U.S. patent application number 12/584417 was filed with the patent office on 2010-06-03 for light emitting diode.
This patent application is currently assigned to Tsinghua University. Invention is credited to Shou-Shan Fan, Kai-Li Jiang, Qun-Qing Li.
Application Number | 20100133569 12/584417 |
Document ID | / |
Family ID | 42221963 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100133569 |
Kind Code |
A1 |
Li; Qun-Qing ; et
al. |
June 3, 2010 |
Light emitting diode
Abstract
A light emitting diode includes a substrate, a first
semiconductor layer, an active layer, a second semiconductor layer,
and at least one transparent conductive layer. The transparent
conductive layer comprises of a carbon nanotube structure.
Inventors: |
Li; Qun-Qing; (Beijing,
CN) ; Jiang; Kai-Li; (Beijing, CN) ; Fan;
Shou-Shan; (Beijing, CN) |
Correspondence
Address: |
PCE INDUSTRY, INC.;ATT. Steven Reiss
288 SOUTH MAYO AVENUE
CITY OF INDUSTRY
CA
91789
US
|
Assignee: |
Tsinghua University
Beijing
CN
HON HAI PRECISION INDUSTRY CO., LTD.
Tu-Cheng
TW
|
Family ID: |
42221963 |
Appl. No.: |
12/584417 |
Filed: |
September 3, 2009 |
Current U.S.
Class: |
257/98 ; 257/79;
257/E33.064; 257/E33.067; 977/742 |
Current CPC
Class: |
B82Y 20/00 20130101;
B82Y 40/00 20130101; H01L 33/32 20130101; H01L 33/06 20130101; B82Y
30/00 20130101; Y10S 977/742 20130101; H01L 33/10 20130101; Y10S
977/95 20130101; H01L 51/0048 20130101; H01L 33/42 20130101; H01L
33/46 20130101; H01L 33/12 20130101; H01L 33/40 20130101; H01L
33/20 20130101; H01L 33/16 20130101; H01L 33/38 20130101; H01L
29/0676 20130101 |
Class at
Publication: |
257/98 ; 257/79;
257/E33.067; 257/E33.064; 977/742 |
International
Class: |
H01L 33/00 20100101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2008 |
CN |
200810217913.3 |
Claims
1. A light emitting diode, comprising: a substrate, a first
semiconductor layer, an active layer, a second semiconductor layer,
and at least one transparent conductive layer, the transparent
conductive layer comprises a carbon nanotube structure.
2. The light emitting diode of claim 1, wherein the carbon nanotube
structure is a free-standing structure.
3. The light emitting diode of claim 1, wherein the transparent
conductive layer comprises the carbon nanotube structure and a
plurality of metal particles, the metal particles are dispersed in
the carbon nanotube structure to form a composite layer.
4. The light emitting diode of claim 1, wherein the carbon nanotube
structure comprises a plurality of carbon nanotubes.
5. The light emitting diode of claim 1, wherein the carbon nanotube
structure comprises at least one carbon nanotube film, the carbon
nanotube film comprises a plurality of carbon nanotubes joined by
van der Waals force.
6. The light emitting diode of claim 1, wherein the carbon nanotube
structure comprises a drawn carbon nanotube film, the drawn carbon
nanotube film comprises a plurality of carbon nanotubes
approximately parallel to each other.
7. The light emitting diode of claim 6, wherein the carbon nanotube
structure comprises two drawn carbon nanotube films, an angle
between aligned directions of the drawn carbon nanotube films is
approximately 90 degrees.
8. The light emitting diode of claim 1, wherein the carbon nanotube
structure comprises a carbon nanotube film, the carbon nanotube
film comprises a plurality of carbon nanotubes, the carbon
nanotubes are entangled with one another.
9. The light emitting diode of claim 1, wherein the carbon nanotube
structure comprises a plurality of twisted carbon nanotube wires,
each of the twisted carbon nanotube wires comprise a plurality of
carbon nanotubes, the carbon nanotubes helically wrap around the
longitudinal axis of the twisted carbon nanotube wires.
