U.S. patent number RE46,004 [Application Number 14/121,840] was granted by the patent office on 2016-05-17 for light-emitting chip device with high thermal conductivity.
This patent grant is currently assigned to KABUSHIKI KAISHA TOSHIBA. The grantee listed for this patent is KABUSHIKI KAISHA TOSHIBA, NATIONAL CHUNG HSING UNIVERSITY. Invention is credited to Ray-Hua Horng, Chuang-Yu Hsieh, Shao-Hua Huang, Chao-Kun Lin, Dong-Sing Wuu.
United States Patent |
RE46,004 |
Horng , et al. |
May 17, 2016 |
Light-emitting chip device with high thermal conductivity
Abstract
This invention provides a light-emitting chip device with high
thermal conductivity, which includes an epitaxial chip, an
electrode disposed on a top surface of the epitaxial chip and a
U-shaped electrode base cooperating with the electrode to provide
electric energy to the epitaxial chip for generating light by
electric-optical effect. The epitaxial chip includes a substrate
and an epitaxial-layer structure with a roughening top surface and
a roughening bottom surface for improving light extracted out of
the epitaxial chip. A thermal conductive transparent reflective
layer is formed between the substrate and the epitaxial-layer
structure. The electrode base surrounds the substrate, the
transparent reflective layer and a first cladding layer of the
epitaxial-layer structure to facilitate the dissipation of the
internal waste heat generated when the epitaxial chip emitting
light. A method for manufacturing the chip device of the present
invention is provided.
Inventors: |
Horng; Ray-Hua (Taichung,
TW), Wuu; Dong-Sing (Taichung, TW), Huang;
Shao-Hua (Pinghen, TW), Hsieh; Chuang-Yu
(Sanchong, TW), Lin; Chao-Kun (San-Jose, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA
NATIONAL CHUNG HSING UNIVERSITY |
Tokyo
Taichung |
N/A
N/A |
JP
TW |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
(Tokyo, JP)
|
Family
ID: |
40672552 |
Appl.
No.: |
14/121,840 |
Filed: |
October 23, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
12047165 |
Mar 12, 2008 |
7858999 |
Dec 28, 2010 |
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Foreign Application Priority Data
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Sep 21, 2007 [TW] |
|
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096135296 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
33/22 (20130101); H01L 33/0093 (20200501); H01L
29/22 (20130101); H01L 33/44 (20130101) |
Current International
Class: |
H01L
29/22 (20060101); H01L 33/22 (20100101) |
Field of
Search: |
;257/98 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Wei Chih Peng & Yew Chung Sermon Wu, Enhanced Output in double
Roughened GaN Light-Emitting Diodes via Various Texturing
Treatments of Undoped-GaN Layer, Japanese Journal of Applied
Physics, Val. 45, No. 10A, 2006, pp. 7790-7712. cited by applicant
.
PCT search report of Nov. 18, 2008, PCT/US08/76773. cited by
applicant .
Wei Chih Peng & Yew Chung Sermon Wu, Performance of InGaN-GaN
LEDs Fabricated Using Glue Bonding on 50-mm Si Substrate,
1041-11335, 2006 IEEE. cited by applicant .
U.S. Appl. No. 12/039,563, filed Feb. 28, 2008, Ray-Hua Horng.
cited by applicant .
U.S. Appl. No. 12/701,336, filed Feb. 5, 2010, Ray-Hua Horng. cited
by applicant.
|
Primary Examiner: Andujar; Leonardo
Attorney, Agent or Firm: Hogan Lovells US LLP
Claims
What is claimed is:
1. A light-emitting chip device with high thermal conductivity,
comprising: an epitaxial chip including a substrate and an
epitaxial-layer structure capable of generating light by
electro-optical effect on said substrate, said epitaxial-layer
structure including a first cladding layer of first conductivity
type having a bottom surface with a roughness not less than 100 nm
rms corresponding to said substrate, a second cladding layer of
second conductivity type opposite to said first conductivity type
having a top surface with a roughness not less than 100 nm rms, and
an active layer sandwiched between said first cladding layer and
said second cladding layer; an electrode disposed on and in ohmic
contact with said top surface of said second cladding layer; and a
U-shaped electrode base under said epitaxial chip and surrounding
said substrate and said first cladding layer, such that said
U-shaped electrode base covers and connects to at least a portion
of a bottom surface of the substrate, said U-shaped electrode being
in ohmic contact with said first cladding layer and in contact with
said electrode to provide electric energy to said epitaxial
chip.
