U.S. patent application number 12/607053 was filed with the patent office on 2014-05-08 for light emitter with coating layers.
This patent application is currently assigned to BRIDGELUX, INC.. The applicant listed for this patent is Steven D. Lester. Invention is credited to Steven D. Lester.
Application Number | 20140124806 12/607053 |
Document ID | / |
Family ID | 49042325 |
Filed Date | 2014-05-08 |
United States Patent
Application |
20140124806 |
Kind Code |
A1 |
Lester; Steven D. |
May 8, 2014 |
Light Emitter with Coating Layers
Abstract
An AlInGaN light emitting device having a coating is used to
improve the extraction of light from a device. A coating has a very
low optical loss and an index of refraction greater than 2,
preferably having an index of refraction close to or greater than
the index of refraction of GaN. The coating can be made from
Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, TiO.sub.2, or SiC and has can
have a thickness between 0.01 and 10 microns. A surface of the
coating material may be textured or shaped to increase its surface
area and improve light extraction. A coating can be applied
directly to one or multiple surfaces of the light emitting device
or can be applied onto a contact material and can serve as a
passivation or as a protection layer for a device.
Inventors: |
Lester; Steven D.; (Palo
Alto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lester; Steven D. |
Palo Alto |
CA |
US |
|
|
Assignee: |
BRIDGELUX, INC.
Sunnyvale
CA
|
Family ID: |
49042325 |
Appl. No.: |
12/607053 |
Filed: |
October 27, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11296006 |
Dec 6, 2005 |
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12607053 |
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Current U.S.
Class: |
257/98 ; 257/76;
257/E33.06; 257/E33.067; 438/29 |
Current CPC
Class: |
H01L 33/44 20130101;
H01L 33/32 20130101; H01L 33/46 20130101 |
Class at
Publication: |
257/98 ; 438/29;
257/76; 257/E33.06; 257/E33.067 |
International
Class: |
H01L 33/00 20100101
H01L033/00 |
Claims
1. A light emitting device comprising: a first substrate portion; a
light emitting portion in contact with a first coating layer
portion, the first coating layer portion in contact with the first
substrate portion, wherein a reflective layer structure is integral
to the first coating layer portion; and a second coating layer
portion in contact with the light emitting portion wherein at least
one of the first and second coating layer portions has a continuous
pattern having a cross section chosen from a group consisting of
ribs, cylinders, slots, polygon shaped ribs, triangular shaped
ridges, hemispherical shaped mounds, horizontal cylindrical shaped
ribs, cylinders, ellipsoids, hemispheres, rectilinear trenches,
rectilinear solids, cones, angled cylinders, angled hemispheres,
angled ellipsoids, angled rectilinear trenches, angled solids and
angled cones and wherein element to element spacing may be uniform
or not and wherein at least one of the first and second coating
layer portions has an index of refraction greater than about 2 and
an optical loss factor less than about 0.2.
2. (canceled)
3. The light emitting device of claim 1 wherein said light emitting
portion comprises: a first cap layer of a first conductivity type
disposed on a side of the light emitting portion, the side of the
light emitting portion facing the first substrate portion; an
active region comprising one or more layers separated from said
first substrate portion by the first cap layer; a second cap layer
of a second conductivity type; one or more contact layers in
contact with the active region through the second cap layer; and
wherein said active region is of an AlInGaN material system.
4. The light emitting device of claim 1 wherein said first and
second coating layer portions are chosen from a group comprising
metal oxides, silicon carbide, GaN, Ta20s, Nb20s, Ti02, AlInGaN
based solid solutions, and their non-stoichiometric mixtures.
5. The light emitting device of claim 1 wherein said second coating
layer portion comprises one or more coating layers wherein at least
a first of the one or more coating layers of said second coating
layer portion has an index of refraction greater than 2 and an
optical loss factor less than 0.2.
