U.S. patent application number 10/700537 was filed with the patent office on 2004-05-20 for gallium nitride based compound semiconductor light-emitting device and manufacturing method therefor.
Invention is credited to Hon, Schang-Jing, Huang, Jenn-Bin, Yih, Nai-Guann.
Application Number | 20040094772 10/700537 |
Document ID | / |
Family ID | 32228156 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040094772 |
Kind Code |
A1 |
Hon, Schang-Jing ; et
al. |
May 20, 2004 |
Gallium nitride based compound semiconductor light-emitting device
and manufacturing method therefor
Abstract
Disclosed are a GaN based compound semiconductor light emitting
diode (LED) and a manufacturing method therefore. In the LED, a
multi-layer epitaxial structure including an active layer is formed
over a substrate, and a light transmissive impurity doped metal
oxide which may be formed over a Ni/Au layer is used as a light
extraction layer while the Ni/Au layer is taken as an ohmic contact
layer between the light extraction layer and the multi-layer
epitaxial structure. Then, an n-type metal electrode is disposed
over an exposing region of an n-type semiconductor and a p-type
metal electrode over the light extraction layer. The LED is thus
formed.
Inventors: |
Hon, Schang-Jing; (Pe Te
City, TW) ; Huang, Jenn-Bin; (Tai Chung Hsien,
TW) ; Yih, Nai-Guann; (Tao Yuan Hsien, TW) |
Correspondence
Address: |
TROXELL LAW OFFICE PLLC
SUITE 1404
5205 LEESBURG PIKE
FALLS CHURCH
VA
22041
US
|
Family ID: |
32228156 |
Appl. No.: |
10/700537 |
Filed: |
November 5, 2003 |
Current U.S.
Class: |
257/102 ;
257/E33.074 |
Current CPC
Class: |
H01L 33/42 20130101;
H01L 33/22 20130101; H01L 33/32 20130101 |
Class at
Publication: |
257/102 |
International
Class: |
H01L 033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 11, 2002 |
TW |
91132695 |
Claims
What is claimed is:
1. A method for manufacturing a GaN based compound semiconductor
light-emitting device, comprising the steps of: (a) forming an
n-GaN based layer over a substrate after a buffer layer is formed
over said substrate; (b) forming a multi-quantum well (MQW) active
layer over said n-GaN based layer; (c) forming a p-GaN based layer
over said MQW layer and etching away a portion of said n-GaN, MQW
active and p-GaN layers whereby an exposing region is formed on
said n-GaN based layer and an exposing surface is formed on said
p-GaN based layer; and (d) forming an impurity doped ZnO based
layer as a light extraction layer over said exposing surface after
said etching of said n-GaN layer, MQW active layer and p-GaN based
layers, wherein said doped ZnO based layer is doped so that said
doped ZnO based layer is light transparent and conductive; and (e)
forming a p-type electrode over said light extraction layer after
said etching and forming an n-type electrode over said exposing
region of said n-GaN layer.
2. According to the method in claim 1, wherein said doped ZnO based
layer comprises ZnO, Sn.sub.xZn.sub.1-xO, In.sub.xZ.sub.1-xO and
In.sub.xSn.sub.yZ.sub.1-x-yO wherein 0.ltoreq.X.ltoreq.1,
0.ltoreq.Y.ltoreq.1 and 0.ltoreq.X+Y.ltoreq.1, and wherein said
impurity comprises p-type and n-type impurities.
3. According to the method in claim 2, wherein said p-type
impurities comprises Al.
4. According to the method in claim 1, wherein said light
extraction layer has a thickness of 50 .ANG. to 50 .mu.m.
5. According to the method in claim 1, wherein said substrate may
be light transmissive or opaque and comprises sapphire, Si or
SiC.
6. According to the method in claim 1, wherein said doped ZnO based
layer is at least transparent to a light having a wavelength of
400-700 nm.
