U.S. patent application number 10/196370 was filed with the patent office on 2003-06-26 for light emitting diode and method of making the same.
This patent application is currently assigned to United Epitaxy Co., Ltd.. Invention is credited to Chang, Chih-Sung, Chen, Tzer-Perng, Yang, Kuang-Neng.
Application Number | 20030116770 10/196370 |
Document ID | / |
Family ID | 21680034 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030116770 |
Kind Code |
A1 |
Chang, Chih-Sung ; et
al. |
June 26, 2003 |
LIGHT EMITTING DIODE AND METHOD OF MAKING THE SAME
Abstract
A light emitting epi-layer structure which contains a
temporality light absorption substrate on one side, the other side
thereof can be adhered to a light absorption free transparent
substrate in terms of a transparent adhesive layer which is light
absorption free too. After that, the light absorption substrate
portion is removed by means of an etching process. The resulted
light emitting diode has significant improvement in light emitting
efficiency. Moreover, the transparent conductive layer is a low
resistance and high transparency layer. The current flow can thus
be distributed evenly than conventional one.
Inventors: |
Chang, Chih-Sung; (Taipei,
TW) ; Yang, Kuang-Neng; (Ping Chen City, TW) ;
Chen, Tzer-Perng; (Hsinchu City, TW) |
Correspondence
Address: |
BRUCE H. TROXELL
SUITE 1404
5205 LEESBURG PIKE
FALLS CHURCH
VA
22041
US
|
Assignee: |
United Epitaxy Co., Ltd.
|
Family ID: |
21680034 |
Appl. No.: |
10/196370 |
Filed: |
July 17, 2002 |
Current U.S.
Class: |
257/79 |
Current CPC
Class: |
H01L 2933/0016 20130101;
H01L 33/0093 20200501; H01L 33/38 20130101 |
Class at
Publication: |
257/79 |
International
Class: |
H01L 027/15 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2001 |
TW |
90132394 |
Claims
What is claimed is:
1. A structure of light emitting diode, comprising: a transparent
substrate; an epi-layers from a bottom thereof, being with a p-type
ohmic contact layer, a light emitting cladding layer, and an n-type
etch stop layer, wherein said epi-layers have a portion of said
n-type etch stop layer, and said light emitting cladding layer is
removed so as to expose said p-type ohmic contact layer and further
said light emitting cladding layer is to generate light in response
to a current injection; a first p-type metal electrode formed
thereon a bottom surface of said p-type ohmic contact epi-layer; an
opening formed on an upper surface of said p-type ohmic contact
layer, which is exposed; a second p-type metal electrode formed and
refilled said opening so as to contact said first p-type metal
electrode a transparent adhesive layer bonding said transparent
substrate and said p-type ohmic contact epi-layer and said first
p-type metal electrode together; a transparent conductive layer
formed on an upper surface of said n-type etch stop layer; and an
n-type metal electrode formed on said transparent oxide layer.
2. The structure of light emitting diode according to claim 1,
wherein said light emitting cladding layer comprises an n-type
cladding layer, an active layer, a p-type cladding layer.
3. The structure of light emitting diode according to claim 1,
wherein said transparent adhesive layer is a BCB (B-staged
bisbenzocyclobutene) resin.
4. The structure of light emitting diode according to claim 1,
wherein said transparent substrate is selected from the group
consisting of ZnSe, ZnS, ZnSSe, SiC, GaP, GaAsP, and sapphire.
5. The structure of light emitting diode according to claim 1,
wherein said transparent substrate is a single crystal or
polycrystalline.
6. The structure of light emitting diode according to claim 1,
wherein said transparent conductive layer is an oxide layer
selected from the group consisting of indium tin oxide (ITO),
indium oxide, tin oxide, zinc oxide, and magnesium oxide.
7. The structure of light emitting diode according to claim 1,
wherein said transparent conductive layer is a metal layer with a
thin thickness so that said transparent conductive layer is
transparent for light generated from said light emitting cladding
layer.