6. (canceled)
7. A light emitting device comprising: a first substrate portion; a
reflective layer directly and physically in contact with the first
substrate portion; a transparent conductive layer in contact with
the reflective layer; a light emitting portion comprising at least
two layers, wherein the light emitting portion is directly and
physically in contact with the transparent conductive layer; and
one or more coating layers adjacent the light emitting portion
having a pattern having a cross section chosen from a group
consisting of ribs, cylinders, slots, polygon shaped ribs,
triangular shaped ridges, hemispherical shaped mounds, horizontal
cylindrical shaped ribs, cylinders, ellipsoids, hemispheres,
rectilinear trenches, rectilinear solids, cones, angled cylinders,
angled hemispheres, angled ellipsoids, angled rectilinear trenches,
angled solids and angled cones and wherein element to element
spacing may be uniform or not wherein at least a first coating
layer of the one or more coating layers has an index of refraction
greater than 2 and an optical loss factor less than 0.2.
8. (canceled)
9. The light emitting device of claim 7 wherein said light emitting
portion further comprises: a first cap layer of a first
conductivity type disposed on a side of the light emitting portion,
the side of the light emitting portion facing the first substrate
portion; an active region comprising one or more layers separated
from said first substrate portion by the first cap layer; a second
cap layer of a second conductivity type; one or more contact layers
in contact with the active region through the second cap layer; and
one or more electrode layers in contact with one of the one or more
contact layers; wherein said active region is of an AlInGaN
material system.
10. The light emitting device of claim 7 wherein said one or more
coating layers are chosen from a group comprising metal oxides,
silicon carbide, GaN, Ta20s, Nb20s, Ti02, AlInGaN based solid
solutions, and their non-stoichiometric mixtures.
11. (canceled)
12. (canceled)
13. (canceled)
14. A light emitting device comprising: a first substrate portion;
a light emitting portion in contact with a first coating layer
portion, the first coating layer portion in contact with the first
substrate portion wherein a reflective layer structure is integral
to the first coating layer portion; and a second coating layer
portion in contact with the light emitting portion wherein at least
one of the first and second coating layer portions has a continuous
pattern having a cross section chosen from a group consisting of
ribs, cylinders, slots, polygon shaped ribs, triangular shaped
ridges, hemispherical shaped mounds, horizontal cylindrical shaped
ribs, cylinders, ellipsoids, hemispheres, rectilinear trenches,
rectilinear solids, cones, angled cylinders, angled hemispheres,
angled ellipsoids, angled rectilinear trenches, angled solids and
angled cones and wherein element to element spacing may be uniform
or not and wherein at least one of the first and second coating
layer portions has an index of refraction greater than about 2 and
an optical loss factor less than about 0.2.
Description
PRIORITY
[0001] This application is a divisional of U.S. application Ser.
No. 11/296,006 filed on Dec. 6, 2005 and claims priority there
from.
CROSS REFERENCE TO RELATED DOCUMENTS
[0002] The present invention is related to application Ser. No.
11/296,006, "Light Emitter with Metal-oxide Coating" and Ser. No.
11/378,763, "Highly Reflective Mounting Arrangement for LEDs",
assigned to the same assignee, incorporated herein in their
entirety by reference.
FIELD OF INVENTION
[0003] This invention relates generally to light emitting devices
and more particularly to new combinations for enhancing their light
output.
BACKGROUND OF INVENTION
[0004] Light emitting devices (LEDs) are an important class of
solid state devices that convert electric energy to light and
commonly comprise an active layer of semiconductor material
sandwiched between additional layers. As the quality of
semiconductor materials have improved, the efficiency of LEDs has
also improved. Commercially-available LEDs are being made from
alloys of indium, aluminum, and gallium with nitrogen (AlInGaN).
These alloys make possible LEDs which operate in the ultra-violet
to green spectral regions. However, the efficiency of LEDs is
limited by their inability to couple all of the light that is
generated by an active layer out of the LED chip. When an LED is
energized, light emitting from its active layer (in all directions)
reaches the LED surfaces at many different angles. Typical
semiconductor materials have a high index of refraction compared to
ambient air (n=1.0) or encapsulating epoxy (n.apprxeq.1.5).
