation
of a Lambert radiator. However, it is known by the expert that
other shapes on reflector elements influence the beam-shaping.
Special designs thus create a .mu.-LED with rear output, which can
be directed at the same time.
[0342] FIG. 7 shows an embodiment of a pixel element 10 with a
reflector element 18 according to the invention. First of all, a
carrier substrate 12 is also provided here, which often has a large
number of .mu.-LEDs 16 arranged next to each other on an assembly
side 20 of the carrier substrate 12. The carrier substrate 12 is
usually provided with an electronic control unit 24, which is used
to control the individual .mu.-LEDs 16. For this purpose,
electrically conductive connections (not shown) may be provided
between the control electronics 24 and the individual .mu.-LEDs 16.
In other cases, as shown below, the carrier substrate can also be
transparent or have other structures for reshaping the light.
[0343] The reflector element 18 here is designed like a dome and
surrounds the .mu.-LED 16 at least on the side where the .mu.-LED
16 emits light 14. For example, if the .mu.-LED 16 emits light 14
in a direction away from the carrier substrate 12, this light hits
a surface of the reflector element 18 directed towards the .mu.-LED
16, is reflected there and returned towards the assembly side 20 of
the carrier substrate 12. If necessary, the light propagates with
refraction at the interface of the assembly side 20 over a cross
section of the carrier substrate 12 in the direction of a display
side 22 of the carrier substrate 12 and is coupled out there, if
necessary with repeated refraction or diffraction.
[0344] The reflector element 18 should have the advantageous shape
and properties that light 14 is incident at an angle of incidence
26 as perpendicular as possible relative to a carrier substrate
plane 28 on the placement side 20 of the carrier substrate 12.
Among other things, this should serve to minimize losses due to
total reflection within the carrier substrate 12 as well as
unfavourable angles when decoupling from display side 22 of carrier
substrate 12. This angle of incidence 26 should be as small as
possible, also to minimize crosstalk between adjacent pixel
elements 10.
[0345] FIG. 8 shows another example of a pixel element 10 according
to the invention with a reflector element 18 configured as a layer
on or around a .mu.-LED 16. This embodiment variant can be useful
in that the reflector element 18 can be processed directly onto a
surface of the .mu.-LED 16, for example as a metallic layer.
Various materials can be used for the reflector element 18, such as
metallic materials, metal alloys or oxides or other suitable
compounds that can be applied using the available manufacturing
processes. FIG. 6 shows a similar embodiment, in which the .mu.-LED
is made directly from the same material as the carrier substrate.
In addition, the reflector element has a specific shape and design.
However, the various aspects of FIG. 6 can also be combined with
the embodiments shown in FIGS. 7 to 8, among others, and disclosed
here.
[0346] In addition, a passivation layer 32 is provided at the mesa
edges 30 between the .mu.-LED 16 and the layer of the reflector
element 18. This passivation layer 32 has light-absorbing or at
least light-blocking properties so that light 14 emitted by the
.mu.-LED in the direction of the carrier substrate plane 28 or in
the direction of the mesa edges 30 is attenuated or absorbed. This
is to prevent light 14 from passing over in the direction of an
adjacent pixel element 10 and causing crosstalk. In addition, the
passivation layers 32 can be configured to cause beam-shaping of
the emitted light 14.
[0347] FIG. 9 shows a pixel element according to the invention with
light-absorbing coatings 34 on a display side 20 and an assembly
side 22 of the carrier substrate 12. This embodiment features a
spherical reflector element 18 surrounding a .mu.-LED 16, which is
arranged on the placement side 20 of the carrier substrate 12.
According to this aspect, the carrier substrate 12 is adapted to be
transparent or at least partially transparent so that light 14 can
propagate within the carrier substrate 12.
[0348] In order to improve the dark impression and contrast of a
display, light-absorbing layers 34 are provided according to this
embodiment, which are applied here outside the reflector element 18
on the carrier substrate 12 on the assembly side 20 and/or on the
display side 22. On the one hand, this can prevent light 14 from
being coupled out outside a desired active area of the pixel
element. On the other hand, an advantageous effect can be that
light 14, which propagates inside the carrier substrate 12, is not
coupled out outside the desired area on display side 22, but is
absorbed or attenuated. For an observer, the light-absorbing layers
34 can be recognized as clearly inactive or black or dark, and due
to the better optical demarcation compared to the active luminous
areas, improved contrast properties of a display can be
achieved.
[0349] FIG. 10 illustrates in a simplified way a further version of
a pixel element 10 according to the invention. In its basic
structure, pixel element 10 corresponds to the examples already
shown in FIGS. 7 to 9. Here, a .mu.-LED 16 is provided on a carrier
substrate 12, which is surrounded by a reflector element 18. By
reflecting the light 14 at the reflector element 18, light 14
propagates through the carrier substrate 12 and reaches a display
page 22 of the carrier substrate 12.
[0350] Here it is desirable that as much of the light 14 that has
passed through carrier substrate 12 is coupled out of carrier
substrate 12 via display screen 22. Here, a roughened surface 36
can cause an improved out-coupling of light 14. More generally
speaking, the surface of the display side 22 comprises a
structuring, which has additional microstructures at an angle to
each other which deviate in their angle from the alignment parallel
to a carrier substrate plane 28 and can thus cause additional
out-coupling.
[0351] FIG. 11A shows a pixel element 10, according to the
invention, with a color filter element 38 on the display side of
the carrier substrate 12 and light-absorbing coatings 34. While the
basic structure of the pixel element 10 corresponds to a large
extent to that of the previous figures, light-absorbing coatings 34
are also provided here, which are provided both on an assembly side
20 and on a display side 22 of the carrier substrate 12 outside an
area of the reflector element 18. In addition, a color filter
element 38 is provided here, which is arranged on the display side
22 of the carrier substrate 12 opposite the reflector element 18.
For example, a red .mu.-LED can be provided with a corresponding
red color filter element 38. The same applies analogueously to
green color filter elements 38 together with green .mu.-LEDs and,
for example, to blue color filter elements 38 together with blue
.mu.-LEDs and the respective emitter chips 16. The advantages here
are lower reflectivity and an improved black impression. Here, too,
the light-absorbing layers 34 absorb unwanted light components 14
that propagate within the carrier substrate 12.
[0352] In an alternative embodiment, again with reference to FIG.
11A, element 38 may also be a color conversion element to convert
light of a first wavelength to a second wavelength. The light
emitted by the .mu.-LED 16 and reflected by the reflector element
18 strikes the converter element and is converted there. The basic
colors can be produced in this way by using different converter
dyes.
[0353] FIG. 11B shows another example of a pixel element 10, where
two adjacent pixel elements 10 are arranged on the carrier
substrate. Between these two pixel elements, light absorbing layers
34 are provided on the different surfaces of the carrier substrate.
This can be used in particular to minimize crosstalk. Depending on
the arrangement and design of the .mu.-LED 16, there is a gap
between the .mu.-LED 16 and the surrounding reflector element 18,
which can act as an aperture or aperture edge. This can mean that
light 14 emerges through this aperture at a small angle relative to
the carrier substrate plane 28 and can pass through the carrier
substrate 12 at an angle in the direction of the adjacent pixel
element 10.
[0354] To prevent this crosstalk, light-absorbing layers 34 are
provided between the two pixel elements 10 and between the two
adjacent reflector elements 18, respectively. These can be arranged
on an assembly side 20 of the carrier substrate 12, but also on a
display side 22 of the carrier substrate 12. The light-absorbing
layers 34 attenuate or eliminate the then unwanted light components
14 and can thus improve the contrast of a display.
[0355] In FIG. 12A, reference is made to the aspect of the control
electronics 24 of a pixel element 10 according to the invention.
These may be adapted as part of the carrier substrate 12, with
transistor structures, for example, being provided as part of the
substrate 12. For the material of the carrier substrate 12, various
materials can be considered, such as amorphous silicon, but also
IGZO or LTPS. IGZO stands for indium gallium zinc oxide and has
partially transparent properties for light and is comparatively
inexpensive to manufacture.
[0356] If an electronic control unit 24 is designed on the basis of
IGZO, it is also conceivable according to an example that the
electronic control unit 24 can be arranged within an inner area of
a reflector element 18 (not shown here). This possibility is based
in particular on the at least partial light transmission of the
IGZO material. According to another example, 24 LTPS is used as the
basis for the control electronics 24 and LTPS as the material for
the carrier substrate 12. LTPS stands for Low Temperature Poly
Silicon and can have better electrical properties than IGZO, but
with more light absorbing properties.
[0357] LTPS can be used for both p-transistors and n-transistors,
whereas IGZO is only suitable for p-transistors. An arrangement of
the control electronics 24, based on LTPS, must therefore be
provided here outside a reflector element 18. A further alternative
can be seen in the use of so-called .mu.ICs. These are often used
together with silicon-based substrates and usually have
light-absorbing properties.
[0358] A challenge here may lie in miniaturizing these ICs, whereby
the electrical performance of the .mu.ICs is often higher than that
of other variants. Here, too, an arrangement would, according to an
example, be made outside an area of a reflector element 18 on the
assembly side 20 of the carrier substrate 12. Contacting of the
emitter chip 16 can be achieved, for example, via a metallic
contact pad on the carrier substrate 12 or via transparent ITO
(indium tin oxide).
[0359] FIG. 12B shows a pixel element 10 according to the invention
with a partial coating of a diffuser layer 40 on the reflector
element 18. The special feature of the pixel element 10 shown in
this embodiment can be seen in a special embodiment of the
reflector element 18. Here, a diffuser layer 40 is provided on the
lateral inner surfaces of the reflector element 18 (here especially
the area 18B). This diffuser layer 40 is intended to cause an
increased deflection of the emitted light 14 and a more
advantageous deflection of the light 14 in the direction of the
carrier substrate 12. It can be advantageous here to provide a
thinner or completely missing diffuser layer 40 in an area 18A of
the reflector located vertically directly above the emitter
chip.
[0360] In particular, this diffuser layer 40 can be made flat or
even in this area 18A in order to focus the most direct possible
back reflection of light emitted transversely to the carrier
substrate plane 28 approximately vertically in the direction of the
placement side 20 of the carrier substrate 12. A relatively thin
diffuser layer 40 can be sufficient for this purpose, since
.mu.-LEDs, due to their properties and construction, come closer to
a Lambertian radiation pattern than previous LED technologies.
Materials that can be used for this purpose include Al.sub.2O.sub.3
or TiO.sub.2.
[0361] FIG. 13 shows another pixel cell in cross-section and top
view. The pixel cell comprises three individual .mu.-LEDs 16r, 16g
and 16b. These are designed to emit the respective basic colors
red, green and blue during operation. In this embodiment, the three
.mu.-LEDs are arranged in the corners of a right-angled triangle.
However, other arrangements are also possible, for example in a
row. Each .mu.-LED is adapted as a vertical .mu.-LED, i.e. a common
contact is located on the side of the .mu.-LEDs facing away from
the carrier substrate. The .mu.-LEDs can be individually controlled
and can be manufactured, for example, in some versions as shown in
FIGS. 49 to 54. Other designs are also conceivable, for example as
individual .mu.-LED modules with or without redundancy. In the
illustration on the right, a common transparent cover contact 17 is
provided for this purpose, which either completely or at least
partially covers the .mu.-LEDs and thus makes electrical contact.
