U.S. patent application number 10/256713 was filed with the patent office on 2003-05-08 for method for producing high-brightness led.
Invention is credited to Chung, Chih-Ru, Horng, Ray-Hua, Huang, Shao-Hua, Wu, Tung-Hsing, Yang, Juin-Jer.
Application Number | 20030087463 10/256713 |
Document ID | / |
Family ID | 21679687 |
Filed Date | 2003-05-08 |
United States Patent
Application |
20030087463 |
Kind Code |
A1 |
Horng, Ray-Hua ; et
al. |
May 8, 2003 |
Method for producing high-brightness LED
Abstract
The present invention discloses a method for producing a
high-brightness light emitting diode (LED), which primarily
includes at least one step of bonding a reflective layer formed on
an LED epitaxial layer to an adhesive layer formed on an Si
substrate. An n-type ohmic contact electrode and a p-type ohmic
contact electrode are deposed on the front side of the LED. In the
present invention, the reflective layer, the adhesive layer and the
ohmic contact electrodes preferably perform single function, so
that the most appropriate materials can be applied. Therefore, the
LED of the present invention can exhibit excellent brightness.
Inventors: |
Horng, Ray-Hua; (Taichung,
TW) ; Wu, Tung-Hsing; (Taichung, TW) ; Huang,
Shao-Hua; (Ping-Chen City, TW) ; Chung, Chih-Ru;
(Chung-Li City, TW) ; Yang, Juin-Jer; (Taipei,
TW) |
Correspondence
Address: |
Charles E. Baxley
Hart, Baxley, Daniels & Holton
59 John Street, Fifth Floor
New York
NY
10038
US
|
Family ID: |
21679687 |
Appl. No.: |
10/256713 |
Filed: |
September 30, 2002 |
Current U.S.
Class: |
438/29 ;
257/E33.068 |
Current CPC
Class: |
H01L 33/405 20130101;
H01L 33/0093 20200501; H01L 33/46 20130101 |
Class at
Publication: |
438/29 |
International
Class: |
H01L 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2001 |
TW |
090127823 |
Claims
What is claimed is:
1. A method for producing a high-brightness light emitting diode,
comprising steps of: A) forming a reflective layer on an LED
epitaxial layer and a first adhesive layer on an Si substrate,
wherein said LED epitaxial layer is grown on a temporary substrate
and has a pn junction structure to define a first-type layer
adjacent to said temporary substrate and a second-type layer; B)
bonding said reflective layer to said first adhesive layer by
thermal pressing and then removing said temporary substrate; C)
forming a first-type ohmic contact electrode on partial top surface
of said LED eptaxitial layer by physical vapor deposition; D)
etching at least partial remained LED epitaxial layer from top
surface thereof and stopping at said second-type layer to form a
metal contact layer; and E) forming a second-type ohmic contact
electrode on said metal contact layer by physical vapor
deposition.
2. The method as claimed in claim 1, wherein said LED eptaxitial
layer further comprises a p-type confining layer and a n-type
confining layer.
3. The method as claimed in claim 1, wherein said first ohmic
contact electrode further comprises a transparent electrode
thereon.
4. The method as claimed in claim 1, wherein said reflective layer
comprises a metal and an insulator.
5. The method as claimed in claim 4, wherein said insulator is
adjacent to said LED epitaxial layer.
6. The method as claimed in claim 4, wherein said metal is selected
from the group consisting of Al, Ag, Au, Pt, Pd.
7. The method as claimed in claim 4, wherein said insulator is
selected from the group consisting of Al.sub.2O.sub.3, MgF.sub.2,
SiO.sub.2, TiO.sub.2 and Si.sub.3N.sub.4.
8. The method as claimed in claim 1, wherein said reflective layer
comprises a high-dielectric material and a low-dielectric
material.
9. The method as claimed in claim 8, wherein said low-dielectric
material is adjacent to said LED epitaxial layer.
10. The method as claimed in claim 8, wherein said high-dielectric
material has a refractive index larger than 2.1, and said
low-dielectric material has a refractive index less than 1.56.
11. The method as claimed in claim 8, wherein said high-dielectric
material is selected from the group consisting of TiO.sub.2,
CeO.sub.2, and Si.