10. The light emitting diode of claim 1, wherein the carbon
nanotube structure comprises a plurality of untwisted carbon
nanotube wires, each of the untwisted carbon nanotube wires
comprise a plurality of carbon nanotubes, the carbon nanotubes are
substantially parallel to each other and the longitudinal axis of
the untwisted carbon nanotube wires.
11. The light emitting diode of claim 1, further comprising a
static electrode formed between the second semiconductor layer and
the transparent conductive layer.
12. The light emitting diode of claim 1, further comprising a
buffer layer located between the substrate and the first
semiconductor layer.
13. The light emitting diode of claim 1, further comprising a
reflecting layer located between the substrate and the first
semiconductor layer.
14. The light emitting diode of claim 1, further comprising a
photon crystal structure located between the substrate and the
first semiconductor layer.
15. A light emitting diode comprising: a substrate, a first
semiconductor layer, an active layer, a second semiconductor layer,
a first transparent conductive layer, and a second transparent
conductive layer; the first semiconductor layer includes a first
surface and a second surface; the active layer and the second
semiconductor layer are formed on the first surface; the second
transparent conductive layer is mounted on an top surface of the
second semiconductor layer; and the first transparent conductive
layer is mounted on the second surface of the first semiconductor
layer; wherein each of the first and second transparent conductive
layers comprise of a carbon nanotube structure.
16. The light emitting diode of claim 15, wherein the first surface
and the second surface of the first semiconductor layer are located
on different planes and form a step-shaped structure.
17. A light emitting diode comprising: a substrate, a first
semiconductor layer, an active layer, a second semiconductor layer,
and a transparent conductive layer; the first semiconductor layer
comprises a first surface and a second surface, and the first and
second surface are located on same side of the first semiconductor
layer; the active layer and the second semiconductor layer are
disposed on the first surface; the transparent conductive layer is
disposed on the second surface of the first semiconductor layer and
electrically connected to the first semiconductor layer; and the
transparent conductive layer comprises of a carbon nanotube
structure.
18. The light emitting diode of claim 17, further comprising a
first electrode and a second electrode, the first electrode is
disposed on a top surface of the transparent conductive layer, and
the second electrode is disposed on the second semiconductor layer.
Description
RELATED APPLICATIONS
[0001] This application is related to applications entitled,
"METHOD FOR FABRICATING LIGHT EMITTING DIODE", filed **** (Atty.
Docket No. US23023).
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure relates to a light emitting diode
(LED).
[0004] 2. Description of the Related Art
[0005] LEDs are semiconductors that convert electrical energy into
light. Compared to conventional light sources, the LEDs have higher
energy conversion efficiency, higher radiance (i.e., they emit a
larger quantity of light per unit area), longer lifetime, higher
response speed, and better reliability. At the same time, LEDs
generate less heat. Therefore, LED modules are widely used in
particular as a semiconductor light source in conjunction with
imaging optical systems, such as displays, projectors, and so
on.
[0006] Referring to FIG. 6, a typical LED 10, according to the
prior art includes a substrate 110, a GaN bumper layer 120, an
N-type GaN layer 132, an active layer 134, a P-type GaN layer 136,
and a transparent contact layer 140. The GaN bumper layer 120, the
N-type GaN layer 132, the active layer 134, the P-type GaN layer
136, and the transparent contact layer 140 are stacked on the
substrate 110. The LED 10 further includes a transparent conductive
layer 150, a first electrode 142, and a second electrode 144. The
first electrode 142 is disposed on the N-type semiconductor layer
132. The transparent conductive layer 150 and the second electrode
144 are disposed on the transparent contact layer 140. The
transparent conductive layer 150 is made of indium tin oxide (ITO)
and the ITO is sputtered on an area of the transparent contact
layer 140. Due to the net structure of the ITO layer, the lateral
distribution of current applied on the transparent conductive layer
150 is uniform, thereby improving the extraction efficiency of
light of the LED. However, the ITO layer has some faults, such as
low mechanical strength and resistance distribution. Furthermore,
the transparency of the ITO layer may be decreased in humid
environments and the ITO layer may absorb some of the light emitted
by the active layer 134 when the ITO fully covers the P-type
semiconductor layer 136.