2. The light-emitting chip device with high thermal conductivity as
claimed in claim 1, further comprising a transparent refractive
layer formed between said substrate and said epitaxial-layer
structure and having a refractive index between that of air and
said substrate.
3. The light-emitting chip device with high thermal conductivity as
claimed in claim 2, wherein said transparent refractive layer has a
thickness not more than 5 .mu.m rms.
4. The light-emitting chip device with high thermal conductivity as
claimed in claim 2, wherein said transparent refractive layer has a
light transmittance greater than 50% for wavelength longer than 300
nm rms.
5. The light-emitting chip device with high thermal conductivity as
claimed in claim 1, wherein said substrate includes a bottom
substrate and a reflective mirror layer on said bottom
substrate.
6. The light-emitting chip device with high thermal conductivity as
claimed in claim 5, wherein said bottom substrate has a material
formed of silicon, diamond or metal with high thermal conductivity,
and said reflective mirror layer has a highly reflective metallic
material or a combination of highly reflective metallic
materials.
7. The light-emitting chip device with high thermal conductivity as
claimed in claim 5, wherein said bottom substrate has a material
formed of silicon, diamond or metal with high thermal conductivity
and a thickness more than 50 .mu.m rms, and said reflective mirror
layer is formed of high-reflective-index dielectric layers and
low-reflective-index dielectric layers alternately disposed to each
other.
8. The light-emitting chip device with high thermal conductivity as
claimed in claim 7, wherein said reflective mirror layer has a
reflectivity not less than 50%.
9. The light-emitting chip device with high thermal conductivity as
claimed in claim 1, wherein said U-shaped electrode base includes a
seed layer and an electrode base layer extending from said seed
layer, and said seed layer connects to exposed surfaces of said
substrate and sidewalls of said first cladding layer.
10. The light-emitting chip device with high thermal conductivity
as claimed in claim 9, wherein said seed layer is formed of a
metallic layer with high thermal conductivity and said electrode
base layer is formed of the same material as said seed layer or its
alloy.
11. The light-emitting chip device with high thermal conductivity
as claimed in claim 9, wherein said seed layer has a reflectivity
not less than 50%.
12. The light-emitting chip device with high thermal conductivity
as claimed in claim 1, wherein the first conductivity type is
N-type or P-type.
Description
RELATED APPLICATION
This application claims priority, under 35 USC .sctn.119, from
Taiwan Patent Application No. .[.096135297.]. .Iadd.096135296
.Iaddend.filed on Sep. 21, 2007, the content of which is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting chip device; and
more particularly to a light-emitting chip device with high light
extraction efficiency and high thermal conductivity.
2. Description of the Related Art
Please refer to FIG. 1, which shows a conventional light-emitting
chip 1. FIG. 1 includes a substrate 11, an epitaxial-layer
structure 12 on the substrate 11 and an electrode unit 13
constituted of an N-type electrode 131 and a P-type electrode
132.
As an example, the epitaxial-layer structure 12 is formed of
GaN-based material and has an N-type first cladding layer 121, an
active layer 122 formed on the first cladding layer 121 and a
P-type second cladding layer 123. The first cladding layer 121 and
the second cladding layer 123 are opposite to each other and form
carrier injectors relative to the active layer 122. As such, when
electric power is provided to the epitaxial-layer structure 12,
electrons and holes would be recombined together and then release
energy in a form of light emission.
The N-type electrode 131 and P-type electrode 132, for example, are
formed of Au, Ni, Pt, Ag, Al, etc. and/or their alloy. The N-type
electrode 131 is disposed on and forms ohmic contact with the first
cladding layer 121 of the epitaxial-layer structure 12. The P-type
electrode 132 is disposed on and forms ohmic contact with the
second cladding layer 123 such that the N-type electrode 131 and
P-type electrode 132 provide electric power supply to the
epitaxial-layer structure 12.
When electric energy is supplied to the N-type electrode 131 and
P-type electrode 132, current spreads and flows through the
epitaxial-layer structure 12, and electrons and holes are injected
into the active layer 122, recombining with each other and
releasing energy in the form of light emission.