8. The structure of light emitting diode according to claim 1,
wherein said first p-type metal electrode has a shape of
donut-like.
9. The structure of light emitting diode according to claim 1
wherein said n-type etch stop layer have a through hole formed
therein, so that said transparent conductive layer not only formed
on said n-type etch stop layer but also refilled said through hole
to contact said light emitting cladding layer.
10. The structure of light emitting diode according to claim 1
wherein said n-type etch stop layer beneath said n-type metal
electrode has an opening formed, which is filled with a dielectric
layer.
11. The structure of light emitting diode according to claim 1
wherein said n-type etch stop layer beneath said n-type metal
electrode has a high resistance region formed therein.
12. The structure of light emitting diode according to claim 1
wherein said transparent conductive layer has a through hole so
that a lower portion of said n-type metal electrode is embedded in
said transparent conductive layer.
13. A structure of light emitting diode, comprising: a transparent
substrate; an epi-layers, stacked sequentially from a bottom
thereof, being with an n-type etch stop layer, an n-type cladding
layer, an active layer, a p-type cladding layer, and a p-type ohmic
contact epi-layer; a p-type metal electrode formed on a bottom
surface of said p-type ohmic contact epi-layer; a transparent
adhesive layer bonding said p-type metal electrode and remnant
exposed portion of said p-type ohmic contact layer to said
transparent substrate; wherein said stack structure has two step
levels, and the lower one of two step level exposes a portion of
upper surface of said p-type ohmic contact layer, and has a contact
channel formed so as to expose a portion of said p-type metal
electrode, and the upper step level is exposed said n-type etch
stop layer; a transparent conductive layer formed on said etch stop
layer; a first bonding metal electrode formed on said transparent
conductive layer; and a second bonding metal electrode formed to
fill said contact channel and protruded said upper surface of said
p-type ohmic contact layer.
14. The structure of light emitting diode according to claim 13,
wherein said transparent adhesive layer is a BCB (B-staged
bisbenzocyclobutene) resin.
15. The structure of light emitting diode according to claim 13,
wherein said transparent substrate is selected from the group
consisting of ZnSe, ZnS, ZnSSe, SiC, GaP, GaAsP, and sapphire.
16. The structure of light emitting diode according to claim 13,
wherein said transparent substrate is a single crystal or
polycrystalline.
17. The structure of light emitting diode according to claim 13
wherein said transparent conductive layer is an oxide layer
selected from the group consisting of indium tin oxide (ITO),
indium oxide, tin oxide, zinc oxide, and magnesium oxide.
18. The structure of light emitting diode according to claim 13,
wherein said transparent conductive layer is a thin metal layer,
which is selected from the group consisting of Au, GeAu, Ti, Al,
and Ni.
19. The structure of light emitting diode according to claim 13,
wherein said transparent conductive layer, and said etch stop layer
have a contact hole, and hence said first bonding metal layer is
formed to contact said lower cladding layer and has an altitude
higher than a surface level of said transparent conductive
layer.
20. The structure of light emitting diode according to claim 13,
wherein said transparent conductive layer, and said etch stop layer
have a contact hole, and hence said first bonding metal layer is
formed to contact said lower cladding layer and has an altitude
higher than a surface level of said transparent conductive
layer.
21. The structure of light emitting diode according to claim 13,
wherein said etch stop layer have a contact hole, and hence said
transparent conductive layer is formed to contact said lower
cladding layer.
22. The structure of light emitting diode according to claim 13,
further comprising a dielectric region, where said dielectric
region is at a position right under said first bonding metal
electrode and formed in said etch stop layer.
Description
[0001] This application incorporates by reference Taiwanese
application Serial No 90132394, filed on Dec. 26, 2001
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a light emitting device,
and more particularly to an AlGalnP light emitting diode
structure.
