U.S. patent application number 12/402466 was filed with the patent office on 2010-06-03 for light emitting devices.
This patent application is currently assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. Invention is credited to Chia-Hsin Chao, Han-Tsung Hsueh, Chen-Yang Huang, Chun-Feng Lai, Chien-Jen Sun, Jih-Fu Wang, Wen-Yung Yeh.
Application Number | 20100133504 12/402466 |
Document ID | / |
Family ID | 42221935 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100133504 |
Kind Code |
A1 |
Wang; Jih-Fu ; et
al. |
June 3, 2010 |
LIGHT EMITTING DEVICES
Abstract
A new light emitting device is disclosed. The device includes a
reflector, a surface layer, and a light emitting layer located
there-between. The light emitting layer emits light at a wavelength
.lamda.. An optical thickness from the light emitting layer to the
reflector is approximately m*.lamda./4, where m is a positive
integer. Furthermore, the said device may, in addition, include an
optical transform layer adjoining to the light emitting layer.
Thus, the light emitted by the device can be not only collimated
but also polarized.
Inventors: |
Wang; Jih-Fu; (Changhua
County, TW) ; Chao; Chia-Hsin; (Taichung County,
TW) ; Huang; Chen-Yang; (Hsinchu County, TW) ;
Hsueh; Han-Tsung; (Taipei City, TW) ; Lai;
Chun-Feng; (Taichung County, TW) ; Yeh; Wen-Yung;
(Hsinchu County, TW) ; Sun; Chien-Jen; (Zhubei
City, TW) |
Correspondence
Address: |
QUINTERO LAW OFFICE, PC
615 Hampton Dr, Suite A202
Venice
CA
90291
US
|
Assignee: |
INDUSTRIAL TECHNOLOGY RESEARCH
INSTITUTE
HSINCHU
TW
|
Family ID: |
42221935 |
Appl. No.: |
12/402466 |
Filed: |
March 11, 2009 |
Current U.S.
Class: |
257/13 ; 257/98;
257/99; 257/E33.061 |
Current CPC
Class: |
H01L 2933/0083 20130101;
H01L 33/02 20130101; H01L 33/405 20130101; H01L 33/22 20130101 |
Class at
Publication: |
257/13 ; 257/98;
257/E33.061; 257/99 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2008 |
TW |
TW097146584 |
Claims
1. A light emitting device, at least comprising: a surface layer; a
light emitting layer which the emitted light has a wavelength; and
a reflective layer, wherein the light emitting layer is disposed
between the reflective layer and the surface layer, and an optical
thickness between the light emitting layer and the reflective layer
is about a value of integer times of a quarter of the
wavelength.
2. The light emitting device as claimed in claim 1, wherein the
optical thickness between the light emitting layer and the
reflective layer is about a value between integer m-1 and m+1 times
of a quarter of the wavelength.
3. The light emitting device as claimed in claim 1, wherein the
optical thickness between the light emitting layer and the
reflective layer is about a value of m times of a quarter of the
wavelength, where m is a positive integer, and is satisfied
1.ltoreq.m.ltoreq.12.
4. The light emitting device as claimed in claim 1, wherein the
surface layer is a light polarizing layer.
5. The light emitting device as claimed in claim 1, wherein the
structure of the light emitting layer is a quantum well structure
or a quantum dot structure.
6. The light emitting device as claimed in claim 1, wherein the
material of the light emitting layer is a fluorescent inorganic
material, a phosphorescent inorganic material, a fluorescent
organic material, or a phosphorescent organic material.
7. The light emitting device as claimed in claim 1, wherein the
reflective layer at least comprises a metallic layer.
8. The light emitting device as claimed in claim 4, wherein the
light polarizing layer is a metal layer, a periodic parallel stripe
interval arranged metal layer, a plurality of dielectric stack of
light polarizing thin films or an organic light polarizing
layer.
9. The light emitting device as claimed in claim 1, wherein a
material of the light emitting layer comprises a III-V group
semiconductor material.
10. The light emitting device as claimed in claim 9, wherein the
III-V group semiconductor material is a nitrided base material, an
eptiaxial GaAs or InP base grown material.
11. The light emitting device as claimed in claim 1, wherein the
optical thickness between the surface layer and the reflective
layer is about equal to or less than 20 times of the wavelength,
but greater than or equal to a half of the wavelength.
12. The light emitting device as claimed in claim 1, further
comprising a conductive layer interposed between the light emitting
layer and the reflective layer.
13. The light emitting device as claimed in claim 1, further at
least comprising: a light transformation layer, wherein the light
transformation layer is adjacent to the light emitting layer.
14. The light emitting device as claimed in claim 13, wherein the
light transformation layer is an interface layer with a plurality
of structures, the structures is distributed on an interface of the
transformation in patterned forms, and a dielectric function of the
interface is a spatial function of pattern variations such that the
emitted light of the light emitting device is collimated.
15. The light emitting device as claimed in claim 1, wherein the
optical thickness between the light emitting layer and the
reflective layer is about a value of m times of a quarter of the
wavelength, where m is a positive integer, and is satisfied
1.ltoreq.m.ltoreq.40.