7. The method according to claim 4, wherein when said light
extraction layer has a thickness being at least 1 .mu.m, said
method further comprises a step between said steps of (d) and (e)
or succeeding to said step (e): (f) subjecting said doped ZnO based
layer to a surface treatment by roughening or particularly
texturizing whereby a plurality of facets are formed on said doped
ZnO based layer.
8. A GaN based compound semiconductor light-emitting device,
comprising: a substrate; a multi-layer epitaxial structure
comprising: a buffer layer being an IT-GAN/HT-GaN layer formed over
an upper surface of said substrate, wherein said LT-GaN is a low
temperature layer first formed over said substrate, and said HT-GaN
layer is a high temperature layer then formed over said LT-GaN
layer; a first semiconductor layer being an n-GaN based compound
semiconductor layer formed over said buffer layer; a light
generating layer being a GaN based compound semiconductor active
layer comprising a GaN multi-layer quantum well (MQW) layer; and a
second semiconductor layer being a p-GaN based compound
semiconductor formed over said light generating layer; a light
extraction layer being an impurity doped metal oxide transmissive
to light and formed over said second semiconductor layer and
comprising impurity doped ZnO based layer; an n-type metal
electrode disposed over an exposing region of said first
semiconductor layer; and a p-type metal electrode disposed over
said light extraction layer.
9. According to the light-emitting device in claim 8, wherein said
substrate has a thickness of 300-450 .mu.m, said LT-GaN has a
thickness of 30-500 .ANG., said HT-GaN has a thickness of 0.5-6
.mu.m, said first semiconductor has a thickness of 2-6 .mu.m and
said second semiconductor layer has a thickness of 0.2-0.5 .mu.m,
and said second semiconductor layer is selected from a group
consisting of a p-GaN, a p-InGaN and a p-AlInGaN epitaxial
layers.
10. According to the light-emitting device in claim 8, wherein said
light generating layer further comprises an InGaN/GaN MQW
layer.
11. According to the light-emitting device in claim 8, wherein said
light generating layer further comprises an AlGaInN based compound
semiconductor epitaxial layer.
12. According to the light-emitting device in claim 8, wherein said
light extraction layer further comprises a layer selected from a
group consisting of an impurity doped In.sub.xZn.sub.1-xO impurity
doped metal oxide layer, an impurity doped Sn.sub.xZn.sub.1-xO
impurity doped metal oxide, wherein 0.ltoreq.X.ltoreq.1, and an
In.sub.xSn.sub.yZn.sub.1-x-yO impurity doped metal oxide layer,
wherein 0.ltoreq.X.ltoreq.1, 0.ltoreq.Y.ltoreq.1 and
0.ltoreq.X+Y.ltoreq.1, and said impurity comprises a p-type
impurity and an n-impurity.
13. According to the light-emitting device in claim 8, wherein said
light extraction layer further comprises an impurity doped metal
oxide having an index of retraction of at least 1.5.
14. According to the light-emitting device in claim 12, wherein
said p-type impurity comprises Al.
15. According to the light-emitting device in claim 8, wherein said
light extraction layer further comprises a metal oxide doped with a
rare earth element.
16. According to the light-emitting device in claim 8, wherein said
light extraction layer comprises an impurity doped metal oxide
having a transmissive range for a light having a wavelength of 400
to 700 nm.
17. According to the light-emitting device in claim 8, wherein said
light extraction layer has a thickness of 50 .ANG. to 50 .mu.m.
18. According to the light-emitting device in claim 17, wherein
when said light extraction layer has a thickness of at least 1
.mu.m, said light extraction layer has a roughened or particularly
textured surface comprising a plurality of facets.
19. According to the light-emitting device in claim 18, wherein
said particularly textured surface comprises a cone-shaped textured
surface, wherein said cone comprises a cone with a triangular
bottom, a cone with a rectangular bottom and a cone with any other
shaped bottom.
20. According to the light-emitting device in claim 19, wherein
said particularly textured surface comprising a plurality of
recesses, each of the recesses has a suitable distance with an
adjacent recess as a conductive path and arranged in a particular
form selected from a group consisting of triangular, rectangular,
polygonal, diamond and any other geometrical forms.