The refractive index of the GaN-based material is about 2.6, and
the refractive index of its surrounding, which generally is air, is
1, or the surrounding is a transparent encapsulating material, used
for packaging and having a refractive index between 1 and 2.6. The
top surface 124 of the second cladding layer 123 of the
epitaxial-layer structure 12 of the light-emitting chip 1 is a flat
surface. Partial light generated from the epitaxial-layer structure
12, due to their propagation direction, would follow Snell's law
and could not escape the epitaxial-layer structure 12 and enter the
surrounding. As a consequence, the light extraction of the
light-emitting chip 1 is not good.
Please refer to FIG. 2. There are literature and patents that
propose roughing the top surface 124' of the light-emitting chip 1
to make the light impinging on the rough top surface 124' have
various incident angles relative to the rough top surface 124'. The
chance of light escaping the epitaxial-layer structure 12' is thus
increased, and the light extraction efficiency is improved.
Nevertheless, the light generated from the epitaxial-layer
structure 12' does not entirely propagate toward the top surface
124'. The light propagating toward the substrate 11 faces similar
situation as that at the top and can not escape the epitaxial layer
12' and enter the surrounding. Thus, the light extraction is still
low.
Please refer to FIG. 3. Some literature proposes to form a
reflective mirror layer 111, which is connected to the
epitaxial-layer structure 12', capable of reflecting light.
Hopefully, the light propagating toward the substrate 11' can be
reflected toward the top surface 124' to improve the possibility of
light generated from the epitaxial-layer structure 12' to escape
the epitaxial-layer structure and enter the surrounding. However,
the light propagating toward the substrate 11' would be confined in
the epitaxial-layer structure 12' due to their propagation
directions and causes total internal reflection within the
epitaxial-layer structure 12'. Furthermore, the light can be
absorbed by the active layer 122. The reflective mirror layer 111
on the substrate 11' cannot substantially improve the light
extraction of the light-emitting chip 1. When a roughened interface
is formed between the epitaxial-layer structure 12' and the
reflective mirror layer 111, and a low-refractive-index transparent
material is added between them, the light entering the
low-refractive-index transparent material from the epitaxial-layer
structure 12' is easily reflected back, and the roughened interface
would easily change the propagation of the reflected light. The
total reflection within the epitaxial-layer structure 12' is
eliminated. The light extraction thus can be increased.
Nevertheless, the N-type electrode 131 is disposed on the first
cladding layer 121 and the P-type electrode 132 is disposed on the
second cladding layer 123, both of them block some light emitted
from the front side of the light-emitting chip 1, and resulting in
the reduction of the light-emitting area. The brightness of the
light-emitting chip 1 is lowered.
Besides, the internal waste heat converted from the light confined
within the epitaxial structure 12' is dissipated through the
substrate 11', and the dissipation efficiency is not good. The
lifetime of the light-emitting chip 1 is adversely affected.
SUMMARY
One aspect of the present invention is to provide a light-emitting
chip device with high light extraction efficiency and high thermal
conductivity.
Another aspect of the present invention is to provide a method for
manufacturing a light-emitting chip device with high light
extraction efficiency and high thermal conductivity.
The light-emitting chip device with high light extraction
efficiency and high thermal conductivity of the present invention
includes an epitaxial chip, an electrode and a U-shaped electrode
base.
The light-emitting chip includes a substrate, an epitaxial-layer
structure capable of generating light by electro-optical effect on
the substrate and a transparent refractive layer sandwiched between
the substrate and the epitaxial-layer structure. The
epitaxial-layer structure includes an N-type first cladding layer
connecting to the transparent refractive layer and having a
roughness not less than 100 nm root means squared (rms), a P-type
second cladding layer having a roughness not less than 100 nm rms
and an active layer sandwiched between the first cladding layer and
second cladding layer. Root mean square means the average between
the height deviations and the mean line/surface, taken over the
evaluation length/area.
The electrode is disposed on and in ohmic contact with a top
surface of the epitaxial-layer structure.
The U-shaped electrode base surrounds the substrate, the
transparent refractive layer and the first cladding layer, and
being in ohmic contact with the first cladding layer. The electrode
base is in contact with the electrode to provide electric energy to
the epitaxial chip for generating light.