[0007] What is needed, therefore, is a light emitting diode, which
can overcome the above-described shortcomings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Many aspects of the embodiments can be better understood
with reference to the following drawings. The components in the
drawings are not necessarily drawn to scale, the emphasis instead
being placed upon clearly illustrating the principles of the
embodiments. Moreover, in the drawings, like reference numerals
designate corresponding parts throughout the several views.
[0009] FIG. 1 is a schematic, partial exploded view of a light
emitting diode according to an embodiment.
[0010] FIG. 2 is a schematic view of the light emitting diode of
FIG. 1.
[0011] FIG. 3 is a scanning electron microscope (SEM) image of a
carbon nanotube film used in the light emitting diode of FIG.
1.
[0012] FIG. 4 is a schematic view of a light emitting diode
according to an another embodiment.
[0013] FIG. 5 is a schematic view of a light emitting diode
according to an embodiment.
[0014] FIG. 6 is schematic, cross-sectional view of a typical light
emitting diode according to prior art.
DETAILED DESCRIPTION
[0015] The disclosure is illustrated by way of example and not by
way of limitation in the figures of the accompanying drawings in
which like references indicate similar elements. It should be noted
that references to "an" or "one" embodiment in this disclosure are
not necessarily to the same embodiment, and such references mean at
least one.
[0016] Referring to FIG. 1 and FIG. 2, a first embodiment of a
light emitting diode (LED) 20 includes a substrate 210, a first
semiconductor layer 232, an active layer 234, a second
semiconductor layer 236, a first electrode 242, a second electrode
244, a transparent conductive layer 250, and a static electrode
240. The first semiconductor layer 232, the active layer 234, the
second semiconductor layer 234 are orderly stacked on the substrate
210. The first electrode 242 is electrically connected to the first
semiconductor layer 232. The transparent conductive layer 250 is
disposed on the top surface of the second semiconductor layer 236
and electrically connected to the second semiconductor layer 236.
The static electrode 240 is interposed between the second
semiconductor layer 236 and the transparent conductive layer 250.
The second electrode 244 is disposed on the top surface of the
transparent conductive layer 250 and electrically connected to the
transparent conductive layer 250.
[0017] The substrate 210 may have a thickness of about 300 microns
(.mu.m) to about 500 .mu.m and a transparent plate for supporting
the other elements, such as the first and second semiconductor
layers 232, 236. The substrate 210 may be made of sapphire, gallium
arsenide, indium phosphate, silicon nitride, gallium nitride, zinc
oxide, aluminum silicon nitride, silicon carbon, or their
combinations. In one embodiment, the substrate 210 is made of
sapphire and has a thickness of 400 .mu.m.
[0018] The first semiconductor layer 232, the active layer 234, and
the second semiconductor layer 236 can be stacked on the substrate
210 via a process of metal organic chemical vapor deposition
(MOCVD).
[0019] The first semiconductor layer 232 has a thickness of about 1
.mu.m to about 5 .mu.m. The second semiconductor layer 236 has a
thickness of about 0.1 .mu.m to about 3 .mu.m. When the first
semiconductor layer 232 is an N-type semiconductor, the second
semiconductor layer 236 is a P-type semiconductor, and vice versa.
In one embodiment, the first semiconductor layer 232 is an N-type
semiconductor and the second semiconductor layer 236 is a P-type
semiconductor. The first semiconductor layer 232 has a step-shaped
structure and includes a first surface 262 and a second surface 264
located on the same side as the first surface 262. The first
surface 262 and the second surface 264 have different heights and
form a step-shaped structure. The active layer 234 and the second
semiconductor layer 236 are arranged on the first surface 262.
[0020] The first semiconductor layer 232 is configured to provide
electrons, and the second semiconductor layer 236 is configured to
provide cavities. When a voltage is applied to the first and second
semiconductor layers 232, 236, the electrons can flow into the
second semiconductor 236 and incorporate with the cavities, thereby
emitting light. The first semiconductor layer 232 may be made of
N-type gallium nitride, N-type gallium arsenide, or N-type copper
phosphate. The second semiconductor layer 236 may be made of P-type
gallium nitride, P-type gallium arsenide, or P-type copper
phosphate. In one embodiment, the first semiconductor layer 232 is
made of N-type gallium nitride and has a thickness of 2 .mu.m, and
the second semiconductor layer 236 is made of P-type gallium
nitride and has a thickness of 0.3 .mu.m.