21. A method for manufacturing a GaN based compound semiconductor
light-emitting device: forming a multi-layer epitaxial structure
over a substrate, wherein said multi-layer epitaxial structure
includes a p-type semiconductor layer, an active layer and an
n-type semiconductor layer; forming an impurity doped metal oxide
having a suitable thickness and a light transmissibility over said
multi-layer epitaxial structure as a light extraction layer; and
disposing an n-type electrode over an exposing region of said
n-type semiconductor layer and disposing a p-type electrode over
said light extraction layer.
22. According to the method in claim 21, wherein said impurity
doped metal oxide layer is selected from a group consisting of an
impurity doped ZnO layer, an impurity doped In.sub.xZn.sub.1-xO
layer, an impurity doped Sn.sub.xZn.sub.1-xO layer and an
In.sub.xSn.sub.yZn.sub.1-x-yO layer, wherein 0.ltoreq.X.ltoreq.1,
0.ltoreq.Y.ltoreq.1 and 0.ltoreq.X+Y.ltoreq.1.
23. According to the method in claim 21, wherein said impurity
doped metal oxide layer is formed through a technology selected
from a group consisting of self-texturing by sputtering, physical
vapor deposition, ion plating, pulsed laser evaporation chemical
vapor deposition and molecular beam epitaxy technologies.
24. According to the method in claim 21, wherein said impurity
comprises a p-type impurity and an n-type impurity.
25. According to the method in claim 24, wherein said p-type
impurity comprises Al.
Description
BACKGROUND OF THE MENTION
[0001] 1. Field of the invention
[0002] The present invention relates to a GaN based compound
semiconductor light-emitting device (LED) and a manufacturing
method therefor, and particularly to a GaN based compound
semiconductor light-emitting device (LED) with better light
transparency and a manufacturing method therefor.
[0003] 2. Description of Related Art
[0004] A light-emitting diode (LED) has been generally known as a
semiconductor device with ability to emitting light, which has been
widely used in digital watches, calculators, communications and
other areas, such as mobile phone and some appliances. Recently,
various efforts and attempts have shifted to use LEDs in more
ordinary human living, such as large panels, traffic lights and
illumination facilities. However, in marching into a brand new
illuminating era with the current illumination facilities replaced
with LEDs, the luminous efficiency of an LED remains a big issue,
which has been challenging those skilled in the art for many years.
Therefore, many developments and researches have been thrown in to
improvement of luminous efficiency of LEDs, and red, green, blue
and white colored lights are alike.
[0005] As is well understood to those skilled in the art, LEDs are
produced based on some semiconductor materials, especially
GaN-based compound semiconductor materials, and emit lights by
virtue of the behaviors aroused in the semiconductor materials in
the presence of an applied electrical bias.
[0006] In particular, an LED is generally composed of some Group
III-V (or Group II-VI, although rarely given forth) compound
semiconductors. In principle, an LED is basically a well-known p-n
junction structured device, i.e., a device having a p region, an n
region and a depletion region therebetween. Upon a forward-biased
voltage or current bias applied, the majority of the carriers in
the p or n regions drift respectively towards the other region
through the depletion region in the device due to the energy
equilibrium principle and a current is accounted for, in addition
to the general thermal effects. When some electrons and holes in
the device jumped into a higher value of energy band with the aid
of electrical and thermal energy, the electrons and the holes
recombine there and then give off lights when they randomly fall
back to a previous lower energy state (turning from an unsteady
state to a steady state) owing to thermal equilibrium principle,
i.e. spontaneous emission. Besides the p-n Junction, in a typical
and basic such device structure comprise also other components,
such as a substrate, a buffer layer, a transparent layer (TCL) and
electrodes. In achieving a high luminous efficiency LED, each
component and their mutual relationship in the device structure are
generally to be considered.