In one aspect, the present invention provides a method for
manufacturing a light-emitting chip device with high thermal
conductivity, which includes steps of forming an epitaxial-layer
structure on a substrate, performing a first roughening step,
forming an electrode on the top surface of the epitaxial-layer
structure, forming a provisional substrate on the top surface of
the epitaxial-layer structure, removing the substrate under the
epitaxial-layer structure, performing a second roughening step,
attaching a substrate onto a bottom surface of the epitaxial-layer
structure, removing the provisional substrate to form an epitaxial
chip, attaching the epitaxial chip upside-down onto a supporting
substrate, forming an electrode base surrounding the epitaxial chip
opposite to the supporting substrate and removing the supporting
substrate.
The light-emitting chip structure is formed on an epitaxial
substrate with an epitaxial growth method. The epitaxial-layer
structure includes an N-type first cladding layer, a P-type second
cladding layer and an active layer sandwiched between the first
cladding layer and second cladding layer.
The first roughening step is to roughen a top surface of the
epitaxial-layer structure far away from the epitaxial
substrate.
The electrode is formed on and in ohmic contact with the top
surface of the epitaxial-layer structure.
The provisional substrate is separably attached onto the top
surface of the epitaxial-layer structure.
The epitaxial substrate is separated from the epitaxial-layer
structure to expose the bottom surface of the epitaxial-layer
structure.
The second roughening step is to roughen the bottom surface of the
epitaxial-layer structure.
The step of attaching a substrate onto a bottom surface of the
epitaxial-layer structure is attaching the substrate onto the
bottom surface of the epitaxial-layer structure by thermal
conductive glue with a predetermined refractive index and
transparent to the light generated from the epitaxial-layer
structure.
The provisional substrate is removed to form an epitaxial chip.
The outer surface of the epitaxial chip is coated with an isolation
glue, and exposing sidewalls of the first cladding layer. The
epitaxial chip is attached upside-down onto the supporting
substrate by the isolation glue.
The electrode base is formed by forming an electrically conductive
and thermally conductive seed layer on exposed surfaces of the
epitaxial chip and then forming an electrically conductive and
thermally conductive electrode base layer from the seed layer to
form the electrode base in ohmic contact with the first cladding
layer.
The supporting substrate is removed to form the light-emitting chip
device with high thermal conductivity of the present invention.
The present invention provides a manufacturing process to produce a
light-emitting chip device with an epitaxial-layer structure having
a roughened top surface and roughened bottom surface to facilitate
the extraction of light from the chip device, and enhancing
brightness of the chip device. The internal waste heat of the chip
device can be directly dissipated through the electrode base such
that the lifetime of the chip device is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of a conventional
light-emitting chip;
FIG. 2 is a schematic cross-sectional view of another conventional
light-emitting chip with a roughened top surface;
FIG. 3 is a schematic cross-sectional view of another conventional
light-emitting chip with a roughened top surface and a reflective
layer;
FIG. 4 is a schematic cross-sectional view of a light-emitting chip
device with high thermal conductivity according to a preferred
embodiment of the present invention;
FIG. 5 is a process flow for manufacturing the light-emitting chip
device with high thermal conductivity of FIG. 4; and
FIG. 6 through FIG. 15 shows a schematic cross-sectional view of
the light-emitting chip device corresponding to various steps of
the process flow of FIG. 5.
DETAILED DESCRIPTION
The light-emitting chip with high thermal conductivity provided by
the present invention will be described and explained in detail
through the following embodiments in conjunction with the
accompanying drawings. It should be noted that like elements in the
following description are designated in the same numerals.
Please refer to FIG. 4, which is a schematic cross-sectional view
of the light-emitting chip device with high thermal conductivity of
the present invention. The light-emitting chip device with high
thermal conductivity of the present invention includes an epitaxial
chip 2, an electrode unit 3 and an electrode base 4.
The epitaxial chip 2 includes a substrate 21, an epitaxial-layer
structure 22 for generating light by electro-optical effect and a
transparent refractive layer 23 joining the epitaxial-layer
structure 22 and the substrate 21. The transparent refractive layer
23 is also thermally conductive.
The substrate 21 includes a bottom substrate 211 and a reflective
mirror layer 212. The substrate 21 connects to the transparent
refractive layer 23. The bottom substrate 211 is used for
supporting the epitaxial-layer structure 22 and includes silicon,
high thermally conductive ceramic or high thermally conductive
metallic material. The reflective mirror layer 212 can be formed of
Al, Ag, Au, Pt, Pd, Rb or a combination thereof, and also can be
formed of high-refractive-index dielectric layers and
low-refractive-index dielectric layers alternately disposed to each
other. The reflective mirror layer 212 is used for reflecting the
light propagating toward the substrate 21.