[0021] The active layer 234, in which the electrons fill the holes,
has a thickness of about 0.01 .mu.m to about 0.6 .mu.m. The active
layer 234 is a photon exciting layer and can be one of a single
quantum well layer or multilayer quantum well films. The active
layer 140 can be made of GaInN, AlGaInN, GaSn, AlGaSn, GaInP, or
GaInSn. In one embodiment, the active layer 234 has a thickness of
0.3 .mu.m and includes one layer of GaInN stacked with a layer of
GaN.
[0022] The static electrode 240 is formed on the top surface of the
second semiconductor layer 236. The static electrode 240 may be a
P-type electrode or an N-type electrode and is a same type as the
second semiconductor layer 236. Therefore, in one embodiment, the
static electrode 236 is a P-type electrode. Understandably, the
static electrode 236 can function as a reflection layer. The static
electrode 236 can have one or more layers of metal and may be made
of titanium, aluminum, nickel, gold, or any combinations thereof In
one embodiment, the static electrode 236 has two layers. One layer
is made of titanium and has a thickness of 15 nanometers (nm). The
other layer is made of gold and has a thickness of 100 nm. The
static electrode 240 is formed on the second semiconductor layer
236 via a process of physical vapor deposition, such as electron
evaporation, vacuum evaporation, ion sputtering, or the like.
[0023] Further, a functioning layer may be formed between the
substrate 210 and the first semiconductor layer 232. The
functioning layer may be one or more of a buffer layers, a
reflective layer, and a photon crystal structure. The buffer layer
is configured to improve epitaxial growth and decrease lattice
mismatch. The buffer layer may be made of GaN, AlN, or the like.
The reflective layer is configured to change the transmission route
of the light to improve extraction efficiency of light in the LED.
The reflective layer may be made of silver, aluminum, rhodium, or
the like. The photon crystal structure is configured to improve
extraction efficiency of light and may be made of silicon, indium
tin oxide, carbon nanotube, or the like. In one embodiment, only
the buffer layer 220 is formed on the substrate 210 and is made of
GaN. The buffer layer 220 has a thickness of about 20 nm to about
50 nm.
[0024] The transparent conductive layer 250 includes a carbon
nanotube structure. The transparent conductive layer 250 can be
directly applied to the top surface of the second semiconductor
layer 236 and the static electrode 240. The transparent conductive
layer 250 may only cover the exposed surface of the second
semiconductor layer 236 and fully or partly cover both the top
surface of the static electrode 240 and the second semiconductor
layer 236. In one embodiment, the transparent conductive layer 250
fully covers both the second semiconductor layer 236 and the static
electrode 240. The carbon nanotube structure may include at least
one carbon nanotube film and/or a number of carbon nanotube wires.
The use of all types of carbon nanotube films and/or carbon
nanotube wires is envisioned to be employed by the transparent
conductive layer 250. There is no particular restriction on the
thickness of the carbon nanotube structure and it may be
appropriately selected depending on the purpose, and may be, for
example, greater than 0.5 nm, and more specifically from about 0.5
.mu.m to 200 .mu.m.
[0025] The carbon nanotube structure can include one or more layers
of carbon nanotube films. When the carbon nanotube structure
includes a number of carbon nanotube films, the carbon nanotube
films are stacked on top of each other. The carbon nanotube
structure can employ more carbon nanotube films to increase the
tensile strength of the carbon nanotube composite 100. The carbon
nanotube film has a thickness in an approximate range from about
0.5 nm to about 100 mm. The carbon nanotubes films may have a
free-standing structure. The film structure being supported by
itself and does not require a substrate to maintain its structural
integrity. As an example, a corner of the carbon nanotube film can
be lifted without resulting in damage to the entire structure.
