U.S. patent application number 12/701853 was filed with the patent office on 2010-06-03 for nitride-based white light emitting device and manufacturing method thereof.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to June O. SONG.
Application Number | 20100136721 12/701853 |
Document ID | / |
Family ID | 37271546 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100136721 |
Kind Code |
A1 |
SONG; June O. |
June 3, 2010 |
NITRIDE-BASED WHITE LIGHT EMITTING DEVICE AND MANUFACTURING METHOD
THEREOF
Abstract
A light emitting device includes an n-type cladding layer. a
p-type cladding layer. an active layer interposed between the
n-type cladding layer and the p-type cladding layer and an ohmic
contact layer contacting the p-type cladding layer or the n-type
cladding layer. The ohmic contact layer includes a first film that
includes a transparent conductive zinc oxide doped with a rare
earth metal and including a one-dimensional nano structure. The
one-dimensional nano structure is one of a nano-column, a nano rod
and a nano wire.
Inventors: |
SONG; June O.; (Yongin-si,
KR) |
Correspondence
Address: |
CANTOR COLBURN, LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
37271546 |
Appl. No.: |
12/701853 |
Filed: |
February 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11503291 |
Aug 11, 2006 |
7687820 |
|
|
12701853 |
|
|
|
|
Current U.S.
Class: |
438/22 ;
257/E21.159; 257/E33.064 |
Current CPC
Class: |
H01L 33/32 20130101;
H01L 33/08 20130101; H01L 33/42 20130101; H01L 33/40 20130101 |
Class at
Publication: |
438/22 ;
257/E21.159; 257/E33.064 |
International
Class: |
H01L 21/283 20060101
H01L021/283 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 14, 2005 |
KR |
10-2005-0074593 |
Claims
1. A method of manufacturing a white light emitting device, the
method comprising: forming an n-type cladding layer, an active
layer, and a p-type cladding layer on a substrate, the active layer
being interposed between the n-type cladding layer and the p-type
cladding layer; forming a transparent conductive zinc oxide film of
an ohmic contact layer, the zinc oxide film being doped with at
least one rare earth metal and including a nano structure; and heat
treating the zinc oxide film.
2. The method of claim 1, wherein the rare earth metal comprises
one of Er, Sm, Ce, Pr, Pm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, Lu, Th, Pa,
U, Np, Pu, Am, Bk, Cf, Es, Fm, Md, No, Lr, and Cm.
3. The method of claim 2, wherein an amount of the rare earth metal
is equal to or smaller than about 20 weight %.
4. The method of claim 1, wherein the formation of the zinc oxide
film comprising: depositing a two-dimensional thin film of zinc
oxide; and etching and re-growing the two-dimensional thin film
under an atmosphere including a hydrogen gas.
5. The method of claim 1, wherein the zinc oxide film comprises one
of aluminum (Al), chromium (Cr), silicon (Si), germanium (Ge),
indium (In), lithium (Li), gallium (Ga), magnesium (Mg), zinc (Zn),
beryllium (Be), molybdenum (Mo), vanadium (V), copper (Cu), iridium
(Ir), rhodium (Rh), ruthenium (Ru), tungsten (W), cobalt (Co),
nickel (Ni), manganese (Mn), titanium (Ti), tantalum (Ta), cadmium
(Cd), lanthanum (La), and oxides thereof.
6. The method of claim 2, further comprising: forming an ohmic
interlayer under the zinc oxide film, wherein the ohmic interlayer
comprises one of metals including Ni, Pd, Pt, Rh, Zn, In, Sn, Ag,
Au, Cd, Mg, Be, Mo, V, Cu, Ti, Ir, Ru, W, Co, Mn, and La,
transparent conductive oxides including ITO, SnO.sub.2, ZnO,
In.sub.2O.sub.3, Ga.sub.2O.sub.3, RhO.sub.2, NiO, CoO, PdO, PtO,
CuAlO.sub.2, CdO, and CuGaO.sub.2, and transparent conductive
nitrides including TiN, TaN, and SiNx.
7. The method of claim 6, further comprising: performing a heat
treatment after the formation of the ohmic interlayer and before
the formation of the zinc oxide film.