The sidewalls of the .mu.-LED are insulated and are not connected
to the cover electrode 17. In addition, a reflector element 18 is
provided which surrounds each of the three .mu.-LEDs and thus forms
a complete pixel.
[0362] Light, which is thus emitted in the direction of the
reflector element, is reflected by the carrier substrate where it
hits a photonic structure 19, which is partly incorporated in the
carrier substrate. The photonic structure 19 is designed to
redirect the emitted light and emit it as a collimated light beam.
Various embodiments of such photonic structures are disclosed in
this application, for example in FIG. 17 to 20, 31 to 39 or even
15A to 15C.
[0363] The photonic structure can also be omitted depending on the
application. For automotive applications, a Lampertian radiation
pattern may be more desirable, in which case it is omitted. In the
field of Augmented Reality a strong directionality may be desired,
which is achieved by the additional photonic structure. In addition
to the photonic structure, a converter material can also be
provided in addition to the structure or alternatively. In the
automotive sector, such directional light applications with white
or other colored light are possible.
[0364] Finally, FIG. 14 shows a process 100 for the production of a
pixel element 10. First, one or more .mu.-LEDs are attached to one
side of a flat carrier substrate. The attachment is preceded by a
corresponding transfer. Details are disclosed in this
application.
[0365] This is followed in step 120 by creating a reflector
element, for example as a reflective layer of the .mu.-LED.
According to an example, before step 110, a display side 22 of the
carrier substrate 12 is processed to produce a roughening 36 or
rough microstructuring of the surface of the display side 22.
[0366] One way to reduce the emission angle of .mu.-LEDs is to
indicate structures on the emission surface that reduce the
propagation of light parallel to the emission surface. This can be
achieved by photonic structures. The photonic crystal structure is
basically not limited to a certain material system. The following
examples and embodiments will give different ones, which are not
limited to a specific design, but are suitable for all embodiments
and designs disclosed herein. Furthermore, different semiconductor
material systems can be used for the .mu.-LEDs, especially on GaN,
AlInGaP, AlN or InGaAs basis. FIGS. 15A to 15C illustrate different
aspects related to the principle of collimation of light by using a
photonic crystal.
[0367] The exemplary optoelectronic device 700 of FIG. 15A
comprises a stack of layers 702, 703 including an active zone 704
for generating electromagnetic radiation, and at least one layer
705 on the main radiation direction, which comprises a photonic
crystal structure 706.
[0368] For example, layer 702 is a p-doped GaN layer and layer 703
is an n-doped GaN layer. The layer on the underside 701 can be a
metallic mirror layer and/or a carrier layer. The growth direction
G goes from the top side to the bottom side, or vice versa, and
orthogonal to the connecting surface of the layers.
[0369] The photonic crystal structure 706 is formed by nanowires
with radius r and height h. The wires form a triangular lattice
with lattice constant a. However, other lattice geometries such as
square lattice are possible. The periodicity and thus the lattice
constant a of the photonic crystal structure are such that they are
about half the wavelength of the light wavelength to be diffracted.
The space between the wires may contain a material, which has a
different refractive index than the material of the layer 705. For
example, layer 705 may be formed of n-doped GaN. Other materials
and SiO.sub.2 are also possible.
[0370] The layer 702 can be supplied with an extension 702a, which
extends through the layer 703 and reaches into the layer 705 but
not into the photonic crystal structure 706 as shown in the lower
view of FIG. 15A.
[0371] The photonic crystal structure 706 can have the effect of
improving the concentration of light passing through it. In
particular, the photonic crystal structure 706 can provide a
virtual bandgap for a region of wavelengths that are perpendicular
to the direction of growth. The photonic crystal structure 706 can
block this light. In contrast, light that runs along the direction
of growth is basically not disturbed by the photonic crystal
structure 706. As shown in the upper view of FIG. 15A, the photonic
crystal structure 706 in layer 705 can be generated twice or even
more. The structures 706 are separated from each other by the
distance D.
[0372] Alternatively, a single photonic crystal structure 706 can
be fabricated to cover the complete layer 705. In this case, more
unit cells of the lattice can be arranged in layer 705, which has a
positive effect on the properties of the photonic crystal
structure, which depend on the periodicity.
[0373] In the exemplary device shown in FIG. 15B, layer 702 is not
supplied with an extension. However, layer 703, which is adjacent
to layer 705 with crystal structure 706, is provided with a
roughened surface, as indicated by projections 703a, 703b, 703c and
703d. The roughened surface can be filled with SiO.sub.2, for
example, to fabricate layer 705 with photonic crystal structure
706.
[0374] In the exemplary device shown in FIG. 15C, the layer 703 is
formed with a wigwam surface roughening 703e. The layer 705 with
the photonic crystal structure 706 may contain SiO.sub.2. The
photonic crystal structure 706 may be etched into the SiO.sub.2
layer. Air or other material may be in the space between the
photonic crystal structure.
[0375] The photonic crystal structure 706 covers the complete layer
703 and is placed at a distance H from the wigwam surface
roughening 703e of the underlying layer 703.
[0376] Layer 701 is a carrier layer, layer 711 can be a compound
layer, layer 712 is a mirror layer, especially a silver mirror
layer, and layer 713 can be a dielectric layer. A mesa dry etch can
be performed during device production and after patterning the
photonic crystal structure 706.
[0377] The different photonic decoupling structures create a
certain roughness and surface structures on the surface, depending
on their design. Therefore, the surface should be planarized to
facilitate a possibly necessary later transfer. FIGS. 15D to 15F
show different aspects of surface planarization according to one of
several methods of making photonic structures on a .mu.-LED.
[0378] Generally, a large number of .mu.-LEDs are first formed in
or on a wafer, then their surface is structured and then, if
necessary, separated. Modules of .mu.-LEDs and other designs are
part of this application. It is clear from this that the .mu.-LEDs
come in different designs. The following surface treatment is thus
independent of the later processing and is suitable for (later
isolated) .mu.-LEDs, .mu.-LED modules and also pixelated optochips
with a plurality of .mu.-LEDs.
[0379] According to FIG. 15D, a .mu.-LED is epitaxially formed with
an active layer in a semiconductor body. The active layer is not
shown here. The .mu.-LED comprises in its surface area, which is
covered by the likewise not shown carrier, a non-ordered, i.e.
random out-coupling structure A, which is formed from the same
semiconductor material as the semiconductor (or parts thereof). The
structured surface region therefore adjoins the doped layers. The
resulting roughness is smoothed again by applying another
transparent material of SiO.sub.2 by means of TEOS
(tetraethylorthosilicate) and subsequently planarizing it. The
decoupling structure improves the decoupling. It is particularly
suitable for the extraction of the light emitted by the active
layer. This also reduces optical crosstalk of an adjacent .mu.-LED
with a different wavelength.
[0380] The other transparent material shows a low refractive index,
especially less than 1.5, which improves the decoupling from the
structured area (higher refractive index). Afterwards the other
material is removed by CMP process to form the smooth surface 7 of
the structured surface area 9. As shown, the removal is either
carried out up to the highest areas of the structured area or a
surface of the material 5 is generally left over. In this respect,
a gradual transition from a high refractive index via the lower
refractive index of the material 5 to air results.
[0381] In addition to SiO.sub.2 material 5, crown glass with a
refractive index of e.g. 1.46, PMMA with a refractive index of e.g.
1.49 and quartz glass with a refractive index of e.g. 1.46 can be
used. These refractive indices result at the wavelength 589 nm of
the sodium D-line. A refractive index of silicon dioxide, for
example, is 1.458.
[0382] FIG. 15E shows a second example of a .mu.-LED with an output
structure. To improve light out-coupling, a transparent second
material 3 with a high refractive index is applied to the planar or
structured surface of the .mu.-LED and structured in a suitable
way.
[0383] For example, a suitable second material 3 with a high
refractive index greater than 2 is Nb.sub.2O.sub.5 with a
refractive index of 2.3. Other usable materials with a high
refractive index are for example zinc sulphide with a refractive
index of for example 2.37, diamond with a refractive index of for
example 2.42, titanium dioxide with a refractive index of for
example 2.52, silicon carbide with a refractive index of for
example 2.65 and titanium dioxide with a refractive index of for
example 3.10. These refractive indices result in particular at the
wavelength 589 nm of the sodium D-line. Other materials can also be
used.
[0384] The structuring of surface area 9 is done, as in FIG. 15D,
by creating a random topology on surface area 9. While according to
FIG. 15D the random topology is created by directly roughening the
surface 7 of the surface region 9 of the semiconductor body
comprising a first material 1, according to FIG. 15E the random
topology is formed by first depositing the transparent second
material 3 and then roughening it.
[0385] After the topology has been created, the rough surface is
smoothed by applying the transparent material 5 described above to
the rough surface and then planarizing it.
[0386] FIG. 15F shows a third example of a .mu.-LED, but this time
with an ordered topology. This is explained in detail as in the
examples in this application by depositing the transparent second
material on the surface. A periodic photonic crystal structure is
then introduced into the second transparent material.
Alternatively, photonic properties can be achieved by non-periodic
structures, especially quasi-periodic or deterministic aperiodic
structures.
[0387] Alternatively, periodic photonic crystals or non-periodic
photonic structures, in particular quasiperiodic or deterministic
aperiodic photonic structures, can in principle be directly
incorporated into the first material 1 of the semiconductor body
without a second material 3.
[0388] After the photonic structure has been formed, the
interstitial spaces are filled with a transparent material with a
lower refractive index. The transparent third material 5, in
particular SiO.sub.2, is planarized, resulting in a smooth and even
surface. As shown in FIG. 15F, both the surface of material 3 and
the interstitial material 5 are flat. However, in an alternative
embodiment, the transparent third material 5 extends beyond the
structure of material 3, so that the surface is completely formed
from material 5. In this way, an out-coupling efficiency can be
improved compared to an unmachined surface. A transfer process
using stamp technology remains possible because of the smooth and
even surface.
[0389] FIG. 16 shows an example of a proposed method. In a first
step S1 an output structure A is formed on a surface of a .mu.-LED.
This is done by structuring the surface. It is possible to
structure the semiconductor material directly or to provide such a
structuring after the deposition of a further material. For this
purpose, the surface is covered with a photomask, which is then
exposed to light, thus defining the structures. The surface is
structured by various other processes including various etching
steps. In step S2, another transparent material is deposited in the
spaces created after etching. The transparent material covers the
previously created structure. Subsequently, in step S3 the surface
is planarized by CMP or other suitable processes and removed to
approximately the height of the structures. The structured .mu.-LED
thus produced can be further processed, separated and
transferred.
[0390] FIG. 17 shows in a top view and a sectional view a radiation
source 6 in the form of a .mu.-LED and with a layer 2 arranged in a
semiconductor substrate 8 of the .mu.-LED 7, which comprises a
photonic structure 4 with a suitable converter material. This is
based on the idea of creating a unification of light-shaping and
converting structure so that a particularly space-saving
arrangement of the individual elements and thus a particularly
small design of an optoelectronic component is possible. The
structured layer 2 with the converter material forms a converter
element 1, whereby the converter material emits converted radiation
into a radiation emission area 3 of the radiation source 6 when
excited by the excitation radiation emitted by the LED 7.
