U.S. patent application number 13/361741 was filed with the patent office on 2012-05-24 for light emitting device and method for enhancing light extraction thereof.
This patent application is currently assigned to WALSIN LIHWA CORPORATION. Invention is credited to CHING-HWA CHANG JEAN, Changho CHEN, CHANG-CHI PAN.
Application Number | 20120129283 13/361741 |
Document ID | / |
Family ID | 43897641 |
Filed Date | 2012-05-24 |
United States Patent
Application |
20120129283 |
Kind Code |
A1 |
PAN; CHANG-CHI ; et
al. |
May 24, 2012 |
LIGHT EMITTING DEVICE AND METHOD FOR ENHANCING LIGHT EXTRACTION
THEREOF
Abstract
A method for enhancing light extraction of a light emitting
device is disclosed. The method includes the steps of: providing a
site layer on the light emitting device; placing a protection layer
on the site layer; forming an array of pores through the protection
layer and the site layer; and growing on the site layer an oxide
layer, having a plurality of rods, each of which is formed in one
of the pores. The shapes of the rods can be well controlled by
adjusting reactive temperature, time and N.sub.2/H.sub.2
concentration ratio of atmosphere such that the shape and light
escape angle of the rods can be changed.
Inventors: |
PAN; CHANG-CHI; (Taoyuan,
TW) ; CHANG JEAN; CHING-HWA; (Taoyuan, TW) ;
CHEN; Changho; (Taoyuan, TW) |
Assignee: |
WALSIN LIHWA CORPORATION
Taoyuan County
TW
|
Family ID: |
43897641 |
Appl. No.: |
13/361741 |
Filed: |
January 30, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12588637 |
Oct 22, 2009 |
8129728 |
|
|
13361741 |
|
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Current U.S.
Class: |
438/29 ;
257/E33.068 |
Current CPC
Class: |
H01L 2933/0058 20130101;
H01L 33/58 20130101; H01L 33/20 20130101; H01L 2933/0083
20130101 |
Class at
Publication: |
438/29 ;
257/E33.068 |
International
Class: |
H01L 33/58 20100101
H01L033/58 |
Claims
1. A method for enhancing light extraction of a light emitting
device, comprising the steps of: providing a site layer on the
light emitting device; placing a protection layer on the site
layer; forming an array of pores through the protection layer and
the site layer; and growing a plurality of oxide rods on the light
emitting substrate, each of which is formed in one of the pores;
wherein the site layer and the protection layer are formed of
different materials, and wherein the shapes of the rods are
controlled by adjusting reactive temperature, time and
N.sub.2/H.sub.2 concentration ratio of atmosphere such that the
shape and light escape angle of the rods can be are changed.
2. The method according to claim 1, wherein the oxide rods comprise
zinc oxide (ZnO), silicon dioxide (SiO.sub.2), titanium dioxide
(TiO.sub.2), or aluminum oxide (Al.sub.2O.sub.3).
3. The method according to claim 1, wherein the oxide rods are
formed by hydrothermal treatment, sol-gel method, electro-plating,
thermal evaporation, chemical vapor deposition (CVD), or molecular
beam epitaxy (MBE).
4. The method according to claim 1, wherein the site layer
comprises ITO, Ni/Au, NiO/Au, p-ZnO, or ZnO.
5. The method according to claim 1, wherein the protection layer
comprises photoresist material or dielectric material.
6. The method according to claim 1, wherein the atmosphere
temperature is higher than 200.degree..
7. The method according to claim 1, wherein the atmosphere
comprises nitrogen, hydrogen, or a mixture thereof.
8. The method according to claim 1, wherein the atmosphere has a
nitrogen/hydrogen concentration ratio larger than 1.
9. The method according to claim 1, wherein the rods have a
nanostructure or a microstructure.
10. The method according to claim 1, wherein the rods have a shape
of a hexagonal pyramid or a truncated hexagonal pyramid.