16. The light emitting device as claimed in claim 13, wherein the
light transformation layer is interposed between the light emitting
layer and the reflective layer.
17. The light emitting device as claimed in claim 13, wherein the
transformation layer is interposed between the light emitting layer
and the surface layer.
18. The light emitting device as claimed in claim 13, wherein the
optical thickness between the surface layer and the reflective
layer is about equal to or less than 20 times of the
wavelength.
19. The light emitting device as claimed in claim 14, wherein the
plurality of structures at least comprise an opening, a pillar, a
pore, or a stripe grating.
20. The light emitting device as claimed in claim 14, wherein the
plurality of structures have a periodic or a non-periodic
pattern.
21. The light emitting device as claimed in claim 20, wherein the
periodic pattern is a honeycomb, a non-equilateral parallelogram,
an equilateral parallelogram, an annular, a ID grating or a quasi
photonic crystal.
22. The light emitting device as claimed in claim 13, wherein a
material of the light transformation layer at least comprises a
transparent conductive material or a carrier conductive layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from a prior Taiwanese Patent Application No. 097146584,
filed on Dec. 1, 2008, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to display devices, and in particular
to light emitting devices capable of emitting collimated and
polarized lights.
[0004] 2. Description of the Related Art
[0005] Light emitting devices, such as display devices, have been
extensively applied in business, entertainment, military, medical,
engineering, and civil regimes. With the application of display
devices gradually expanding and being more popular, the development
trends of the display devices are intended to become lighter,
thinner, and more compact for the purpose of lower power
consumption and more environmental friendliness to human
beings.
[0006] Generally speaking, all of the display devices require light
sources. For example, conventional projector adapts high efficient
high-pressure mercury lamps (UHE) or (UHP) as light sources. Light
emission of UHE or UHP, however, preferably has to be a collimated
light beam, which is regulated by optical systems for the projector
application. In reality, most of emitted light angles of the
abovementioned lamps exceed 10 degrees, the light at these emission
angles cannot be collimated completely resulting in waste of light
energy. In addition, he UHE and UHP, moreover, also emits infrared
light, which also can not be used in projector application and most
of these infrared is transformed into heat, scattered light, and
thermal noise. Therefore the more widely spread application of the
projector is limited. Furthermore, for the flat panel display
(FPD), lots of polarizer films and filters are required to
implement in these devices. The multiple light absorption and
reflection of these optical components also results in inefficient
consumption of light energy for the flat panel display
application.
[0007] Accordingly, light emitting devices capable of emitting
collimated and polarized lights to reduce optical components are
indispensable in the industry to overcome the abovementioned
problems.
BRIEF SUMMARY OF THE INVENTION
[0008] According to techniques of the invention, light emitting
devices capable of emitting collimated and polarized lights are
presented.
[0009] According to techniques of the invention, an embodiment of
the light emitting device comprises: a surface layer; a light
emitting layer which the emitted light has a wavelength; and a
reflective layer, wherein the light emitting layer is disposed
between the reflective layer and the surface layer, and an optical
thickness between the light emitting layer and the reflective layer
is about a value of integer times of a quarter of the
wavelength.
[0010] According to techniques of the invention, another embodiment
of the light emitting device comprises: a surface layer; a light
emitting layer which the emitted light has a wavelength; a
reflective layer; and a light transformation layer, wherein the
light emitting layer is disposed between the reflective layer and
the surface layer, and an optical thickness between the light
emitting layer and the reflective layer is about a value of integer
times of a quarter of the wavelength, wherein the light
transformation layer is adjacent to the light emitting layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0012] FIG. 1A is a schematic diagram illustrating light emitting
devices 100a and 100b according to the first or the second
embodiment of the invention;
[0013] FIG. 1B is a schematic diagram illustrating a thin GaN LED
structure 100b according to the first or the second embodiment of
the invention;
[0014] FIG. 1C and FIG. 1D are cross section views schematically
illustrating the first embodiment of the light emitting device
according to the invention;
[0015] FIG. 1E and FIG. 1F respectively show simulated diagrams of
luminance and P/S ratio of the light emitting device according to
the first embodiment of the invention;
[0016] FIG. 2 shows a reference diagram of the lambertian light
distribution according to an embodiment of the invention;
[0017] FIGS. 2A and 3A are cross section views of the light
emitting device according to the second embodiment of the
invention;
[0018] FIG. 2B and FIG. 3B are cross section views of the light
emitting device 100 (FIG. 1A) or the light emitting device 100b
(FIG. 1B);
[0019] FIGS. 2C, 3C, 2D and 3D are schematic diagrams illustrating
openings 124 on the surface of the conductive layer 104 in the
light emitting device according to the second embodiment of the
invention; and
[0020] FIGS. 2E and 2F respectively show simulated diagrams of
luminance and P/S ratio of the light emitting device according to
the second embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0021] It is understood that the following disclosure provides many
different embodiments, or examples, for implementing different
features of various embodiments. Specific examples of components
and arrangements are described below to simplify the present
disclosure. These are merely examples and are not intended to be
limited. In addition, the present disclosure may repeat reference
numerals and/or letters in the various examples. This repetition is
for the purpose of simplicity and clarity and does not in itself
indicate a relationship between the various embodiments and/or
configurations discussed. Moreover, the formation of a first
feature over or on a second feature in the description that follows
may include embodiments in which the first and second features are
formed in direct contact or not in direct contact.
