U.S. patent application number 10/852151 was filed with the patent office on 2005-04-28 for electrode structure, and semiconductor light-emitting device having the same.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Cho, Jae-Hee, Kim, Hyun-Soo, Yoon, Suk-Ho.
Application Number | 20050087755 10/852151 |
Document ID | / |
Family ID | 34511114 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050087755 |
Kind Code |
A1 |
Kim, Hyun-Soo ; et
al. |
April 28, 2005 |
Electrode structure, and semiconductor light-emitting device having
the same
Abstract
A semiconductor light emitting device including: a transparent
substrate; an electron injection layer which is formed on the
transparent substrate; an active layer which is formed on a first
region of the electron injection layer; a hole injection layer
which is formed on the active layer; a first electrode structure
which is formed on the hole injection layer and concurrently
provides a high reflectivity and a low contact resistance; a second
electrode structure which is formed on a second region of the
electron injection layer; and a circuit substrate which is
electrically connected with the first and second electrode
structures, the first electrode structure includes: a contact metal
structure which has any one selected from the group consisting of
nickel, palladium, platinum and ITO (Indium Tin Oxide) that have
low contact resistance; and a reflective layer which has aluminum
or silver.
Inventors: |
Kim, Hyun-Soo; (Gyeonggi-do,
KR) ; Cho, Jae-Hee; (Gyeonggi-do, KR) ; Yoon,
Suk-Ho; (Seoul, KR) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
Samsung Electronics Co.,
Ltd.
Gyeonggi-do
KR
|
Family ID: |
34511114 |
Appl. No.: |
10/852151 |
Filed: |
May 25, 2004 |
Current U.S.
Class: |
257/98 ;
257/E33.068 |
Current CPC
Class: |
H01L 33/32 20130101;
H01L 2924/01079 20130101; H01L 2224/05669 20130101; H01L 2224/05666
20130101; H01L 33/405 20130101; H01L 2224/05568 20130101; H01L
2224/06102 20130101; H01L 2224/0603 20130101; H01L 2924/01046
20130101; H01L 2924/01078 20130101; H01L 2224/1703 20130101; H01L
2224/05644 20130101; H01L 2224/16 20130101; H01L 2924/12041
20130101; H01L 24/06 20130101; H01L 2224/05624 20130101; H01L 24/05
20130101; H01L 2224/05573 20130101; H01L 33/387 20130101; H01L
2224/05624 20130101; H01L 2924/00014 20130101; H01L 2224/05644
20130101; H01L 2924/00014 20130101; H01L 2224/05666 20130101; H01L
2924/00014 20130101; H01L 2224/05669 20130101; H01L 2924/00014
20130101 |
Class at
Publication: |
257/098 |
International
Class: |
H01L 033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 27, 2003 |
KR |
10-2003-0075220 |
Claims
What is claimed is:
1. A semiconductor light emitting device comprising: a transparent
substrate; an electron injection layer formed on the transparent
substrate; an active layer formed on a first region of the electron
injection layer; a hole injection layer formed on the active layer;
a first electrode structure which is formed on the hole injection
layer and concurrently providing a high reflectivity and a low
contact resistance; a second electrode structure formed on a second
region of the electron injection layer; and a circuit substrate
electrically connected with the first and second electrode
structures.
2. The light emitting device of claim 1, wherein the first
electrode structure comprises: a contact metal structure which has
any one selected from the group consisting of nickel, palladium,
platinum and ITO (Indium Tin Oxide) that have low contact
resistance; and a reflective layer formed on the contact metal
structure.
3. The light emitting device of claim 2, wherein the contact metal
structure is island-shaped.
4. The light emitting device of claim 2, wherein the contact metal
structure is mesh-shaped.
5. The light emitting device of claim 3, wherein an area ratio of
the contact metal structure to the reflective layer is from 1% to
90%.
6. The light emitting device of claim 5, wherein the thickness of
the contact metal structure is less than 200 nm.
7. The light emitting device of claim 4, wherein an area ratio of
the contact metal structure to the reflective layer is from 1% to
90%.
8. The light emitting device of claim 7, wherein the thickness of
the contact metal structure is less than 200 nm.
9. The light emitting device of claim 2, wherein the reflective
layer is formed of aluminum (Al) or silver (Ag) that has a high
reflectivity.
10. The light emitting device of claim 1, wherein the transparent
substrate is formed of sapphire.