[0007] In a typical LED in which the produced light is emitted
upward (through the overlaying epitaxy structure), TCL is a layer
coated on an LED structure and below a p-type electrode of the LED
structure. Since the p-type electrode is normally not transparent
or not transparent enough and will have blockage on the emitted
light to a user's eyes, the p-type electrode should be sized and
disposed at a limited portion on the underlying layer contact
therewith. However, the electrical force lines resulted from
between the p-type electrode and an n-type electrode may not
uniformly distribute in the p-n structure in the device. Hence, the
electrical charges provided by the applied electrical bias may not
efficiently and uniformly stimulate the p-n structure, which is the
source of light generation. Further, the p-type electrode is
inhered with poor immobility as compared to that of the n-type
electrode and thus the stimulation efficiency of the electric bias
on the device may not be satisfactory. A thin TCL is in this
occasion introduced over the toppest layer of the device (in fact,
below the p-type electrode). The TCL is a transparent material to a
light generated from the device and equipped with ability of
electricity conduction. Once an electric bias is fed from the
p-type electrode, the corresponding charges will spread uniformly
in the p-n structure with an aid of the TCL underlying the p-type
electrode and the poor stimulation efficiency of the electric bias
slay be overcome. In this regard, a TCL is a layer indispensable to
an LED structure.
[0008] In a prior art, a Ni/Au material (with the Ni layer at the
lower and the Au layer thereon) is used as the TCL in the GaN based
light-emitting device in achieving an improved light emitting
device. However, Ni/Au is not a material with good light
transparency and should thus be made considerably thin, about
0.005-0.2 It m. On the other hand, according to the critical angle
theory, TCL should possess suitable thickness and will then
facilitate extraction of the generated light out of the device.
Further, too thin a Ni/Au layer will not exhibit a good ohmic
contact characteristic. Therefore, Ni/Au material may not be the
most appropriate choice for an LED in terms of light transparency
and extraction owing to the thickness issue. Further, since Ni/Au
as the TCL in such a GaN based light emitting device may not be
formed with more facets by use of a surface treatment under the
thickness 0.005-0.2 .mu.m of the Ni/Au layer, the Ni/Au layer based
light extraction stands little possibility to be promoted.
[0009] In view of the foregoing problems, it is needed to set forth
a GaN based compound semiconductor LED that really provides an
improved TCL. To this end, the inventors of the present invention
provide herein a GaN based compound semiconductor LED with a TCL
other than Ni/Au and may achieve better light transparency and
extraction characteristics.
SUMMARY OF THE INVENTION
[0010] It is therefore an object of the present invention to
provide a GaN based compound semiconductor light emitting device
(LED) which has a better transparent contact layer (TCL), may be
made bulky and facet-rich, and thus has a higher light extraction
characteristic, and a corresponding manufacturing method.
[0011] To achieve the object of the present invention, an impurity
doped metal oxide is used as the TCL of the LED, instead of Ni/Au
material used in the state of the art. In a preferred embodiment,
the impurity doped metal oxide may be an impurity doped ZnO based
layer. When the doped ZnO based layer is thick enough, the surface
thereof may be subject to a surface treatment so that facets
thereon may be made more.
[0012] With the inventive GaN based compound semiconductor LED
having an impurity doped metal oxide as the TCL and its
manufacturing method, the obtained light extraction efficiency is
enhanced.
[0013] In the inventive LED structure, the constituent materials
comprise: a substrate, a multi-layer epitaxial structure, a light
extraction layer, an n-type electrode and a p-type electrode. In
the multi-layer epitaxial structure, there include a buffer layer,
a first semiconductor layer, a light generating layer and a second
semiconductor layer.
[0014] A manufacturing method for the inventive LED comprises: (a)
forming an n-GaN based layer over a substrate; (b) forming a
multi-quantum well (MQV) active layer over the n-GaN based layer;
(c) forming a p-GaN based layer over the MQW layer and etching away
a portion of the n-GaN layer, MQW active layer and p-GaN layer,
whereby an exposing region is formed on the n-GaN layer; (d)
forming an impurity doped metal oxide layer as a light extraction
layer over the p-GaN based layer; and (e) forming an n-type
electrode over an exposing region after the etching of the n-GaN
based layer, the MQW active layer and the p-GaN layer and forming a
p-type electrode over the light extraction layer. In a preferred
embodiment, the doped metal oxide layer is an Al-doped ZnO-based
layer.