11. The method according to claim 1, wherein the rod has a bottom
surface with a diameter ranging from 100 nm.about.1 .mu.m.
12. The method according to claim 1, wherein the pores are formed
by wet etching process, dry etching process, photolithography and
exposure development process, laser cutting process, or electron
beam writing process.
13.-24. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for enhancing
light extraction of a light emitting device. More particularly, the
present invention relates to a method for enhancing light
extraction of a light emitting device by forming an oxide layer,
such as a zinc oxide layer, with a controllable roughness on the
light emitting device.
BACKGROUND OF THE INVENTION
[0002] Recently, since development of integrated circuits (IC) has
been down sized to nano-scale, application to nano-scale elements
becomes more and more popular. Among all inventions,
short-wavelength light emitting devices, such as laser diodes (LD)
and light emitting diodes (LED), have been the mainstream. For
development of short-wavelength light emitting devices, III-V
compounds semiconductors are the common materials for manufacturing
LED. However, with development of new systematic materials, II-VI
compounds semiconductors are valued again. In practice, Zinc oxide
(ZnO) has advantages of low cost and easy synthesis. Hence, study
on ZnO is a hot topic today, especially on the ZnO nanorods.
[0003] ZnO has a direct band-gap of 3.37 eV which is higher than
other high direct band-gap semiconductor materials. In addition,
ZnO has higher excitation binding energy (excitation binding energy
of Gallium Nitride (GaN) is around 20 meV while that of ZnO is much
higher and about 60 meV.). Therefore, its lighting efficiency is
higher than other materials under room temperature. During recent
years, a lot of reports on study of ZnO show that it can be applied
to short-wavelength elements and laser diodes due to the good
lighting efficiency. Since data accessing can be improved by using
ultraviolet (UV) laser, application of ZnO to UV laser source has a
great potential. For ZnO, membrane elements are very popular.
[0004] Besides, another main direction of development of ZnO is
one-dimensional nanorods (nanowires). Scientists can grow highly
aligned nanorod array successfully. With photoluminescence, UV
laser is excited out of the nanorods. Although UV laser can be
commercialized in many ways, how to enhance light extraction and
control light escape angle of nanorods still has two problems to be
solved. Otherwise, lighting efficiency will be significantly
affected.
[0005] Therefore, the present invention provides a solution to the
problems mentioned above. Via the invention, light extraction of a
light emitting device can be enhanced.
SUMMARY OF THE INVENTION
[0006] Accordingly, it is an object of the present invention to
provide a method for enhancing light extraction of a light emitting
device by forming an oxide layer with a controllable roughness on
the light emitting device.
[0007] In accordance with an aspect of the present invention, a
method for enhancing light extraction of a light emitting device,
includes the steps of: providing a site layer on the light emitting
device; placing a protection layer on the site layer; forming an
array of pores through the protection layer and the site layer; and
growing on the site layer an oxide layer, having a plurality of
rods, each of which is formed in one of the pores. The shapes of
the rods can be well controlled by adjusting N.sub.2/H.sub.2
concentration ratio, reactive temperature and time such that the
shape and light escape angle of the rods can be changed.
[0008] Preferably, the oxide layer comprises zinc oxide (ZnO),
silicon dioxide (SiO.sub.2), titanium dioxide (TiO.sub.2), or
aluminum oxide (Al.sub.2O.sub.3).
[0009] Preferably, the oxide layer is formed by hydrothermal
treatment, sol-gel method, electro-plating, thermal evaporation,
chemical vapor deposition (CVD), or molecular beam epitaxy
(MBE).
[0010] Preferably, the site layer comprises ITO, Ni/Au, NiO/Au,
p-ZnO, or ZnO.
[0011] Preferably, the protection layer comprises photoresist
material or dielectric material.
[0012] Preferably, the atmosphere temperature is higher than
200.degree. C.
[0013] Preferably, the atmosphere comprises nitrogen, hydrogen, or
a mixture thereof.