12. The method as claimed in claim 8, wherein said low-dielectric
material is selected from the group consisting of Al.sub.2O.sub.3,
MgF.sub.2, SiO.sub.2 and Si.sub.3N.sub.4.
13. The method as claimed in claim 1, wherein said etching of step
D) is chemical wet etching or dry etching.
14. The method as claimed in claim 1, wherein said physical vapor
deposition of steps C) and E) is e-gun evaporation deposition.
15. The method as claimed in claim 1, wherein said physical vapor
deposition of steps C) and E) is thermal evaporation
deposition.
16. The method as claimed in claim 1, wherein said physical vapor
deposition of steps C) and E) is sputter deposition.
17. The method as claimed in claim 1, wherein said reflective layer
further comprises a second adhesive layer therebelow to reinforce
attachment with said first adhesive layer.
18. The method as claimed in claim 17, wherein said second adhesive
layer is a metal.
19. The method as claimed in claim 1, wherein said first adhesive
layer is a metal.
20. The method as claimed in claim 1, wherein said first adhesive
layer is a polymer nonconductor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for producing a
light emitting diode (LED) and, more particularly, to a method for
producing a high-brightness light emitting diode by bonding a
reflective layer formed on an LED epitaxial layer to an adhesive
layer formed on an Si substrate.
[0003] 2. Description of Related Art
[0004] Currently, a trend of developing the light emitting diodes
is to promote the brightness. In order to achieve this object, one
or more reflective metal layers are combined therein. However, this
metal layer has to also possess properties of adhesion and ohmic
contact.
[0005] For example, R.O.C. Patent No. 369731 disclosed an LED in
which the GaAs substrate is replaced with a Si substrate having a
reflective metal layer thereon by wafer bonding technology.
Unfortunately, such design cannot improve the lighting effect of
short wavelengths.
[0006] Additionally, in U.S. Pat. No. 5,376,580, the GaAs substrate
is a temporary substrate for epitaxying and then removed after
being bonded to a transparent substrate. Though this method
prevents absorption of the GaAs substrate, the processes have to be
carried out at high temperature, which might damage the structure
and thus decrease the lighting effect. Additionally, this
transparent substrate is made by GaP, which can absorb the
short-wavelength light.
[0007] R.O.C. Patent No. 415116 mentioned an LED 10 as shown in
FIG. 1, in which two reflective adhesive metal layers 16, 12 are
respectively attached on the bottom surface of the LED epitaxial
layer 15 and the top surface of the substrate 11. By bonding the
two reflective adhesive metal layers 16, 12, the light beams can be
propagated from the front side of the LED 10 and the brightness can
be promoted.
[0008] FIG. 2 shows another conventional LED 20, in which a metal
adhesive layer 22 is formed on a top surface of the SiO.sub.2
substrate 21, and an LED epitaxial layer 25 is bonded to the top
surface of the metal adhesive layer 22. Brightness of the LED 20
can be improved due to ohmic contact between the substrate 21 and
the metal adhesive layer 22.
[0009] For the above LED structures, all of the reflective layers
have combining functions of adhesion and ohmic contact, therefore
only metal material is suitable. A disadvantage of such material is
that atomic diffusion occurs at the interface of the metal layer
and the LED epitaxial layer. When a light source more than 600 nm
is applied, the lighting effect will be reduced since total
reflection in the metal layer is not available. FIG. 3 shows the
reflectivity varied with wavelengths, in which the reflectivity is
0.9 at 600 nm. Further, the reflectivity rapidly reduces at
wavelength less than 600 nm, for example, 590 nm or 570 nm of
yellow-green light. Consequently, the reflective layer can hardly
perform expected effect. Both the reflective metal layers as shown
in FIGS. 1 and 2 exist such problem.
[0010] Therefore, it is desirable to provide a method for producing
an improved LED structure to promote the brightness, particularly
at short wavelength.
SUMMARY OF THE INVENTION
[0011] An object of the present invention is to provide a method
for producing a high-brightness light emitting diode, which can
exhibit superior lighting effect at long wavelength.