11. The light emitting device of claim 1, wherein the hole
injection layer is formed of P-type GaN.
12. An electrode structure used in a semiconductor light emitting
device having an active layer and a hole injection layer formed on
one surface of the active layer, the structure comprising: a
contact metal structure which is formed on one surface of the hole
injection layer to face with the active layer, and has any one
selected from the group consisting of nickel, palladium, platinum
and ITO that have low contact resistance; and a reflective layer
formed on the contact metal structure.
13. The electrode structure of claim 12, wherein the contact metal
structure is island-shaped.
14. The electrode structure of claim 12, wherein the contact metal
structure is mesh-shaped.
15. The electrode structure of claim 13, wherein an area ratio of
the contact metal structure to the reflective layer is from 1% to
90%.
16. The electrode structure of claim 15, wherein the thickness of
the contact metal structure is less than 200 nm.
17. The electrode structure of claim 14, wherein an area ratio of
the contact metal structure to the reflective layer is from 1% to
90%.
18. The electrode structure of claim 17, wherein the thickness of
the contact metal structure is less than 200 nm.
19. The electrode structure of claim 12, wherein the reflective
layer is formed of aluminum (Al) or silver (Ag) that has a high
reflectivity.
20. The electrode structure of claim 12, wherein the hole injection
layer is formed of P-type GaN
Description
BACKGROUND OF THE INVENTION
[0001] This application claims the priority of Korean Patent
Application No. 2003-75220, filed on Oct. 27, 2003, in the Korean
Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
[0002] 1. Field of the Invention
[0003] The present invention relates to a semiconductor
light-emitting device using a nitride semiconductor or a like
material, and more particularly, to a high reflective electrode
structure concurrently satisfying a low contact resistance and a
high reflectivity, and a flip-chip light emitting device having the
same.
[0004] 2. Description of the Related Art
[0005] A nitride-based compound semiconductor, which is generally
used for a visible light emitting device, is being currently
advanced to an ultraviolet light region for a white light emitting
device going through a visible light region of blue and green. The
nitride-based compound semiconductor is mainly classified into a
structure of extracting an upward light from light emitting from
the active layer, and a structure of extracting a downward light
passing through a transparent substrate such as a sapphire
substrate.
[0006] In a flip-chip light emitting device having the structure of
extracting light through the transparent substrate, reflectivity at
an interface of a P-type electrode is of importance to again
reflect the upward light to direct downward.
[0007] In the meantime, it is advantageous that a light emitting
device has a low operation voltage. At present, the most general
method for lowering an operation voltage of the light emitting
device decreases resistance of a material layer formed between an
electrode layer and an active layer. Especially, since a hole
injection layer and a P-type electrode are Ohmic contacted each
other in the flip-chip light emitting device, it is very desirable
that the hole injection layer and the P-type electrode have low
Ohmic contact resistance formed therebetween so as to reduce the
operation voltage.
[0008] FIG. 1 is a schematic sectional view illustrating a
conventional nitride semiconductor light-emitting device.
[0009] As illustrated in FIG. 1, the conventional flip-chip nitride
semiconductor light emitting device 10 includes a sapphire
substrate 11; an N-type GaN layer 12 sequentially formed on the
sapphire substrate 11; an active layer 16 formed of InGaN; a P-type
GaN layer 18; a nickel layer 20; a P-type reflective electrode 22;
and an N-type electrode 14 formed on one side surface of the N-type
GaN layer 12. The light emitting device 10 has a dual hetero
structure where the N-type GaN layer 12 functions as a cladding
layer for a first conductive type, and the P-type GaN layer 18
functions as a cladding layer for a second conductive type.
[0010] Further, the nickel layer 20 is formed on the P-type GaN
layer 18 to have a thickness of below about 10 nm, and functions as
a contact metal layer for forming the Ohmic contact. Since the
P-type reflective electrode 22 is formed of aluminum (Al) or silver
(Ag), light transmitting the nickel layer 20 that is the contact
metal is reflected at an interface between the P-type reflective
electrode 22 and the nickel layer 20.
[0011] The conventional light emitting device 10 can directly
extract light from the P-type reflective electrode that is formed
of material such as aluminum (Al) or silver (Ag) with a high
reflectivity, and can obtain a high efficiency of light extraction.
However, the conventional light emitting device has a disadvantage
in which contact resistance is increased when the P-type reflective
electrode 22 with the high reflectivity is directly employed.