[0014] Preferably, the atmosphere has a nitrogen/hydrogen
concentration ratio larger than 1.
[0015] Preferably, the rods have a nanostructure or a
microstructure.
[0016] Preferably, the rods have a shape of a hexagonal pyramid or
a truncated hexagonal pyramid.
[0017] Preferably, the rod has a bottom surface with a diameter
ranging from 100 nm.about.order of micrometers.
[0018] Preferably, the pores are formed by wet etching process, dry
etching process, photolithography and exposure development process,
laser cutting process, or electron beam writing process.
[0019] In accordance with another aspect of the present invention,
a light emitting device having enhanced light extraction includes a
light emitting substrate; a site layer provided on the light
emitting substrate; an array of pores formed in the site layer; a
protection layer placed on the site layer having the pores exposed;
and an oxide layer formed on the site layer, having a plurality of
rods, each of which is formed in one of the pores. The shapes of
the rods are adjusted by controlling temperature and concentration
of atmosphere such that light escape angle of the rods can be
changed.
[0020] Preferably, the oxide layer comprises zinc oxide (ZnO),
silicon dioxide (SiO.sub.2), titanium dioxide (TiO.sub.2), or
aluminum oxide (Al.sub.2O.sub.3).
[0021] Preferably, the oxide layer is formed by hydrothermal
treatment, sol-gel method, electro-plating, thermal evaporation,
chemical vapor deposition (CVD), or molecular beam epitaxy
(MBE).
[0022] Preferably, the site layer comprises ITO, Ni/Au, NiO/Au,
p-ZnO, or ZnO.
[0023] Preferably, the protection layer comprises photoresist
material or dielectric material.
[0024] Preferably, the atmosphere temperature is higher than
200.degree. C.
[0025] Preferably, the atmosphere comprises nitrogen, hydrogen, or
a mixture thereof.
[0026] Preferably, the atmosphere has a nitrogen/hydrogen
concentration ratio larger than 1.
[0027] Preferably, the rods have a nanostructure or a
microstructure.
[0028] Preferably, the rods have a shape of a hexagonal pyramid or
a truncated hexagonal pyramid.
[0029] Preferably, the rod has a bottom surface with a diameter
ranging from 100 nm.about.order of micrometers.
[0030] Preferably, the pores are formed by wet etching process, dry
etching process, photolithography and exposure development process,
laser cutting process, or electron beam writing process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The above objects and advantages of the present invention
will become more readily apparent to those ordinarily skilled in
the art after reviewing the following detailed description and
accompanying drawings, in which:
[0032] FIG. 1 is a flow chart of a preferred embodiment according
to the present invention;
[0033] FIG. 2 is a three dimensional view of the present
invention;
[0034] FIG. 3 is a cross-sectional view along the A-A' cross
section in FIG. 2 to show formation of pores;
[0035] FIG. 4 is cross-sectional view along the A-A' cross section
in FIG. 2 to show formation of rods;
[0036] FIG. 5 is an enlarged view of a rod;
[0037] FIG. 6 shows structures of the rods formed under different
atmospheres;
[0038] FIG. 7 shows a light path in the rod which has a shape of a
hexagonal column; and
[0039] FIG. 8 shows a light path in the rod which has a shape of a
hexagonal pyramid.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0040] The present invention will now be described more
specifically with reference to the following embodiment. It is to
be noted that the following descriptions of preferred embodiment of
this invention are presented herein for purpose of illustration and
description only; it is not intended to be exhaustive or to be
limited to the precise form disclosed.
[0041] FIG. 1 is a flow chart of a preferred embodiment according
to the present invention showing a method for enhancing light
extraction of a light emitting device by forming an oxide layer
with a controllable roughness on a light emitting device. FIG. 2 is
a three dimensional view of the present invention. It also shows
the relative position for each element in the present invention.