[0012] Another object of the present invention is to provide a
method for producing a high-brightness light emitting diode, which
can exhibit much better lighting effect than the conventional at
short wavelength.
[0013] In order to achieve the above object, the method primarily
includes steps of: A) forming a reflective layer on an LED
epitaxial layer and a first adhesive layer on an Si substrate,
wherein the LED epitaxial layer is grown on a temporary substrate
and has a pn junction structure to define a first-type layer
adjacent to the temporary substrate and a second-type layer; B)
bonding the reflective layer to the first adhesive layer by thermal
pressing and then removing the temporary substrate; C) forming a
first-type ohmic contact electrode on partial top surface of the
LED eptaxitial layer by physical vapor deposition; D) etching at
least partial remained LED epitaxial layer from top surface thereof
and stopping at the second-type layer to form a metal contact
layer; and E) forming a second-type ohmic contact electrode on the
metal contact layer by physical vapor deposition.
[0014] The LED eptaxitial layer aforementioned can further include
a p-type confining layer and a n-type confining layer. The first
ohmic contact electrode can further include a transparent electrode
thereon to enhance electric conduction. The reflective layer
preferably includes at least two materials, for example, a metal
and an insulator, a high-dielectric material and a low-dielectric
material, etc, wherein the insulator and the low-dielectric
material are preferably adjacent to the LED epitaxial layer.
[0015] The metal can be Al, Ag, Au, Pt, Pd, etc. The insulator can
be Al.sub.2O.sub.3, MgF.sub.2, SiO.sub.2, TiO.sub.2,
Si.sub.3N.sub.4, etc. The high-dielectric material preferably has a
refractive index larger than 2.1, and the low-dielectric material
has a refractive index less than 1.56. The high-dielectric material
can be TiO.sub.2, CeO.sub.2, Si, etc. The low-dielectric material
can be Al.sub.2O.sub.3, MgF.sub.2, SiO.sub.2, Si.sub.3N.sub.4,
etc.
[0016] The etching process of step D) is preferably chemical wet
etching or dry etching. The physical vapor deposition of steps C)
and E) can be e-gun evaporation deposition, thermal evaporation
deposition, or sputter deposition.
[0017] The reflective layer can further include a second adhesive
layer therebelow to reinforce attachment with the first adhesive
layer. The first or second adhesive layer is preferably made from
metal, for example, Au, Au/Be alloy, Au/Zn alloy, Pt, Pd, Cu, Ni,
In and Al. The first adhesive layer can be also a polymer
nonconductor.
[0018] Other objects, advantages, and novel features of the
invention will become more apparent from the following detailed
description when taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows the cross section view of a conventional
LED.
[0020] FIG. 2 shows the cross section view of another conventional
LED.
[0021] FIG. 3 shows the reflectivity varied with wavelengths.
[0022] FIG. 4 shows the flow diagram for producing the LED in
accordance with the present invention.
[0023] FIG. 5 shows the cross section view in the step of combining
the LED epitaxial layer and the Si substrate of the present
invention.
[0024] FIG. 6 shows the cross section view in the step of
depositing the first-type ohmic contact electrode on the LED
epitaxial layer of the present invention.
[0025] FIG. 7 shows the cross section view in the step of etching
the LED epitaxial layer to form the metal contact layer and the
second-type ohmic contact electrode of the present invention.
[0026] FIG. 8 shows the cross section view of the second embodiment
in accordance with the present invention.
[0027] FIG. 9 shows the cross section view of the third embodiment
in accordance with the present invention.