[0022] Accordingly, an embodiment of a light emitting device of the
invention is disclosed. The light emitting device includes a
plurality of layers of stacked structures. The stack structures
include a reflective layer; a light emitting layer which emitted
light has a wavelength; and a surface layer, wherein the light
emitting layer is interposed between the reflective layer and the
surface layer, and an optical thickness or on optical path between
the light emitting layer and the reflective layer is about a value
of m times of a quarter of the wavelength (.lamda.), and the
optical thickness is in a range which approximately satisfies
nD=m.times..lamda./4. The optical thickness can alternatively
satisfy (m-1).times..lamda./4<nD<(m+1).times..lamda./4, and
can tolerate .+-.15% variations. The light emitted by the device
can be not only collimated but also polarized. The optical
thickness equals to the real thickness between the light emitting
layer and the reflective layer multiply refractive index of each
corresponding layer. Parameters can be indicated as
(nD=n.sub.1.times.d.sub.1+n.sub.2.times.D.sub.2 . . .
n.sub.m.times.d.sub.m) and (D=d.sub.1+d.sub.2+ . . . +d.sub.m),
where nD is depicted as the optical thickness, D is real total
thickness, n imeans refractive index, n.sub.i is refractive index
of the i.sup.th layer material, d.sub.i is the thickness of the
i.sup.th layer material, i=1, 2, . . . m, where m is a positive
integer, and 1.ltoreq.m.ltoreq.12.
[0023] According to another embodiment of the invention, the light
emitting device includes a plurality of layers of stacked
structures. The stack structures include a reflective layer; a
light transformation layer; a light emitting layer which emitted
light has a wavelength; and a surface layer, wherein the light
transformation layer is interposed between the reflective layer and
the light emitting layer, wherein the light emitting layer is
interposed between the reflective layer and the surface layer,
wherein an optical thickness exists between the light emitting
layer and the reflective layer, wherein the optical thickness is
about a value of m times of a quarter of the wavelength (.lamda.),
and the optical thickness is in a range which approximately
satisfies nD=m.times..lamda./4. The optical thickness can
alternatively satisfy
(m-1).times..lamda./4<nD<(m+1).times..lamda./4, and can
tolerate .+-.15% variations. The light transformation layer is an
interface layer with a plurality of structures. These structures
are distributed in patterned forms on an interface of the light
transforming layer, and the dielectric function of the interface is
a spatial function varied with the patterned forms such that the
light emitted by the device can be not only collimated but also
polarized.
[0024] In the following descriptions, an example of a light
emitting diode (LED) is in conjunction as an implementation
embodiment. However, it should be understood that in other
embodiments other light emitting devices such as an organic light
emitting diode (OLED), polymer light emitting diode (PLED), or
semiconductor optic amplifier (SOA) etc., are also applicable
thereto.
[0025] As shown in FIG. 1A and 1B, a schematic diagram of light
emitting devices 100a and 100b such as light emitting diodes are
respectively provided. The light emitting diodes can comprise a
plurality of deposition layers of stacked structure which can be
disposed overlying a substrate (not shown) such as a sapphire or
silicon. The aforementioned deposition layers can include a
reflective layer 102, a conductive layer 104, a first carrier
conductive layer 106 such as a p-type carrier conductive layer, a
light emitting layer 108, a second carrier conductive layer 110
such as an n-type carrier conductive layer, and a polarized layer
116 which is a thin film layer polarizing the transmission light.
Furthermore, as shown in FIG. 1A, a conductive electrode 112 is
disposed on the second carrier conductive layer 110 to serve as a
contact pad on the n-type side, while another conductive electrode
114 is disposed on the reflective layer 112 to serve as a contact
pad on the p-type side, wherein, in contrast with the conductive
electrode 112 on the n-type side, the conductive electrode 114 on
the p-type side is sustained with a positive voltage. In addition,
in another embodiment, the first carrier conductive layer 106 can
be an n-type carrier conductive layer, while the second carrier
conductive layer 110 can be a p-type carrier conductive layer.
Accordingly, in this embodiment, the conductive electrode 112
serves as a contact pad on the p-type side, while the conductive
electrode 114 serves as a contact pad on the n-type side. In
addition, according to embodiments of the light emitting device
structure 100 and the thin LED structure 100b of the invention, the
bottom conductive electrode 114 is not necessarily made up of
Cu.
[0026] A plurality of layers of stacked structure in the light
emitting device 100 include a reflective layer 102, a light
emitting layer 108 and a surface layer, wherein the light emitting
layer is interposed between the reflective layer and the surface
layer, and an optical path exists between the light emitting layer
and the reflective layer. Moreover, the equals to the real
thickness between the light emitting layer and the reflective layer
multiply refractive index of each corresponding layer.
[0027] The light emitting layer emits a light with a wavelength,
wherein the optical thickness is about m times of a quarter of the
wavelength, where m is a positive integer. The optical thickness
can approximately satisfy nD=m.times..lamda./4, or satisfy
(m-1).times..lamda./4<nD<(m+1).times..lamda./4, and can
tolerate .+-.15% variations such that the light emitted by the
device can be not only collimated but also polarized.
