U.S. patent application number 12/569435 was filed with the patent office on 2010-09-09 for light emitting device.
Invention is credited to Sun Kyung Kim, Jin Wook LEE.
Application Number | 20100224854 12/569435 |
Document ID | / |
Family ID | 42101548 |
Filed Date | 2010-09-09 |
United States Patent
Application |
20100224854 |
Kind Code |
A1 |
LEE; Jin Wook ; et
al. |
September 9, 2010 |
LIGHT EMITTING DEVICE
Abstract
A light emitting device (LED) is provided. The LED comprises a
light emitting structure and a mixed-period photonic crystal
structure. The light emitting structure comprises a first
conductivity type semiconductor layer, an active layer, and a
second conductivity type semiconductor layer. The mixed-period
photonic crystal structure is on the light emitting structure.
Inventors: |
LEE; Jin Wook; (Seoul,
KR) ; Kim; Sun Kyung; (Yongin-si, KR) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
42101548 |
Appl. No.: |
12/569435 |
Filed: |
September 29, 2009 |
Current U.S.
Class: |
257/13 ; 257/76;
257/98; 257/E33.001 |
Current CPC
Class: |
H01L 33/20 20130101;
H01L 2933/0083 20130101 |
Class at
Publication: |
257/13 ; 257/98;
257/76; 257/E33.001 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2009 |
KR |
10-2009-0017997 |
Claims
1-20. (canceled)
21. A light emitting device (LED), comprising: a light emitting
structure comprising a first conductivity type semiconductor layer,
an active layer, and a second conductivity type semiconductor
layer; and a mixed-period photonic crystal structure on the light
emitting structure.
22. The LED of claim 21, wherein the mixed-period photonic crystal
structure comprises: a first photonic crystal structure having a
first period in a partial region of the first conductivity type
semiconductor layer; and a second photonic crystal structure having
a second period in the partial region of the first conductivity
type semiconductor layer that includes the first photonic crystal
structure.
23. The LED of claim 22, wherein the second period is smaller than
the first period.
24. The LED of claim 23, wherein the second period is
non-uniform.
25. The LED of claim 23, wherein the second period is uniform.
26. The LED of claim 23, wherein the second period is about 100 nm
to about 800 nm.
27. The LED of claim 21, further comprising an undoped
semiconductor layer on the first conductivity type semiconductor
layer.
28. The LED of claim 27, wherein the mixed-period photonic crystal
structure comprises: a first photonic crystal structure having a
first period in a partial region of the undoped semiconductor
layer; and a second photonic crystal structure having a second
period in the partial region of the undoped semiconductor layer
that includes the first photonic crystal structure.
29. The LED of claim 21, further comprising a nonconductive
substrate on a side of the light emitting structure that is
opposite to a side of the light emitting structure with the
mixed-period photonic crystal structure.
30. The LED of claim 29, wherein the mixed-period photonic crystal
structure is on the second conductivity type semiconductor
layer.
31. A light emitting device (LED), comprising: a light emitting
structure comprising a first conductivity type semiconductor layer,
an active layer, and a second conductivity type semiconductor
layer; a conductive substrate on the light emitting structure; and
a mixed-period photonic crystal structure on the conductive
substrate.
32. The LED of claim 31, wherein the mixed-period photonic crystal
structure comprises: a first photonic crystal structure having a
first period in a partial region of the conductive substrate; and a
second photonic crystal structure having a second period in the
partial region of the conductive substrate that includes the first
photonic crystal structure.
33. The LED of claim 32, wherein the second period is smaller than
the first period.
34. The LED of claim 32, wherein the second period is
non-uniform.
35. The LED of claim 32, wherein the second period is uniform.
36. The LED of claim 33, wherein the first period is about 400 nm
to about 3,000 nm and the second period is about 100 nm to about
800 nm.
37. The LED of claim 31, further comprising a first electrode on a
portion of the conductive substrate without the mixed-period
photonic crystal structure.
38. The LED of claim 37, wherein the first electrode comprises at
least one of an ohmic contact layer, a reflection layer, and a
coupling layer.
39. The LED of claim 31, further comprising a second electrode
layer on the second conductivity type semiconductor layer.
40. The LED of claim 39, wherein the second electrode layer
comprises at least one of an ohmic contact layer, a reflection
layer, a coupling layer, and a second substrate.