Accordingly, the nickel layer 20 is formed as the contact metal for
forming the Ohmic contact, thereby reducing the contact
resistance.
[0012] However, in the flip-chip nitride semiconductor light
emitting device 10 having the nickel layer 20 as the contact metal,
since light emitting from the active layer 16 formed of InGaN
passes through the nickel layer 20, and then is reflected at the
interface of the nickel layer 20 and the P-type reflective
electrode 22, and then again passes through the nickel layer 20 and
the sapphire substrate 11 for emission, a large amount of light is
absorbed by the nickel layer 20. Therefore, the conventional
flip-chip nitride semiconductor light emitting device 10 has a
drawback in that it is very difficult to increase the
reflectivity.
[0013] In other words, since the nickel layer 20, which is the
contact metal, is used to be in reliable contact with the P-type
GaN layer 18, the thicker nickel layer 20 can provide a better
contact with the P-type GaN layer 18. However, if the nickel layer
20 has a thickness of above 10 nm, it is difficult to have enough
reflectivity.
[0014] Accordingly, the semiconductor light emitting device is
required to have a reflection structure for maintaining the high
reflectivity while maintaining the low contact resistance.
SUMMARY OF THE INVENTION
[0015] The present invention provides a semiconductor
light-emitting device having a P-type electrode structure
concurrently satisfying a low contact resistance and a high
reflectivity.
[0016] Further, the present invention provides an electrode
structure concurrently satisfying a low contact resistance and a
high reflectivity in a semiconductor light-emitting device.
[0017] According to an aspect of the present invention, there is
provided a semiconductor light emitting device including: a
transparent substrate; an electron injection layer which is formed
on the transparent substrate; an active layer which is formed on a
first region of the electron injection layer; a hole injection
layer which is formed on the active layer; a first electrode
structure which is formed on the hole injection layer and
concurrently provides a high reflectivity and a low contact
resistance; a second electrode structure which is formed on a
second region of the electron injection layer; and a circuit
substrate which is electrically connected with the first and second
electrode structures, wherein the first electrode structure
includes: a contact metal structure which has any one selected from
the group consisting of nickel, palladium, platinum and ITO (Indium
Tin Oxide) that have low contact resistance; and a reflective layer
which has aluminum or silver.
[0018] According to another aspect of the present invention, there
is provided an electrode structure including: a transparent
substrate; an electron injection layer which is formed on the
transparent substrate; a contact metal structure which has any one
selected from the group consisting of nickel, palladium, platinum
and ITO that have low contact resistance to be used in a
semiconductor light emitting device having an active layer and a
hole injection layer; and a reflective layer having the high
reflectivity such as aluminum or silver.
[0019] Here, the contact metal structure may be island-type or
mesh-type.
[0020] An area ratio of the contact metal structure to the
reflective layer may be from 1% to 90%, and the thickness of the
contact metal structure is less than 200 nm.
[0021] Further, the reflective layer may be formed of aluminum (Al)
or silver (Ag) that has the high reflectivity.
[0022] Furthermore, the transparent substrate may be formed of
sapphire or silicon carbide.
[0023] Also, the electron injection layer may be formed of N-type
GaN, the active layer may be formed of InGaN, and the hole
injection layer may be formed of P-type GaN.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above and other features and advantages of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
[0025] FIG. 1 is a schematic sectional view illustrating a
conventional nitride semiconductor light-emitting device;
[0026] FIG. 2 is a sectional view illustrating a semiconductor
light-emitting device according to a preferred embodiment of the
present invention;
[0027] FIGS. 3A and 3B are sectional views illustrating an
electrode structure used in a semiconductor light-emitting device
of FIG. 2 according to a preferred embodiment of the present
invention;
[0028] FIGS. 4A through 4F are plane views illustrating electrode
structures depending on varied area ratios of a palladium layer to
a silver layer according to the present invention; and
[0029] FIGS. 5A and 5B are graphs illustrating the correlation of
light emission and respective meshed regions shown in FIGS. 4A
through 4F, and the correlation of operation voltage and the
respective meshed regions in a semiconductor light-emitting
device.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The present invention will now be described more fully with
reference to the accompanying drawings, in which exemplary
embodiments of the invention are shown. The invention may, however,
be embodied in many different forms and should not be construed as
being limited to the embodiments set forth herein; rather, these
embodiments are provided so that this disclosure will be thorough
and complete, and will fully convey the concept of the invention to
those skilled in the art. In the drawings, the thicknesses of
layers and regions are exaggerated for clarity. It will also be
understood that when a layer is referred to as being "on" another
layer or substrate, it can be directly on the other layer or
substrate, or intervening layers may also be present.