[0028] In implementation, the surface layer can be a polarized
layer 116, a surface layer with micro-structures, a near planar
surface layer, or any combinations of the abovementioned material
layers. Moreover, the optical path (thickness) between the surface
layer and the reflective layer is equal to or less than 5 times or
20 times of the wavelength, wherein the emitted light finally
leaves the surface layer of the device. Most of the lights emitted
from the light emitting device are concentrated on directions
perpendicular to the surface layer plane. Alternatively, most of
the lights emitted from the light emitting device are concentrated
on two lateral directions perpendicular to the surface layer plane
if the optical thickness is properly chosen.
[0029] The reflective layer 102 includes a metal, a mixture of
multiple metals, a metal alloy, a multi-layered dielectric mirror
layer, or any combinations of the abovementioned materials.
Further, the reflective layer 102 can reflect the lights emitted
from the light emitting layer 108 towards the reflective layer 102
which has at least 50% reflectance.
[0030] The conductive layer 104 can be a transparent conductive
layer such as an indium tin oxide (ITO) layer. The conductive layer
104 can improve conductivity between the first carrier conductive
layer 106 and the reflective layer 102. The conductive layer 104 is
not necessarily made up of the indium tin oxide (ITO) layer, but
can be transparent conductive materials which refractive indices
(n) are less than that of the first carrier conductive layer 106.
Additionally, in one embodiment, if a preferred conductivity is
generated between the first carrier conductive layer 106 and the
reflective layer, the conductive layer 104 can be optionally
omitted during implementation.
[0031] In an embodiment of the light emitting diode based on
gallium nitride (GaN), the first carrier conductive layer 106 can
be a magnesium doped GaN deposition layer (p-doped), while the
second carrier conductive layer 110 can be a silicon doped GaN
deposition layer (n-doped). In this embodiment, the light emitting
layer 108 can be InGaN/GaN quantum well deposition layers. The
light emitting layer emits a light at a characteristic wavelength
(.lamda.) with bandwidth .DELTA..lamda.. The light emitting layer
is preferably disposed a position departing from integral times of
a quarter of the wavelength. That is, the thickness of the first
carrier conductive layer 106 and the conductive layer 104 is
preferably integral times of a quarter of the wavelength. In
addition, a total optical thickness of the stack layers of the
second carrier conductive 110 and the conductive layer 104 can be
less than 5 times of the wavelength of the light emitting layer
108, wherein the emitted light finally leaves the surface layer.
Most of the lights emitted from the light emitting device are
concentrated on directions perpendicular to the surface layer
plane. Alternatively, most of the lights emitted from the light
emitting device are concentrated on two lateral directions
perpendicular to the light surface layer plane if the optical
thickness is properly chosen. In one embodiment, such as the light
emitting diode based on gallium nitride (GaN), the thickness of the
conductive layer 104 can be equal to or less than about 0.3
.mu.m.
[0032] Furthermore, the light emitting layer includes a quantum
well structure, a quantum dot, a fluorescent inorganic material, a
phosphorescent inorganic material, a fluorescent organic material,
a phosphorescent organic material, or any combinations of the
aforementioned materials. The wavelength emitted from the light
emitting layer is approximately in a range including a visible
light, a UV light, an infrared light, or other wavelength
range.
[0033] In FIG. 1A and FIG. 1B, the polarized layer 116 can be a
plurality of parallel interval of metal layers which contains
nano-wire gratings. The metal layers is periodically or
non-periodically arranged on the surface of the second carrier
conductive layer 110 capable of polarizing the lights from the
light emitting layer 108. The light emitting diode 100 and 110b can
thus generate polarized lights. In one embodiment, the thickness
(H) of the metal layers of the light polarizing layer can be about
100 nm and each metal layer is periodically arranged with an
interval about 120 nm. It should be understood that the thickness
of the metal layers and the arrangement period of the metal layers
are dependent on the wavelength of the light emitting layer.
Therefore, the thickness and the arrangement period of the metal
layers are not limited to embodiment of the invention.
[0034] Additionally, the light polarizing layer 116 in FIGS. 1A and
1B can be a structure with partial reflection, such as a
multi-layered stack of dielectric layers, an extremely thin metal
layer, a planar layer with multiple parallel arranged strips of
metal layers, an organic light polarizing material layered, a light
polarizing thin film with multiple dielectric stacked structures,
or any combinations of the abovementioned materials. In one
embodiment of the invention, the metal layers arranged with
multiple intervals can also be periodically or non-periodically
parallel interval arranged.
[0035] The stack layers of the light emitting diodes 100 (FIG. 1A)
and 100b (FIG. 1B) can be formed by several different fabrication
processes. For example, a deposition process, a laser process,
lithography and etching processes are adapted to form each of the
aforementioned deposition layers. However, for the embodiment of
the light polarizing layer 116 with nano-metal grating structures,
a metal layer can be first deposited, and nano-imprint lithography
and etching processes can be subsequently implemented.