[0026] Referring to FIG. 3, the carbon nanotube films each are
formed by the carbon nanotubes, orderly or disorderly, and has
substantially a uniform thickness. Ordered carbon nanotube films
include films where the carbon nanotubes are arranged along a
primary direction. Examples include films wherein the carbon
nanotubes are arranged approximately along a same direction or have
two or more sections within each of which the carbon nanotubes are
arranged approximately along a same direction (different sections
can have different directions). In the ordered carbon nanotube
films, the carbon nanotubes are oriented along the same preferred
orientation and approximately parallel to each other. A film can be
drawn from a carbon nanotube array, to form the ordered carbon
nanotube film, namely a drawn carbon nanotube film. Examples of
drawn carbon nanotube film are taught by U.S. Pat. No. 7,045,108 to
Jiang et al., and WO 2007015710 to Zhang et al. The drawn carbon
nanotube film includes a plurality of successive and oriented
carbon nanotubes joined end-to-end by van der Waals attractive
force therebetween. The drawn carbon nanotube film is a
free-standing film. The carbon nanotube film can be treated with an
organic solvent to increase the mechanical strength and toughness
of the carbon nanotube film and reduce the coefficient of friction
of the carbon nanotube film. A thickness of the carbon nanotube
film can range from about 0.5 nanometers to about 100
micrometers.
[0027] The ordered carbon nanotube film may be a pressed carbon
nanotube film having a number of carbon nanotubes arranged along a
same direction. The carbon nanotubes in the pressed carbon nanotube
film can rest upon each other. Adjacent carbon nanotubes are
attracted to each other and combined by van der Waals attractive
force. An angle between a primary alignment direction of the carbon
nanotubes and a surface of the pressed carbon nanotube film is 0
degree to approximately 15 degrees. The greater the pressure
applied, the smaller the angle formed. The thickness of the pressed
carbon nanotube film ranges from about 0.5 nm to about 1 mm.
Examples of pressed carbon nanotube film are taught by US
application 20080299031A1 to Liu et al.
[0028] The disordered carbon nanotube film comprises carbon
nanotubes arranged in a disorderly fashion. Disordered carbon
nanotube films include randomly aligned carbon nanotubes. When the
disordered carbon nanotube film comprises of a film wherein the
number of the carbon nanotubes aligned in every direction is
substantially equal, the disordered carbon nanotube film can be
isotropic. The disordered carbon nanotubes can be entangled with
each other and/or are substantially parallel to a surface of the
disordered carbon nanotube film. The disordered carbon nanotube
film may be a flocculated carbon nanotube film. The flocculated
carbon nanotube film can include a plurality of long, curved,
disordered carbon nanotubes entangled with each other. The carbon
nanotubes can be substantially uniformly dispersed in the
flocculated carbon nanotube film. Adjacent carbon nanotubes are
attracted by van der Waals attractive force to form an entangled
structure with micropores defined therein. It is understood that
the flocculated carbon nanotube film is very porous. Sizes of the
micropores can be less than 10 .mu.m. Due to the carbon nanotubes
in the flocculated carbon nanotube film being entangled with each
other, the carbon nanotube structure employing the flocculated
carbon nanotube film has excellent durability, and can be fashioned
into desired shapes with a low risk to the integrity of the
flocculated carbon nanotube film. The thickness of the flocculated
carbon nanotube film can range from about 0.5 nm to about 1
millimeter (mm).
[0029] The disordered carbon nanotube film may be a pressed carbon
nanotube film having a number of carbon nanotubes arranged along
different directions. The pressed carbon nanotube film can be a
free-standing carbon nanotube film. When the carbon nanotubes in
the pressed carbon nanotube film are arranged along different
directions, the pressed carbon nanotube film can be isotropic. As
described above, the thickness of the pressed carbon nanotube film
ranges from about 0.5 nm to about 1 mm. Examples of pressed carbon
nanotube film are taught by US application 20080299031A1 to Liu et
al.
[0030] Length and width of the carbon nanotube film can be
arbitrarily set as desired. A thickness of the carbon nanotube film
is in a range from about 0.5 nm to about 100 .mu.m. The carbon
nanotubes in the carbon nanotube film can be single-walled,
double-walled, multi-walled carbon nanotubes, and combinations
thereof. Diameters of the single-walled carbon nanotubes, the
double-walled carbon nanotubes, and the multi-walled carbon
nanotubes can, respectively, be in the approximate range from about
0.5 nm to about 50 nm, about 1 nm to about 50 nm, and about 1.5 nm
to about 50 nm.