[0004] 2. Description of the Prior Art
[0005] The conventional AlGaInP LED has a double heterostructure
(DH), as shown in FIG. 8. The LED stacked sequentially, from a
bottom thereof, has an n-type ohmic contact electrode 2, a GaAs
substrate 3, an n-type (Al.sub.xGa.sub.1-x).sub.0.5In.sub.0.5P
lower cladding layer 4 with an Al composition between about
70%-100%, an (Al.sub.xGa.sub.1-x).sub.0.5In.sub- .0.5P active layer
5 with an Al composition of 0%-45%, a p-type
(Al.sub.xGa.sub.1-x).sub.0.5In.sub.0.5P upper cladding layer 6 with
an Al composition 70%-100%, a p-type high energy band gap current
spreading layer 7 such as layers of GaP, GaAsP, AlGaAs or GalnP,
and a p-type ohmic contact layer 8 as well as a bonding pad 9.
[0006] With the composition alternation of the active layer 5, the
wavelengths of the light emitted are varied from 650 nm: red to 555
nm: green. A drawback is generally found in the conventional LED,
that is: while the light emitted from the active layer 5 towards
the substrate 3 will be totally absorbed by GaAs substrate 3. It is
because the GaAs substrate has an energy gap smaller than that of
the active layer 5. Therefore, the light generated is absorbed
resulted in lower light generated efficiency for this kind of
conventional AlGaInP LED.
[0007] To overcome the substrate 3 light absorption problem,
several conventional LED fabrication technologies have been
disclosed. However, those conventional technologies still accompany
with several disadvantages and limitations. For example, Sugawara
et al. disclosed a method published in Appl. Phys. Lett. Vol. 61,
1775(1992), Sugawara et al. inserted a distributed Bragg reflector
(DBR) layer in between GaAs substrate and lower cladding layer so
as to reflect those light emitted toward the GaAs substrate.
However, the reflectivity of DBR layer is usefully only for those
light which almost vertically towards the GaAs substrate. With the
decrease of injection angle, the reflectivity is drastically
decreased. Consequently, the improvement of external quantum
efficiency is limited.
[0008] Kish et al. disclosed a wafer-bonded transparent-substrate
(TS) (Al.sub.xGa.sub.1-x).sub.0.5In.sub.0.5P/GaP light emitting
diode, entitled "Very high efficiency semiconductor wafer-bonded
transparent-substrate (Al.sub.xGa.sub.1-x).sub.0.5In.sub.0.5P/GaP
light emitting diodes" on Appl. Phys. Lett. Vol. 64, No. 21, 2839
(1994). The TS AlGaInP LED was fabricated by growing a very thick
(about 50 .mu.m) p-type GaP window layer by hydride vapor phase
epitaxy (HVPE) formed on epi-layers light emitting structure.
Subsequently, the temporary n-type GaAs substrate is selectively
removed using conventional chemical etching techniques. After
removing the GaAs substrate, the LED epilayer structure is then
bonded to an 8-10 mil thick n-type GaP substrate.
[0009] For the light illuminated concerned, the TS AlGaInP LED
exhibits a two fold improvement in light output compared to
absorbing substrate (AS) AlGaInP LEDs. However, the fabrication
process of TS AlGaInP LED is very complicated. Since the bonding
process is to make two III-V semiconductor wafers directed bond
together by heating and pressing for a period of time. Even worse,
a non-ohmic contact interface between them is generally found to
have high resistance. To manufacture these TS AlGaInP LEDs in high
yield and low cost is difficult as a result.
[0010] Another conventional technique was proposed by Horng et al.,
on Appl. Phys. Lett. Vol. 75, No. 20, 3054 (1999) entitled "AlGaInP
light-emitting diodes with mirror substrates fabricated by wafer
bonding." Horng et al., reported a mirror-substrate (MS) of
AlGaInP/metal/SiO.sub.2/Si LED fabricated by wafer-fused
technology. In LED, AuBe/Au stack layer function as a bonding layer
for silicon substrate and epi-layer LED. However, the intensity of
the AlGaInP LED is only about 90 mcd under 20 mA injecting current.