[0015] Owing to the large bandgaps of some metal oxides such as
ZnO, the LED with a TCL composed of such metal oxides exhibiting
better light transparency and extraction is thus achieved;
[0016] Additionally, the LED according to the present invention
also includes at least the following advantages: bulky light
extraction layer and the corresponding light extraction efficiency,
surface treated light extraction layer with more facets and the
corresponding light extraction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] To better understand the other features, technical concepts
and objects of the present invention, one may clearly read the
description of the following preferred embodiment and the
accompanying drawings, in which:
[0018] FIG. 1 depicts schematically a manufacturing method of a
preferred embodiment according to the present invention;
[0019] FIG. 2 is a schematically perspective diagram of a
light-emitting device of a preferred embodiment according to the
present invention;
[0020] FIG. 3 depicts schematically a structure of a light-emitting
device of a preferred embodiment according to the present
invention;
[0021] FIG. 4 depicts schematically energy the bandgaps of a ZnO
and a p-GaN materials;
[0022] FIG. 5 depicts schematically light extraction of a
light-emitting device;
[0023] FIG. 6 depicts schematically a manufacturing method of
another embodiment according to the present invention;
[0024] FIG. 7 and FIG. 8 depict schematically a surface treatment
of a light extraction layer;
[0025] FIG. 9 depicts schematically light extraction from
particularly textured area;
[0026] FIG. 10 and FIG. 11 depict schematically a particularly
textured area of another embodiment according to the present
invention;
[0027] FIG. 12 depicts schematically a method of a second
embodiment according to the present invention;
[0028] FIG. 13 depicts schematically a device of a second
embodiment according to the present invention;
[0029] FIG. 14 depicts schematically another example of a second
method embodiment according to the present invention;
[0030] FIG. 15 depicts schematically a method of a third embodiment
according to the present invention;
[0031] FIG. 16 depicts schematically a device of a third embodiment
according to the present invention;
[0032] FIG. 17 depicts schematically another example of a third
method embodiment according to the present invention;
[0033] FIG. 18 depicts schematically a method of a fourth
embodiment according to the present invention;
[0034] FIG. 19 depicts schematically a device of a fourth
embodiment according to the present invention; and
[0035] FIG. 20 depicts schematically anther example of a fourth
method embodiment according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] In a preferred (first) embodiment of an LED of the present
invention schematically shown in FIGS. 1 through 3, the LED is
included with an impurity doped ZDO based layer at the toppest
thereof (but under a p-type electrode in the LED). The doped ZnO
based layer is formed over a multi-layer epitaxial structure and
has a better light transmissibility and a suitable thickness,
entitling itself to better light extraction for the LED.
Specifically, the method and the LED structure are described in
FIGS. 1 and 2 respectively and each step thereof will be first
explained as follows accompanying with its element labels.
[0037] Step 1: forming an n-GaN based epitaxial layer 21 over a
substrate 10. The substrate 10 may be a sapphire or SiC and have a
thickness of 300-450 .mu.m, The substrate 10 may be first formed
with a buffer layer 22 at an upper surface 11 thereof, and then
formed over with the n-GaN based epitaxial layer 21 having a
thickness of 2-6 .mu.m. The buffer layer may be composed of some
layers, such as a coarse grain nucleation layer made of GaN and an
undoped GaN layer. The nucleation layer is a low temperature layer,
i.e. formed under a low temperature condition, and has a thickness
of 30-500 .ANG. and will be referred to as an LT-GaN layer herein.
The undoped GaN is a high temperature layer and has a thickness of
0.5-6 .mu.m, and will be named as an HT-GAN layer here. These
buffer layers may be formed by molecular beam epitaxy (MBE), metal
organic chemical vapor deposition (MOCVD) and some other suitable
technologies, currently in existence or set forth in the
future.