Now, please refer to FIGS. 1 and 2. The method of the present
invention for enhancing light extraction of a light emitting device
by forming an oxide layer with a controllable roughness on a light
emitting device includes the following steps. First, a light
emitting device 102 having a surface layer 104 formed on the top
surface thereof is provided (as shown at step S101). In this
embodiment, the surface layer 104 is made of p-GaN. However, it
should be noted that the surface layer 104 of the present invention
is not limited to p-GaN. It can also be made of p-AlGaN, p-InGaN,
p-GaN/InGaN SLs, p-AlGaN/GaN SLs, p-AlInGaN, p-InAlGaN/InAlGaN SLs,
n+-(In)(Al)GaN, ITO, p-ZnO, ZnO, or Ni/Au. In other words, the
surface layer 104 is not limited to a conductive type of P or
N.
[0042] The light emitting device 102 used in this embodiment is a
nitride light emitting diode which has an energy band gap
equivalent to wavelength of 200 to 650 nm.
[0043] Later, a site layer 106 is provided on the surface layer 104
of the light emitting device 102 (as shown at step S102). The site
layer 106 can be made of ITO, Ni/Au, NiO/Au, p-ZnO, or ZnO.
[0044] Next, a protection layer 107 is placed on the site layer 106
(as shown at step S103). Please refer to FIG. 3. It is a
cross-sectional view along the A-A' cross section in FIG. 2. An
array of pores 109 are formed through the protection layer 107 and
the site layer 106 by wet etching process, dry etching process,
photolithography and exposure development process, laser cutting
process, or electron beam writing process (as shown at step S104).
The protection layer 107 is made of photoresist material while
photolithographic process is used, whereas the protection layer 107
is made of dielectric material while etching process is used.
[0045] Then, an oxide layer having a plurality of rods 108 is grown
on the site layer 106 such that each of the rods 108 is formed in
one of the pores 109. The protection layer 107 is for positioning
the rods 108 into the pores 109 and preventing the rods 108 from
growing at a place other than the pores 109.
[0046] The shapes of the rods 108 are adjusted by controlling
temperature and concentration of atmosphere such that light escape
angle of the rods can be changed (as shown at steps
S105.about.S106).
[0047] The oxide layer can be made of zinc oxide (ZnO), silicon
dioxide (SiO.sub.2), titanium dioxide (TiO.sub.2), or aluminum
oxide (Al.sub.2O.sub.3). In this embodiment, the oxide layer is
made of ZnO.
[0048] In this embodiment, the oxide layer is formed by
hydrothermal treatment. First, the light emitting device including
the site layer is cleaned with acetone, methanol, and deionized
water for about 5 minutes, respectively. Then, the light emitting
device and the site layer are dried by a nitrogen spray gun. Next,
a seed layer of ZnO is formed on the site layer for increasing
adhesion. The light emitting device, site layer, and seed layer is
together called a mediator.
[0049] The seed layer of ZnO is prepared by dissolving zinc acetate
(Zn(CH.sub.3COO).sub.2.H.sub.2O) in 2MOE
(CH.sub.3O(CH.sub.2).sub.2OH, 2-methoxyethanol), each having a
concentration of 0.5M, and then stirring the resultant solution for
2 hours while heating at a temperature of 65.degree. C., so that a
transparent gel solution is obtained. Later, the transparent gel
solution is spin coated onto the top surface of the site layer.
Next, a ZnO seed layer is obtained by thermal annealing having the
transparent gel solution deposited thereon at a temperature of
130.degree. C. for 60 minutes. In this embodiment, the ZnO seed
layer is used for ZnO particles to grow as a ZnO layer.
[0050] It should be understood that the seed layer is not limited
to be made of ZnO, and can also be made of gold (Au), silver (Ag),
Tin (Sn), or cobalt (Co). The oxide layer may be formed randomly or
orderly.