[0391] The structure 4 provided in layer 2 with the converter
material is designed in such a way that the converted radiation is
emitted exclusively as a directed beam in a specific radiation area
3. According to the embodiment shown in FIG. 17, the converted
radiation is emitted perpendicular to a plane in which the .mu.-LED
chip with its semiconductor substrates is located.
[0392] The structured layer 2 shown in FIG. 17 is a two-dimensional
photonic crystal etched into the LED semiconductor substrate above
the active layer of the .mu.-LED. The individual, here rod-shaped
and periodically arranged recesses of structure 4 have been filled
with the converter material. The layer thickness of structure 4 is
at least 500 nm, so that a band gap is created in the crystalline
solid-state material, which causes a directionality of the
converted radiation emitted by converter element 1. In this
example, the recesses are round and arranged in a hexagonal pattern
in the center of which a recess is also arranged. However, the
recess itself can also take other shapes, for example hexagonal or
square. Round recesses have the advantage that they are easier to
produce. The recesses show the same distance and have the same
size. This circumstance is also due to the application.
[0393] For example, the recesses can be of different sizes or have
different spacing. This results in a different periodicity, so that
a different optical band gap is formed. In a similar embodiment,
the recesses can have a first periodicity in a first direction
(i.e. first distance from each other and size) and a second
periodicity in another, e.g. orthogonal direction. This result in a
different band gap in the two spatial directions and a
wavelength-dependent selection can be made. With a suitable
setting, a full conversion of the incident light is possible, so
that the .mu.-LED emits converted light substantially parallel to
the recesses.
[0394] Such a photonic structure can significantly increase
directionality and thus efficiency, especially of etendue-limited
systems. Due to the provision of a layer 2 with a corresponding
structure 4 and suitable converter material directly on the surface
of the .mu.-LED 7, the otherwise additionally provided optical
elements can be dispensed and thus a comparatively small radiation
source can be realized by exploiting the invention. In addition, a
particularly efficient radiation source is made available, since on
the one hand, no light is emitted in an unneeded direction that is
not perpendicular to the LED chip surface, and on the other hand,
all the converted light can be used. Furthermore, modes of the
excitation radiation emitted by the .mu.-LED 7, which are guided in
the active zone 9 and have a low extraction efficiency from the
.mu.-LED 7, can be efficiently converted.
[0395] In addition, FIG. 18 shows the sectional view of a radiation
source 6, which is configured as explained in connection with FIG.
17, but additionally has a filter element 5 applied to the top
layer of the radiation source 6 in the form of a filter layer 5,
which is opaque to radiation of selected wavelength ranges. The
filter layer 5 has the function of a color filter.
[0396] Such a technical design is particularly suitable for
radiation sources 6, in which a .mu.-LED 7 and a converter element
1 are combined in such a way that the light emitted by the .mu.-LED
7 is fully converted. With the aid of a suitably designed filter
layer 5, the radiation emitted in the emission range 3 can thus be
limited to radiation with a desired wavelength. Such a filter layer
5 also ensures that the excitation radiation emitted by LED 7,
which is not converted into converted radiation by converter
element 1, is prevented from escaping into emission range 3 by
means of filter layer 5 if necessary.
[0397] In an alternative embodiment, layer 3 of FIG. 18 assumes an
out-coupling function in order to appropriately couple out the
light formed by the photonic structure. However, a combination of
these two functionalities is also possible. In this context, layer
3 can also be structured, for example roughened, in order to better
couple out the light.
[0398] FIG. 19 again shows a radiation source 6, which has a
.mu.-LED 7 and a converter element 1 applied to a semiconductor
substrate 8 of the .mu.-LED 7. Converter element 1 comprises a
layer 2 with converter material and a structure 4, which is applied
to a semiconductor substrate 8 of LED 7. The structured layer 2 is
preferably a photonic crystal, a quasi-periodic or
deterministically aperiodic photonic structure. The structure 4 of
layer 2 is filled with suitable converter material.
[0399] In contrast to the embodiment explained in FIG. 17, however,
the structured layer 2 is not only arranged in a semiconductor
substrate in the upper area of the radiation source 6, but extends
into the active zone 9 of the .mu.-LED 7. Again, a structured layer
2 with a layer thickness greater than 500 nm is provided, thus
creating an optical band gap. Also in this case, modes of the
excitation radiation emitted by the .mu.-LED 7, which are guided in
the active zone 9 and have a low extraction efficiency from the
LED, can be efficiently converted.
[0400] In addition, FIG. 20 shows a configuration of a radiation
source 6, which is configured as shown in FIG. 19 and additionally
has a filter element 5 applied to the top layer of the radiation
source 6, which is designed in the form of a filter layer serving
as a color filter. Such color filters offer the possibility to
limit the emission of the converted radiation into the emission
range in case of a full conversion of the excitation radiation
emitted by the .mu.-LED 7 or to selectively suppress the emission
of unconverted excitation radiation in case of a not complete
conversion.
[0401] FIGS. 21A and 21B show a .mu.-display with a photonic
structure for the emission of light that preferably emerges
vertically from a light emission surface 21. The device comprises
an array 11 having pixels, wherein optically acting nanostructures
in the form of a photonic crystal K are formed over the entire
emitting surface of the light exit surface 21. The array 11 also
comprises an array-like arrangement of light sources, each of which
comprises a recombination zone 2, which lies in a recombination
plane 1.
[0402] The recombination zones 2 are formed in a first layer of
optically active semiconductor material 3 of array 11. The zones 2
can comprise quantum dots, one or more quantum wells or even a
simple pn junction. In order to obtain more localized recombination
regions, it may be intended to limit recombination to predefined
areas by current confinement or other structural measures.
[0403] In the layer with the semiconductor material 3, the photonic
crystal or photonic crystal structures K are structured, namely in
the form of a two-dimensional photonic crystal. The photonic
crystal K is located between the recombination zones 2 and the
light-emitting surface 21. The photonic crystal structures K can be
arranged independently of the positioning of individual pixels,
whereby in the example shown one pixel corresponds to one or three
light sources with a recombination zone 2. Three light sources,
therefore, so that any color can be produced by suitable color
mixing.
[0404] The optically active photonic crystal structures K are
filled free-standing in air or, as shown, with a first filling
material 7, in particular electrically insulating and optically
transparent, in particular SiO.sub.2, with a refractive index which
is lower than the refractive index of the semiconductor material 3.
The filling material 7 preferably also comprises a low absorption
coefficient.
[0405] In the array 11, both electrical poles of each light source
are electrically connected by means of an optically reflective
contact layer 5 for the electrical contacting of the light sources.
The contacting layer 5 is located on a side of the optically active
semiconductor material 3 facing away from the optically active
photonic crystal structures K and is arranged below as shown in
FIG. 21B. This type of contacting enables very strongly localised
recombination zones 2. For this purpose, the contacting layer 5
comprises at least two electrically insulated areas in order to be
able to connect the poles electrically separately.
[0406] The photonic crystal K can be structured over the entire
emitting surface 21 in such a way that at least approximately only
light with a propagation direction perpendicular to the surface 21
can leave the component. If the photonic crystal K is close to the
recombination plane 1 and the layer thickness of the photonic
crystal K is large in comparison to the distance to the
recombination zone 2, the optical density of states in the area of
light generation is additionally changed.
[0407] This makes it possible to generate a complete bandgap for
optical modes with propagation direction parallel and at a small
angle to the surface of the, in particular, planar, i.e. in
particular flat and/or smooth, pixel-containing array 11. The
emission of light with propagation direction parallel to the
emitting surface is then completely suppressed.
[0408] In particular, light can only be generated in a limited
emission cone, which is defined by the photonic crystal K. In this
case, directionality is already ensured at the level of light
generation, which effectively increases efficiency compared to an
angle-selective optical element, since such an element only
influences light extraction.
[0409] The alignment of the photonic crystal K is independent of
the positioning of the individual pixels, especially in such a way
that an alignment of the pixel structure to the photonic structure
K is not necessary and processing of an entire wafer surface is
possible. It is a reasonable embodiment if the device is
homogeneous in its optical properties over the entire surface of
the array 11 or varies only slightly so as not to disturb the
optical environment of the photonic crystal K.
[0410] FIGS. 22A and 22B show a second proposed optoelectronic
device in a plan view and in cross-section respectively. In the
pixelated array 11, the photonic crystal K is arranged in a second
layer of a material 9, in particular Nb.sub.2O.sub.5, above a first
layer of the optically active semiconductor material 3, as an
alternative to the embodiment shown in FIGS. 21A and 21B. The
material 9 thereby has a large optical refractive index and it is
arranged on the flat and/or smooth surface of the semiconductor
material 3. Preferably, the material 9 also comprises a low
absorption and is therefore very transparent. The contacting is
similar to that shown in FIGS. 21A and 21B and allows very
localized recombination zones 2.
[0411] Alternatively, some embodiments may provide that the
material is also electrically conductive. This is especially useful
if the different pixels are designed with vertical .mu.-LED
packages and are to be connected to a common contact.
[0412] As shown in FIGS. 21A and 21B, columns are formed from the
material 9 and the photonic crystal K is in turn formed as a
free-standing two-dimensional photonic crystal. The space between
the columns is filled with a different material with a lower
refractive index than in FIGS. 21A and 21B. A possible filling
material is for example SiO.sub.2.
[0413] FIGS. 23A and 23B show a third proposed optoelectronic
device in a top view and in a cross-section, respectively. The
device shown comprises as light sources an array of vertical
.mu.-LEDs 13 and a two-dimensional photonic crystal structure K
arranged in an overlying layer, which extends over the entire
emitting surface 21 and is formed from a material 9 with a high
refractive index. The free space of the structure K is in turn
filled with filler material 7 with a lower optical refractive
index.
[0414] The vertical light-emitting diodes 13 have an upper and a
lower electrical contact along a vertically oriented longitudinal
axis, which is perpendicular to the light-emitting surface 21. The
light-emitting diodes thus comprise an electrical contact on the
front side and an electrical contact on their rear side. The rear
side is the side of the .mu.-LEDs 13 facing away from the light
emission surface 21, while the front side faces the light emission
surface 21.
[0415] The device comprises an electrically conductive and the
generated light reflecting contacting layer 5 for the electrical
contacting of the contacts on the back of the LEDs 13 The
contacting layer 5 is designed in such a way that the individual
.mu.-LEDs can be controlled separately. For the electrical
contacting of the contacts on the front of the LEDs 13, a third
layer is provided, which comprises an electrically conductive and
optically transparent material 17, for example ITO. An electrical
connection to the corresponding pole of a power source can be
established via a bonding wire 19.
[0416] In and along the recombination level 1, a further, in
particular electrically insulating, filling material 15 can be
arranged between the third layer and the optically reflective
contacting layer 5. This electrically separates the .mu.-LED from
each other. In addition to this structure shown here, other
pixelated components disclosed in this application may also be
provided with the structure K. These include, for example, the
disclosed antenna structures, the .mu.-LED in bar form or the
.mu.-LED modules. Likewise, in all the embodiments shown here,
reflective structures may be provided in layer 5 which deflect the
light in the direction of the exit surface. These include the
structures surrounding the actual .mu.-LED, which are disclosed in
this application.