8. The method of claim 7, wherein the heat treatment before the
formation of the zinc oxide film is performed at a temperature
equal to or lower than about 800.degree. C. and under a vacuum or
under an atmosphere of oxygen (O.sub.2), nitrogen (N.sub.2), argon
(Ar), hydrogen (H.sub.2), or air.
Description
[0001] This Application claims priority to Korean patent
application number 10-2005-0074593, filed on Aug. 14, 2005 and all
the benefits accruing therefrom under 35 U.S.C. .sctn.119, and the
contents of which in its entirety are herein incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to a white light emitting
device and a manufacturing method thereof, and, in particular, to a
top-emission nitride-based white light emitting device and a
manufacturing method thereof.
[0004] (b) Description of the Related Art
[0005] Generally, a top-emission nitride-based light emitting
device includes a p-type nitride-based cladding layer, an n-type
nitride-based cladding layer, and a nitride-based active layer
interposed therebetween. In the nitride-based light emitting
device, light generated in the active layer passes through the
n-type or p-type cladding layer and is emitted.
[0006] The p-type nitride-based cladding layer has a low hole
concentration to have high sheet resistance. In order to compensate
for the high sheet resistance, a thin ohmic contact layer including
a nickel (Ni) thin film and a gold (Au) thin film is suggested to
be employed.
[0007] However, when the light passes through the p-type cladding
layer, the light emitting device has low emission efficiency due to
the poor transmittance of the Ni--Au thin films and is thermally
unstable due to the small thickness of the Ni--Au thin films.
[0008] Therefore, transparent conductive oxides such as indium-tin
oxide (ITO) and zinc oxide (ZnO) are introduced as the material of
the ohmic contact layer.
[0009] However, ITO or ZnO forms a schottky contact at an interface
to cause great voltage drop and has large sheet resistance such
that the operating voltage of the light emitting device is
increased.
[0010] In the meantime, a structure for emitting light through the
n-type nitride-based cladding layer is suggested. The structure
includes a reflective p-type ohmic contact layer under the active
layer and an n-type ohmic contact layer along with an electrode pad
having a small contact area on the active layer so that the
emission efficiency may be increased and heat generated during the
operation of the light emitting device may be easily dissipated.
However, the surface of the n-type nitride-based cladding layer in
the above-described light emitting device may be apt to be oxidized
due to the heat generated during the operation of the light
emitting device, thereby degrading the reliability of the light
emitting device. Accordingly, transparent conductive materials that
are hardly oxidized are introduced as the material of the ohmic
contact layer for the n-type nitride-based cladding layer.
[0011] Examples of transparent conductive materials include
transparent conductive oxides such as ITO, In.sub.2O.sub.3,
SnO.sub.2, and ZnO and transparent conductive nitrides such as
titanium nitride (TiN).
[0012] However, when the above-described transparent conductive
oxides and nitrides are deposited by processes including chemical
vapor deposition ("CVD") and physical vapor deposition such as
sputtering, electron beam deposition and thermal deposition,
deposited thin films have large sheet resistance. In addition, the
transparent conductive oxides and nitrides have workfunction that
is small and difficult to be adjusted, thereby forming high contact
barrier and resistance.
[0013] Moreover, the transparent conductive thin films have high
reflectance and absorbance for the light generated in the active
layer and have refractive indices higher than air and
two-dimensional flat interfaces, thereby further decreasing the
emission efficiency of the light emitting device.
[0014] In the meantime, a nitride-based light emitting device
emitting white light may include a light emitting member emitting
ultraviolet light, near ultraviolet light, blue light, or green
light and a phosphor, or may include a plurality of laminated light
emitting members. However, the phosphor may cause environmental
pollution and heat generation and may absorb significant amount of
light to decrease the efficiency of the light emitting device. In
addition, the lamination of light emitting members for
manufacturing a light emitting device having high efficiency may be
difficult.