[0031] The carbon nanotube structure include a number of carbon
nanotube wires. The carbon nanotube wires may be arraigned side by
side on the top surface of the second semiconductor layer or may be
weaved into a carbon nanotube layer. The weaved carbon nanotube
layer is applied to the second semiconductor layer. The carbon
nanotube wire includes untwisted carbon nanotube wire and twisted
carbon nanotube wire. The untwisted carbon nanotube wire includes a
number of carbon nanotubes parallel to each other. The twisted
carbon nanotube wire includes a number of carbon nanotube helically
twisted along a longitudinal axis of the twist carbon nanotube
wire.
[0032] The untwisted carbon nanotube wire can be formed by treating
the drawn carbon nanotube film with an organic solvent. The drawn
carbon nanotube film is treated by applying the organic solvent to
the carbon nanotube film while being free to bundle. After being
soaked by the organic solvent, the adjacent paralleled carbon
nanotubes in the drawn carbon nanotube film will bundle together,
due to the surface tension of the organic solvent when the organic
solvent volatilizing, and thus, the drawn carbon nanotube film will
be shrunk into untwisted carbon nanotube wire. The carbon nanotubes
of the untwisted carbon nanotube wires are substantially parallel
to each other along the longitudinal axis of the untwisted carbon
nanotube wires. Examples of the untwisted carbon nanotube wire are
taught by U.S. Pat. No. 7,045,108 to Fan et al. and US publication
No. 20070166223 to Fan et al.
[0033] The twisted carbon nanotube wire can be formed by twisting a
drawn carbon nanotube film by using a mechanical force to turn the
two ends of the drawn carbon nanotube film in opposite directions.
Further, the twisted carbon nanotube wire can be treated by
applying the organic solvent. After applying the organic solvent,
the adjacent carbon nanotubes in the twisted carbon nanotube film
will bundle together, due to the surface tension of the organic
solvent when the organic solvent volatilizing, and thus, the
twisted carbon nanotube wire may have less specific surface area,
and larger density and strength than an untreated twisted carbon
nanotube wire.
[0034] The transparent conductive layer 250 may be made by steps of
forming a metal layer (not shown) on the carbon nanotube structure
and heating the metal layer in a temperature of about 300 degrees
centigrade to about 500 degrees centigrade for about 3 minutes to
about 10 minutes. The metal layer may be a single-layer structure
or a multi-layered structure. In one embodiment, the metal layer
includes a nickel layer stacked with a gold layer. The nickel layer
has a thickness of about 2 nm. The gold layer has a thickness of 5
nm. Since the metal layer decreases in thickness because of the
heating, the metal molecule of the metal layer can be melted and
can aggregate into a number of metal particles by surface tension.
The carbon nanotube structure has a plurality of micropores between
adjacent carbon nanotubes of the carbon nanotube structure. These
metal particles uniformly disperse in the micropores of the carbon
nanotube structure to form a composite film. The composite film,
which functions as the transparent conductive layer 250, has better
electrical conductivity than the pure carbon nanotube structure,
thereby improving current injection efficiency and electrical
contact between the carbon nanotube structure and the static
electrode 240, the first electrode 242, and the second
semiconductor layer 236.
[0035] In one embodiment, two drawn carbon nanotube films are
coated on the second semiconductor layer 236 and the static
electrode 340. An angle between the primary directions of the two
drawn carbon nanotube films ranges from about 0 degrees to about 90
degrees. In one embodiment, the primary directions of the two drawn
carbon nanotube films are perpendicular to each other.
[0036] The first electrode 242 can be deposited on the transparent
conductive layer 250 via physical vapor deposition and may have
single-layer structure or multi-layered structure. The first
electrode 242 can be made of titanium or gold. In one embodiment,
the first electrode 242 includes two layers, one layer is titanium
and has a thickness of 15 nm and another layer is gold and has a
thickness of 200 nm. At least a portion of the carbon nanotube
structure is located between the static electrode 240 and the first
electrode 242. The first electrode 242 may be P-type or N-type
electrode and is the same type as the static electrode 240 and the
second semiconductor layer 236. Since the static electrode 240 is
made of P-type material, the first electrode 242 is a P-type
electrode. When the LED 20 has the static electrode 240, the first
electrode 242 should be located above the static electrode 240.