[0417] FIGS. 24A and 24B show a fourth version of a .mu.-display in
a top view and cross-section. The .mu.-display or module device
comprises an array of horizontal .mu.-LEDs 13 with respective
recombination zones 2 and an optically effective two-dimensional
photonic crystal structure K below the total emitting surface 21.
The photonic crystal structure K is located in a layer of a
material 9 with a high refractive index, for example
Nb.sub.2O.sub.5. Free spaces are in turn filled with filling
material 7, for example silicon dioxide, with a lower optical
refractive index.
[0418] In the case of the horizontal LEDs 13, both electrical
contacts are located on the rear of the LEDs 13. Both poles of the
LEDs 13 are electrically connected by means of electrically
separated areas of the optically reflective contact layer 5. In the
area of the recombination level 1, a filling material 15, in
particular an electrically insulating one is arranged between the
material layer 9 and the contacting layer 5.
[0419] The efficiency with respect to light generation is
relatively high in the embodiments according to FIGS. 21A to 24B,
since in these embodiments directionality or directionality of the
light is already achieved during light generation, especially if a
higher photonic state density can be achieved in the area of the
recombination zones 2 for the emission of light in the direction
perpendicular to the light exit surface by means of the band
structure of the photonic crystal K. A further advantage is that
the structuring of the photonic crystal K can be carried out
homogeneously over an entire wafer. A certain positioning or
orientation of the photonic crystal to the individual pixels or
micro light emitting diodes is not necessary. This will
significantly reduce manufacturing complexity, especially compared
to alternative approaches where structures are placed individually
over each pixel.
[0420] FIGS. 25A and 25B show a fifth proposed optoelectronic
device in a top view and cross-section. The device comprises a
pixelated array 11 and optically acting columnar or pillar
structures P, in particular with pillars or columns structured over
the entire emitting surface 21. The array 11 is smooth and flat on
its surface.
[0421] The pixelized array 11 in this configuration comprises a
large number of subpixels, each with a light source that includes a
respective recombination zone 2. The recombination zones 2 of the
pixels are located in a recombination plane 1 and they are arranged
in a first layer with optically active semiconductor material
3.
[0422] Above this first layer the pillar structures P are formed.
One pillar P is assigned to a light source, so that each Pillar P
is located directly above the recombination zone 2 of the assigned
light source. A longitudinal axis L of each pillar P runs in
particular through the center M of the recombination zone 2 of the
assigned light source 2. The pillars P consist of a material 9 with
a high refractive index, for example Nb.sub.2O.sub.5. A filler
material 7 with a lower refractive index, such as silicon dioxide,
can be arranged in the spaces between the pillars P.
[0423] The pillars P can be arranged above the layer with the light
sources, in particular by additionally applying the pillars P above
array 11. Alternatively, the pillars can be etched into the
semiconductor material 3. For this purpose, the semiconductor
material layer must be appropriately high. Since the semiconductor
material normally comprises a high refractive index, material can
be etched away in such a way that the pillars 9 remain standing.
The areas freed up by etching can be filled with material of low
refractive index.
[0424] The pillars P act like waveguides which guide light upwards
in the direction of the longitudinal axis L, so that the pillars P
can cause an improved emission of light in a direction
perpendicular to the light emission surface 21. In addition to the
design shown here, the periodicity of the pillar structures can
also be different, for example, the pillars can be located
alternately above one .mu.-LED and between two adjacent .mu.-LEDs.
This results in a double density of columns. The periodicity
determines the optical band structure and thus the properties with
regard to light extraction.
[0425] In the array 11, both electrical poles of a light source are
electrically connected to the recombination zones 2 by means of a
reflective contact layer 5. The contacting layer 5 is formed on a
side of the semiconductor material 3 that is turned away from the
optically active pillar structures P. The contacting layer 5 can
have two separate areas in order to be able to contact electrically
the two poles separately. This type of contacting allows very
localized recombination zones 2.
[0426] FIGS. 26A and 26B show a sixth optoelectronic device in a
top view and cross-section. The device comprises an array of
vertical .mu.-LEDs 13. Optically active pillar structures P, in
particular with pillars or columns, are arranged above the array of
.mu.-LEDs 13. The longitudinal axis L of the pillars P runs at
least essentially through the centers of the recombination zones 2
of the .mu.-LEDs 13.
[0427] Pillar structures P may be free-standing in air or filled
with a first filling material 7, in particular electrically
insulating and optically transparent, above the light-emitting
diodes. The filling material 7 may comprises a lower refractive
index than the refractive index of the material 9 of the pillars P
and/or the semiconductor material 3 of the .mu.-LEDs 3. The reverse
form is also possible, i.e. material 7 has a higher refractive
index than the material of the pillars, but this changes the light
guidance of the pillars.
[0428] As already mentioned, the .mu.-LEDs are vertical micro-light
emitting diodes 13, which comprise one, especially positive,
electrical pole on their back side facing the reflective contact
layer 5 and another electrical pole on the front side facing the
pillars P.
[0429] The pole at the front of the light sources is electrically
connected to an appropriate power supply (not shown) by means of a
layer of an electrically conductive and optically transparent
material 17, in particular ITO, and by means of a contact wire 19.
The layer of material 17 is placed between the light sources and
the pillars 17, as shown.
[0430] A second filling material 15 can be arranged in free spaces
in the layer of .mu.-LEDs 13 and thus between the layer with the
material 17 and the contacting layer 5.
[0431] Pillar structures P can also be described as micropillar
structures or micropillars, since their dimensions, in particular
their cross-section, can at least approximately correspond to the
dimensions of the micro light-emitting diodes 13 or the pixels of
an array 11.
[0432] FIGS. 27A and 27B show a seventh optoelectronic device in a
top view and cross-section. In contrast to the variant in FIGS. 26A
and 26B, the device in FIGS. 27A and 27B comprises an array of
horizontal micro-light-emitting diodes 13, the electrical poles of
which are located at the rear of the microlight-emitting diodes 13.
For electrical contacting, therefore, both electrical poles of a
light source can be electrically connected via two electrically
separated areas of the reflective contacting layer 5. The
intermediate layer with the material 17 as in the variant with
vertical micro light emitting diodes described above is therefore
not required.
[0433] In comparison to the arrangements with the photonic crystal
structures K according to FIGS. 21A to 24B, the variants with the
pillars P can be manufactured more easily with standard
technologies, since the structure sizes with diameters of up to 1
.mu.m or more are significantly larger. The process requirements
are therefore lower and high-resolution lithography can be
sufficient for the manufacture of the pillars.
[0434] Pillar structures, in particular pillars or columns, made of
the optically active semiconductor material 3 or a material 9 with
a refractive index as high as possible can be precisely structured
via individual pixels of the array 11 or via vertical micro-light
emitting diodes 13 (FIGS. 26A and 26B) or via horizontal
micro-light emitting diodes 13 (FIGS. 27A and 27B). The individual
pixels or micro-lighting diodes 13 may be smaller than 1 .mu.m in
diameter and the pillars may have an aspect ratio height:diameter
of at least 3:1. Pillars are preferably etched directly into the
semiconductor material 3, as is possible in FIGS. 25A and 25B and
in FIGS. 27A and 27B, because there is no third layer 17 as shown
in FIG. 26B, or they are made of another material 9 with a high
refractive index and preferably low absorption, which is applied to
the surface of the array 11. A possible material with a high
refractive index is for example Nb.sub.2O.sub.5. Pillar structures
can be free-standing or filled with a material 7 of low refractive
index. A possible filling material with low refractive index is for
example SiO.sub.2. Due to the higher refractive index of the
pillars compared to the surrounding material, the emission parallel
to the longitudinal axis of the pillars is enhanced compared to
other spatial directions. Due to a waveguide effect, light along
the longitudinal axis of the pillars is additionally coupled out
more efficiently than light with other propagation directions. This
improves the directionality of the emitted light.
[0435] FIGS. 28A and 28B show an eighth proposed optoelectronic
device in a top view and cross-section. The device comprises an
array of .mu.-LED 13, each of which is configured with pillar P and
thus in column form.
[0436] The length of the pillars P can correspond to half a
wavelength of the emitted light in the semiconductor material 3 and
the recombination zone 2 can preferably be located in the center M
of a respective pillar and thus in a local maximum of the photonic
state density. The aspect ratio height:diameter of the pillars P
can be at least 3:1.
[0437] In the arrangement shown, the pillars P can be about 100 nm
high and have a diameter of only about 30 nm. This requires a very
finely resolved structuring technique and can be realized with
current production technologies at wafer level with a lot of
effort.
[0438] Alternatively, the dimensions can be upscaled to simplify
manufacture, with the directionality of the emitted light
decreasing as the size of the pillar structure increases. The
length of the pillars P is preferably a multiple of half the
wavelength of the emitted light in the semiconductor material, and
the respective recombination zone 2 can be at a maximum of the
photonic state density.
[0439] Due to the pillar structuring of the .mu.-LED 13, the
emission parallel to the longitudinal axis of the pillars P is
effectively amplified by the higher photonic state density. Due to
a waveguide effect, light with a direction of propagation along the
longitudinal axis of the pillars P is additionally coupled out more
efficiently than light with other directions of propagation. The
space between the pillars P is filled with a material 7, which
preferably comprises a very low absorption coefficient and a lower
refractive index than the semiconductor material 3. A possible
filling material with a low refractive index is for example
SiO.sub.2.
[0440] In this arrangement of micro-lighting diodes 13, in
particular vertical micro-lighting diodes 13 formed as pillars P or
columns, a first pole, in particular a positive pole is
electrically connected by means of a reflective contacting layer 5
for contacting recombination zones 2 arranged in a recombination
plane 1. The contacting layer 5 is formed at the lower, first
longitudinal ends of the .mu.-LEDs 13.
[0441] The respective other, in particular negative, second pole is
electrically connected to a third layer of a conductive transparent
material 17, in particular ITO, and connected by means of a bonding
wire 19 for example to the corresponding pole of a power
supply.
[0442] According to this arrangement, the third layer is formed in
and along the recombination plane 1 in the longitudinal centers of
the .mu.-LEDs 13, which are shaped as pillars P or columns.
[0443] FIGS. 29A and 29B show a ninth optoelectronic device in a
top view and cross-section. In contrast to the variant in FIGS. 28A
and 28B, the device in FIGS. 29A and 29B comprises vertical
.mu.-LEDs in the form of pillars P.
[0444] The electrical contact at the bottom, in particular the
p-contact, is established via the bottom of the pillars P and in
particular by contacting the contact layer 5. The electrical
contact at the top, especially the n-contact, is on the upper side
of the pillars P. The contact is established via an upper layer of
optically transparent and electrically conductive material 17. The
upper layer extends over the pillars P and the first filling
material 7, with which the free spaces between the pillars P are
filled. A possible material 17 for the upper layer is ITO (indium
tin oxide), for example. A connection to a power supply can be
established via the bonding wire 19.