BRIEF SUMMARY OF THE INVENTION
[0015] An exemplary embodiment of a white light emitting device
according the present invention includes an n-type cladding layer,
a p-type cladding layer, an active layer interposed between the
n-type cladding layer and the p-type cladding layer and an ohmic
contact layer contacting the p-type cladding layer or the n-type
cladding layer. The ohmic contact layer includes a first film that
includes a transparent conductive zinc oxide doped with a rare
earth metal and having a one-dimensional nano structure. The
one-dimensional nano structure is one of a nano-column, a nano rod,
and a nano wire.
[0016] In an exemplary embodiment, the one rare earth metal may
include Er, Sm, Ce, Pr, Pm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, Lu, Th, Pa,
U, Np, Pu, Am, Bk, Cf, Es, Fm, Md, No, Lr, and CmAn amount of the
rare earth metal may be equal to or smaller than about 20 weight
%.
[0017] In an exemplary embodiment, the n-type cladding layer, the
p-type cladding layer, and the active layer may include nitrogen.
The n-type cladding layer, the p-type cladding layer, and the
active layer may include a group III nitride-based compound such as
a compound having Al.sub.xIn.sub.yGa.sub.zN, where x, y and z are
integers.
[0018] In an exemplary embodiment, the first film further may
include an additional ingredient including one of aluminum (Al),
chromium (Cr), silicon (Si), germanium (Ge), indium (In), lithium
(Li), gallium (Ga), magnesium (Mg), zinc (Zn), beryllium (Be),
molybdenum (Mo), vanadium (V), copper (Cu), iridium (Ir), rhodium
(Rh), ruthenium (Ru), tungsten (W), cobalt (Co), nickel (Ni),
manganese (Mn), titanium (Ti), tantalum (Ta), cadmium (Cd),
lanthanum (La), and oxides thereof. An amount of the additional
ingredient may be from about 0.1 weight % to about 49 weight %.
[0019] In an exemplary embodiment, the first film may have a
thickness equal to or greater than about five nanometers.
[0020] In an exemplary embodiment, the ohmic contact layer may
further include a second film disposed between the first film and
the p-type cladding layer or the n-type cladding layer. The second
film may include a metal including Ni, Pd, Pt, Rh, Zn, In, Sn, Zn,
Ag, and Au, transparent conductive oxides including ITO, SnO.sub.2,
ZnO, In.sub.2O.sub.3, Ga.sub.2O.sub.3, RhO.sub.2, NiO, CoO, PdO,
PtO, CuAlO.sub.2, CdO, and CuGaO.sub.2, and transparent conductive
nitrides including TiN, TaN, and SiNx.
[0021] In an exemplary embodiment, the white light emitting device
may further include a first electrode pad contacting the ohmic
contact layer and a second electrode pad electrically connected to
the p-type cladding layer or the n-type cladding layer and
disconnected from the first electrode pad.
[0022] In an exemplary embodiment, the white light emitting device
may further include a substrate, a bonding layer disposed on the
substrate, a reflective layer disposed on the bonding layer and
disposed under the p-type cladding layer or the n-type cladding
layer and an electrode pad contacting the ohmic contact layer.
[0023] An exemplary embodiment of a method of manufacturing a white
light emitting device includes forming an n-type cladding layer, an
active layer, and a p-type cladding layer on a substrate, forming a
transparent conductive zinc oxide film of an ohmic contact layer,
the zinc oxide film doped with a rare earth metal and having a nano
structure and heat treating the zinc oxide film.
[0024] In an exemplary embodiment, the rare earth metal may include
one of Er, Sm, Ce, Pr, Pm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, Lu, Th, Pa,
U, Np, Pu, Am, Bk, Cf, Es, Fm, Md, No, Lr, and Cm. An amount of the
rare earth metal may be equal to or smaller than about 20 weight
%.
[0025] In an exemplary embodiment, the formation of the zinc oxide
film may include depositing a two-dimensional thin film of zinc
oxide, and etching and re-growing the two-dimensional thin film
under an atmosphere including a hydrogen gas.
[0026] In an exemplary embodiment, the zinc oxide film may include
one of aluminum
[0027] (Al), chromium (Cr), silicon (Si), germanium (Ge), indium
(In), lithium (Li), gallium (Ga), magnesium (Mg), zinc (Zn),
beryllium (Be), molybdenum (Mo), vanadium (V), copper (Cu), iridium
(Ir), rhodium (Rh), ruthenium (Ru), tungsten (W), cobalt (Co),
nickel (Ni), manganese (Mn), titanium (Ti), tantalum (Ta), cadmium
(Cd), lanthanum (La), and oxides thereof.