[0036] The materials of the light emitting device include a III-V
group semiconductor material, an organic material, a polymer
material, or any combinations of the aforementioned materials. The
III-V group semiconductor material includes a nitrided base
material, or an eptiaxial GaAs or InP base grown material. The
nitrided base material includes a non-polar material or a
semi-polar material. In another embodiment, the light emitting
device further includes a surface layer plane which most of the
emitted light with an included angle is equal to or less than 30
degrees to the normal lint of the surface layerplane. The normal
line is perpendicular to the surface layer plane (indicated as
angles between 90-60 degrees in FIG. 1E).
[0037] FIG. 1C and FIG. 1D are cross section views schematically
illustrating a first embodiment of the light emitting device
according to the invention. As shown in FIG. 1C and FIG. 1D, the
light emitting layer is departed from the reflective layer 102
short enough such as a quarter or other integral times of the
wavelength of the light emitting layer 108 with 15% tolerances such
that the lobes of the radiation patterns of the light emission from
the light emitting layer can be preferably determined. The lights
which is emitted from the light emitting layer 108 towards the
surface layer plane 122 has a preferable emission angle, thus
further collimating light emitted form the light emitting layer
108. Besides, since the distance between the light emitting layer
108 and the reflective layer 102 is short enough, emitted light
patterns and angles of the escape cones can thus be controlled such
that the light emitting device can provide lights with a preferable
collimated light distribution instead of a lambertian light
distribution. The lambertian light distribution of the conventional
LED is shown in FIG. 2. FIG. 1C and FIG. 1D are local cross
sections of the light emitting device 100 (FIG. 1A) or the light
emitting device 100b (FIG. 1B). In FIGS. 1C and 1D, the polarized
layer 116 is depicted as a continuous deposition layer for
simplicity. As shown in FIGS. 1C and 1D, the distance between the
light emitting layer 108 and the reflective layer 102, i.e., the
thickness of the first carrier conductive layer 106 (p-type carrier
conductive layer) and the conductive layer 104 is depicted as
thickness D1. The distance between the light polarizing layer 116
and the light emitting layer 108, i.e., the thickness of the second
carrier conductive layer 110 and the light emitting layer 108 is
depicted as thickness D2. The distance between the polarized layer
116 and the reflective layer 102, i.e., the thickness of the second
carrier conductive layer 110 (n-type carrier conductive layer), the
light emitting layer 108, the first carrier conductive layer 106,
and the conductive layer 104 is depicted as total thickness D.
[0038] In one embodiment, the thickness D2 (micrometers) of the
second carrier conductive layer 110 (such as n-type carrier
conductive layer) and the light emitting layer 108 can be greater
than or equal to 0.164 times of the mean value of refractive
indices of the light polarizing layer 116, the second carrier
conductive layer 110 and the light emitting layer 108 in FIG. 1A or
FIG. 1B (i.e., 0.164.times.n.sub.1 .mu.m, where n.sub.1 is the mean
value of refractive indices of the light polarizing layer, the
second carrier conductive layer and the light emitting layer).
However, the total thickness D from the second carrier conductive
layer 110 to the conductive layer 104 can be less than or equal to
0.82 times of the mean value of refractive indices of the light
polarizing layer 116, the second carrier conductive layer 110, the
light emitting layer 108, the first carrier conductive layer 106,
and the conductive layer 104 in FIG. 1A or FIG. 1B (i.e.,
0.82.times.n .mu.m, where n is the mean value of refractive indices
of the light polarizing layer, the second carrier conductive layer,
the light emitting layer, the first carrier conductive layer, and
the conductive layer). In a specific embodiment, for example a
gallium nitride based light emitting diode with an emission
wavelength of 475 nm, the value of n.sub.1 can be about 2.45, and
D2 can be equal to or less than 0.4 .mu.m. In the same embodiment,
the value of n.sub.1 can be about 2.45, and D can be equal to or
less than 2 .mu.m.
[0039] Furthermore as shown in FIG. 1C and FIG. 1D, when the light
emitting layer 108 emits lights, the emitted light is towards the
surface layer plane (the light polarizing layer 116), such as
indicated as arrows A and B in FIG. 1D, and towards the reflective
layer 102, such as indicated as arrow C in FIG. 1D. Since the
polarized layer 116 in FIG. 1A or polarized layer 116 in FIG. 1b of
the first embodiment of light emitting device of the invention are
designed such that part of the emitted light is directly
transmitted trough such as B, part of the emitted light is
refracted such as A, and the light emitted from the light emitting
layer 108 is polarized. The light refracted by the light polarizing
layer 116 passes through the first carrier conductive layer 106 and
the conductive layer 104 to the reflective layer 102, and then
reflects by the reflective layer 102 and passes through the
conductive layer 104, the first carrier conductive layer 106, the
light emitting layer 108, the second carrier conductive layer 110
to the light polarizing layer 116 (as indicated in arrows 1-5 in
FIG. 1D). The emission lights are cycling forwards and backwards
between the light polarizing layer 116 and the reflective layer 102
until the directions of the emitted lights almost is toward a
specific direction (i.e., falling within the cone .theta..sub.c of
FIG. 1C), thereby passing through the light polarizing layer 116.