[0445] The electrical contacting of the light-emitting diodes in
the pillars P enables very strongly localized recombination zones
2, whereby the upper contact, in particular an n-contact, can be
formed at the level of the recombination zones 2 or on the upper
side of the pillars P. Each pillar P generates an individual
pixel.
[0446] The emission of light parallel to the longitudinal axis of
.mu.-LEDs 13 in the form of pillars as shown in FIGS. 28A to 29B is
increased. This improves the directionality of the emitted light
compared to conventional micro-light emitting diodes with small
aspect ratio. Compared to an arrangement according to FIGS. 25A to
27B, the process of light generation can be influenced much more
strongly by an arrangement according to FIGS. 28A to 29B, thus
achieving high directionality and efficiency.
[0447] FIG. 30 shows a cross-sectional view of another
optoelectronic device in which a two-dimensional photonic crystal K
is arranged over a layer with an array of light sources with
recombination zones 2. The photonic crystal K is thereby arranged
so close to the recombination zones 2 that the photonic crystal K
changes an optical state density present in the region of the
recombination zones 2, in particular in such a way that a band gap
is generated for at least one optical mode with a direction of
propagation parallel and/or at a small angle to the light exit
surface 21 and/or the state density is increased for at least one
optical mode with a direction of propagation perpendicular to the
light exit surface 21.
[0448] This can be achieved in particular by the fact that the
height H of the photonic crystal K is at least 300 to 500 nm,
preferably up to 1 .mu.m. The height H of the photonic crystal may
depend on the high refractive index material of the photonic
crystal.
[0449] Furthermore, a distance A between the center M of the
recombination zones 2 and the bottom of the photonic crystal K is
at most 1 .mu.m and preferably a few 10 to a few hundred nm.
[0450] All the described configurations with a photonic crystal K
are two-dimensional photonic crystals, which exhibit a periodic
variation of the optical refractive index in two spatial directions
perpendicular to each other and parallel to the light-emitting
surface. Furthermore, it is preferably a pillar structure
comprising an array of pillars P or columns, the longitudinal axis
L of the pillars P being perpendicular to the light-emitting
surface 21.
[0451] FIG. 31 shows an optoelectronic device 1 with a photonic
structure for emitting polarized light. The component 1 comprises
an emitter unit 2, which has a light-emitting surface 3 and on
which a polarizing element 4 in the form of a polarizing layer with
a three-dimensional photonic structure is applied. With the help of
photonic structures for polarization of electromagnetic radiation,
it is especially possible to take special pictures and show them on
suitable displays. According to the embodiment shown in FIG. 31,
emitter unit 2 is a .mu.-LED 5, which emits light in the visible or
possibly also in the ultraviolet wavelength range. The light
emitted by the .mu.-LED 5 is guided into the three-dimensional
photonic structure and here it is polarized in a certain direction
of oscillation depending on the design and dimensioning of the
structure. Depending on the design of the three-dimensional
photonic structure, either circular or linear polarization can be
used. The light emitted in this way therefore comprises a specific
polarization, which is predetermined by the photonic structure.
[0452] If the three-dimensional photonic structure of polarization
element 4 has spiral structure elements 6 as shown in FIG. 32, a
circular polarization occurs. If, on the other hand, the structural
elements of the three-dimensional photonic structure are
rod-shaped, in particular in the form of so-called nanorods, this
causes a linear polarization of the radiation guided through the
three-dimensional photonic structure.
[0453] The optoelectronic device 1 shown in FIG. 31 is manufactured
by the two-photon lithography process, the glancing angle
deposition process, laser interference lithography or by
holographic patterning. It should be noted that the spiral-shaped
features 6 shown in FIG. 32 have been fabricated using the glancing
angle deposition technique.
[0454] The illustration in FIG. 31 shows only a single
optoelectronic component. However, a large number of these
components can be manufactured together and provided as an array or
.mu.-LED module, as shown in FIGS. 187, 189 to 192, for example. In
this way, different components can be interconnected, but with
complementary properties. Thus, components 1 or also arrays or
.mu.-LED modules are combined for imaging, which have different
polarization and/or transmission properties.
[0455] The radiation generated by several illumination units, each
with complementary properties, polarized in different directions of
oscillation, is projected onto a display or screen by means of
common optics disclosed therein.
[0456] With the three-dimensional photonic structure arranged on
the surface or light-emitting surface 3 of an LED chip as shown in
FIG. 31, which forms a polarization element 4, it is possible to
generate light with fundamentally different properties, in
particular with defined polarization, than is possible with the
currently known LEDs. The advantage is that due to the provision of
a three-dimensional photonic structure on the chip surface, no
additional optical components, such as a classical polarization
filter, are required. This is particularly useful in the area of
.mu.-LEDs, since such photonic structures are easier to produce by
means of lithographic processes than by positioning and attaching
separate polarization filters. The illumination unit can therefore
be made comparatively small. Due to the structuring directly on the
semiconductor chip of the LED 5, such an optoelectronic component 1
is also more energy-efficient than the known components in which
the polarization is subsequently selected. Any photon that does not
pass through the three-dimensional photonic structure due to its
properties remains in the .mu.-LED chip and can be re-emitted by a
reabsorption process.
[0457] FIG. 33 shows an illumination unit or an optoelectronic
component 1 with an emitter unit 2, which comprises a
light-emitting surface 3 on which a polarizing element 4 with a
three-dimensional photonic structure that has wavelength-selective
properties is applied. The photonic structure in this case is a
three-dimensional photonic crystal. Alternatively, several
two-dimensional photonic crystals can be arranged in layers one
above the other.
[0458] The three-dimensional photonic structure is designed to have
wavelength-specific transmittance and polarization properties. This
means that the transmittance and polarization properties of the
three-dimensional photonic structure vary depending on the
wavelength of the incident radiation.
[0459] Component 1 shown in FIG. 33 has an emitter unit, which in
turn has a .mu.-LED 5. A converter element 7 with a layer of
converter material is also provided. The converter material emits a
converted radiation 9 due to excitation by the excitation radiation
8 emitted by the LED 5, which comprises a different wavelength than
the excitation radiation 8.
[0460] If both unconverted excitation radiation 8 and converted
radiation 9 impinge on the three-dimensional photonic structure,
these radiations are influenced in different ways depending on
their wavelength with respect to transmission and polarization. As
shown in FIG. 33, the converted radiation 9 is coupled out
perpendicular to the surface of the LED chip, while the excitation
radiation 8 is deflected laterally.
[0461] Such lighting units can be used in a preferred way in
components in which radiation with different wavelengths is
generated, whereby different functions can be implemented with a
combination of .mu.-LEDs and converter elements. Depending on the
design of the three-dimensional photonic structure and the
wavelength of the excitation radiation 8 emitted by each LED, it is
possible to achieve complete suppression of the excitation
radiation 8, while the converted radiation 9 passes through the
three-dimensional photonic structure. It is also conceivable that
the excitation radiation 8 is deflected while the converted
radiation 9 is coupled out perpendicular to the chip surface, as
shown in FIG. 33. Of course, the mechanism can also be reversed.
Furthermore, it is also conceivable to polarize the converted
radiation 9 in a special way, while the excitation radiation 8
emerges unchanged via the chip surface. Here too, the mechanism can
be reversed.
[0462] The variant of an illumination unit shown in FIG. 34
comprises an emitter unit, here again in the form of a .mu.-LED 15,
and a three-dimensional photonic structure 11, for example a
spiral-shaped photonic structure 11. Converter material 13 is
filled into structure 11.
[0463] The optoelectronic component 11 shown in FIG. 35 comprises
at least one .mu.-LED 13, which is designed to emit electromagnetic
radiation 19, such as visible or infrared light of one wavelength,
via a light emission surface 15. A photonic structure 17 is
provided for beam-shaping of the electromagnetic radiation before
it exits via the light exit surface 15. The photonic structure 17
shapes the electromagnetic radiation 19 in such a way that the
electromagnetic radiation 19 comprises a defined characteristic 23
(Far-field characteristics).
[0464] In particular, the photonic structure 17 of the illumination
unit 11 of FIG. 35 is a one-dimensional photonic crystal 25, which
in the variant shown extends to the light-emitting surface 15. The
front side of the photonic crystal 25 thus forms the light-emitting
surface 15. The one-dimensional photonic crystal 25 exhibits a
periodic variation of the optical refractive index along a first
direction R1.
[0465] The crystal 25 or the periodic variation are adjusted to
beam the electromagnetic radiation emitted by a light source (not
shown) of the .mu.-LED. Especially a light propagation along the
first direction R1 is blocked. As a result, the emitted radiation
19 in far-field 21 comprises only a slight extension along the
first direction R1. A characteristic feature of electromagnetic
radiation 19 in far-field 21 is therefore that it forms a narrow
strip 27. The electromagnetic radiation 19 is therefore collimated
with respect to the first direction 19.
[0466] The light source is a .mu.-LED. This is typically a
Lambertian radiator. By using the photonic structure 17 and the
resulting beam-shaping a directed, collimated electromagnetic
radiation 19 can be generated.
[0467] As FIG. 35 schematically shows, the emitted electromagnetic
radiation 19 leaves the .mu.-LED 13 in the form of a light cone
that substantially fans out along a second direction R2. The
central axis of the light cone extends along a main radiation
direction H, which is perpendicular to the light exit surface 15.
Not shown is a collimating, optional optical system arranged
downstream of the light exit surface 15 when viewed in the main
radiation direction H. By means of the optics, the electromagnetic
radiation 19 can be collimated in the second spatial direction R2,
which is orthogonal to the first spatial direction R1. The
electromagnetic radiation 19 can thus be collimated in the far
field 21 with respect to the two directions R1, R2. A luminous
point is created. This luminous point is particularly favourable
for displays as mentioned at the beginning, because the beam is
strongly collimated in both directions in space.
[0468] An optoelectronic component 11 as shown in FIG. 35 is
particularly well suited for use in an optical scanner. Here, the
illumination device 11 can be used especially for line scan
applications due to the stripe-like light image in far field
21.
[0469] In the optoelectronic device 11 shown in FIG. 36, a
one-dimensional photonic crystal 25 is formed on the upper side of
an emitter unit 13a. The front face of the crystal 25 forms the
light-emitting surface 15 for electromagnetic radiation generated
by an unrepresented optoelectronic light source, for example an LED
or .mu.-LED, which is emitted through the photonic crystal 25 via
the light-emitting surface 25.
[0470] In contrast to the variant shown in FIG. 35, the main
direction of radiation H of the electromagnetic radiation 19 of the
lighting unit of FIG. 36 is at an angle .alpha. to the normal N of
the light-emitting surface 15. The angle .alpha. is not equal to
zero degrees. For example, the angle .alpha. can be in the range
between 30 and 60 degrees. This is achieved by the fact that the
one-dimensional photonic crystal 25 comprises a periodically
repeating sequence of two materials 31, 33 with different optical
refractive indices extending in a first direction R1. The materials
31, 33 have a parallelogram-like cross-section and abutting
interfaces of the materials 31, 33 do not run orthogonally but are
inclined to the light-emitting surface 15, as shown schematically
in FIG. 36.