When the LED has no static electrode 240, the first electrode 242
can be located at any position on the transparent conductive layer
250. In one embodiment, since the LED employs the static electrode
240, the first electrode 242 is located above the static electrode
242. The first electrode 242 and the static electrode 240 function
together as the
[0037] P-type electrode of the LED. The second electrode 244 is a
same polarity type with the first semiconductor layer 236 and may
be made of N-type material. The second electrode 244 is deposited
on the second surface 264 of the first semiconductor layer 236. The
second electrode 244 has a same structure as the first electrode
242 and includes a titanium layer and a gold layer stacked on the
titanium layer. The titanium layer has a thickness of about 15 nm
and the gold layer has a thickness of about 200 nm. The method of
depositing the second electrode 244 can be the same as that of the
first electrode 242. The first and second electrodes 242, 244 can
be deposited at the same time.
[0038] Referring to FIG. 4, in one embodiment, an LED 30 includes a
substrate 310, a buffer layer 320, a first semiconductor layer 332,
an active layer 334, a second semiconductor layer 336, a first
electrode 342, a second electrode 344, a transparent conductive
layer 350, and a static electrode 340. The buffer layer 320, the
first semiconductor layer 332, the active layer 334, the second
semiconductor layer 336 are orderly stacked on the substrate
310.
[0039] The first semiconductor layer 332 includes a first surface
362 and a second surface 364 located on the same side as the first
surface 362. The first surface 362 and the second surface 364 have
different heights and form a stepped structure. The active layer
334 and the second semiconductor layer 336 are disposed on the
first surface 362. The transparent conductive layer 350 is disposed
on the second surface 364 of the first semiconductor layer 332 and
electrically connected to the first semiconductor layer 332.
Further, the static electrode 340 is interposed between the first
semiconductor layer 332 and the transparent conductive layer 350.
The first electrode 342 is disposed on the top surface of the
transparent conductive layer 350 and electrically connected to the
transparent conductive layer 350. The second electrode 344 is
electrically connected to the second semiconductor layer 336.
[0040] Referring to FIG. 5, in one embodiment, an LED 40 includes a
substrate 410, a buffer layer 420, a first semiconductor layer 432,
an active layer 434, a second semiconductor layer 436, a first
electrode 442, a second electrode 444, a first transparent
conductive layers 450, a second transparent conductive layer 452,
and a first static electrode 440, a second static electrode 446.
The buffer layer 420, the first semiconductor layer 432, the active
layer 434, the second semiconductor layer 436 are orderly stacked
on the substrate 310.
[0041] The first semiconductor layer 432 includes a first surface
462 and a second surface 464 located on the same side a the first
surface 462. The first surface 462 and the second surface 464 have
different heights and form a stepped structure. The second
transparent conductive layer 452 is mounted on the second
semiconductor layer 436, and the first transparent conductive layer
450 is mounted on the second surface 464 of the first semiconductor
layer 432. Further, the first static electrode 440 is located
between the second semiconductor layer 436 and the second
transparent conductive layer 452, and the second electrode 444 is
disposed on the top surface of the second transparent conductive
layer 452. The second static electrode 446 is interposed between
the first semiconductor layer 436 and the first transparent
conductive layer 450, and the first electrode 442 is disposed on
the top surface of the first transparent conductive layer 450.
[0042] Since the carbon nanotubes have better electrical
conductivity and mechanical strength than conventional material,
such as indium tin oxide, the carbon nanotube structure has better
electrical conductivity and mechanical strength, thereby improving
power efficiency and life span. Further, the carbon nanotube
structure is stays transparent in varied humid environments.
Therefore less of the light emitted by the active layer is
absorbed. Thus, the LED has good extraction efficiency in
comparison with the typical LED.
[0043] It is to be understood, however, that even though numerous
characteristics and advantages of the present embodiments have been
set forth in the foregoing description, together with details of
the structures and functions of the embodiments, the disclosure is
illustrative only, and changes may be made in detail, especially in
matters of shape, size, and arrangement of parts within the
principles of the disclosure to the full extent indicated by the
broad general meaning of the terms in which the appended claims are
expressed.
* * * * *