[0028] In an exemplary embodiment, the method may further include
forming an ohmic interlayer under the zinc oxide film. The ohmic
interlayer may include a metal including Ni, Pd, Pt, Rh, Zn, In,
Sn, Ag, Au, Cd, Mg, Be, Mo, V, Cu, Ti, Ir, Ru, W, Co, Mn, and La,
transparent conductive oxides including ITO, SnO.sub.2, ZnO,
In.sub.2O.sub.3, Ga.sub.2O.sub.3, RhO.sub.2, NiO, CoO, PdO, PtO,
CuAlO.sub.2, CdO, and CuGaO.sub.2, and transparent conductive
nitrides including TiN, TaN, and SiNx.
[0029] In an exemplary embodiment, the method may further include
performing heat treatment after the formation of the ohmic
interlayer and before the formation of the zinc oxide film. The
heat treatment before the formation of the zinc oxide film may be
performed at a temperature equal to or lower than about 800.degree.
C. and under a vacuum or under an atmosphere of oxygen (O.sub.2),
nitrogen (N.sub.2), argon (Ar), hydrogen (H.sub.2), or air.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a sectional view of an exemplary embodiment of a
top-emission nitride-based white light emitting device having a
mesa structure according to the present invention.
[0031] FIG. 2 is a sectional view of an exemplary embodiment of a
top-emission nitride-based white light emitting device having a
vertical structure according to the present invention.
[0032] FIG. 3 is a sectional view of another exemplary embodiment
of a top-emission nitride-based white light emitting device having
a vertical structure according to the present invention.
[0033] FIG. 4 is a sectional view of another exemplary embodiment
of a top-emission nitride-based white light emitting device having
a vertical structure according to the present invention.
[0034] FIG. 5A, FIG. 5B, and FIG. 5C show exemplary embodiments of
shapes of grown zinc oxides (ZnO) having one-dimensional nano
structure for forming the ohmic contact layer shown in FIG. 1 to
FIG. 4.
[0035] FIG. 6A, FIG. 6B, FIG. 6C, and FIG. 6D show exemplary
embodiments of various shapes made by etching zinc oxides (ZnO)
doped with a rare earth metal to have one-dimensional nano
structure for forming the ohmic contact layer shown in FIG. 1 to
FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0036] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. The present
invention may, however, be embodied in many different forms and
should not be construed as limited to the embodiments set forth
herein. In the drawings, the thickness of layers, films, panels,
regions, etc. are exaggerated for clarity. Like numerals refer to
like elements throughout. It will be understood that when an
element such as a layer, film, region or substrate is referred to
as being "on" another element, it can be directly on the other
element or intervening elements may also be present. In contrast,
when an element is referred to as being "directly on" another
element, there are no intervening elements present. As used herein,
the term "and/or" includes any and all combinations of one or more
of the associated listed items.
[0037] It will be understood that, although the terms first,
second, third, etc., may be used herein to describe various
elements, components, regions, layers and/or sections, these
elements, components, regions, layers and/or sections should not be
limited by these terms. These terms are only used to distinguish
one element, component, region, layer or section from another
region, layer or section. Thus, a first element, component, region,
layer or section discussed below could be termed a second element,
component, region, layer or section without departing from the
teachings of the present invention.
[0038] Spatially relative terms, such as "lower," "upper" and the
like, may be used herein for ease of description to describe the
relationship of one element or feature to another element(s) or
feature(s) as illustrated in the figures. It will be understood
that the spatially relative terms are intended to encompass
different orientations of the device in use or operation, in
addition to the orientation depicted in the figures. For example,
if the device in the figures is turned over, elements described as
"lower" relative to other elements or features would then be
oriented "upper" the other elements or features. Thus, the
exemplary term "lower" can encompass both an orientation of above
and below. The device may be otherwise oriented (rotated 90 degrees
or at other orientations) and the spatially relative descriptors
used herein interpreted accordingly.