[0471] Such a structure can be formed, for example, by etching
trenches 29 running parallel to each other at an angle to the light
emission surface 15 into the substrate 31 having the light emission
surface 15. The trenches 29 can be filled with a material 33, which
comprises a different optical refractive index than the substrate
material 33, which has been etched away. The angle .alpha. may
depend on the inclination of the trenches 29 to the light-emitting
surface 15. The width of the trenches 29 and the width of any
substrate material 31 remaining between two trenches 29 influences
the wavelengths at which the photonic crystal 25 can be affected.
Typically, the width of the trenches 29 and the width of the
substrate material 33 remaining between two trenches, and thus also
the periodicity of the photonic crystal structure 25, are adapted
to the wavelength of the electromagnetic radiation provided by the
light source or a converter material located between the light
source and the photonic crystal.
[0472] Using the one-dimensional photonic crystal 25, component 11
of FIG. 36 can in turn generate a light strip 27 in the far field
21, as described in relation to FIG. 35. In contrast to the variant
in FIG. 35, the main radiation direction H in the variant in FIG.
36 is tilted by the angle .alpha. relative to the normal N. By
means of a downstream collimating optic, the strip 27 can be
brought into a point-like or circular structure in the far field
21.
[0473] The variant shown in FIG. 37 comprises a linear or array
arrangement of several optoelectronic components 11 of FIG. 36, the
light beams 19 emitted by the individual components 11 having the
same main radiation direction H. The light beams 19 can also be
collimated by an additional collimating optic 35, in particular a
lens, in a second direction, which, in the representation of FIG.
37, is perpendicular to the image plane. This results in a point or
circular image of the emitted radiation 19 in the far field behind
the lens 35.
[0474] The use of a photonic crystal in an illumination device 11
as shown in FIGS. 36 and 37 results in an effectively higher
resolution for a line-array arrangement of illumination devices 11
as shown in FIG. 37. .mu.-display or modules having such features
allow very directional radiation, so that the pixel sharpness is
very high. This means that the contrast remains very high even with
adjacent pixels and optical crosstalk is reduced. In addition,
smaller beam cross-sections can be realized, especially in the far
field, downstream of optics 35. Since collimation in the first
direction R1 (cf. FIG. 36) is already achieved by the photonic
crystals 25 integrated in the illumination devices 11, optics 35
and possibly further, subsequent optics can be made more
compact.
[0475] In the variant of FIG. 38, the optoelectronic component or
lighting unit 11 comprises a photonic structure 17, which is a
two-dimensional photonic crystal 37, whose front side forms the
light-emitting surface 15. Viewed from the light exit surface 15,
at least one optoelectronic light source, optionally with converter
material, is arranged behind the photonic crystal 37. The photonic
crystal 37 is designed to shape the electromagnetic radiation 19
emitted via the light exit surface in such a way that it produces a
defined, discrete pattern 39 in the far field 21. In the example
shown, the pattern 39 consists of several distributed light spots
41, although other patterns are also possible. In particular, the
photonic crystal can be formed to produce only one central pixel.
This structure is particularly useful for displays.
[0476] The illumination device 11 in FIG. 38 is suitable for use in
a surface topography detection system 43, for example, as shown in
the block diagram in FIG. 39. In addition to the illumination
device 11, the system 43 includes a detection unit 45 with a camera
47, which is designed to detect the pattern 39 when it illuminates
an object (not shown).
[0477] Furthermore, an analysis device 49 is provided which is
designed to detect a distortion of the pattern 39 in relation to a
given reference pattern. The reference pattern can, for example, be
determined from the detection of pattern 39 when it is projected
onto a flat surface. The analyser 49 is also adapted to determine a
shape and/or a structure of the object illuminated by the pattern
39 in the far field 39 depending on the detected distortion of the
pattern 39. By means of the system 43, face recognition can thus be
realized, for example. In the case of applications in the Augmented
Reality area, some pixels can be formed with a crystal such as the
one shown in FIG. 38 in order to detect the reflection on the eye a
direction of vision or its change. This allows a user to follow and
superimpose information into the field of view for sharp
vision.
[0478] In the variant shown in FIG. 39, downstream optics for
pattern generation can be dispensed with, since pattern 39 can
already be generated using photonic crystal 37. The lighting device
11 as shown in FIG. 38 and the associated system 43 as shown in
FIG. 39 can therefore be implemented in a particularly compact
form.
[0479] In the following, various devices and arrangements as well
as methods for manufacturing, processing and operating as items are
again listed as an example. The following items present different
aspects and implementations of the proposed principles and
concepts, which can be combined in various ways. Such combinations
are not limited to those listed below:
[0480] 565. .mu.-LED, comprising: [0481] a layer stack of a p-doped
layer; [0482] an n-doped layer; [0483] an active region located
between the p-doped and n-doped layer; wherein the layer stack
rises above a major surface and the active region is located above
a center of the layer stack as viewed from the major surface,
wherein the layer stack has a reducing diameter from the major
surface; a reflective layer over a surface of the layer stack.
[0484] 566. .mu.-LED according to item 565,
in which the stack of layers comprise the shape of a hemisphere or
a paraboloid or an ellipsoid. 567. .mu.-LED according to any of the
preceding items, in which areas of the active layer adjacent to the
reflective layer comprise an increased bandgap. 568. .mu.-LED
according to any of the preceding items, in which areas of the
active layer adjacent to the reflective layer exhibit quantum well
intermixing. 569. .mu.-LED according to any of the preceding items,
in which the reflective layer comprises a dielectric between the
active region and the layer of the layer stack adjacent to the
surface region. 570. .mu.-LED arrangement for generating a pixel of
a display, comprising [0485] a flat carrier substrate; and [0486]
at least one .mu.-LED, which is arranged on a mounting side of the
carrier substrate wherein the .mu.-LED is adapted to emit light
transverse to a carrier substrate plane in a direction away from
the carrier substrate; [0487] a flat reflector element; wherein the
reflector element is spatially arranged on the assembly side
relative to the at least one .mu.-LED and is configured to reflect
light emitted by the at least one .mu.-LED in the direction of the
carrier substrate; wherein the carrier substrate is at least
partially transparent so that light reflected from the reflector
element propagates through the carrier substrate and emerges at a
display side of the carrier substrate opposite the mounting
side.
[0488] 571. .mu.-LED arrangement according to item 570, wherein a
diffuser layer is provided and/or a reflector material has diffuser
particles for scattering the light reflected by the at least one
.mu.-LED on the side of the reflector element directed towards the
at least one .mu.-LED.
[0489] 572. .mu.-LED arrangement according to item 571, wherein the
diffuser layer and/or the diffuser particles comprise
Al.sub.2O.sub.2 and/or TiO.sub.2.
[0490] 573. .mu.-LED arrangement according to any of the preceding
items, wherein the reflector element surrounds the at least one
.mu.-LED in a circular, polygonal or parabolic shape.
[0491] 574. .mu.-LED arrangement according to any of the preceding
items, wherein the reflector element forms an electrical contact of
the at least one .mu.-LED.
[0492] 575. .mu.-LED arrangement according to any of the preceding
items, wherein the reflector element is configured and shaped such
that at least 90% of the light emitted by the at least one .mu.-LED
is incident on the mounting side of the carrier substrate at an
angle between 45 and 90 degrees relative to the carrier substrate
plane.
[0493] 576. .mu.-LED arrangement according to any of the preceding
items, in which the at least one .mu.-LED comprises three .mu.-LEDs
surrounded by the reflector element
[0494] 577. .mu.-LED arrangement according to item 576, in which
the at least three .mu.-LEDs have a contact area on the side facing
the reflector element, which is covered with a transparent cover
layer for common electrical contact.
[0495] 578. .mu.-LED array according to any of the preceding items,
wherein the supporting substrate comprises polyamide, a transparent
plastic, resin or glass.
[0496] 579. .mu.-LED arrangement according to any of the preceding
items, wherein the reflector element is formed as a reflective
layer of the at least one .mu.-LED.
[0497] 580. .mu.-LED arrangement according to any of the preceding
items, wherein a passivation layer is additionally provided for
attenuating or eliminating reflections of the light at mesa edges
of the at least one .mu.-LED.
[0498] 581. .mu.-LED arrangement according to any of the preceding
items, wherein a light absorbing coating is provided on the
assembly side and/or display side of the carrier substrate outside
the reflector element.
[0499] 582. .mu.-LED arrangement according to any of the preceding
items, wherein the display side of the supporting substrate has an
uneven and/or roughened structure.
[0500] 583. .mu.-LED arrangement according to any of the preceding
items, wherein a color filter element is arranged on the display
side of the carrier substrate opposite the reflector element;
[0501] wherein the color filter element allows a primary color
spectrum of the at least one .mu.-LED to pass and attenuates
deviating color spectra.
[0502] 584a. .mu.-LED arrangement according to any of the preceding
items, in which a light-shaping structure, in particular a photonic
structure with features after one of the following objects is
incorporated in the carrier substrate, which first and second
regions with different refractive indexes are incorporated.
[0503] 584b. .mu.-LED arrangement according to any of the preceding
items, in which a light-shaping and/or light-converting structure
having first and second areas is arranged on the display side of
the carrier substrate.
[0504] 585. .mu.-LED arrangement according to item 583 or 584,
where first areas comprise a converter material.
[0505] 586. .mu.-LED arrangement according to any of the preceding
items, comprising a converter material surrounding the at least one
.mu.-LED and filling the space between .mu.-LED and reflector
material.
[0506] 587. .mu.-LED arrangement according to any of the preceding
items, comprising a converter material on the display side of the
supporting substrate.
[0507] 588. Optical display comprising a plurality of pixel
elements each according to any of the preceding items.
[0508] 589. A method for producing an optical pixel element,
comprising the steps of [0509] fixing of at least one .mu.-LED on
an assembly side of a flat carrier substrate; [0510] creating a
reflector element; [0511] wherein the reflector element is formed
as a light-reflecting layer on the at least one .mu.-LED so that
light emitted from the at least one .mu.-LED is reflected towards
the carrier substrate.
[0512] 590. Photonic structure on an optoelectronic device, in
particular a .mu.-LED, comprising
[0513] a set of layers including an active zone for generating
electromagnetic radiation forming the optoelectronic device, and at
least one layer on a main radiation surface having a photonic
crystal structure.
[0514] 591. Photonic structure on an optoelectronic device
according to item 590, the layers of the set of layers and the at
least one layer having the photonic crystal structure are arranged
one upon another along a growth direction of the layers, and
wherein the photonic crystal structure comprise a periodicity in a
plane perpendicular to the growth direction.
[0515] 592. Photonic structure on an optoelectronic device
according to item 590, in which the photonic crystal structure has
first and second regions of different refractive index.
[0516] 593. Photonic structure on an optoelectronic device
according to any of the preceding items, wherein the photonic
structure has a first periodicity in a first direction and a second
periodicity in a second direction.
[0517] 594. Photonic structure on an optoelectronic device as
defined in item 593, in which the first and second periodicity are
the same.
[0518] 595. Photonic structure on an optoelectronic device
according to any of the preceding items, in which the photonic
crystal structure extends at least partially into one of the layers
of the set of layers.
[0519] 596. Photonic structure on an optoelectronic device
according to any of the preceding items, the periodicity
corresponding to about half a specific wavelength, the wavelength
corresponding to the wavelength of electromagnetic radiation to be
diffracted by the photonic crystal structure.