The epitaxial-layer structure 22 is formed of GaN-based
semiconductor materials epitaxially grown on an epitaxial substrate
21, and then joining to the substrate 21 by the transparent
refractive layer 23 (the detailed process will be described in the
following). The epitaxial-layer structure 22 includes an N-type
first cladding layer 221, a P-type second cladding layer 223 and an
active layer 222 sandwiched between the first cladding layer 221
and second cladding layer 223. The first cladding layer 221 and
second cladding layer 223 constitute quantum barriers relative to
the active layer 222 such that the epitaxial-layer structure 22 can
generate light by electro-optical effect.
The epitaxial-layer structure 22 has a roughened bottom surface 224
(i.e. the bottom surface of the first cladding layer 221)
connecting to the transparent refractive layer 23. The bottom
surface 224 of the epitaxial-layer structure 22 is roughened with
wet etching. The epitaxial-layer structure 22 also includes a
roughened top surface 225 (i.e. the top surface of the second
cladding layer 223) with electrical conductivity opposite to the
roughening bottom surface 224. The top surface 225 of the
epitaxial-layer structure 22 is roughened by inductively-coupled
plasma etching, wet etching or epitaxial growth. The
epitaxial-layer structure 22 also includes a sidewall 226 (i.e.,
the sidewalls of the first cladding layer 221, the second cladding
layer 223 and the active layer 222) connecting the bottom surface
224 and top surface 225. The sidewall 226 has an electrical
conduction portion 227, which is extended upward from the periphery
of the bottom surface 224 and has the same electrical conductivity
with the bottom surface 224. Namely, the electrical conduction
portion 227 is constituted by the sidewall of the first cladding
layer 221.
The transparent refractive layer 23 has a refractive index between
air and the substrate 21 and a light transmission percentage more
than 50% for wavelength longer than 300 nm rms. The transparent
refractive layer 23 joins the substrate 21 and the epitaxial-layer
structure 22 together and has a thickness not more than 5 .mu.m
rms.
The electrode 3 is formed of Ag, Al, Au, Ti, Ni, Cr or their alloy.
The electrode 3 is disposed on and in ohmic contact with the
roughened top surface 225 of the epitaxial-layer structure 22.
The electrode base 4 surrounds the epitaxial chip 2 partially and
includes a seed layer 41 and an electrode base layer 42. The seed
layer 41 connects to exposed surfaces of the substrate 21,
transparent refractive layer 23 and the electrical conduction
portion 227 of the epitaxial-layer structure 22, as well as
including an electrode base layer 42 extending from the seed layer
41.
The electrode base 4 is in ohmic contact with the electric
conduction portion 227. The seed layer 41 is formed of
high-thermally-conductive metallic material and has a reflectivity
not less than 50%. The electrode base layer 42 has the same
material as the seed layer 41, or has its alloy as the material.
The electrode base 4 and electrode 3 cooperate with each other to
provide electric energy to the epitaxial chip 2 for generating
light.
When the electrode 3 and the electrode base 4 apply electric energy
to the epitaxial chip 2, the electrode 3, the top surface 225 of
the epitaxial-layer structure 22 (i.e. the top surface of the
second cladding layer 223), the second cladding layer 223, the
active layer 222, the first cladding layer 221, the sidewall of the
first cladding layer 221 (i.e. the electrical conduction portion
227 of the sidewall 226 of the epitaxial-layer structure 22), and
the electrode base 4 constitute an electrical conduction path to
make the epitaxial-layer structure 22 generating light by
electro-optical effect.
The light propagating upward through the roughened top surface 225
of the epitaxial-layer structure 22 would have various incident
angles relative to the roughened top surface 225. The confinement
of the light propagation governed by Snell's law is destroyed, and
the chance of light escaping epitaxial-structure largely
increases.