According to Snell's law, light traveling from a material having an
index of refraction, n.sub.1, to a material with a lower index of
refraction, n.sub.2, at an angle less than a certain critical angle
.theta..sub.c relative to the surface normal direction will cross
to the lower index region, where
.theta..sub.C=sin.sup.-1(n.sub.2/n.sub.1) (1)
[0005] Light that reaches the semiconductor surface at angles
greater than .theta..sub.C will experience total internal
reflection. This light is reflected back into the LED chip where it
can be absorbed within the chip or in metal contact layers that are
attached to the chip. For conventional LEDs, the vast majority of
light generated within the structure suffers total internal
reflection before escaping from the semiconductor chip. In the case
of conventional GaN-based LEDs on sapphire substrates .about.70% of
the emitted light is trapped between the sapphire substrate and the
outer surface of the GaN. This light is repeatedly reflected,
greatly increasing its chance for reabsorption and loss.
[0006] Several techniques have been described to improve light
extraction from LEDs. Providing the device with reflective contacts
is one such technique. This improves LED efficiency because light
that is trapped within the structure and is incident on the contact
metals will be reflected back into the device rather than being
absorbed. This allows the light to have another opportunity to
escape the chip the next time it is incident on the LED surface.
While reflective contacts improve light extraction, conventional
LEDs still suffer from significant absorption losses. Roughening
the top surface is another technique to improve light extraction.
Roughening scatters, or sometimes randomizes, the angle of
reflected light so that trapped light is redirected. This prevents
light from being repeatedly reflected by parallel interfaces. Some
of the scattered light then has an opportunity to strike a surface
within the critical angle for internal reflection before being
absorbed. Typical semiconductor layers are thin so only fine-scale
roughening is usually possible. Also, roughened surfaces can cause
other problems with the LED fabrication process. For example,
contacts to roughened surfaces can be problematic. Also, roughened
surfaces can cause it to be difficult to align photomasks to the
wafer. And they make it difficult for the pattern recognition
equipment that are used to bond and inspect the wafers to work
properly. Therefore another technique to redirect trapped light is
desirable. Another technique to scatter trapped light is to provide
a rough interface between the GaN and the underlying substrate.
This can be done by patterning and roughening the substrate prior
to the growth of the semiconductor layers. This technique is
effective at improving light extraction; however, the textured
surface of the substrate affects the subsequent growth of the
semiconductor layers. The quality of the semiconductor layers is
often adversely affected, and the reproducibility of the growth is
poor.
[0007] Additional methods of improving light output efficiency are
reviewed in U.S. Pat. No. 6,657,236 which is included herein in its
entirety by reference. U.S. Pat. No. 6,657,236 and U.S. Pat. No.
6,821,804 teach another method requiring a first spreading layer of
a n type doped AlInGaN based material; a second spreading layer is
preferably a thin, semi-transparent metal such as Pd, Pt, Pd/Au,
Ni/Au, NiO/Au or some combination thereof deposited on, preferably,
a p-type AlInGaN surface. Light extraction structures are then
fashioned as arrays of light extraction elements or disperser
layers. The light extraction elements are formed from a material
having an index of refraction higher than the devices encapsulating
material.
[0008] U.S. Pat. No. 6,831,302 teaches a structure comprising a
multi-layer stack of materials, a layer of reflective material
capable of reflecting at least about 50% of light impinging thereon
and wherein a surface of a n-doped material, such as n-GaN, has a
dielectric function that varies spatially according to some
pattern. U.S. 2005/0227379 teaches shaping a surface of a
semiconductor layer with a laser to improve the light extraction
efficiency. Alternatively a substrate may contain three dimensional
geometric light extraction patterns or a light emitting element on
a substrate contains at least one layer with a pattern to produce
light extraction features.
[0009] All of the prior art suffer from marginal improvement of
light extraction efficiency or high manufacturing cost or both. A
simple solution is needed which improves the overall light
delivered from a light emitting device at a low cost.
SUMMARY OF THE INVENTION
[0010] One object of the present invention is to provide a low cost
device structure with improved light extraction efficiency. In
contrast to the prior art no changes are made in the basic
semiconductor portion of a light emitting device, so that virtually
all of current light emitting diodes or other light emitting device
structures can employ the benefits of this invention. The invention
improves light extraction from LEDs by providing a medium, as a
coating material, that light can enter easily and can propagate
through with minimum attenuation. Surfaces of the medium may be
configured to facilitate light exiting into air or an encapsulant.
Additionally, the invention improves light extraction by greatly
increasing the surface area of the device.