[0520] 597. Photonic structure on an optoelectronic device
according to any of the preceding items, wherein the layer having
the photonic crystal structure is a dielectric layer containing or
consisting of, for example, silicon dioxide, SiO.sub.2, and/or
wherein the space within the photonic crystal structure is filled
with or consists of a second material having a refractive index
different from the refractive index of a first material forming the
photonic crystal structure.
[0521] 598. Photonic structure on an optoelectronic device
according to any of the preceding items, wherein a lower surface of
the layer having the photonic crystal structure is disposed on an
upper surface of the set of layers.
[0522] 599. Photonic structure on an optoelectronic device
according to item 598, wherein a portion of at least one layer of
the set of layers protrudes into the layer with the photonic
crystal structure.
[0523] 600. Photonic structure on an optoelectronic device
according to item 597 or 599, wherein the upper surface of the set
of layers is provided with a surface roughening, for example, a
wigwam surface roughening.
[0524] 601. Photonic structure on an optoelectronic device after
any of the foregoing, wherein the photonic crystal structure is
located at a distance from the upper surface of the set of
layers.
[0525] 602. Photonic structure on an optoelectronic device
according to any of the preceding items, further comprising a
mirror layer disposed on the layer having the photonic crystal
structure.
[0526] 603. Photonic structure on an optoelectronic device
according to any of the preceding items, further comprising a metal
mirror layer, with the set of semiconductor layers disposed between
the metal mirror layer and the layer containing the photonic
crystal structure.
[0527] 604. Photonic structure on an optoelectronic device
according to any of the preceding items, wherein the optoelectronic
device is a .mu.-LED.
[0528] 605. Optoelectronic device comprising:
[0529] at least one optoelectronic light emitting device, for
example a .mu.-LED, wherein said optoelectronic light emitting
device is configured to emit light through at least one light
emitting surface of said optoelectronic light emitting device,
[0530] at least one photonic crystal structure, said photonic
crystal structure being disposed between the light-emitting surface
of said optoelectronic light-emitting device and a light-emitting
surface of said optoelectronic device.
[0531] 606. Method for producing an optoelectronic device, in
particular according to any of the preceding items, comprising
method: [0532] growing of a set of layers including an active zone
for the generation of electromagnetic radiation, [0533] growing at
least one layer having a photonic crystal structure on the upper
side of the set of layers,
[0534] optionally providing a mirror layer over the layer with the
photonic crystal structure,
[0535] optionally providing a mirror layer under the set of layers
with the active zone,
[0536] optionally executing an etching process, such as a Mesa dry
etching process.
[0537] 607. Method for producing a .mu.-LED comprising a creating
of an out-coupling structure in a surface region of a semiconductor
body providing the active layer of the .mu.-LED by means of
[0538] structuring of the surface area; and
[0539] planarizing the structured surface area to obtain a
planarized surface of the surface area.
[0540] 608. Method according to item 607, wherein the step of
structuring the surface area comprises at least one of the
following steps: [0541] generating of a random topology at the
surface area; [0542] roughening the surface of the surface region
of the semiconductor body comprising a first material; [0543]
applying, in particular layer-by-layer applying of a transparent
second material having a high refractive index, in particular
greater than 2, to the surface region and roughening of the second
material; [0544] creating an ordered topology on the surface
area;
[0545] applying, in particular layer-by-layer applying of a
transparent second material having a high refractive index, in
particular greater than 2, to the surface region and structuring of
periodic photonic structures or non-periodic photonic structures,
in particular quasi-periodic or deterministic aperiodic photonic
structures, into the second material.
[0546] 609. Method according to item 608, characterised in that
[0547] the transparent second material with the high refractive
index Nb.sub.2O.sub.5.
[0548] 610. Method according to any of the preceding items, in
which the step of planarizing comprises:
[0549] applying, in particular layer by layer, a transparent third
material of low refractive index, in particular less than 1.5, to
the structured surface region; and
[0550] optionally thinning the applied transparent third material
of low refractive index until the surface of the structured surface
region terminates flat and/or smooth with highest elevations in the
first material of the semiconductor body or in the second material
of high refractive index.
[0551] 611. Method according to item 610, in which
[0552] the transparent third material having a low refractive index
SiO.sub.2, and is applied in particular by means of TEOS
(tetraethylorthosilicate).
[0553] 612. .mu.-LED comprising an out-coupling structure in a
surface region of a semiconductor body providing the .mu.-LED
[0554] in which the surface area is planarized so that a smooth
surface area is created.
[0555] 613. .mu.-LED according to item 612, characterised in that
the smooth surface region comprises a roughness in the range of
less than 20 nanometres, in particular less than 1 nanometre, as
mean roughness value.
[0556] 614. .mu.-LED to any of the preceding items, wherein
[0557] the out-coupling structure comprises a transparent third
material with a low refractive index, in particular SiO.sub.2, on a
roughened first material of the semiconductor of the device.
[0558] 615. .mu.-LED according to any of the preceding items, in
which the output coupling structure comprises a transparent third
material of low refractive index, in particular SiO.sub.2, on a
roughened transparent second material of high refractive index, in
particular Nb.sub.2O.sub.5, the second material being attached to a
first material of the semiconductor of the device.
[0559] 616. .mu.-LED according to any of the preceding items, in
which the output structure comprises a transparent third material
of low refractive index, in particular SiO.sub.2, on a transparent
second material of high refractive index, the second material being
attached to a first material of the semiconductor of the device and
comprising periodic photonic crystals or non-periodic photonic
structures, in particular quasi-periodic or deterministic aperiodic
photonic structures.
[0560] 617. Converter element for an optoelectronic component,
which has at least one layer comprising a converter material which,
when excited by an incident excitation radiation, emits a converted
radiation into an emission region,
[0561] characterized in that the layer has at least in some areas a
structure on which the converter material is arranged at least in
sections and which is configured in such a way that the radiation
is emitted as a directed beam of rays into the emission area.
[0562] 618. Converter element according to item 617,
[0563] characterised in that the structure is quasi-periodic or
deterministically aperiodic.
[0564] 619. Converter element according to item 617 or 618,
[0565] characterised in that the layer comprises at least one
photonic crystal, a quasi-periodic photonic structure or a
deterministically aperiodic photonic structure.
[0566] 620. Converter element according to any of the preceding
items, characterised in that the structure comprises at least one
recess in which the converter material is located.
[0567] 621. Converter element according to any of the preceding
items, characterised in that the layer comprises an optical band
gap.
[0568] 622. Converter element according to any of the preceding
items, characterized in that the structure comprises an average
thickness of at least 500 nm.
[0569] 623. Converter element according to any of the preceding
items, characterized in that the layer with the structure is
configured such that the directed beam of rays is emitted
perpendicularly to a plane in which the layer is arranged.
[0570] 624. Converter element according to any of the preceding
items, characterized in that an optical filter element is arranged
at least on one side of the layer.
[0571] 625. Light-shaping structure for an optoelectronic device
comprising at least one layer with a converter material which, when
excited by an incident excitation radiation, emits a converted
radiation into an emission region
[0572] characterized in that the layer has at least in some areas a
structure on which the converter material is arranged at least in
sections and which is configured in such a way that the radiation
is emitted as a directed beam of rays into the emission area.
[0573] 626. Light-shaping structure according to item 625,
[0574] characterised in that the structure is quasi-periodic or
deterministically aperiodic.
[0575] 627. Light-shaping structure according to item 625 or 626,
characterised in that the layer comprises at least one photonic
crystal, a quasi-periodic photonic structure or a deterministically
aperiodic photonic structure.
[0576] 628. Light-shaping structure according to any of the
preceding items,
[0577] characterised in that the structure comprises at least one
recess in which the converter material is located.
[0578] 629. Light-shaping structure according to any of the
preceding items,
[0579] characterised in that the layer comprises an optical band
gap.
[0580] 630. Light-shaping structure according to any of the
preceding items,
[0581] characterized in that the structure comprises an average
thickness of at least 500 nm.
[0582] 631. Light-shaping structure according to any of the
preceding items,
[0583] characterized in that the layer with the structure is
configured such that the directed beam of rays is emitted
perpendicularly to a plane in which the layer is arranged.
[0584] 632. Light-shaping structure according to any of the
preceding items,
[0585] characterized in that an optical filter element is arranged
at least on one side of the layer.
[0586] 633. .mu.-LED arrangement comprising a .mu.-LED and a
converter element according to any of the preceding items, wherein
the .mu.-LED is adapted to radiate an excitation radiation into the
converter element, and wherein the converter element comprises at
least one layer comprising a converter material.
[0587] 634. .mu.-LED arrangement comprising a .mu.-LED and having a
light-shaping structure according to any of the preceding items,
wherein the .mu.-LED is adapted to irradiate an excitation
radiation into the light-shaping structure, and wherein the
light-shaping structure comprises at least one layer comprising a
converter material.
[0588] 635. .mu.-LED arrangement according to item 633 or 634,
characterized in that the layer is part of a semiconductor
substrate of the .mu.-LED.
[0589] 636. .mu.-LED arrangement according to any of the items 633
to 635, characterized in that the structure of the converter
element or light-shaping structure is formed in the semiconductor
substrate of the .mu.-LED.
[0590] 637. .mu.-LED arrangement according to any of the items 633
to 636, characterized in that the structure with the converter
material is configured in such a way that the converted radiation
is emitted into the emission region perpendicular to a plane in
which the semiconductor substrate is arranged.
[0591] 638. .mu.-LED arrangement according to any of the items 633
to 637, characterised in that the structure of the converter
element or light-shaping structure is at least partially disposed
in an active layer of the .mu.-LED.
[0592] 639. Method for producing a .mu.-LED arrangement according
to any of the items 633 to 638,
[0593] characterized in that the structure of the converter element
or the light-shaping structure is formed by at least one etching
step in a semiconductor substrate of the .mu.-LED.
[0594] 640. Method according to item 639,
[0595] characterised in that the structure of the converter element
or light-shaping structure is at least partially filled with the
converter material.
[0596] 641. Optoelectronic device or .mu.-LED array,
comprising:
[0597] an arrangement comprising a plurality of .mu.-LEDs for
generating light emerging from a light exit surface from the
optoelectronic device, and
[0598] at least one photonic structure arranged between the
light-emitting surface and the plurality of .mu.-LEDs.
[0599] 642. Optoelectronic device according to item 641, in which
the photonic structure is configured for beam-shaping of the light
generated by the .mu.-LEDs, in particular in such a way that the
light emerges at least substantially perpendicularly from the light
exit surface.
[0600] 643. Optoelectronic device according to any of the preceding
items, in which the photonic structure comprises a photonic
crystal.
[0601] 644. Optoelectronic device according to any of the preceding
items, in which
[0602] the arrangement is an array in which the .mu.-LEDs represent
a plurality of pixels and are arranged in a layer, and in that a
photonic structure is arranged or formed in the layer.
[0603] 645. Optoelectronic device according to any of the preceding
items, characterized in that
[0604] the arrangement is an array in which the .mu.-LEDs represent
a plurality of pixels arranged in a first layer and in that a
photonic crystal is arranged in a further, second layer, the second
layer being located between the first layer and the light-emitting
surface.