The light propagating downward through the roughening bottom
surface 224 of the epitaxial-layer structure 22 (i.e. the bottom
surface of the first cladding layer 221) also has various incident
angles relative to the roughened bottom surface 224, and
facilitating the light entering the transparent refractive layer
23. The transparent refractive layer 23 has a thickness not more
than 5 .mu.m rms and a refractive index between air and the
substrate 21. The transparent refractive layer 23 forms a medium
between the epitaxial-layer structure 22 and the reflective mirror
layer 212 of the substrate 21. The light enters the interface of
the transparent refractive layer 23 and the reflective mirror layer
212 is reflected back by the reflective mirror layer 212 and
passing through the transparent refractive layer 23, the
epitaxial-layer structure 22, and then entering the external. In
other words, the light entering the transparent refractive layer 23
from the epitaxial-layer structure 22 is easily reflected back
because the former has a refractive index lower than the latter.
The roughened bottom surface 224 of the epitaxial-layer structure
22 would change the propagation direction of the reflected light,
and hence increasing the chance of light escaping the epitaxial
chip 2.
Besides, the light passing through the top surface 225 of the
epitaxial-layer structure 22 is only blocked by the electrode 3
disposed thereon. The utilization of the emitting light from the
epitaxial-layer structure 22 is improved compared to the
conventional light-emitting chip device 1 shown in FIG. 1 through
FIG. 3 that have two electrodes 131, 132 to cover some
light-emitting areas, and resulting in the decrease of the
utilization of the emitting light from the epitaxial-layer
structure 12.
The U-shaped electrode base 4 is covering and connecting to the
bottom surface and sidewall of the substrate 21, the sidewall of
the transparent refractive layer 23, and the sidewall of the first
cladding layer 221 of the epitaxial-layer structure 22 (i.e. the
electrical conduction portion 227). The electrode base 4 has a
large contact area with the epitaxial chip 2. The heat generated in
the epitaxial chip 2 can be rapidly dissipated out through the
electrode base 4. The lifetime of the light-emitting chip device of
the present invention is improved. The deterioration of the
reflective mirror layer 212 is avoided, and the stability of the
light-emitting chip device of the present invention is
maintained.
A method for manufacturing the light-emitting chip device will be
described in detail in the following.
Please refer to FIG. 5, the method for manufacturing the
light-emitting chip device includes step 501 of forming an
epitaxial-layer structure on a substrate, step 502 of performing a
first roughening step, step 503 of forming an electrode on a top
surface of a second cladding layer of the epitaxial-layer
structure, step 504 of forming a provisional substrate on the top
surface of the second cladding layer of the epitaxial-layer
structure, step 505 of removing the substrate under the
epitaxial-layer structure, step 506 of performing a second
roughening step, step 507 of attaching a substrate onto a bottom
surface of a first cladding layer of the epitaxial-layer structure,
step 508 of removing the provisional substrate to form an epitaxial
chip, step 509 of attaching the epitaxial chip upside-down onto a
supporting substrate, step 510 of forming an electrode base, step
511 of removing the supporting substrate to obtain the
light-emitting chip device.
Please refer to FIG. 6, in step 501, the epitaxial-layer structure
22 from bottom to top including a first cladding layer 221, an
active layer 222 and a second cladding layer 223 that epitaxially
is grown on an epitaxial substrate 91. A GaN-based semiconductor
material can epitaxially grow on the epitaxial substrate 91. The
process for forming the epitaxial-layer structure 22 is well known,
and will not be described again herein.
Please refer to FIG. 5 and FIG. 7, in step 502, the first
roughening step is performed to roughen the top surface of the
second cladding layer 223 of the epitaxial-layer structure 22 (i.e.
the top surface 225 of the epitaxial-layer structure 22) by
inductively-coupled plasma etching. The epitaxial-layer structure
22 also can form a roughened top surface by the epitaxial growth
method.
Please refer to FIG. 5 and FIG. 8, in step 503, the electrode 3 is
formed on the roughened top surface 225 of the second cladding
layer 223, and forming ohmic contact with the second cladding layer
223. The epitaxial-layer structure 22 is partially removed to form
a mesa portion.
Please refer to FIG. 5 and FIG. 9, in step 504, a provisional
substrate 92 is separatably attached onto the top surface 225 of
the epitaxial-layer structure 22 with wax. Any removable glue also
can be used instead of wax.
Please refer to FIG. 5 and FIG. 10, in step 505, the epitaxial
substrate 91 is removed to expose the bottom surface of the first
cladding layer 221.