[0011] The present invention provides for a medium, as a dielectric
coating or material within a given index of refraction and light
extinction coefficient range, to be placed on the surface, or
surfaces, of a solid state light-emitting device. When the
refractive index of the dielectric coating is close to or higher
than that of the light emitting surfaces then there are only
minimal Fresnel reflections at the light emitting/dielectric
interfaces. Also, the critical angle for light to enter the
dielectric coating will be close to 90 degrees; thus, a very high
percentage of the light that is incident from the semiconductor
layers can enter the dielectric coating layers. If the dielectric
coating is made to have very low loss then light can travel through
the layer without appreciable attenuation. Further, if the
dielectric coating is rough or appropriately patterned the surface
area for light emission is increased. Since the dielectric coating
can be thick compared to many semiconductor layers, larger-scale
patterns can be formed in them compared to what is typically
possible in semiconductors. This provides a greater opportunity for
the photons to strike a surface where they may be extracted rather
than being reflected back into lossy semiconductor or metal layers.
One example of a material with an index of refraction greater than
GaN is silicon carbide, which can be deposited by plasma-enhanced
chemical vapor deposition, for example.
[0012] In one embodiment the dielectric medium is added to the top
layer of the structure of a light emitting device to improve the
extraction of light from the device. The coating has low optical
loss and an index of refraction about 2 or greater, preferably
having an index of refraction close to or greater than the index of
refraction of the uppermost semiconductor layer, for instance, GaN
in an AlInGaN based materials system. The coating is made from one
or combinations of a group of metal oxides comprising
Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, TiO.sub.2; certain other
materials are also acceptable such as silicon carbide and GaN based
solid solutions. The coating has a thickness ranging from about
0.01 to about 10 microns. In alternative embodiments the surface of
the coating material may be textured or shaped or patterned to
increase the surface area, improve light extraction and to engineer
the directionality of light escaping the layer. The coating may be
applied directly to a primary surface or multiple surfaces of a
light emitting device and may be applied over a contact electrode
pattern. In alternative embodiments a coating layer is comprised of
more than one coating layer, designed for specific optical
functions such as improving or impeding the transmission of
specific wavelength ranges or gradually diminishing the refractive
index of a composite film as a films outer surface is approached.
In these embodiments a coating may comprise additional materials
such as SiO.sub.2 in order to achieve specific optical properties
of a multilayer coating. The coating layer may replace a
passivation or protective layer on the device or function as one.
The coating layer may be crystalline or not.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic of one embodiment of the invention
with a metal-oxide coating layer on top of a light emitting
device.
[0014] FIG. 2 is a schematic of another embodiment of the invention
with a back reflector.
[0015] FIG. 3 is a schematic of another embodiment of the invention
with a coating on a transparent metallic layer.
[0016] FIG. 4 is a schematic of another embodiment of the invention
with a reflector layer over a substrate.
[0017] FIG. 5 is a schematic of another embodiment of the invention
with a reflector structure over a substrate.
[0018] FIG. 6 is a schematic of another embodiment of the invention
with a flip chip design.
[0019] FIG. 7 is a schematic of another embodiment of the invention
with a flip chip design with a submount substrate.
[0020] FIGS. 8a-8d are schematics of alternative patterns for a
metal-oxide coating.
[0021] FIG. 9 is a schematic of another embodiment of a metal-oxide
coating with a photonic crystal pattern.
DETAILED DESCRIPTION OF EMBODIMENTS
[0022] FIG. 1 shows a schematic view of one embodiment of the
invented light emitting structure 100 comprising a substrate
portion 101, a light emitting device portion 110 and a metal-oxide
coating portion 120. As used herein a substrate or submount portion
provides at least a mechanical support for a light emitting device
portion and metal-oxide coating portion. A substrate is chosen from
a group comprising Al.sub.2O.sub.3, Si, SiC, AlInGaN based
materials, metals, ceramics and glasses; these materials may be
single crystal or not. A submount is chosen based on manufacturing
convenience; typically a submount is chosen from a group comprising
Al.sub.2O.sub.3, Si, SiC, metals, ceramics, plastics and glasses.
As used herein a light emitting device portion is chosen from a
group comprising light emitting diodes, light emitting
heterojunctions, light emitting quantum well structures and other
solid state devices capable of emitting light. As used herein a
metal-oxide coating portion is chosen from a group comprising metal
oxides, silicon carbide, gallium nitride based materials and other
materials of appropriate optical and manufacturing characteristics.