[0038] Step 2: forming a multi-quantum well (MQW) active layer 23
over the n-GaN based layer 21. As generally known, an MQW layer is
a multi-layered structure and used to enhance possibility of
recombination of holes and electrons in the p-and-n junction
structure of the LED. In the present invention, the thickness and
layer number of the MQW layer may be carefully chosen so that the
MQW layer may efficiently increase light generating efficiency. In
addition, the active layer 23 may be served by an AlGaInN based
compound semiconductor epitaxial layer.
[0039] Step 3: forming a p-GaN based epitaxial layer 25 over the
MQW active layer 23 and etching away a portion of the n-GaN based
layer 21, the MQW active layer 23 and the p-GaN based layer 25
whereby an exposing region 21a is formed on the n-GaN based layer
21, wherein the p-GaN based epitaxial layer 25 may be such as
p-GaN, p-InGaN and p-AlInGaN layers and have a thickness of 0.2-0.5
.mu.m. It is noted that the etching may be performed with chlorine
plasma dry etching, etc.
[0040] Step 4: forming a doped ZnO based layer 31 over the
remaining p-GaN based layer 25 after said etching. Since the layer
31 is provided at the toppest of the LED structure for light
exiting excepted for a p-electrode 50, the layer is also termed as
a window layer. The thickness of this doped ZnO based layer may be
arranged between 50 .ANG. and 50 .mu.m. Preferably, the thickness
is made larger than 1 .mu.m, and the reason will be stated in the
following related to the LED structure. In a prefer embodiment, the
impurity doped in the doped ZnO based layer 31 may be a p-type
impurity or an n-type impurity, and the p-type impurity may at
least be Al. Once the activation issue of the impurity doped ZnO
based layer 31 may be overcome, all Group-III elements may be the
suitable dopants.
[0041] Step 5: forming a p-type electrode 50 over the doped ZnO
based layer 31 and forming an n-type electrode 40 over said
exposing region 21a of said n-GaN based layer 21.
[0042] As far as formation of the doped metal oxide layer ZnO is
concerned, either of self-texturing by sputtering, physical vapor
deposition, ion plating, pulsed laser evaporation chemical vapor
deposition and molecular bean epitaxy and other suitable
technologies may be employed.
[0043] In fact, to completely form a marketed LED, some treatments
are also needed comprising wire bonding and packaging molded by
such as epoxy (not shown). Since the wire bonding and packaging
technology is well known to those persons skilled in the art, they
are omitted in the detailed descriptions, for simplicity, of the
inventive LED for both its structure and method.
[0044] The following is dedicated to the inventive LED structure.
Referring to FIG. 3, the LED structure 12, corresponding to the
above manufacturing method, includes a substrate 10, a multi-layer
epitaxial structure 20, a first semiconductor layer 24, a light
generating layer 26 and a second semiconductor Specifically, said
substrate 10 is made of sapphire or SiC and has a thickness of
300-450 .mu.m. The buffer layer 22 is a multi-layer structure such
as a double layered one. In this case, the buffer layer 22 is
composed of an LT-GaN layer and an HT-GaN layer, as has been
explained in the preferred method embodiment, formed over an upper
surface 11 of the substrate 10.
[0045] The first semiconductor layer 24 is an n-GaN based III-V
group compound semiconductor, which may range from 2 to 6 .mu.m in
thickness. The light generating layer 26 is an. GaN based III-V
group compound semiconductor, generally known as an active layer,
and may be a GaN multi quantum well (MQW) or an InGaN multi-quantum
well. The second semiconductor layer 28 is a p-type GaN based 111-V
group compound semiconductor, which may be such as p-GaN, p-InGaN
and p-AlInGaN.
[0046] The light extraction layer 30 is made of an impurity doped
metal oxide, which is light transmissive and formed over the second
semiconductor layer 28. As an example and a preferred embodiment,
the light extraction layer 30 is composed of doped ZnO. The n-type
electrode 40 is disposed over an exposing region 24a of the first
semiconductor layer 24 and the p-type 50 over the light extraction
layer 30.