Please refer to FIG. 5 and FIG. 11, in step 506, the second
roughening step is performed to roughen the bottom surface of the
first cladding layer 221 with wet etching to form the roughened
bottom surface 224 of the epitaxial-layer structure 22.
Please refer to FIG. 5 and FIG. 12, in step 507, the substrate 21
is attached to the bottom surface of the epitaxial-layer structure
22 with glue which has a predetermined refractive index and
transparent to the light emitted from the epitaxial-layer structure
22. The glue is cured to become the transparent refractive layer
23. And the cured glue is controlled to have a thickness less than
5 .mu.m rms so as to obtain best optical and thermal performance.
The transparent refractive layer 23 also can be formed by film
deposition on the bottom surface 224 of the first cladding layer of
the epitaxial-layer structure 22. Then, the substrate 21 is
attached to the transparent refractive layer 23. The substrate 21
can include a bottom substrate 211 and a reflective mirror layer
212 on the bottom substrate 211. The substrate 21 can be previously
prepared by using a silicon substrate as the bottom substrate 211
and coating one or more layers of reflective material as the
reflective mirror layer 212 on the silicon substrate.
Please refer to FIG. 5 and FIG. 13, in step 508, the wax 93 is
removed from the epitaxial-layer structure 22 so as to remove the
provisional substrate 92. The residue of wax 93 left on the
epitaxial-layer structure 22 is cleaned to expose the electrode
3.
Please refer to FIG. 5 and FIG. 14, in step 509, the outer surface
of the epitaxial-layer structure 22 of the epitaxial chip 2 is
coated with protective glue 94 except that the electrical
conduction portion 227 is exposed. The epitaxial chip 2 is
upside-down separatably attached onto a supporting substrate 95
with the protective glue 94. The protective glue 94 can be wax for
attaching the epitaxial chip 2 onto the supporting substrate 95,
and also isolating the active layer 222 and the second cladding
layer 223 to facilitate the formation of the electrode base 4.
Please refer to FIG. 5 and FIG. 15, in step 510, a seed layer 41 is
formed on the exposed surfaces of the epitaxial chip 2 (i.e. the
exposed surfaces of the substrate 21, transparent refractive layer
23 and the electrical conduction portion 227 of the first cladding
layer 221 of the epitaxial-layer structure 22). The seed layer 41
can be selected from electrically and thermally conductive material
such as Cu, Ti, Au or Pt. Then, for example, an electroplating
process is performed to form an electrically and thermally
conductive electrode base layer 42 from the seed layer 41. The seed
layer 41 and electrode base layer 42 constitute the electrode base
4.
Please refer to FIG. 5, finally, in step 511, the supporting
substrate 95 and protective glue 94 are removed. The light-emitting
chip device with high thermal conductivity is completed.
Additionally, a transparent electrical conductive layer 223 can be
formed between the electrode 3 and the second cladding layer 223 of
the epitaxial-layer structure 22 to spread current injected from
the electrode 3 more uniformly. The quantum effect of the
epitaxial-layer structure 2 is hence improved.
The light-emitting chip device of the present invention employs the
roughened top surface 225 and roughened bottom surface 224 of the
epitaxial-layer structure 22 to improve the light extraction from
the chip device. The transparent refractive layer 23 with the
predetermined thickness as an interface between the epitaxial-layer
structure 22 and the substrate 21 can more effectively reflect the
light propagating toward the substrate 21 back toward the top
surface 225 to further improve the light extraction.
Furthermore, the U-shaped electrode base 4 largely increases
thermal conductive area of the chip device, and the excess heat of
the epitaxial-layer structure 22 can be rapidly dissipated through
the electrode base 4. The lifetime of the chip device is improved.
The deterioration of the reflective mirror layer 212 is avoided,
and the stability of the chip device is maintained.
The electrode base 4 does not block the light emitting from the
front side of the chip device. Compared to the conventional
light-emitting device as shown in FIG. 1 through FIG. 3, the chip
device of the present invention would have larger light-emitting
area, and hence increasing the utilization of the emitting light.
The brightness of the chip device is enhanced.
The examples given above serve as the preferred embodiments of the
present invention only. The examples should not be construed as a
limitation on the actual applicable scope of the invention, and as
such, all modifications and alterations without departing from the
spirits of the invention and appended claims, including other
embodiments, shall remain within the protected scope and claims of
the invention.
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