As used herein, preferably, a metal-oxide coating portion has an
index of refraction of about 2.0 or greater and transmits a high
percentage of radiation passing through it; the thickness of a
coating may be from about 10 nm to more than 10 microns depending
on device requirements. Preferably, the coating's light extinction
coefficient (the complex portion of the index of refraction) is
about 0.2 or less, preferably 0.1 or less. Preferably a metal-oxide
coating portion is chosen from a group comprising niobium pentoxide
(Nb.sub.2O.sub.5), titanium dioxide (TiO.sub.2), tantalum pentoxide
(Ta.sub.2O.sub.5), silicon carbide (SiC) and gallium nitride (GaN).
A metal-oxide coating also has a dielectric property; the term
dielectric layer is used interchangeably herein.
[0023] Propagation of light within a specific material is
characterized by the material's complex index of refraction,
defined as:
n*=n-i.kappa. (2)
Here, n is the refractive index indicating the phase velocity
relative to the speed of light in vacuum, while K is called the
light extinction coefficient or optical loss factor, which
indicates the amount of absorption loss when the electromagnetic
wave propagates through the material. Both n and K are dependent on
the wavelength of the radiation; values for different materials are
readily available. In a preferred embodiment of the present
invention, the n value of the metal-oxide coating is close to or
greater than the n of GaN, .about.2.45. The proximity of the
refractive indices insures very little reflection of light occurs
as light passes from a GaN layer and to a metal oxide layer. The K
value, a measure of absorption, should be as small as possible,
preferably below 0.2 and more preferably below 0.1, so that light
can travel within the coating with minimal attenuation.
[0024] When a dielectric layer has an index of refraction, n, that
is somewhat less than that of a semiconductor then the critical
angle for internal reflection of light incident from a
semiconductor will be very large. The result is that a vast
majority of light incident on a dielectric layer from a GaN based
LED will be transmitted into the dielectric layer. Niobium
pentoxide (Nb.sub.2O.sub.5), titanium dioxide (TiO.sub.2), and
tantalum pentoxide (Ta.sub.2O.sub.5) are examples of such
dielectric layer materials. These dielectrics have indices of
refraction of approximately 2.39, 2.46, and 2.08, respectively,
compared to GaN which has an index of refraction of approximately
2.4. Dielectric coatings can be formed readily using sputtering,
reactive sputtering, ion-beam assisted sputtering, e-beam
evaporation, or ion-assisted, e-beam evaporation. Other deposition
techniques such as chemical vapor deposition, PECVD, MOCVD, ALD and
others known to one knowledgeable in the art are considered
equivalent embodiments.
[0025] Another advantage of a preferred dielectric coating is that
it can be deposited in relatively thick layers and have extremely
low optical losses. The thickness of a film can be on the order of
the thickness of the semiconductor layers, approximately 3 to 4
microns. The limit on thickness is only limited by deposition time
and by built up stresses in the films. Since a dielectric layer can
be made thick it can be patterned to have textures or shapes with
dimensions of several microns. This is an advantage compared to
texturing semiconductor layers since larger structures cannot be
formed; additionally semiconductor layers are expensive to form.
Also, texturing or shaping a coating layer provides more surface
area for light emission, increasing the light extraction
efficiency. A coated dielectric layer can also be easily patterned
into lenses or other specific shapes intended to maximize light
extraction or reflect light in particular directions.
[0026] Coated dielectric layers can be combined with textured
semiconductor surfaces. Also when there is a good index match
between a semiconductor active or cap layers and a dielectric then
a semiconductor surface can be smooth and not textured and an outer
surface of a dielectric coating can be textured or otherwise
patterned. This is an advantage because it allows for processing of
smooth wafers which are less costly to manufacture.