On the contrary, the emitted lights towards the reflective layer
102, such as arrow C in FIGS. 1C and 1D, can be transmitted in the
same manner until passing through the light polarizing layer
116.
[0040] In FIGS. 1C and 1D, since the emitted lights from the light
emitting layer 108 has preferable collimated effects, an included
angle .theta. (a light emission angle) between the light vector 120
of the surface layer plane on the light emitting device and the
normal line 118 perpendicular to the surface layer plane is mostly
equal to or less than a maximum emitted light angle .theta..sub.c
(where .theta..sub.c.apprxeq.30 degrees relative to the GaN based
LED 100 or 100b). The normal line is perpendicular to the surface
layer plane.
[0041] FIG. 1E and FIG. 1F respectively shows simulated diagrams of
luminance and P/S ratio of the light emitting device 100 (FIG. 1A)
or 100b (FIG. 1B) according to one embodiment (FIG. 1D) of the
invention. As shown in FIG. 1E and FIG. 1F, in the radiation
pattern diagram of the lights emitted from the light emitting
device 100 or 100b of this embodiment, the emitted angles are
converged within .+-.30 degrees. In FIGS. 1E and 1F, it is observed
that when the light wavelength of the light emitting device 100 or
100b is about 460 nm, the P/S ratio can reach at least 75.
[0042] Since the emitted light from the light emitting layer 108 in
the aforementioned embodiment is preferably collimated, an included
angle .theta. (a emitted light angle) between the light vector 120
of the light emitting device and the normal line 118 perpendicular
to the surface layer plane is mostly equal to or less than a
maximum emitted light angle .theta..sub.c (where
.theta..sub.c.apprxeq.30 degrees relative to the GaN based LED 100
or 100b), where the normal line is perpendicular to the light
emission plane.
[0043] The .theta. value corresponding to FIGS. 1C, 1D and 1E can
be between 10 degrees and 30 degrees, which is dependent from
design parameters.
[0044] According to a second embodiment of the invention, the light
emitting device further includes a first carrier conductive layer
106 interposed between the light emitting layer 108 and the
reflective layer 102, and a second carrier conductive layer 110
interposed between the surface layer and the light emitting layer
108. A light transformation layer is interposed between the first
carrier conductive layer 106 and reflective layer 102 (indicated as
105 in FIGS. 2A and 2B) or interposed between the second carrier
conductive layer 110 and the surface layer (indicated as 109 in
FIGS. 3A and 3B). The light transformation layer can be made of a
transparent conductive material or a carrier conductive material.
In one embodiment, the total thickness of the second carrier
conductive layer and the light emitting layer is equal to or
greater than 0.164 times of the mean value of refractive indices of
the polarized layer 116, the second carrier conductive layer, and
the light emitting layer. In another embodiment, the total
thickness from the second carrier conductive layer to the
conductive layer is equal to or greater than 0.82 times or 2 times
of the mean value of refractive indices of the polarized layer, the
second carrier conductive layer, the light emitting layer, the
first carrier conductive layer, and the transparent conductive
layer.
[0045] In the aforementioned second embodiment, the optical
thickness between the light emitting layer and the reflective layer
is about m times of a quarter of the wavelength, wherein m is a
positive integer and is satisfied 1.ltoreq.m.ltoreq.40.
[0046] In addition, in one embodiment, the aforementioned
conductive layer 104 can be optionally adapted or omitted according
to whether a preferable conductivity is existed between the first
carrier conductive layer 106 and the reflective layer.
[0047] In another embodiment, the light transformation layer can be
an interface layer with a plurality of structures, wherein the
dielectric function of the interface is a spatial function of
pattern distributions as shown in FIGS. 2C, 2D, 3C, and 3D. The
plurality of structures includes an opening 124, a pillar, a pore
126, a stripe grating 128, or any combinations thereof. Further,
the pattern distributions include a periodic repeating pattern, a
non-periodic pattern, or any combinations thereof. Moreover, the
periodic pattern includes a honeycomb, a non-equilateral
parallelogram, an equilateral parallelogram, an annular, a 1D
grating, a quasi photonic crystal, or any combinations thereof.
[0048] In implementation, the surface layer can be a light
polarizing layer 116, a surface layer with micro-structures, a near
planar surface layer, or any combinations of the abovementioned
material layers. Moreover, the optical path (thickness) between the
surface layer and the reflective layer is equal to or less than 5
times or 20 times of the wavelength, wherein the emitted light
leaves the surface layer plane. Most of the light emitted from the
light emitting device is concentrated on directions perpendicular
to the surface layer plane. Alternatively, most of the light is
emitted from the light emitting device are concentrated on two
lateral directions perpendicular to the surface layer plane.
[0049] According to the structural embodiment of the light emitting
device 100 or LED 100b, the first and the second carrier conductive
layers 106 and 110 can correspond to a p-type and an n-type carrier
conductive layers, but switching thereof can also be applicable.
The bottom conductive electrode 114 can be not necessarily made up
of Cu.
[0050] As shown in FIGS. 2A and 3A, a light emitting device
structure 100 or 100b is provided which includes a stacked
structure of multiple deposition layers. The stacked structure can
include a reflective layer 102, a conductive layer 104, a first
carrier conductive layer 106, a light emitting layer 108, a second
carrier conductive layer 110, and a light polarizing layer 116.