41. The LED of claim 31, wherein the conductive substrate comprises
at least one of gallium nitride, gallium oxide, zinc oxide, silicon
carbide, and a metal oxide.
42. The LED of claim 31, wherein the conductive substrate is
polished to a thickness of about 70 .mu.m to about 100 .mu.m.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C. 119
and 35 U.S.C. 365 to Korean Patent Application No. 10-2009-0017997
(filed on Mar. 3, 2009), which is hereby incorporated by reference
in its entirety.
BACKGROUND
[0002] The present disclosure relates to light emitting devices
(LEDs).
[0003] Light emitting devices (LEDs) are semiconductor devices that
convert a current into light. After red LEDs was commercialized,
red LEDs and green LEDs have been used as light sources for
electronic devices including information communication devices.
[0004] For example, because a nitride semiconductor such as a
gallium nitride (GaN) semiconductor has a high thermal stability
and a wide band gap, it is being extensively researched in the
field of photonic devices and high-power electronic devices. The
research on a nitride semiconductor LED is being focused to improve
the light emitting efficiency.
[0005] In terms a semiconductor thin layer, the implementation of a
high-efficiency LED requires a method for improving an internal
quantum efficiency by increasing the probability of the radiative
combination of electrons and holes injected into a light emitting
layer, and a method for improving a light extraction efficiency so
that the light formed in a light emitting layer is effectively
outputted from the thin layer.
[0006] The improvement of the internal quantum efficiency requires
a technology for growing a high-quality thin layer, and a
technology for optimizing a thin layer lamination structure to
maximize the quantum effect. For the improvement of the light
extraction efficiency, Extensive research is being conducted to
control the geometric shape of a semiconductor thin layer.
SUMMARY
[0007] Embodiments provide light emitting devices (LEDs) having a
good light extraction efficiency.
[0008] In one embodiment, an LED comprises: a light emitting
structure including a first conductivity type semiconductor layer,
an active layer, and a second conductivity type semiconductor
layer; and a mixed-period photonic crystal structure on the light
emitting structure.
[0009] In another embodiment, an LED comprises: a light emitting
structure including a first conductivity type semiconductor layer,
an active layer, and a second conductivity type semiconductor
layer; a conductive substrate under the light emitting structure;
and a mixed-period photonic crystal structure on the conductive
substrate.
[0010] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features
will be apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a vertical sectional view of a mixed-period
photonic crystal structure of a light emitting device (LED)
according to an embodiment.
[0012] FIG. 2 is a vertical sectional view of a mixed-period
photonic crystal structure of an LED according to another
embodiment
[0013] FIGS. 3 to 5 are horizontal sectional views of the
mixed-period photonic crystal structure of the LED according to the
embodiment of FIG. 1.
[0014] FIGS. 6 and 7 are graphs showing the light extraction
efficiency of an LED according to an embodiment.
[0015] FIGS. 8 to 14 are sectional views showing a method for
fabricating an LED according to an embodiment 1.
[0016] FIGS. 15 to 17 are sectional views showing a method for
fabricating an LED according to an embodiment 2.
[0017] FIGS. 18 and 19 are the GaN electron microscope surface
pictures when a wet etching process is performed immediately after
removal of a substrate.
[0018] FIGS. 20 and 21 are GaN electron microscope surface pictures
when a wet etching process is performed after a dry etching process
for a portion of the GaN surface.
[0019] FIGS. 22 and 23 are electron microscope surface pictures
when a dry etching process is performed using an etch mask and a
wet etching process is performed after removal of the etch
mask.
[0020] FIG. 24 is a sectional view of an LED according to an
embodiment 3.
[0021] FIG. 25 is a sectional view of an LED according to an
embodiment 4.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0022] Light emitting devices (LEDs) according to embodiments will
be described in detail with reference to the accompanying
drawings.
[0023] In the description of embodiments, it will be understood
that when a layer (or film) is referred to as being "on/over"
another layer or substrate, it can be directly on/over another
layer or substrate, or intervening layers may also be present.
Further, it will be understood that when a layer is referred to as
being "under/below" another layer, it can be directly under/below
another layer, and one or more intervening layers may also be
present. In addition, it will also be understood that when a layer
is referred to as being "between" two layers, it can be the only
layer between the two layers, or one or more intervening layers may
also be present.