[0039] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof.
[0040] Embodiments of the invention are described herein with
reference to cross-section illustrations that are schematic
illustrations of idealized embodiments (and intermediate
structures) of the invention. As such, variations from the shapes
of the illustrations as a result, for example, of manufacturing
techniques and/or tolerances, are to be expected. Thus, embodiments
of the invention should not be construed as limited to the
particular shapes of regions illustrated herein but are to include
deviations in shapes that result, for example, from
manufacturing.
[0041] For example, an implanted region illustrated as a rectangle
will, typically, have rounded or curved features and/or a gradient
of implant concentration at its edges rather than a binary change
from implanted to non-implanted region. Likewise, a buried region
formed by implantation may result in some implantation in the
region between the buried region and the surface through which the
implantation takes place. Thus, the regions illustrated in the
figures are schematic in nature and their shapes are not intended
to illustrate the actual shape of a region of a device and are not
intended to limit the scope of the invention.
[0042] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0043] Hereinafter, the present invention will be described in
detail with reference to the accompanying drawings.
[0044] Now, exemplary embodiments of white light emitting devices
according to the present invention are described in detail with
reference to FIG. 1, FIG. 2, FIG. 3 and FIG. 4.
[0045] FIG. 1 is a sectional view of an exemplary embodiment of a
top-emission nitride-based white light emitting device having a
mesa structure according to the present invention.
[0046] Referring to FIG. 1, a nitride-based buffer layer 120, an
n-type nitride-based cladding layer 130, a nitride-based active
layer 140, a p-type nitride-based cladding layer 150, and an ohmic
contact layer 160 are sequentially formed on a substrate 110. A
p-type electrode pad 170 is formed at a side of the ohmic contact
layer 160. An n-type electrode pad 180 is formed on a side on the
n-type cladding layer 130 and is disconnected from the p-type
electrode pad 170.
[0047] In an exemplary embodiment, the substrate 110 may be made of
an insulating material such as sapphire (Al.sub.2O.sub.3), and the
nitride-based buffer layer 120 may be omitted.
[0048] In exemplary embodiments, each layer from the buffer layer
120 to the p-type cladding layer 150 includes a group III
nitride-based compound, e.g., a compound having
Al.sub.xIn.sub.yGa.sub.zN (where x, y and z are integers). In one
exemplary embodiment, the n-type cladding layer 130 may further
include an n-type dopant as well as the group III nitride-based
compound and the p-type cladding layer 150 may further include a
p-type dopant as well as the group III nitride-based compound. The
active layer 140 generates light and may be single crystalline. The
active layer 140 may have a single-layer structure or a
multi-quantum well ("MQW") structure.
[0049] In one exemplary embodiment, when employing a gallium
nitride (GaN) compound, the nitride-based buffer layer 120 may be
made of GaN, and the n-type cladding layer 130 may be made of GaN
doped with n-type dopant such as Si, Ge, Se or Te. The active layer
140 may have a MQW structure of InGaN and GaN or a MQW structure of
AlGaN and GaN The p-type cladding layer 150 may be made of GaN
doped with p-type dopant such as Mg, Zn, Ca, Sr or Ba.
[0050] Referring to FIG. 1, the n-type cladding layer 130 includes
a thick portion and a thin portion taken in a direction
perpendicular to the substrate 100. The active layer 140, the
p-type cladding layer 150 and the ohmic contact layer 160 are
disposed on the thick portion of the n-type cladding layer 130, and
the n-type electrode pad 180 on the thin portion thereof. This
structure can be obtained by sequentially depositing the n-type
cladding layer 130, the active layer 140, the p-type cladding layer
150 and the ohmic contact layer 160 and then removing a portion of
these layers, such as by etching them.
[0051] In an exemplary embodiment, an n-type ohmic contact layer
(not shown) may be interposed between the n-type cladding layer
130, such as on the thin portion of the n-type cladding layer 130,
and the n-type electrode pad 180. In one exemplary embodiment, the
n-type ohmic contact layer may have various structures, e.g. a
sequentially deposited structure of a titanium thin film and an
aluminum thin film.