The light intensity is at least lower than that of TS AlGaInP LED
by 40%. It could not be satisfied.
SUMMARY OF THE INVENTION
[0011] An object of the present invention is thus to provide a LED
structure which is composed a newly bonding layer and a transparent
substrate.
[0012] Firstly, a temporary semiconductor substrate having
epi-layers thereon sequentially formed, from a bottom thereof, with
an n-type etch stop layer, an n-type cladding layer, an active
layer epi-layers, a p-type cladding layer, and a p-type ohmic
contact epi-layer is prepared. And then a first metal electrode is
formed on the p-type ohmic contact epi-layer.
[0013] Thereafter the temporary semiconductor substrate is bonded
to a transparent substrate with the p-type ohmic contact epi-layer
and the first metal electrode face to the transparent substrate by
a BCB, a transparent resin or the like. Next the temporary
semiconductor substrate is removed by etching and stopping at the
etch stop layer.
[0014] After that, two steps of lithographic and etching methods
are carried out successively so as to form an opening that exposes
the first metal electrode. In the first lithographic and etching
step, a trench of about 3 to 6 mils in width is formed, which
exposes a portion of the p-type ohmic contact epi-layer. In the
second lithographic and etching step, a contact channel of about
0.5 to 3 mils in width is formed to contact the first metal
electrode. Thereafter, the processes are performed to form a
transparent conductive layer atop the etch stop layer, to form a
first boding metal on the contact channel, and a second boding
metal (or called second electrode) on the transparent conductive
layer.
[0015] The second preferred embodiment is modified from the first
preferred embodiment. The approaching of forming a trench and a
contact channel are as the first preferred embodiment The modified
portion is the second boding metal, which is refilled in a
preserved hole constructed by photoresist and transparent
conductive layer, Thus after the photoresist removal, the second
bonding layer is higher than a surface level of the transparent
conductive layer.
[0016] In the third preferred embodiment, the two step etchings to
form a trench and a contact channel are the same as prior two
preferred embodiments. Thereafter a contact hole or a recess region
is formed in the etch stop layer first, and then a transparent
conductive layer is formed on the etch stop layer including
refilled the contact hole or the recess region.
[0017] In the fourth preferred embodiment, the two step etchings to
form a trench and a contact channel are the same as before, A
dielectric region is then formed in the etch stop layer. Thereafter
the processes of forming the transparent conductive layer and two
bonding metals are as the first prior embodiment.
[0018] In the fifth preferred embodiment, the processes are
modified from the fourth preferred embodiment. Instead of forming a
dielectric region, a high resistance region is formed in the etch
stop layer by ion implant with nonconductive ions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
becomes better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0020] FIG. 1 is a schematic cross-sectional view of the light
emitting diode before bonding with a transparent substrate
according to the present invention.
[0021] FIG. 2 is a schematic cross-sectional view of the
transparent substrate coated with transparent adhesive layer
according to the present invention.
[0022] FIG. 3A to FIG. 3E are schematic cross-sectional views of a
series of fabricating process for a light emitting diode according
to the first preferred embodiment of the present invention.
[0023] FIG. 4A to FIG. 4C are schematic cross-sectional views of a
series of fabricating process for a light emitting diode according
to the second preferred embodiment of the present invention.
[0024] FIG. 5 is a schematic cross-sectional view of fabricating a
light emitting diode according to the third preferred embodiment of
the present invention.
[0025] FIG. 6 is a schematic cross-sectional view of fabricating a
light emitting diode according to the fourth preferred embodiment
of the present invention.
[0026] FIG. 7 is a schematic cross-sectional view of fabricating a
light emitting diode according to the fifth preferred embodiment of
the present invention.
[0027] FIG. 8 is a schematic cross-sectional view of fabricating a
light emitting diode according to the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] The present invention disclosed a new LED structure and the
making method. The detailed descriptions accompany with the FIG. 1
to FIG. 7 are as follows.