Embodiment 1
[0024] FIG. 1 is a vertical sectional view of a mixed-period
photonic crystal structure of a light emitting device (LED)
according to an embodiment. FIGS. 3 to 5 are horizontal sectional
views of the mixed-period photonic crystal structure of the LED
according to the embodiment of FIG. 1. FIG. 1 shows an example
where a second photonic crystal structure 115b of the mixed-period
photonic crystal structure has a uniform second period b. FIG. 2
shows another example where a second photonic crystal structure
115b' of the mixed-period photonic crystal structure has a
non-uniform second period b'. Hereinafter, a description will be
focused on the mixed-period photonic crystal structure of FIG. 1,
to which the embodiment is not limited.
[0025] The mixed-period photonic crystal structure can be a
structure where a first photonic crystal structure with a large
period is filled with a second photonic crystal structure with a
small period. Such a mixed-period photonic crystal structure is
very difficult to implement through a lithography process.
[0026] The surface roughness serves to extract the light confined
in an LED by total reflection.
[0027] In the embodiment, when the roughness or hole of a surface
has a spatial period, it is referred to as a photonic crystal.
Structural factors representing the photonic crystal are closely
related to a light extraction efficiency. Examples of the
structural factors include a period, an etching depth, the radius
of a hole, and the arrangement of lattices.
[0028] In particular, an incident angle providing an effective
diffraction efficiency is determined according to the period of the
photonic crystal. Therefore, a photonic crystal structure with
mixed periods maintains a high diffraction efficiency for various
incident angles in comparison with a photonic crystal structure
with a single period, thus increasing the light extraction
efficiency.
[0029] FIG. 1 shows a mixed-period photonic crystal structure 115
where a second photonic crystal structure 115b with a second period
b of about 250 nm is disposed in the space of a first photonic
crystal structure 115a with a first period a of about 1800 nm.
[0030] FIGS. 3 to 5 are horizontal sectional views of the
mixed-period photonic crystal structure of the LED according to the
embodiment of FIG. 1, which are taken along lines U (upper), M
(middle) and L (lower) of FIG. 1 to reveal the characteristics of
the mixed-period photonic crystal structure.
[0031] FIGS. 6 and 7 are graphs showing the light extraction
efficiency of an LED according to an embodiment.
[0032] FIGS. 6 and 7 are simulation results showing that a
mixed-period photonic crystal structure provides a better light
extraction efficiency than a single-period photonic crystal
structure.
[0033] Referring to FIG. 6, a line S represents the light
extraction efficiency depending on the radius of a hole (unit: a)
of a photonic crystal structure with a single period of 1800 nm,
and a line 115 represents the light extraction efficiency of a
mixed-period photonic crystal structure. The mixed photonic crystal
structure 115 of FIG. 1 or 2 provides a better efficiency than the
single-period photonic crystal structure S with a period of 1800
nm, regardless of the radius of a hole of the photonic crystal
structure.
[0034] Referring to FIG. 7, a line 115 represents the light
extraction efficiency depending on the period of a second photonic
crystal structure with a second period when the second photonic
crystal structure is introduced in a first photonic crystal
structure with a first period of 1800 nm. In FIG. 7, the X axis
represents the second period b of the second photonic crystal
structure.
[0035] It can be seen from FIG. 7 that the extraction efficiency
varies depending on the second period of the second photonic
crystal structure. If the first period of the first photonic
crystal structure is 1800 nm and the radius of a hole of the first
photonic crystal structure is 0.40 a, the extraction efficiency
varies depending on the second period of the second photonic
crystal structure as shown in FIG. 7. Under the above condition of
the first photonic crystal structure, the second period of the
second photonic crystal structure may have the maximum efficiency
value within the range from about 300 nm to about 650 nm, to which
the embodiment is not limited. That is, the second period of the
second photonic crystal structure capable of providing the maximum
efficiency may vary depending on the first period of the first
photonic crystal structure and the radius of the hole.
[0036] In order to fabricate a mixed-period photonic crystal
structure, the space of a first photonic crystal structure with a
first period must be filled with a second photonic crystal
structure with a second period smaller than the first period. This
is difficult to implement through a lithography process. The
embodiment provides a method for fabricating a mixed-period
photonic crystal structure by forming a first photonic crystal
structure through a lithography process and a dry etching process
and forming a second photonic crystal structure through a wet
etching process.