[0047] With the improved doped ZnO light extraction layer 30, the
light generated from the active layer 26 in the inventive LED is
more penetratable through when it encounters the layer 30 in the
course of going out of the LED. Further, because the light
extraction layer 30 may be subject to surface treatment to have the
surface roughened and some form textured, the surface of the light
extraction layer may obtain more facets and thus the light
extracted to a user's eyes may be increased.
[0048] Here, there are some descriptions supplemented to the above
embodiment. The light generating layer 26, i.e., active layer, may
alternatively be a single AlGaInN III-V group compound
semiconductor layer. The light extraction layer 30 may further be
other metal oxides with impurity doped, such as impurity doped
In.sub.xZn.sub.1-xO, impurity doped Sn.sub.xZn.sub.1-xO and
In.sub.xSn.sub.yZn.sub.1-x-yO, one having an index of refraction of
at least 1.5, one being n-type conductive or p-type conductive, one
doped with a rare earth element, or one having a transmissive range
of a light with a wavelength of 400-700 nm.
[0049] The afro-mentioned is the preferred embodiment of the
present invention, which may be easily modified by those persons
skilled in the art. Hence, devices or methods deduced with
reference to the disclosed one are deemed to fall within the spirit
of the present invention. For example, although the description of
the LED and its manufacturing method of the present invention are
limited to the Group III-V compound semiconductor based LED, the
inventive impurity doped metal oxide light extraction layer may be
employed onto the Group II-VI group compound semiconductor based
LED as long as the lattice matching issue on such LED may not be
problematic.
[0050] The following will be made to the reason that doped ZnO may
be more appropriate to serve as the light extraction layer as
compared to the prior light extraction layer in an LED. Referring
to FIG. 4, the bandgap energy B1 of ZnO is approximately 3.4 eV,
and the bandgap B2 of p-GaN is also near 3.4 eV. Owing to the small
bandgap energy offset, lattice matching will not be an issue to
their bonding and the operating voltage will not be too large. In
this regard, bonding the impurity doped ZnO extraction layer over
the p-GaN layer is well possible. For numerical information, GaN
has a lattice constant of about 3.189 .ANG., ZnO of about 3.24
.ANG., and sapphire of about 4.758 .ANG..
[0051] In an LED device, as generally known, only those lights with
emitting angles smaller than the critical angle may really extract
out of the device, schematically shown in FIG. 5. In response to
this, a light extraction layer with a suitable thickness may be
benefited with increased light extraction amount. As the example of
the present invention, the light extraction layer 30 has a
thickness of at least 1 .mu.m, which makes the lights emitted from
the active layer easier to penetrate through the surface 301 and
the sides 302 and thus enhance the light extraction efficiency.
[0052] Referring to FIG. 6, since the light extraction layer 30 in
the present invention may be ranged between about 50 .ANG.-50 .mu.m
in thickness, the layer 30 may be made thick enough to be bulky
one. When the thickness of the light extraction layer 30 is at
least 1 .mu.m, the above method embodiment may further include a
step, Step 6, i.e., subjecting an exposing surface of the doped ZnO
based layer 30 (i.e., the portion of the light extraction layer 30
other than the portion thereof contacted with the p-type electrode
50) to a surface treatment. With the surface treatment, the surface
of the layer 30 may be further roughened so that more facets may be
formed thereover. With the facet-rich surface, light extraction
efficiency may be considerably increased.
[0053] Proceeding to the above paragraph, the light extraction
layer 30 may be further subject to particular texturization and
obtained with textured surface. Similar to the recitation of the
above paragraph, texturization treatment may also increase facet
number of the light extraction layer 30. And the goal to increasing
light extraction may be achieved. The particular textured surface
may be in the form of a cone, comprising one with a triangular 303
bottom shown in FIG. 7 and one with a rectangular bottom 305 shown
in FIG. 8, and may be other geometrical cones, which may either be
applied onto the light extraction layer 30.
[0054] Referring to FIG. 0.9, that light extraction may be
benefited from the roughened or textured surface of the light
extraction layer 30 is schematically explained therein. For a flat
light extraction layer, a portion of the emitted light is reflected
by the flat surface. However, the two facets 302 may provide the
emitted light with several times of reflection and the extracted
portion of the emitted light may well be increased.