DETAILED DESCRIPYION OF THE PREFERRED EMBODIMENTS
[0028] Referring to FIG. 4, the flow diagram for producing the
high-brightness LED 50 of the present invention is shown. In step
A, also with refer to FIG. 5, an Si substrate 51 having a first
adhesive layer 52 and a LED epitaxial layer 55 having a
nonconductive reflective layer 56 or a mirror layer formed on a
bottom surface thereof are provided. The LED epitaxial layer 55 is
an active structure and fabricated by II-VI or III-V alloys, for
example, direct-bandgap LEDs, AlGaInP. The LED epitaxial layer 55
previously grows on a temporary GaAs substrate 59 and has a pn
junction structure, wherein the upper one is a p-type layer 55A and
the lower one is an n-type layer 55B. In this embodiment, the
p-type layer 55A is arranged to be adjacent to the reflective layer
56 and the n-type layer 55B to the temporary substrate 59. The
reflective layer 56 is a composite material including two
materials. In this embodiment, the reflective layer 56 includes a
metal 561 and a insulator 562, wherein the metal 561 is not
provided for omhic contact, and the insulator 562 is adjacent to
the LED epitaxial layer 55. The composite reflective layer 56 is
not restricted, and can be Al/Al.sub.2O.sub.3, Al/SiO.sub.2,
Al/MgF.sub.2, Pt/Al.sub.2O.sub.3, Pt/SiO.sub.2, Pt/MgF.sub.2,
Ag/Al.sub.2O.sub.3, Ag/SiO.sub.2, Ag/MgF.sub.2, etc.
[0029] In step B, the LED eptaxitial layer 55 and the reflective
layer 56 are bonded to the Si substrate 51 by thermal pressing,
wherein the metal 561 is attached and adjacent to the first
adhesive layer 52, as shown in FIG. 5. The temporary substrate 59
is then removed.
[0030] In step C, an n-type ohmic contact electrode 60 having the
same type as the n-type layer 55B of the LED eptaxitial layer 55 is
formed on the left top surface thereof by physical vapor
deposition. FIG. 6 shows the cross section view of the structure
developed in this step.
[0031] In step D, the right top surface of the LED epitaxial layer
55 is etched and stopped beneath the pn junction to form a metal
contact layer 58 and expose the p-type layer 55A. In step E, a
p-type ohmic contact electrode 65 having the same type as the
p-type layer 55A of the exposed LED eptaxitial layer 55 is formed
by physical vapor deposition. FIG. 7 shows the cross section view
of the structure developed in these two steps. By supplying
appropriate voltage to the ohmic contact electrodes 60, 65, the LED
epitaxial layer 55 can be excited and emit light, wherein the
backward light can be reflected by the reflective layer 56.
Therefore, the light beams are all propagated frontward and the
short-wavelength light would not be absorbed by the Si substrate
51, the brightness is hence promoted.
[0032] The LED eptaxitial layer in the present invention is not
limited to the above form, and can alternatively has the p-type
layer on the lower layer and the n-type layer on the upper layer,
or further includes confining layers having the same types as
adjacent layers on their surfaces respectively.
[0033] FIG. 8 shows the cross section view of the second embodiment
in accordance with the present invention. In this embodiment, a
transparent electrode 70 is applied on the n-type ohmic contact
electrode 60 and the exposed n-type layer 55B of the LED epitaxial
layer 55 to advance electric conduction. Additionally, a second
adhesive layer 57 is applied below the reflective layer 56 to
reinforce the attachment of the structures.
[0034] FIG. 9 shows the cross section view of the third embodiment
in accordance with the present invention, in which the reflective
layer 56 is composed of a high-dielectric material 563 and a
low-dielectric material 564. The high-dielectric material 563 has a
refractive index larger than 2.1, and the low-dielectric material
564 has a refractive index less than 1.56, for example,
(TiO.sub.2/SiO.sub.2)n, (Si/SiO.sub.2)n, (Si/Si.sub.3N.sub.4)n,
wherein n is number of pairs. By means of properly arranging the
layers of different refractive indices and thicknesses, high
reflection of desired wavelengthes can be achieved.
[0035] In the present invention, the reflective layer 56, the first
and second adhesive layers 52, 57 and the ohmic contact electrodes
60, 65 preferably perform single function, so that the most
appropriate materials can be applied. For example, the first
adhesive layer 52 and/or the second adhesive layer 57 can be a
polymer nonconductor. Furthermore, reflectivity of the LED
according to the present invention can be promoted above 98% at
wavelength larger than 600 nm and above 90% at wavelength less than
600 nm.
[0036] Although the present invention has been explained in
relation to its preferred embodiments, it is to be understood that
many other possible modifications and variations can be made
without departing from the spirit and scope of the invention as
hereinafter claimed.
* * * * *