[0029] Referring to FIG. 1, the cross-sectional view shows an
epi-LED stack structure comprises, from a bottom thereof, an n-type
temporary GaAs substrate 26, an etching stop layer 24, a lower
cladding layer 22, an active layer 20 an upper cladding layer 18, a
p-type ohmic contact epi-layer 16 and a p-type metal electrode 28.
The shape of the metal electrode 28 is arbitrary, shown in the
figure is a ring shape, so two electrode blocks 28 are observed in
a cross-sectional view.
[0030] The lower cladding layer 22 is an n-type
(Al.sub.xGa.sub.1-x).sub.0- .5In.sub.0.5P. The active layer 20 is
an undoped (Al.sub.xGa.sub.1-x).sub.- 0.5In.sub.0.5P layer and the
upper cladding layer 18 is a p-type
(Al.sub.xGa.sub.1-x).sub.0.5In.sub.0.5P layer.
[0031] The p-type ohmic contact epi-layer 16 can be a layer
selected from GaP, GaAsP, AlGaAs or GaInP. All of the candidates
for serving as the p-type ohmic contact epi-layer 16 require having
an, energy band gap higher than those of the active layer thereby
alleviating the light absorption. Moreover, the p-type ohmic
contact epi-layer 16 usually has high carrier concentrations doped
therein so as to form a good ohmic contact. The
(Al.sub.xGa.sub.1-x).sub.0.5In.sub.0.5P active layer 20 is with Al
composition of about x=0 to 0.45. The Al dosage in the upper
cladding layer 18 and lower cladding layer 22 is of about x=0.5 to
1.0. For situation of without Al containing, the wavelength of the
light emitted from Ga.sub.0.5In.sub.0.5P LED is about 635 nm, which
is in range of red visible light.
[0032] As is known by skilled in the art, the ratio of forgoing
compound is, for example of the preferred embodiment only, not
intended to limit the claim scope. The invention is also applied to
any ratio of the composition. Furthermore, the structure of active
layer 20 can be a single hetero-structure (SH), a double
hetero-structure (DH), or multiple quantum wells (MQW). For DH, it
comprised: the n-type (Al.sub.xGa.sub.1-x).sub.0.5In.sub.0.5P lower
cladding layer 22, the (Al.sub.xGa.sub.1-x).sub.0.5In.sub.0.5P
active layer 20 and the p-type
(Al.sub.xGa.sub.1-x).sub.0.5In.sub.0.5P upper cladding layer 18.
The typical thickness of the layer 22, 20, and 18 are respectively,
between about 0.5-10 .mu.m, 0.5-2.0 .mu.m and 0.5-3.0 .mu.m in
thickness, The thicker of lower cladding layer 22 is with, the more
evenly spread the current will be. Since, the lower cladding layer
22 does not absorb the light emitting from the active layer. Thus
it does not affect the light emitting efficiency.
[0033] The preferred material of the etching stop layer 24
according to the present invention can be any III-V compound
semiconductor material that has an etching selectively to that of
the GaAs substrate 26. As to the lattice matched with that of the
GaAs substrate 26 is not crucial. It's for sure, if the lattice
matched well is also preferred because it can reduce the
dislocation density. The good candidates of those satisfied above
conditions, for examples, InGaP or AlGaAs can be served as the etch
stop layer 24. The lower cladding layer 22 can also be served as
the etching stop layer 24 since it has a high selectivity to GaAs
substrate 26, and thus if the thickness of the lower cladding layer
22 is thick enough, the etch stop layer 24 becomes optional.
[0034] Subsequently, a structure as shown in FIG. 2 is prepared.