[0055] FIGS. 10 and 11 are planar diagram and partial perspective
diagram respectively for illustration of another textured surface
embodiment. In the two figures, the textured portion of the surface
may further include a plurality of recesses 307, which may be
triangular, rectangular, diamond, polygonal or other arrangements.
Between recesses 307 is a distance of a suitable value, which is
provided for conductive path of current.
[0056] Referring to FIGS. 12 and 13, which illustrate a second
embodiment of the present invention. In the embodiment, an impurity
doped In.sub.xZn.sub.1-xO is used as the light extraction layer 32,
which is grown to a suitable thickness over the multi-layer
structure as mentioned in the first embodiment, wherein
0.ltoreq.X.ltoreq.1. The steps used in this embodiment are
generally similar to those in the preferred embodiment except for
the step, Step 4a. Step 4a is a step of forming an impurity doped
In.sub.xZ.sub.1-xO based layer over the p-GaN layer.
[0057] Referring to FIG. 14, the second embodiment according to the
present invention may further comprise a step, Step Sa, as compared
to that in FIG. 12: subjecting the doped In.sub.xZ.sub.1-xO based
layer to a surface treatment. In the step, the treatment is applied
only to the region of the layer 32 not covered by the p-type
electrode 50. Similarly, the increase of facets on the layer 32 may
efficiently enhance light extraction.
[0058] Referring to FIGS. 15 and 16, which illustrate a third
embodiment of the present invention. In the embodiment, an impurity
doped Sn.sub.xZn.sub.1-xO 33 is used as the light extraction layer,
which is grown to a suitable thickness over the multi-layer
structure as mentioned in the first embodiment, wherein
0.ltoreq.X.ltoreq.1. The steps used in this embodiment are
generally similar to those in the preferred embodiment except for
the step, Step 4b. Step 4b is a step of forming an impurity doped
Sn.sub.xZn.sub.1-xO based layer over the etched p-GaN layer.
[0059] Referring to FIG. 17, the third embodiment according to the
present invention may further comprise a step, Step 5b: subjecting
the impurity doped Sn.sub.xZn.sub.1-xO based layer to a surface
treatment. In this step, the treatment is applied only to the
region of the layer 33 not covered by the p-type electrode 50.
Similarly, the increase of facets on the layer 33 may efficiently
enhance light extraction.
[0060] Referring to FIGS. 18 and 19, which illustrate a fourth
embodiment of the present invention. In the embodiment, an impurity
doped In.sub.xSn.sub.yZn.sub.1-x-yO is used as the light extraction
layer 34, which is grown to a suitable thickness over a multi-layer
structure as mentioned in the first embodiment, wherein
0.ltoreq.X.ltoreq.1, 0.ltoreq.Y.ltoreq.1 and 0.ltoreq.X+Y.ltoreq.1.
The steps used in this embodiment are generally similar to those in
the preferred embodiment except for a step, Step 4c. Step 4c is a
step of forming an impurity doped In.sub.xSn.sub.yZn.sub.1-x-yO
based layer over the etched p-GaN layer 25.
[0061] Referring to FIG. 20, the fourth embodiment according to the
present invention may further comprise a step, Step 5c: subjecting
the impurity doped In.sub.xSn.sub.yZn.sub.1-x-yO based layer to a
surface treatment. In this step, the treatment is applied only to
the region of the layer 34 not covered by the p-type electrode 50.
Similarly, the increase of facets on the layer 34 may efficiently
enhance light extraction. If the exposing surface of the above
mentioned structure is thin enough, the exposing surface can dope
no Zno as well.
[0062] While the invention has been described by way of examples
and in terms of preferred embodiments, it is to be understood that
the invention is not limited thereto. On the contrary, it is
intended to cover various modifications and similar arrangements
and procedures, and the scope of the appended claims therefore
should be accorded the broadest interpretation so as to encompass
all such modifications and similar arrangements and procedures.
* * * * *