[0027] FIG. 2 is a schematic of another embodiment of the
invention; light emitting structure 200 comprises a back reflector
230 on a transmissive substrate 102, such as sapphire or silicon
carbide, with one or more n-type layers 280, one or more p-type
layers 270 and, optionally, additional intervening layers (not
shown), a transmissive contact layer 260, such as ITO, n-layer
contact 250, p-layer contact 240 and metal-oxide coating 120. One
or more n-type layers 280, one or more p-type layers 270 and,
optionally, additional intervening layers (not shown), comprise an
active region of an LED structure. Alternative LED structures may
be a simple p-n junction diode or double heterojunction structure
or multiple quantum well structure or others familiar to one
knowledgeable in the art. An embodiment of a light emitting portion
in a AlInGaN material system based light emitting device comprises
a buffer layer, one or more first cap layers at least one of which
is a first conductivity type, an active region comprising one or
more layers, one or more second cap layers at least one of which is
a second conductivity type, one or more contact layers and one or
more electrode layers. For instance, one embodiment of a light
emitting portion comprises an InGaN nucleation and/or buffer
layers, followed by GaN and/or n-type GaN cap layers, followed by
an active region comprising multiple quantum well active layers of
InGaN type and barrier layers of n type GaN, followed by p-type
AlGaN type cap layers, followed by n type GaN and/or InGaN cap
layers, followed by one or more electrode layers. An electrode
layer may be of aluminum, Ti/Al, Cr/Al, Ni/Au, Ni/Pd, Ni/Pt, or
other combinations well known in the art. The preceding
descriptions of various active regions apply equally to active
regions 350, 450, 550, 650 and 750. In a FIG. 2 embodiment a back
reflector 230 may be of aluminum or silver or multiple reflective
layers to reflect light back into a LED structure and recapture its
utility. Transmissive contact layer 260 may be of indium tin oxide;
alternatively, a transmissive contact layer may be of nickel/gold
(Ni/Au) composition or other alloys having high light
transmission.
[0028] FIG. 3 is a schematic of another embodiment of the invention
with a metal-oxide coating 120 on a transparent metallic layer 261
which is already textured or roughened. Transparent substrate 103
may be sapphire or silicon carbide. A roughened transparent
metallic layer provides for additional angles of incidence for
entering and departing light; in combination with metal-oxide
coating 120 of a predetermined index of refraction light extraction
efficiency is increased.
[0029] FIG. 4 is a schematic of another embodiment of the invention
with a reflector layer 410 over a substrate serving as a mechanical
support. In this embodiment a light emitting device portion 450,
comprising, at least, one or more n-type layers 280, one or more
p-type layers 270 and, optionally, additional intervening layers
(not shown), is manufactured on another substrate, removed and
attached to substrate 104. Substrate 104 may comprise one or more
layers such as reflector 410 and conductivity layer 262;
optionally, reflector layer 410, conductivity layer 262, metal
traces 420 and 421 and metal-oxide coating 120 may be formed on
light emitting device portion 450 prior to separation from an
original substrate.
[0030] One technique for separating a light emitting device portion
from its original substrate is termed "laser liftoff". This
technique is described in U.S. Pat. No. 6,071,795 and "Laser
Liftoff of Gallium Nitride from Sapphire Substrates", Sands, T., et
al.; Nov. 18, 2005:
http://www.ucop.edu/research/micro/98.sub.--99/98.sub.--133.pdf. An
alternative description is provided by Ambacher, O., et al., "Laser
Liftoff and Laser Patterning of Large Free-standing GaN
Substrates"; Mat. Res. Soc. Symp., Vol. 617, .COPYRGT. 2000
Materials Research Society. All three publications are included in
their entirety herein by reference.
[0031] FIG. 5 is a schematic of another embodiment of the invention
similar to FIG. 4. A reflector structure 411 is formed over a
patterned metal-oxide coating 121 on substrate 105. As in the
previous embodiment a laser liftoff technique is used to transfer
active light emitting region 550 to substrate structure 105.
Substrate 105 may comprise one or more layers such as reflector 411
and metal-oxide layer 121; optionally, conductivity layer 262 and
metal-oxide coating 120 may be formed on light emitting device
portion 450 prior to separation from an original substrate or after
combination with substrate 105 comprising reflector 411 and coating
121. Reflector structure 411 over a patterned metal-oxide coating
121 on substrate 105 may take on various configurations and shapes;
only one example is shown. One knowledgeable in the art of silicon
on insulator wafer processing is familiar with alternative methods
for transferring an active layer(s) to another substrate.