[0031] FIG. 2 is a sectional view illustrating a semiconductor
light-emitting device according to a preferred embodiment of the
present invention.
[0032] As shown in FIG. 2, the semiconductor light-emitting device
100 includes a transparent substrate 102 formed of transparent
material such as sapphire (Al.sub.2O.sub.3) or silicon carbide
(SiC); an electron injection layer 104 formed of an N-type GaN on
the transparent substrate 102; an active layer 106 formed of InGaN;
and a hole injection layer 108 formed of a P-type GaN. The electron
injection layer 104 includes a first portion and a second portion,
and step-shaped with the first portion thinner than the second
portion. The active region 106 and the hole injection layer 108 are
formed on the second portion.
[0033] Further, the semiconductor light-emitting device 100 further
includes a P-type electrode structure 110 also functioning as a
reflective layer formed on the hole injection layer 108 according
to a preferred embodiment of the present invention, the P-type
electrode structure 110 may include a contact metal structure
functioning as a contact metal forming Ohmic contact to reduce
contact resistance; and a reflective layer formed of metal such as
silver (Ag) or aluminum (Al) with the high reflectivity.
[0034] FIGS. 3A and 3B are sectional views illustrating an
electrode structure used in the semiconductor light-emitting device
of FIG. 2 according to a preferred embodiment of the present
invention.
[0035] Referring first to FIG. 3A, the P-type electrode structure
110 according to a first embodiment of the present invention is
formed on the hole injection layer 108, and includes a contact
metal structure 110A that functions as the contact metal forming
the Ohmic contact to reduce the contact resistance; and a
reflective layer 110B. Additionally, the contact metal structure
110A may be formed of any one selected from the group consisting of
nickel (Ni), palladium (Pd), platinum (Pt) or indium tin oxide
(ITO) that have a low contact resistance. The reflective layer 110B
may be formed of metal having the high reflectivity such as
aluminum (Al) or silver (Ag).
[0036] Further, the P-type electrode structure 110 according to a
preferred embodiment of the present invention performs a function
of uniformly distributing current, which is applied from a circuit
board assembled later on, in the hole injection layer 108, as well
as a function of contact.
[0037] In the meantime, in the active layer 106, electrons injected
from the electron injection layer 104 are combined with holes
injected from the hole injection layer 108. The combined electrons
and holes fall to a low energy band to cause light emission. At
this time, the emitting light is reflected at an interface between
the reflective layer 110B and the contact metal structure 110A of
the P-type electrode structure 110 and at an interface between the
reflective layer 110B and the hole injection layer 108. The
reflected light sequentially goes through the hole injection layer
108, the active layer 106, the electron injection layer 104 and the
transparent substrate 102 while emitting in the direction of an
arrow of FIG. 2.
[0038] The contact metal structure 110A is island-shaped, and the
reflective layer 110B covers the resultants including the hole
injection layer 108 and the contact metal structure 110A. Though
the contact metal structure 110A is rectangular island-shaped, but
can have other shapes such as a semispherical shape or a
regular-tetrahedron within a scope or spirit of the present
invention.
[0039] Referring to FIG. 3B, a P-type electrode structure 210
according to a second embodiment of the present invention is formed
on the hole injection layer 208, and includes a contact metal
structure 210A that function as the contact metal forming the Ohmic
contact to reduce the contact resistance; and a reflective layer
210B. The reflective layer 210B may be formed of metal having the
high reflectivity such as aluminum (Al) or silver (Ag).
[0040] The contact metal structure 210A is mesh-shaped, and the
reflective layer 210B covers the resultants including the hole
injection layer 208 and the contact metal structure 210A. Though
the mesh-shaped contact metal structure 210A has a square bar
shape, but can have other shapes such as a cylindrical shape or a
rectangular shape within a scope or spirit of the present
invention.
[0041] Referring again to FIG. 2, an N-type electrode 112 is formed
on the thinner first portion of the electron injection layer 104.
The N-type electrode 112 can be also formed to have an electrode
structure such as Ti/Al/Pt/Au in which metals are deposited. As
described above, after semiconductor light-emitting parts are
mounted on the transparent substrate 102, the resultant transparent
substrate 102 is aligned on a sub-mount 118 having an Au layer 116
and a solder ball 114 formed on the Au layer 116. The Au layer 116
is wire-shaped such as a lead frame.