Compared with the aforementioned embodiments, several openings are
formed on the surface of the conductive layer 104 in this
embodiment. The dielectric function of the surface of the
conductive layer 104 varies with the composed patterns of the
openings which are disclosed in detail in the following
description. Accordingly, in the second embodiment, similar
elements are depicted as the same references. Fabrication methods
and materials can also refer to the aforementioned embodiments, and
for simplicity detail description is omitted.
[0051] In the light emitting device of the second embodiment, the
light transformation is made of a transparent conductive material
or a carrier conductive material.
[0052] In FIGS. 2A and 3A, the light emitting layer 108 is disposed
away from the reflective layer 102 with a quarter of the emission
wavelength or man integral times of a quarter of the emission
wavelength. A tolerance of .+-.15% is acceptable. The optical
thickness of the second carrier conductive layer 110, the light
emitting layer 108, the first carrier conductive layer 106 and the
conductive layer 104 (the light polarizing layer may also be
included) is equal to or less than 20 times of the emission
wavelength of the light emitting layer 108. As shown in FIGS. 1A
and 1B of the first embodiment, the light emitting layer 108 is
disposed away from the reflective layer with a short enough
distance; therefore, emitted lights from the light emitting layer
108 is collimated.
[0053] Referring to FIG. 3A, in one embodiment, the light
polarizing layer 116 can be metal layers with multiple parallel
stripe intervals therebetween and the metal layers are periodically
or non-periodically arranged on the surface of the second carrier
conductive layer 110. In the second embodiment, the thickness and
arrangement period of the metal layers of the polarized layer 116
are similar to those of the first embodiment. In addition, in the
first embodiment, such as a GaN based LED, the thickness of the
first carrier conductive layer 106 and the conductive layer 104 is
preferably equal to or less than 0.3 .mu.m. The depth of the
openings on the surface of the conductive layer 104, such as pores
126 or trenches 128 can be about 0.2 .mu.m. Moreover, the surface
of the openings can be as close to the light emitting layer 108 as
possible, as indicated h in FIGS. 2A and 3A, to enhance collimation
effects.
[0054] FIG. 2B and FIG. 3B are cross section views of the light
emitting device 100 (FIG. 1A) or the light emitting device 100b
(FIG. 1B). As shown in FIG. 2B, the distance between the light
emitting layer 108 and the reflective layer 102, i.e., the
thickness of the first carrier conductive layer 106 and the
conductive layer 104 is depicted as thickness D1. The distance
between the light polarizing layer 116 and the light emitting layer
108, i.e., the thickness of the second carrier conductive layer 110
and the light emitting layer 108 is depicted as thickness D2. The
distance between the light polarizing layer 116 and the reflective
layer 102, i.e., the thickness of the second carrier conductive
layer 110, the light emitting layer 108, the first carrier
conductive layer 106, and the conductive layer 104 is depicted as
total thickness D.
[0055] In one embodiment, the thickness D2 (micrometers) of the
second carrier conductive layer 110 and the light emitting layer
108 can be greater than or equal to 0.164 times of the mean value
of refractive indices of the light polarizing layer 116 (FIG. 1a)
or 116b (FIG. 1B), the second carrier conductive layer 110 and the
light emitting layer 108 in FIG. 1A or FIG. 1B (i.e.,
0.164.times.n.sub.1 .mu.m, where n.sub.1 is the mean value of
refractive indices of the light polarizing layer, the carrier
conductive layer and the light emitting layer). However, the total
thickness D from the second carrier conductive layer 110 to the
conductive layer 104 can be less than or equal to 0.82 times of the
mean value of refractive indices of the polarized layer 116 (FIG.
1a) or 116b (FIG. 1B), the second carrier conductive layer 110, the
light emitting layer 108, the first carrier conductive layer 106,
and the conductive layer 104 in FIG. 1A or FIG. 1B (i.e.,
0.82.times.n .mu.m, where n is the mean value of refractive indices
of the light polarizing layer, the carrier conductive layer, the
light emitting layer, the carrier conductive layer, and the
conductive layer). In a specific embodiment, for example a gallium
nitride based light emitting diode with an emitted wavelength of
475 nm, the value of n.sub.1 can be about 2.45, and D2 can be equal
to or less than 0.4 .mu.m. In the same embodiment, the value of
n.sub.1 can be about 2.45, and D can be equal to or less than 4.5
.mu.m.
[0056] Further as shown in FIG. 2B and FIG. 3B, when the light
emitting layer 108 emits lights, the emitted light isowards the
surface layer plane, indicated as arrows A and B in FIGS. 1C and
1D, and towards the reflective layer 102. Since the surface layer
plane of the light emitting device is designed with a light
polarizing layer in the second embodiment of the invention such
that part of the emitted light is directly transmitted through such
as arrow A, part of the emitted light is refracted such as arrow B,
and the light emitted from the light emitting layer 108 is
polarized. The light refracted by the light polarizing layer 116
passes through the first carrier conductive layer 106 and the
conductive layer 104 to the reflective layer 102, and then reflects
by the reflective layer 102 and passes through the conductive layer
104, the first carrier conductive layer 106, the light emitting
layer 108, the second carrier conductive layer 110 to the light
polarizing layer 116 (as indicated in arrows 1-3 in FIGS. 2B and
3B). The emitted lights are cycling forwards and backwards between
the light polarizing layer 116 and the reflective layer 102 until
the directions of the emitted light is are toward a specific
direction thereby passing through the polarized layer 116.