The structure comprises a transparent adhesive layer 14, for
example, a BCB (B-staged bisbenzocyclobutene; BCB) layer and a
transparent substrate (TS) 10. The material of the adhesive layer
14 is not limited to BCB. Any adhesive material with similar
property, such as epoxy is also applicable to the invention. The
transparent substrate 10 can be a substrate selected from glass,
sapphire, SiC, GaP, GaAsP, ZnSe, ZnS, or ZnSSe. Other materials can
also be chosen as the transparent substrate 10 as long as the light
absorbed by the material is minor. One advantage of the present
invention is that the transparent substrate 10 is not limited to be
a single crystal substrate. The transparent substrate herein is
used for supporting the LED epitaxial layer and avoids the LED
epi-layers from breaking. In addition, the injected current does
not need to flow through the transparent substrate 10. In other
words, either poly-crystal or amorphous crystal can be used as the
TS 10. Accordingly, the manufacture can be cost down.
[0035] Thereafter, the epi-layer structure as shown in FIG. 1 is
bonded together with the TS 10 by BCB layer 14. The adhesion
process is carried out at a temperature of about 250.degree. C.
with pressure and heat for a while. To improve the adhesion well,
prior to coat a BCB layer 14 on the surface of the TS 10, a step of
coating an adhesion prompter on the surface of TS 10 can be
optionally done. Alternatively, after epi-layers bonded with
transparent surface by BCB, the thermal process can be firstly
performed at 60 to 100.degree. C. for a while to evaporate organic
solvent away, and then heated and pressed at a temperature of about
200-600.degree. C.
[0036] Thereafter, the opaque n-type GaAs substrate 26 is then
removed and stopped at the etching stop layer 24 by an etchant
mixture, for example, 5H.sub.3PO.sub.4:3H.sub.2O.sub.2:3H.sub.2O or
1NH.sub.4OH:35H.sub.2O.sub.- 2.
[0037] Referring to FIG. 3A, a first photoresist pattern 29 is then
coated on the etch stop layer 24 to define a first trench 30. A dry
etching, for example, RIE (reactive ion etching), is then applied
to sequentially remove the exposed portion of the etch stop layer
24, the lower cladding layer 22, the active layer 20 and upper
cladding layer 18 and slightly etch the p-type ohmic contact
epitaxial layer 16 so as to further remove a portion thickness
thereof, as is shown in FIG. 3B. Two step levels are formed.
[0038] After stripping the first photoresist pattern 29, as is
shown in FIG. 3B, a second photoresist pattern 32 having a strip of
opening of about 0.5 to 3 mil is formed on the p-type ohmic contact
epitaxial layer 16 so as to define a contact channel 33 therein to
connect the p-type ohmic contact metal electrode 28. Thereafter, a
second dry etch is performed using the second photoresist pattern
32 as a mask to form a contact channel 33.
[0039] After etching is implemented, the second photoresist pattern
32 is removed, as is shown in FIG. 3C, a third photoresist pattern
34 is coated on the exposed sidewall surface and bottom surface of
first trench 30. Next, a lithographic process is performed to
expose the surface of the etch stop layer 24. Then, an n-type ohmic
contact transparent electrode 35 is deposited on the etch stop
layer 24 and on the third photoresist resist pattern 34. The n-type
ohmic contact transparent conductive layer 35 is selected from
materials with properties of low resistance, and high transparent
oxide layer such as a layer of indium tin oxide (ITO), indium
oxide, tin oxide, zinc oxide or magnesium oxide. The thickness of
ohmic contact transparent electrode 35 of about 100 .ANG. to 10000
.ANG. is preferred. Alternatively, a thin metal layer with 30 .ANG.
to 300 .ANG. in thickness can replace for the ohmic contact
transparent conductive layer 35. The thin metal layer 35 can be
chosen from Au, GeAu, Al, Ti, Ni and the combination thereof. The
metal layer 35 is transparent for a layer with such thickness.