[0032] FIG. 6 is a schematic of another embodiment of the invention
with a flip chip design. Light emitting device 600 comprises
metal-oxide coating portion 622, transmissive substrate 106, for
instance sapphire, active region 650, n contact 651, p contact 641
and submount 601. N contact 651, p contact 641 and submount 601 are
in mechanical contact and electrical communication. Submount 601
contains electrical circuits, not shown, to provide electrical
connection to external circuits or packages. Optionally, submount
601 may comprise additional layers such as reflector 411 and
metal-oxide coating 121 to enhance reflection of light back through
layers 452 and 106 while maintaining mechanical contact and
electrical communication to contacts 651 and 641.
[0033] FIG. 7 is a schematic of another embodiment of the invention
with a flip chip design with a submount substrate 701 and the
original substrate removed. Light emitting device 700 comprises
metal-oxide coating portion 722, active region 750, n contact 751,
p contact 741 and submount 701. N contact 751, p contact 741 and
submount 701 are in mechanical contact and electrical
communication. Submount 701 contains electrical circuits, not
shown, to provide electrical connection to external circuits or
packages. Optionally, submount 701 may comprise additional layers
such as reflector 411 and metal-oxide coating 121 to enhance
reflection of light back through active region 750 while
maintaining mechanical contact and electrical communication to
contacts 751 and 741.
[0034] FIGS. 8a-8d are schematics of alternative patterns and
shapes for a metal-oxide coating. Patterns and shapes for
metal-oxide coating layer 801, 802, 803, and 804 are chosen from a
group comprising ribs, cylinders, slots, polygon shaped ribs,
triangular shaped ridges, hemispherical shaped mounds, horizontal
cylindrical shaped ribs, cylinders, ellipsoids, hemispheres,
rectilinear trenches or solids, cones, angled cylinders, angled
hemispheres, angled ellipsoids, angled rectilinear trenches or
solids and angled cones. FIG. 9 is a schematic of an alternative
embodiment of a metal-oxide coating with a pattern or shape that
also functions as a photonic crystal lattice 901. Not shown in
FIGS. 8 and 9 are substrates or submounts. Patterns and shapes for
elements for metal-oxide coating layer 801, 802, 803, 804 and 901
have a geometrical shape chosen from the group comprising
cylinders, ellipsoids, hemispheres, rectilinear trenches or solids,
cones, angled cylinders, angled hemispheres, angled ellipsoids,
angled rectilinear trenches or solids and angled cones and wherein
element to element spacing may be uniform or not. In alternative
embodiments, a metal-oxide coating layer may comprise one or more
metal-oxide layers of different compositions resulting in one or
more different refractive indices in the one or more layers.
Non-stoichiometric compositions of metal-oxide materials may be
incorporated to achieve varying indices of refraction and
extinction coefficients. In embodiments where multiple layers are
employed a layer of silicon dioxide integral to other layers may be
of utility to enable additional light transmissive or inhibiting
capabilities of a multilayer coating. Feature sizes of patterns and
photonic crystal shapes may vary from about 10 nm to more than
several microns depending on a requirement.
[0035] In some embodiments a light emitting device comprises a
first substrate portion; a first coating layer portion in contact
with the substrate portion wherein a reflective layer structure is
integral to the first coating layer; a light emitting portion in
contact with the first coating layer portion; and a second coating
layer portion in contact with the light emitting portion wherein at
least one of the first and second coating layer portions has a
continuous, three dimensional pattern chosen from a group
consisting of ribs, cylinders, slots, polygon shaped ribs,
triangular shaped ridges, hemispherical shaped mounds, horizontal
cylindrical shaped ribs, cylinders, ellipsoids, hemispheres,
rectilinear trenches, rectilinear solids, cones, angled cylinders,
angled hemispheres, angled ellipsoids, angled rectilinear trenches,
angled solids and angled cones and wherein element to element
spacing may be uniform or not and an index of refraction greater
than about 2 and an optical loss factor less than about 0.2;
optionally, a light emitting device further comprises a second
substrate in contact with said second coating layer portion;
optionally, a light emitting device further comprises a first cap
layer of a first conductivity type adjacent to said substrate
portion; an active region comprising one or more layers separated
from said substrate portion by the first cap layer; a second cap
layer of a second conductivity type; one or more contact layers in
contact with the active region through the second cap layers; and
wherein said active region is of the AlInGaN material system;
optionally, a light emitting device comprises a first and second
coating layer portions chosen from a group comprising metal oxides,
silicon carbide, GaN, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, TiO.sub.2,
AlInGaN based solid solutions, and their non-stoichiometric
mixtures; optionally, a light emitting device further comprises a
second coating layer portion comprising one or more coating layers
wherein at least the first of the one or more coating layers of
said second coating layer has an index of refraction greater than 2
and an optical loss factor less than 0.2; optionally, a light
emitting device further comprises a first and second substrate
portions chosen from a group comprising sapphire, silicon carbide,
GaN, silicon, glass, ceramic, plastic and metal.