[0605] 646. Optoelectronic device according to any of the preceding
items, characterized in that
[0606] the arrangement comprises a plurality of .mu.-LEDs arranged
in a first layer, and that a photonic crystal is arranged in the
further, second layer, the second layer being located between the
first layer and the light-emitting surface.
[0607] 647. Optoelectronic device according to any of the preceding
items, characterized in that
[0608] each of the .mu.-LEDs comprises a recombination zone and the
photonic structure is located so close to the recombination zones
that the photonic structure changes an optical state density
present in the region of the recombination zones, in particular in
such a way that a band gap is generated for at least one optical
mode with a direction of propagation parallel and/or at a small
angle to the light exit surface.
[0609] 648. Optoelectronic device according to any of the preceding
items, characterized in that
[0610] the photonic structure is arranged in relation to a plane
parallel to the light-emitting surface independently of the
positioning of the light points, and/or
[0611] the photonic structure is a two-dimensional photonic
crystal, which exhibits a periodic variation of the optical
refractive index in two spatial directions perpendicular to each
other and spanning the plane.
[0612] 649. Optoelectronic device according to any of the preceding
items, characterized in that
[0613] the photonic structure comprises a plurality of pillar
structures extending at least partially between the light-emitting
surface and the plurality of .mu.-LEDs, wherein one pillar is
associated with each .mu.-LED and is aligned with the
light-emitting surface when viewed in a direction perpendicular to
the light-emitting surface.
[0614] 650. Optoelectronic device according to item 649,
characterised in that
[0615] the device is an array in which the .mu.-LEDs represent a
plurality of pixels arranged in a first layer and in that the
pixels are arranged in a further, second layer, the second layer
being located between the first layer and the light-emitting
surface.
[0616] 651. Optoelectronic device according to item 649,
characterised in that
[0617] the device comprises a plurality of .mu.-LEDs, arranged in a
first layer, and that the pillars are arranged or formed in a
further, second layer, the second layer being located between the
first layer and the light-emitting surface.
[0618] 652. Optoelectronic device according to item 649,
characterised in that
[0619] the arrangement is an array in which the .mu.-LEDs represent
a plurality of pixels, one pixel being formed by each pillar.
[0620] 653. Method for producing an optoelectronic device,
[0621] in particular a device according to any of the preceding
items, wherein an arrangement comprising a plurality of .mu.-LEDs
is provided or made for generating light emerging from a light exit
surface from the optoelectronic device, and
[0622] at least one photonic structure is arranged between the
light-emitting surface and the plurality of .mu.-LEDs.
[0623] 654. .mu.-LED arrangement having at least one .mu.-LED which
emits radiation via a light-emitting surface, and having a
polarization element which adjoins the light-emitting surface at
least in sections and changes a polarization and/or an intensity of
a radiation emanating from the .mu.-LED when the radiation passes
through the polarization element, characterised in that
[0624] the polarizing element comprises a photonic structure.
[0625] 655. .mu.-LED arrangement according to item 654,
characterized in that
[0626] it is a three-dimensional photonic structure and/or that the
polarizing element is configured in the form of a layer which is
arranged at least in regions on the light-emitting surface.
[0627] 656. .mu.-LED arrangement according to item 654 or 655, in
which the .mu.-LED is a vertical .mu.-LED with one connecting
contact on opposite sides.
[0628] 657. .mu.-LED arrangement according to any of the preceding
items, characterized in that
[0629] the .mu.-LED, which is configured to emit light, in
particular red, green, blue, ultraviolet or infrared light, which
is irradiated into the polarizing element, and that the polarizing
element polarizes the radiation in an oscillation direction when
passing through the polarizing element.
[0630] 658. .mu.-LED arrangement according to any of the preceding
items, wherein
[0631] the polarising element has spiral and/or rod-shaped
structural elements.
[0632] 659. .mu.-LED arrangement according to any of the preceding
items, wherein
[0633] the .mu.-LED comprises at least one converter element with a
converter material which, excited by excitation radiation emanating
from the .mu.-LED, emits converted radiation.
[0634] 660. .mu.-LED arrangement according to any of the preceding
items, characterised in that
[0635] the polarizing element comprises at least one
three-dimensional photonic crystal.
[0636] 661. .mu.-LED array according to any of the preceding items,
wherein
[0637] the polarizing element comprises at least two
two-dimensional photonic crystals arranged one behind the other
along a beam path of the radiation penetrating the polarizing
element.
[0638] 662. .mu.-LED array according to any of the preceding items,
wherein
[0639] the polarizing element has at least two different
polarization properties and/or degrees of transmission depending on
a wavelength of the radiation passing through the polarizing
element.
[0640] 663. .mu.-LED arrangement according to any of the preceding
items, characterised in that
[0641] the .mu.-LED has a converter element with a converter
material which, excited by excitation radiation emanating from the
.mu.-LED, emits converted radiation, and in that excitation
radiation incident on the polarizing element is polarized
differently and/or absorbed to a different extent when passing
through the polarizing element compared with converted radiation
passing through.
[0642] 664. .mu.-LED arrangement according to any of the preceding
items, where
[0643] a three-dimensional structure of the polarizing element is
at least partially incorporated in a semiconductor layer of the
.mu.-LED adjacent to the light-emitting surface.
[0644] 665. .mu.-LED array according to any of the preceding items,
which is a three-dimensional photonic structure and converter
material is disposed in the three-dimensional photonic
structure.
[0645] 666. Method for producing a .mu.-LED arrangement having at
least one .mu.-LED which emits radiation via a light-emitting
surface, and having a polarization element which adjoins the
light-emitting surface at least in sections and changes a
polarization and/or an intensity of a radiation emanating from the
.mu.-LED when the radiation passes through the polarization
element, characterised in that
[0646] an in particular three-dimensional photonic structure, in
particular by two-photon lithography or glancing angle deposition,
is applied to the light-emitting surface of the .mu.-LED as
polarization element and/or the photonic structure is arranged in a
semiconductor layer of the .mu.-LED adjoining the light-emitting
surface.
[0647] 667. Method according to item 666, characterized in that the
photonic structure is dimensioned as a function of the wavelength
of the radiation emitted by the .mu.-LED
[0648] 668. Use of a .mu.-LED array according to any of the
preceding items in a device for generating three-dimensional
images.
[0649] 669. Use of a .mu.-LED array according to any of the
preceding items, characterized in that
[0650] the .mu.-LED arrangement is used after one of the objects
654 to 665 for computer-aided generation of three-dimensional
images for an augmented reality application.
[0651] 670. Optoelectronic component, in particular comprising a
.mu.-LED array
[0652] at least one .mu.-LED which emits electromagnetic radiation
via a light emission surface, and
[0653] a photonic structure for beam-shaping of the electromagnetic
radiation before it exits via the light emission surface, wherein
the photonic structure shapes the electromagnetic radiation such
that the electromagnetic radiation has a specific far field.
[0654] 671. Optoelectronic component according to item 670,
characterized in that
[0655] the photonic structure is a one-dimensional photonic
structure, in particular a one-dimensional photonic crystal
[0656] 672. Optoelectronic component according to item 670 or 671,
characterized in that
[0657] the photonic structure is formed, in particular as a
one-dimensional photonic crystal, in such a way that the radiated
electromagnetic radiation is at least approximately collimated in a
first spatial direction.
[0658] 673. Optoelectronic component according to item 672,
characterized in that
[0659] a collimating optical system is arranged downstream of the
light exit surface, as viewed in the main radiation direction, the
optical system being designed to collimate the electromagnetic
radiation in a further, second spatial direction (R2), which is
orthogonal to the first spatial direction.
[0660] 674. Optoelectronic component according to one of the
preceding items, characterized in that
[0661] the photonic structure, in particular formed as a
one-dimensional photonic crystal, is designed in such a way that a
main radiation direction of the electromagnetic radiation runs at
an angle to the normal of the light exit surface, the angle being
not equal to zero degrees.
[0662] 675. Optoelectronic component according to item 674,
characterized in that
[0663] the photonic structure formed as a one-dimensional photonic
crystal is arranged in a layer below the light-emitting surface,
wherein the one-dimensional photonic crystal comprises a
periodically repeating sequence of two materials with different
optical refractive indices extending in a first direction, wherein
the materials have abutting interfaces, which are not orthogonal
but inclined to the light-emitting surface.
[0664] 676. Optoelectronic component according to one of the
preceding items, characterized in that
[0665] the photonic structure is a two-dimensional photonic
structure, in particular a two-dimensional photonic crystal
[0666] 677. Optoelectronic component according to item 676,
characterized in that
[0667] the two-dimensional photonic structure is designed such that
the electromagnetic radiation produces a defined, in particular a
discrete, pattern in the far field.
[0668] 678. Optoelectronic component according to any of the
preceding items, characterized in that
[0669] the photonic structure is arranged in a layer, in particular
a semiconductor layer, below the light emission surface, and/or the
photonic structure is formed in a semiconductor layer of the
optoelectronic emitter unit, and/or
[0670] the optoelectronic emitter unit comprises a converter
material layer and the photonic structure is formed in the
converter material layer or in a layer between the converter
material layer and the light-emitting surface.
[0671] 679. Optoelectronic component according to one of the
preceding items, characterized in that
[0672] the photonic structure, in particular instead of a photonic
crystal, is a quasi-periodic or deterministically aperiodic
photonic structure.
[0673] 680. Surface topography recognition system, with:
[0674] an optoelectronic device, comprising:
[0675] at least one optoelectronic emitter unit which emits
electromagnetic radiation via a light exit surface, and
[0676] a photonic structure for beam-shaping of the electromagnetic
radiation before it exits via the light emission surface, wherein
the photonic structure shapes the electromagnetic radiation such
that the electromagnetic radiation has a specific far field,
[0677] wherein the photonic structure is a two-dimensional photonic
structure, in particular a two-dimensional photonic crystal,
and
[0678] wherein the two-dimensional photonic structure is designed
such that the electromagnetic radiation generates a defined, in
particular a discrete, pattern in the far field, and
[0679] wherein said surface topography detection system further
comprises a detection unit, in particular with a camera, which is
designed to detect the pattern in the far field
[0680] 681. surface topography recognition system according to item
680 characterized in that
[0681] it comprises an analysis device adapted to detect a
distortion of the pattern with respect to a predetermined reference
pattern.
[0682] 682. Surface topography detection system according to item
681, characterized in that
[0683] the analysis means is adapted to determine a shape and/or a
structure of an object illuminated by the pattern as a function of
the distortion detected.
[0684] 683. Scanner for scanning an object, comprising at least one
optoelectronic component for one of the previous objects.
[0685] The description with the help of the exemplary embodiments
does not limit the various embodiments shown in the examples to
these. Rather, the disclosure depicts several aspects, which can be
combined with each other and also with each other. Aspects that
relate to processes, for example, can thus also be combined with
aspects where light extraction is the main focus. This is also made
clear by the various objects shown above.
[0686] The invention thus comprises any features and also any
combination of features, including in particular any combination of
features in the subject-matter and claims, even if that feature or
combination is not explicitly specified in the exemplary
embodiments.
* * * * *