[0037] FIGS. 8 to 14 are sectional views showing a method for
fabricating an LED according to an embodiment 1.
[0038] Referring to FIG. 8, a light emitting structure including a
first conductivity type semiconductor layer 110, an active layer
120, and a second conductivity type semiconductor layer 130 can be
formed on a first substrate 100.
[0039] The first substrate 100 may be a sapphire (Al.sub.2O.sub.3)
substrate, to which the embodiment is not limited. A wet cleaning
process may be performed to remove the impurities of the surface of
the first substrate 100.
[0040] A first conductivity type semiconductor layer 110 can be
formed on the first substrate 100. For example, a chemical vapor
deposition (CVD) process, a molecular beam epitaxy (MBE) process, a
sputtering process, or a hydride vapor phase epitaxy (HVPE) process
may be used to form the first conductivity type semiconductor layer
110. Also, the first conductivity type semiconductor layer 110 may
be formed by injecting tri-methyl gallium gas (TMGa), ammonia gas
(NH.sub.3), nitrogen gas (N.sub.2), or silane gas (SiH.sub.4)
containing n-type impurity such as silicon (Si) into a process
chamber.
[0041] An active layer 120 can be formed on the first conductivity
type semiconductor layer 110. The active layer 120 emits a light of
energy determined by the specific energy band of the active layer
(light emitting layer) material when electrons injected through the
first conductivity type semiconductor layer 110 recombine with
holes injected through the second conductivity type semiconductor
layer 130. The active layer 120 may have a quantum well structure
that is formed by alternately laminating nitride semiconductor
layers with different energy bands once or several times. For
example, the active layer 120 may have a quantum well structure
with an InGaN/GaN structure that is formed by injecting tri-methyl
gallium gas (TMGa), ammonia gas (NH.sub.3), nitrogen gas (N.sub.2),
or tri-methyl indium gas (TMIn), to which the embodiment is not
limited.
[0042] A second conductivity type semiconductor layer 130 can be
formed on the active layer 120. For example, the second
conductivity type semiconductor layer 130 may be formed by
injecting tri-methyl gallium gas (TMGa), ammonia gas (NH.sub.3),
nitrogen gas (N.sub.2), or bisethylcyclopentadienyl magnesium
(EtCp.sub.2Mg){Mg(C.sub.2H.sub.5C.sub.5H.sub.4).sub.2} containing
p-type impurity such as magnesium (Mg) into a process chamber, to
which the embodiment is not limited.
[0043] A second electrode layer 140 may be formed on the second
conductivity type semiconductor layer 130. The second electrode
layer 140 may include an ohmic contact layer, a reflection layer, a
coupling layer, and a second substrate.
[0044] For example, the second electrode layer 140 may include an
ohmic contact layer, and may be formed by laminating a single metal
or a metal alloy several times in order to provide efficient hole
injection. Also, the ohmic contact layer may include metal oxide
material or metal material. For example, the ohmic contact layer
may include at least one of ITO, IZO (In--ZnO), GZO (Ga--ZnO), AZO
(Al--ZnO), AGZO (Al--Ga ZnO), IGZO (In--Ga ZnO), IrOx, RuOx,
RuOx/ITO, Ni/IrOx/Au, and Ni/IrOx/Au/ITO, to which the embodiment
is not limited.
[0045] Also, the second electrode layer 140 may include a
reflection layer and/or a coupling layer. For example, if the
second electrode layer 140 includes a reflection layer, the
reflection layer may be formed of a metal layer containing aluminum
(Al), argentum (Ag), or an Al or Ag-containing metal alloy. The Al
or Ag effectively reflects the light generated from the active
layer, thus making it possible to greatly improve the light
extraction efficiency of the LED.
[0046] Also, for example, if the second electrode layer 140 can
include a coupling layer, the reflection layer may serve as the
coupling layer or the coupling layer may be formed using nickel
(Ni) or aurum (Au).
[0047] Also, in the embodiment, the second electrode layer 140 may
include a second substrate 200. If the first conductivity type
semiconductor layer 110 has a sufficient thickness of about 50
.mu.m or more, a process of forming the second substrate 200 may be
omitted.