[0052] In an exemplary embodiment, the p-type electrode pad 170 may
have a sequentially deposited structure of a Ni thin film and an Au
thin film, or of an Ag thin film and an Au thin film
[0053] The ohmic contact layer 160 includes a lower film 160p, an
intermediate film 160q, and an upper film 160r. In an alternative
embodiment, one of the lower film 160p and the intermediate film
160q may be omitted.
[0054] In an exemplary embodiment, the upper film 160r includes a
one-dimensional nano structure such as nano-columns, nano-rods, or
nano-wires. In addition, the upper film 160r may have a
two-dimensional lattice structure.
[0055] In exemplary embodiments, the upper film 160r may be made of
a transparent conductive zinc oxide (ZnO) doped with a rare earth
metal. The rare earth metal may include, but is not limited to, Er,
Sm, Ce, Pr, Pm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, Lu, Th, Pa, U, Np, Pu,
Am, Bk, Cf, Es, Fm, Md, No, Lr, and Cm. In one exemplary
embodiment, the amount of the rare earth metal may be equal to or
lower than 20 weight percent (wt %).
[0056] In exemplary embodiments where the upper film 160r may only
include zinc, oxide, and at least one rare metal, the upper film
160r may further include an additional ingredient for adjusting
electron concentration, energy bandgap, or refractive index of the
zinc oxide. The additional ingredient may be a metal or an oxide
thereof including, but not limited to, aluminum (Al), chromium
(Cr), silicon (Si), germanium (Ge), indium (In), lithium (Li),
gallium (Ga), magnesium (Mg), zinc (Zn), beryllium (Be), molybdenum
(Mo), vanadium (V), copper (Cu), iridium (Ir), rhodium (Rh),
ruthenium (Ru), tungsten (W), cobalt (Co), nickel (Ni), manganese
(Mn), titanium (Ti), tantalum (Ta), cadmium (Cd), and lanthanum
(La). That is, the upper film 160r may include at least one of the
above-listed metals and oxides thereof as the additional
ingredients.
[0057] In an exemplary embodiment, the amount of the additional
ingredient may be from about 0.1 weight % to about 49 weight %.
[0058] In an exemplary embodiment, the thickness of the upper film
160r may be equal to or greater than about 5 nanometers (nm). In
one exemplary embodiment, the thickness of the upper film 160r may
be equal to or greater than about 10 nanometers.
[0059] In an exemplary embodiment, the upper film 160r may be
directly grown to have the one-dimensional nano structure. In an
alternative embodiment, the upper film 160r may be formed by
depositing a two-dimensional thin film of zinc oxide and by etching
and re-growing the two-dimensional thin film with heat treatment
under an atmosphere including hydrogen gas (H.sub.2).
[0060] In an exemplary embodiment, the lower film 160p and the
intermediate film 160q may be an ohmic interlayer for improving the
ohmic contact characteristic between the p-type nitride-based
cladding layer 150 and the upper film 160r.
[0061] In exemplary embodiments, the lower film 160p and/or the
intermediate film 160q may be made of a metal including, but not
limited to, Ni, Pd, Pt, Rh, Zn, In, Sn, Ag, Au, Cd, Mg, Be, Mo, V,
Cu, Ti, Ir, Ru, W, Co, and Mn, transparent conductive oxides
including ITO, SnO.sub.2, ZnO, In.sub.2O.sub.3, Ga.sub.2O.sub.3,
RhO.sub.2, NiO, CoO, PdO, PtO, CuAlO.sub.2, CdO, and CuGaO.sub.2,
and transparent conductive nitrides including TiN, TaN, and
SiNx.
[0062] In an exemplary embodiment of a method of forming the ohmic
contact layer 160, after the lower film 160p and the intermediate
film 160q are deposited, and before or after the upper film 160r is
deposited, heat treatment may be performed at a temperature equal
to or lower than about 800.degree. C. and under a vacuum or under
an atmosphere of various gases such as oxygen (O.sub.2), nitrogen
(N.sub.2), argon (Ar), hydrogen (H.sub.2), or air. The heat
treatment may improve light transmittance and conductivity of the
ohmic contact layer 160. Furthermore, plasma treatment may be
performed by using ions of such as oxygen (O.sub.2), nitrogen
(N.sub.2), hydrogen (H.sub.2), or argon (Ar) for improving optical
and electrical characteristics of the upper film 160r.