[0051] After the seed layer is formed, the mediator is placed
facing downwards in a growth solution of zinc nitrate hexahydrate
(Zn(NO.sub.3).sub.2.6H.sub.2O) having a purity of 98% and
hexamethylenetetramine (C.sub.6H.sub.12N.sub.4, HMT) having a
purity of 99.5%, each having a concentration of 0.5M. Later, it is
heated in a dryer at a low temperature of 90.degree. C. for about 3
hours. After being heated, it is taken out and washed with
deionized water. Then, a ZnO layer having a plurality of rods could
be obtained. Otherwise, the growth rate, dimension and height of
ZnO rods can be well controlled by adjusting the temperature,
concentration and growth time.
[0052] During the hydrothermal treatment, ZnO is formed according
to the following formulas:
##STR00001##
[0053] In the aforementioned deposition mechanism, ZnO begins to
form onto the seed layer once the concentrations of zinc ions and
hydroxide ions reach saturation. Due to anisotropic characteristic
of atomic bonding, atoms tend to flow towards low energy during
nucleation causing asymmetric growth in a specific direction which
thereby forms a rod/thread shape array structure.
[0054] Although hydrothermal treatment is used in the present
embodiment, it should be understood that the present invention is
not limited to hydrothermal treatment, and can also use thermal
evaporation, sol-gel method, chemical vapor deposition (CVD), or
molecular beam epitaxy (MBE).
[0055] Moreover, even though spin coating is used for disposing the
seed layer onto the GaN substrate in the present embodiment, it
should not be limited thereto, and can also use dip coating,
evaporation, sputtering, atomic layer deposition, electrochemical
deposition, pulse laser deposition, metal-organic chemical vapor
deposition, or thermal annealing.
[0056] The atmosphere can include nitrogen, hydrogen, or a mixture
thereof. In this embodiment, the atmosphere has a nitrogen/hydrogen
concentration ratio larger than 1 while the atmosphere includes a
mixture of nitrogen and hydrogen. Moreover, the atmosphere
temperature for the controllable roughness of ZnO rods is higher
than 200.degree. C.
[0057] Under the aforementioned atmosphere conditions, the rods 108
may have shapes of hexagonal pyramids or truncated hexagonal
pyramids with a size order between nanometer and micrometer. The
rods 108 have a bottom surface with a diameter ranging from 100
nm.about.order of micrometers.
[0058] Please see FIG. 4. The sketch illustrates how the rods 108
of the ZnO layer are formed in the pores 109 of the site layer 106.
Each rod 108 has a hexagonal cross section and a Wurtzite structure
as shown in FIG. 5. In the present invention, it has a hexagonal
column appearance. The light beams emit in a specified direction
from the light emitting device 102 according to the structure of
the rods 108.
[0059] Please refer to FIG. 6. FIG. 6 illustrates different shapes
of the rod 108 which are formed under different temperature and
concentration of atmosphere conditions. For example, the rod 108
shown in FIG. 6A which is shaped as a hexagonal pyramid is formed
under an atmosphere having a nitrogen/hydrogen concentration ratio
smaller than that of FIG. 6C which is shaped as a truncated
hexagonal pyramid. Furthermore, the rod 108 shown in FIG. 6A can
also be achieved by providing a temperature higher than that of
FIG. 6C. Therefore, roughness of a light emitting device can be
controlled by changing the shape (sharpness) of the pyramids of the
rods 108 of the oxide layer.
[0060] Please refer to FIGS. 7 and 8. These two figures show
different light paths in a hexagonal prism and a hexagonal pyramid.
It is obvious that the hexagonal pyramid will change light
direction by refraction and increase the light escape angle, which
can be compared with FIG. 7. Therefore, the light extraction of the
light emitting device can be enhanced and the light escape angle
can be controlled by the present invention.
[0061] While the invention has been described in terms of what is
presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention needs not be
limited to the disclosed embodiment. On the contrary, it is
intended to cover various modifications and similar arrangements
included within the spirit and scope of the appended claims, which
are to be accorded with the broadest interpretation so as to
encompass all such modifications and similar structures.
* * * * *