[0057] The patterns of the opening on the surface of the conductive
layer 104 are composed of a photonic lattice which can enhance
collimation of the emitted lights from the light emitting layer 108
and can further transform the cycling lights forwards and backwards
between the polarized layer 116 and the reflective layer 102 into a
polarized state. For example, referring to FIG. 3B, the reflected
lights from the polarized layer 116 pass through the surface of the
photonic lattice and transformed into a polarized state which can
directly pass through the polarized layer 116. The openings of the
photonic lattice formed on the surface of the conductive layer 104
not only can enhance light collimation effects, but also the
emitted polarized light efficiency.
[0058] Referring to FIGS. 2B and 3B, since the emitted lights from
the light emitting layer 108 is preferably collimated, an included
angle .theta. (a light emission angle) between the light vector 120
of the light emitting device and the normal line 118 perpendicular
to the light emission plane is mostly equal to or less than 15
degrees (as indicated between 90-75 degrees in FIG. 2E). The normal
line 118 is perpendicular to the surface layer plane.
[0059] FIGS. 2C, 3C, 2D and 3D are schematic diagrams illustrating
openings 124 on the surface of the conductive layer 104 in the
light emitting device according to the second embodiment of the
invention. As shown in FIG. 3C, the openings 124 can be pores 126
entirely or locally formed on the surface of the conductive layer
104. The pores 126 can be arranged with a specific interval
therebetween or can be randomly arranged. Furthermore, the pores
126 can also be arranged in sub-pattern forms with several pores
aggregated together and each sub-pattern are spaced with a specific
interval therebetween. For example, the opening pattern composed of
the pores 126 can be periodic or non-periodic.
[0060] The periodic pattern includes a honeycomb, a non-equilateral
parallelogram, an equilateral parallelogram, an annular, a ID
grating, a quasi photonic crystal, or any combinations thereof.
[0061] Referring to FIG. 3D, the openings 124 on the surface of the
conductive layer 104 can alternatively be grooves 128 which can be
periodically or non-periodically arranged. By doing so, lights
passed through the surface of the conductive layer are transformed
into the polarized state. In one embodiment, the openings 124 on
the surface of the conductive layer 104 can be formed before
formation of the first carrier conductive layer 106. For example,
the openings 124 can be formed by a nano-imprint lithography and
etching processes to create pores 126 or grooves 128. In addition,
the depth of the pores 126 or grooves 128 can reach with the
conductive layer 104, or on the interface between the conductive
layer 104 and reflective layer 102, or even extending into the
reflective layer 102.
[0062] FIGS. 2E-2F respectively show simulated diagrams of
luminance and P/S ratio of the light emitting device according to
the second embodiment of the invention. Since the emission lights
from the light emitting layer 108 of the second embodiment has
preferable collimated effects, an included angle .theta. (a light
emission angle) between the light vector 120 of light emitting
device and the normal line 118 perpendicular to the surface layer
plane is mostly equal to or less than 15 degrees (as indicated
between 90-75 degrees in FIG. 2E).
[0063] According to the first and the second embodiments of the
light emitting devices, the collimated and polymerized elements are
fabricated in a conventional LED structure 100 as shown in FIG. 1A.
Alternatively, the collimated and polymerized elements can also be
fabricated in a thinned LED structure 100b in FIG. 1B. The first
and the second carrier conductive layers 106 and 110 can correspond
to a p-type and an n-type carrier conductive layers, but switching
thereof can also be applicable. The bottom conductive electrode 114
can be not necessarily made up of Cu.
[0064] In summary, according to the light emitting devices of
embodiments of the invention, the light emitting layer emits lights
with specific wavelengths. The lights with specific wavelengths
have a peak wavelength .lamda. and a bandwidth .DELTA..lamda.. The
light emitting layer can be disposed away from the reflective layer
with a quarter of the emitted wavelength or m an integral times of
a quarter of the emitted wavelength. A light polarizing layer can
be disposed on the light emission plane of the light emitting
device such that the light emitting device can emit both collimated
and polarized light. Moreover, a photonic lattice of opening
patterns can be optionally formed on an interface between any two
adjacent deposition layers such as between the carrier conductive
layer and the conductive layer. The photonic lattice of opening
patterns can transform polarity of lights inside the light emitting
devices and can further enhance collimation effects and P/S ratio
of the emitted light from the light emitting devices.
[0065] While the invention has been described by way of example and
in terms of the preferred embodiments, it is to be understood that
the invention is not limited to the disclosed embodiments. To the
contrary, it is intended to cover various modifications and similar
arrangements (as would be apparent to those skilled in the art).
Therefore, the scope of the appended claims should be accorded to
the broadest interpretation so as to encompass all such
modifications and similar arrangements.
* * * * *