[0063] In an exemplary embodiment, each layer may be formed by
chemical vapor deposition ("CVD") or physical vapor deposition
("PVD").
[0064] The CVD may include, but is not limited to, metalorganic
chemical vapor deposition ("MOCVD").
[0065] The PVD may include, but is not limited to, evaporation,
laser deposition, and sputtering. The evaporation includes, but is
not limited to, thermal evaporation and electron beam evaporation.
The laser deposition may include, but it not limited to, a laser
beam having high energy. The sputtering may include, but is not
limited to, ions of oxygen (O.sub.2), nitrogen (N.sub.2), or argon
(Ar), and the sputtering may use two or more sputtering guns, which
is referred to as co-sputtering.
[0066] The active layer 140 of the white light emitting device may
emit ultraviolet light, near ultraviolet light, blue light, or
green light. The ohmic contact layer 160 containing the rare earth
metal can adjust the wavelength of the light emitted by the active
layer 140, supplies charge carriers to the active layer 140, and
spreads the current. Since the ohmic contact layer 160 is
transparent, the luminous efficiency of the light emitting device
increases.
[0067] In the light emitting device shown in FIG. 1, the light
generated in the active layer 140 passes through the p-type
cladding layer 150 and is emitted Advantageously, the light
emitting device may be used for small emitting area, low capacity,
and low luminance.
[0068] FIG. 2 is a sectional view of an exemplary embodiment of a
top-emission nitride-based white light emitting device having a
vertical structure according to the present invention.
[0069] The layered structure of a light emitting device shown in
FIG. 2 is similar to that shown in FIG. 1.
[0070] That is, a nitride-based buffer layer 220, an n-type
nitride-based cladding layer 230, a nitride-based active layer 240,
a p-type nitride-based cladding layer 250, and an ohmic contact
layer 260 are sequentially formed on a substrate 210. The ohmic
contact layer 260 includes a lower film 260p, an intermediate film
260q, and an upper film 260r.
[0071] Unlike the light emitting device shown in FIG. 1, the
substrate 210 of the light emitting device shown in FIG. 2 may be
made of conductive silicon carbide (SiC). An n-type electrode pad
280 is disposed opposite to the buffer layer 220 with respect to
the substrate 210 and covers an entire surface of the substrate
210. A p-type electrode pad 270 is formed on the ohmic contact
layer 260 and may be disposed substantially near the middle of the
ohmic contact layer 260.
[0072] In an exemplary embodiment, the n-type electrode pad 280 is
an ohmic electrode pad and may be made of a metal including, but
not limited to, rhodium, or silver having high reflectance. The
n-type electrode pad 280 may have various layered structures.
[0073] The n-type cladding layer 230 has a substantially uniform
thickness and thus no etching may be needed.
[0074] Since the light emitting device shown in FIG. 2 use the
conductive substrate 210, heat is effectively dissipated from the
light emitting device. Advantageously, the light emitting device
may be used for large area, large capacity, and high luminance.
[0075] Many features of the light emitting device shown in FIG. 1
may be applicable to the light emitting device shown in FIG. 2.
[0076] FIG. 3 is a sectional view of another exemplary embodiment
of a top-emission nitride-based white light emitting device having
a vertical structure according to the present invention.
[0077] The layered structure of a light emitting device shown in
FIG. 3 is similar to that shown in FIG. 2.
[0078] That is, an n-type nitride-based cladding layer 330, a
nitride-based active layer 340, a p-type nitride-based cladding
layer 350, an ohmic contact layer 360, and a p-type electrode pad
370 are sequentially formed on a substrate 310. The ohmic contact
layer 360 includes a lower film 360p, an intermediate film 360q,
and an upper film 360r.
[0079] Unlike the light emitting device shown in FIG. 2, the light
emitting device shown in FIG. 3 includes no n-type electrode pad,
and includes a bonding layer 320 instead of the buffer layer. The
substrate 310 may be made of a conductive semiconductor, a metal,
etc.