[0042] Next, flip-chip bonding is performed to assemble the
sub-mount 118 with the transparent substrate 102 mounting the
semiconductor light-emitting parts thereon, so that the
semiconductor light-emitting device 100 is completed. Though not
illustrated in detail in the drawings, but a process of forming a
bonding metal for bonding the P-type electrode structure 110 and
the N-type electrode 112 with the sub-mount 118 can be additionally
performed.
[0043] FIGS. 4A through 4F are plane views illustrating the
electrode structures depending on varied area ratios of the
palladium (Pd) layer to the silver (Ag) layer according to the
present invention.
[0044] FIGS. 4A through 4F illustrate a contact metal layer formed
of palladium (Pd) that is formed on the hole injection layer to
have a thickness of about 3 nm. This represents experimental
results of the electrode structures where the area ratios of the Pd
layer to the Ag layer are varied going from FIG. 4A to FIG. 4F so
as to describe the effect of the present invention.
[0045] Describing in detail, in FIG. 4A, all portions denoted by
402 are formed as the Pd layer that is a standard type with a
thickness of about 25-35 .ANG.. In FIGS. 4B through 4E, regions
(mesh_1 to mesh_4) 402 respectively correspond to the Pd layer.
Each area ratio of the Pd layer to the Ag layer of the regions is
1.25, 0.78, 0.56 and 0.44, respectively. Here, a reference numeral
400 denotes the reflective layer formed of Ag, and a reference
numeral 402 denotes the contact metal layer formed of Pd. In FIG.
4F, only the Ag layer is formed without the Pd layer.
[0046] FIGS. 5A and 5B are graphs illustrating the correlation of
light emission with respective meshed regions shown in FIGS. 4A
through 4F and the correlation of operation voltage with respective
meshed regions in a semiconductor light-emitting device.
[0047] FIG. 5A illustrates the correlation of the light emission of
the light emitting device in the standard electrode structure, the
mesh_1 to mesh_4 electrode structure and the electrode structure
with only the Ag layer that are shown in FIGS. 4A through 4F.
[0048] As shown in the drawing, it can be appreciated that
luminance is lowest in the standard electrode structure with the Pd
layer being entirely formed as the contact metal layer and then,
the Al layer being entirely formed on the Pd layer. As described
above, this phenomenon occurs because light emitting from the
active layer is reflected at an interface between the Pd layer and
the P-type electrode structure such that the reflected light emits
toward the transparent substrate, thereby being much absorbed into
the Pd layer.
[0049] According to a preferred embodiment of the present
invention, when the electrode structure employs the combination of
the Pd layer and the Ag layer, luminance is improved by above 10%.
Further, as the area ratio of the Ag layer to the Pd layer is
decreased, the luminance is gradually increased. In the meantime,
the standard electrode structure has the lowest luminance, and the
electrode structure with only the Ag layer has the highest
luminance.
[0050] FIG. 5B illustrates the correlation of the operation voltage
of the light emitting device in the standard electrode structure,
the mesh_1 to mesh_4 electrode structure and the electrode
structure with only the Ag layer that are respectively shown in
FIGS. 4A through 4F.
[0051] As shown in FIG. 5A, the electrode structure having only the
Ag layer without the Pd layer has the highest luminance in the
light emitting device, but has the operation voltage exceeding
4.99V as shown in FIG. 5B. Accordingly, the electrode structure has
the operation voltage greatly exceeding 3.80V that can be applied
to an actual device. This is because the contact resistance is
increased in the electrode structure with only the Ag layer.
[0052] However, when the electrode structure employs the
combination of the Pd layer and the Ag layer according to a
preferred embodiment of the present invention, the electrode
structure has the operation voltage that is not so large in
comparison with the conventional electrode structure while
providing the high reflectivity such that the light emission of the
light emitting device can be maintained. Further, the present
invention controls the area of the Pd layer to control the
operation voltage and the reflectivity of the P-type electrode
structure, thereby optimizing light efficiency of the light
emitting device.
[0053] As described above, the present invention has an effect in
that light absorption made by the contact metal layer can be
reduced while light efficiency of the semiconductor light emitting
device can be improved, by controlling the area of the contact
metal layer that is in contact with the hole injection layer formed
of the P-type semiconductor.
[0054] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims.
* * * * *