Since the adhesion of the transparent oxide layer or thin metal
layer 35 on the photoresist layer 34 is much weaker than those on
the etch stop layer 24, a lift off technique which is tapping an
adhesive tap and then pull it up is thus easier to strip the weaker
adhesive portions layer away. Thereafter, referring to FIG. 3D, a
lithographic is carried out to coat a fourth photoresist pattern 37
on the resulting surfaces. The fourth photoresist pattern 37
includes opening 39A and 39B. The opening 39A is slightly larger
than the contact channel 33 to expose the metal electrode 28 and
the opening 39B is to define the position of electrode on the
transparent conductive layer 35. Thereafter, a meal layer 40 is
deposited on the resulting surface by sputtering or by E-beam
process as is shown in FIG. 3D. A lift off technique is then done
to strip the portion of metal layer 40 on the fourth photoresist
pattern 37 and then removes the residue fourth photoresist 37, as
is shown in FIG. 3E. Thus, the remnant metal layer 40A is only left
on the contact channel 33 and the metal layer 40B on transparent
conductive layer 35.
[0040] The method of second preferred embodiment according to the
present invention is shown in FIG. 4A. After two etching steps are
sequentially implemented for forming the first trench 30 and the
contact channel 33 as the first preferred embodiment, a fifth
photoresist pattern 42 is coated on a side wall, on a bottom of the
first trench 30 and contains also a photoresist block 42A on an
etch stop layer 24 by lithographic method. A transparent oxide
layer or thin metal layer is then formed on the resulting surface,
including the exposed portion of the etch stop layer 24 and on the
fifth photoresist layer 42, the photoresist block 42A. Then a lift
off process is performed so that a transparent conductive layer 44
contains an opening refilled is formed on the etch stop layer 24.
Finally, as is shown in FIG. 4B a sixth photoresist pattern 46,
including an opening 45A exposed contact channel 33, and an opening
45B exposed etch stop layer 24 on the transparent conductive layer
44, is formed by coating and lithographic method. Next a metal
layer 48 formed on all surfaces, a lift off process to strip away
those of weak bonding portions and remnant photoresist removal are
successively carried out. The result is shown in FIG. 4C, where the
metal layer 48A and 48B are not only filled in the contact channel
33 and opening, 45B, respectively but also have an altitude higher
than the surface level of the transparent conductive layer 44.
Note, the contact between the metal layer 48B and the transparent
electrode 44 is of Shockley contact. Consequently, the metal layer
48B is served as a current block so as to distribute the current
evenly.
[0041] The third preferred embodiment according to the present
invention is shown in FIG. 5. Slightly different from two prior
preferred embodiments, before forming the transparent electrode 55,
a lithographic and an etching step are sequentially performed to
form a recessive region50 in the etch stop layer 24 and expose the
lower cladding layer 22 thereto. Then transparent conductive layer
52 and metal layer 55A and 55B are formed as second preferred
embodiment. The transparent electrode 52 filled in the etch stop
layer is to distribute the injunction current uniformly.
[0042] The fourth preferred embodiment according to the present
invention is shown in FIG. 6, which is modified from the third
preferred embodiment. After forming a recess region 50 in the etch
stop layer 24, a dielectric layer 51 is refilled in the recession
region 50. The dielectric layer 51 is chosen from silicon dioxide
silicon nitride or aluminum oxide. The dielectric layer 51 is a
current block which makes the current flow distributed out of the
second electrode 57B. The successively steps of forming the
transparent electrode 56 and the metal bonding layer 57A and 57B
are similar to those steps of forming the metal bonding layer 40A
and the transparent electrode 35.
[0043] The fifth preferred embodiment according to the present
invention is shown in FIG. 7, which is modified from the fourth
preferred embodiment. Instead of forming a recess region and then
refilled in by a dielectric layer 51, the current block of a high
resistance region 61 is formed by performing a lithographic process
to pattern a region and then performing ion implantation with
oxygen ions or hydrogen ions into the etch stop layer 24. The
transparent conductive layer 63 and the metal bonding layer 65A and
65B are formed as the same steps as depicted in the first preferred
embodiment. Another approaching of forming high resistance region
61 is through diffusion of oxygen and hydrogen instead of ion
implant.
[0044] The power output of the AlGaInP four components LED,
operated at 20 mA in accordance with the present invention is of
about 4 mW which is about two times as light intensity as
conventional LED including absorption substrate.
[0045] While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention.
* * * * *