[0080] A reflective layer 390 is formed between the bonding layer
320 and the n-type cladding layer 330 and the reflective layer 390
reflects the light from the active layer 340.
[0081] In an exemplary embodiment of manufacturing the light
emitting device shown in FIG. 3, a structure including at least one
of the reflective layer 390, the n-type nitride-based cladding
layer 330, the nitride-based active layer 340, the p-type
nitride-based cladding layer 350, the ohmic contact layer 360, and
the p-type electrode pad 370 is formed on an insulation substrate
(not shown) made of sapphire, etc. The structure is separated from
the insulation substrate, such as using laser lift off, and bonded
onto the conductive substrate 310 via the bonding layer 320.
[0082] The light emitting device shown in FIG. 3 also has excellent
heat dissipation and may advantageously used for large area, large
capacity, and high luminance.
[0083] Many features of the light emitting device shown in FIG. 2
may be applicable to the light emitting device shown in FIG. 3.
[0084] FIG. 4 is a sectional view of another exemplary embodiment
of a top-emission nitride-based white light emitting device having
a vertical structure according to the present invention.
[0085] The layered structure of a light emitting device shown in
FIG. 4 is similar to that shown in FIG. 3.
[0086] That is, a bonding layer 420 and a reflective layer 490 are
sequentially formed on a substrate 410, and an n-type nitride-based
cladding layer 430, a nitride-based active layer 440, a p-type
nitride-based cladding layer 450, and an ohmic contact layer 460
are formed thereon. The ohmic contact layer 460 includes a lower
film 460p, an intermediate film 460q, and an upper film 460r.
[0087] However, the relative positions of the n-type nitride-based
cladding layer 430 and the p-type nitride-based cladding layer 450
in the light emitting device shown in FIG. 4 are exchanged as
compared with those shown in FIG. 3. In addition, an n-type
electrode pad 480 are formed instead of the p-type electrode pad
370.
[0088] Many features of the light emitting device shown in FIG. 3
may be applicable to the light emitting device shown in FIG. 4.
[0089] The white light emitting device as in the illustrated
exemplary embodiment including the nano-structured ohmic contact
layer improves the interface characteristic of the ohmic contact
layer to show improved current-voltage characteristics and
increases emission efficiency.
[0090] FIG. 5A, FIG. 5B, and FIG. 5C show exemplary embodiment of
shapes of grown zinc oxides (ZnO) doped with a rare earth metal and
having a one-dimensional nano structure for forming the ohmic
contact layer shown in FIG. 1 to FIG. 4.
[0091] The zinc oxides doped with a rare earth metal shown in FIG.
5A, FIG. 5B, and FIG. 5C are formed under different process
conditions, e.g., at different temperatures and for different
process times.
[0092] FIG. 6A, FIG. 6B, FIG. 6C, and FIG. 6D show exemplary
embodiments of various shapes made by etching zinc oxides (ZnO)
doped with a rare earth metal to have one-dimensional nano
structure for forming the ohmic contact layer shown in FIG. 1 to
FIG. 4.
[0093] FIG. 6A shows a two-dimensional thin film formed by
depositing zinc oxide (ZnO). FIG. 6B, FIG. 6C, and FIG. 6D show
zinc oxides made by etching the zinc oxide thin film shown in FIG.
6A under an atmosphere of hydrogen gas or ions, which have slightly
different shapes depending on the process temperature and the
process time for the etching.
[0094] In order to improve the optical and electrical
characteristics of the nano-structured zinc oxide, in one exemplary
embodiment, the zinc oxide is subjected to plasma treatment using
ions of oxygen (O.sub.2), nitrogen (N.sub.2), hydrogen (H.sub.2),
and at a temperature equal to or lower than about 800.degree.
C.
[0095] Although preferred embodiments of the present invention have
been described in detail hereinabove, it should be clearly
understood that many variations and/or modifications of the basic
inventive concepts herein taught which may appear to those skilled
in the present art will still fall within the spirit and scope of
the present invention, as defined in the appended claims.
* * * * *