[0036] In some embodiments a light emitting device comprises a
first substrate portion; a reflective layer in contact with the
first substrate portion; a transparent conductive layer in contact
with the reflective layer; a light emitting portion comprising at
least two layers in contact with the transparent conductive layer;
and one or more coating layers adjacent the light emitting portion
having a three dimensional pattern chosen from a group consisting
of ribs, cylinders, slots, polygon shaped ribs, triangular shaped
ridges, hemispherical shaped mounds, horizontal cylindrical shaped
ribs, cylinders, ellipsoids, hemispheres, rectilinear trenches,
rectilinear solids, cones, angled cylinders, angled hemispheres,
angled ellipsoids, angled rectilinear trenches, angled solids and
angled cones and wherein element to element spacing may be uniform
or not wherein at least the first coating layer of the one or more
coating layers has an index of refraction greater than 2 and an
optical loss factor less than 0.2; optionally, a light emitting
device further comprises a second substrate in contact with one of
said one or more coating layers; optionally, a light emitting
device further comprises a first cap layer of a first conductivity
type adjacent to said substrate portion; an active region
comprising one or more layers separated from said substrate portion
by the first cap layer; a second cap layer of a second conductivity
type; one or more contact layers in contact with the active region
through the second cap layer; and one or more electrode layers in
contact with one of the one or more contact layers; wherein said
active region is of the AlInGaN material system; optionally, a
light emitting device further comprises one or more coating layers
are chosen from a group comprising metal oxides, silicon carbide,
GaN, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, TiO.sub.2, AlInGaN based
solid solutions, and their non-stoichiometric mixtures; optionally,
a light emitting device further comprises a first and second
substrate portions chosen from a group comprising sapphire, silicon
carbide, GaN, silicon, glass, ceramic, plastic and metal.
[0037] The instant invention discloses a method of improving light
extraction efficiency of a light emitting device comprising the
steps:
[0038] choosing a composition of one or more coating layers wherein
at least the first coating layer has an index of refraction greater
than 2 and an optical loss factor less than 0.2;
[0039] depositing the one or more coating layers on a light
emitting device; and
[0040] patterning the one or more coating layers with a three
dimensional pattern chosen from a group consisting of ribs,
cylinders, slots, polygon shaped ribs, triangular shaped ridges,
hemispherical shaped mounds, horizontal cylindrical shaped ribs,
cylinders, ellipsoids, hemispheres, rectilinear trenches,
rectilinear solids, cones, angled cylinders, angled hemispheres,
angled ellipsoids, angled rectilinear trenches, angled solids and
angled cones and wherein element to element spacing may be uniform
or not wherein at least the first coating layer of the one or more
coating layers has an index of refraction greater than 2 and an
optical loss factor less than 0.2; optionally, a light emitting
device of the disclosed method further comprises one or more
coating layers chosen from a group comprising metal oxides, silicon
carbide, GaN, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, TiO.sub.2, AlInGaN
based solid solutions, and their non-stoichiometric mixtures.
[0041] Foregoing described embodiments of the invention are
provided as illustrations and descriptions. They are not intended
to limit the invention to precise form described. In particular, it
is contemplated that functional implementation of invention
described herein may be implemented equivalently. Alternative
construction techniques and processes are apparent to one
knowledgeable with integrated circuit and MEMS technology. Other
variations and embodiments are possible in light of above
teachings, and it is thus intended that the scope of invention not
be limited by this Detailed Description, but rather by Claims
following.
* * * * *
References