[0048] The second substrate 200 may be formed of highly conductive
metal, metal alloy, or conductive semiconductor material in order
to provide efficient hole injection. For example, the second
substrate 200 may be formed of at least of one of copper (Cu), Cu
alloy, Mo, carrier wafer such as Si, Ge, SiGe. The second substrate
200 may be formed using an electrochemical metal deposition process
or a eutectic metal based bonding process.
[0049] Referring to FIG. 9, the first substrate 100 can be removed
to expose the first conductivity type semiconductor layer 110.
[0050] The first substrate 100 may be removed using a high-power
laser lift-off process or a chemical etching process. Also, the
first substrate 100 may be removed using a physical grinding
process. The removal of the first substrate 100 exposes the first
conductivity type semiconductor layer 110. The exposed first
conductivity type semiconductor layer 110 may have a surface defect
layer generated when the first substrate 100 is removed. The
surface defect layer may be removed through a wet etching process
or a dry etching process.
[0051] A mixed-period photonic crystal structure can be formed in a
partial region R of the exposed first conductivity type
semiconductor layer 110. The partial region R of the first
conductivity type semiconductor layer 110 may be formed around a
first electrode to be formed later.
[0052] If a rough surface is applied to an electrode in fabrication
of a device based on a mixed-period photonic crystal structure
(i.e., a surface roughness), it causes an additional optical loss.
According to the embodiment, a mixed-period photonic crystal
structure may be formed in a certain region R and an electrode
region may be maintained to be planar, as shown in FIG. 9.
[0053] Hereinafter, with reference to FIGS. 10 to 12, a detailed
description will be given of a process for forming a mixed-period
photonic crystal structure in a certain region R of the first
conductivity type semiconductor layer 110.
[0054] Referring to FIG. 10, a first pattern 310 can be formed in a
partial region of the exposed first conductivity type semiconductor
layer 110. The first pattern 310 can serve as a mask used for a dry
etching process. The first pattern 310 may be formed of dielectrics
(e.g., SiO.sub.2 and Si.sub.3N.sub.4) or metals (e.g., Cr and Ni),
which may be materials that do not react with basic solution (e.g.,
KOH or NaOH) used for wet etching of n-type GaN in the subsequent
process.
[0055] Referring to FIG. 11, using the first pattern 310 as a mask,
the partial region R of the first conductivity type semiconductor
layer 110 can be dry-etched to form a first photonic crystal
structure 115a with a first period. The first period may be about
400 nm to about 3,000 nm, to which the embodiment is not
limited.
[0056] Referring to FIG. 12, using the first pattern 310 as a mask,
a wet etching process may be performed to form a second photonic
crystal structure 115b with a second period in the partial region
of the first conductivity type semiconductor layer 110 having the
first photonic crystal structure 115a formed therein. The second
period may be smaller than the first period. For example, if the
first period is about 400 nm to about 3,000 nm, the second period
may be about 100 nm to about 800 nm.
[0057] When the wet etching process is performed after the dry
etching without removing the first pattern mask, a roughness can be
formed on a surface not covered with the first pattern mask and the
height of a hole (or pillar) is further increased.
[0058] In the embodiment, the second photonic crystal structure may
be formed to have a non-uniform second period as shown in FIG.
2.
[0059] Referring to FIG. 13, a first electrode layer 150 can be
formed in the region of the first conductivity type semiconductor
layer 110, except the region of the mixed-period photonic crystal
structure 115. The first electrode layer 150 may include an ohmic
layer, a reflection layer, and a coupling layer.
[0060] FIG. 14 is a sectional view of an LED according to an
embodiment 1. Referring to FIG. 14, an undoped semiconductor layer
112 may be further included on a first conductivity type
semiconductor layer 110, and a photonic crystal structure 115 may
be formed on the undoped semiconductor layer 112. For example, an
undoped GaN layer 112 may be formed on a first conductivity type
semiconductor layer 110, and a photonic crystal structure 115 may
be formed on the undoped GaN layer 112.
Embodiment 2
[0061] FIGS. 15 to 17 are sectional views showing a method for
fabricating an LED according to an embodiment 2.
[0062] Unlike the embodiment 1, the embodiment 2 can remove a first
pattern 310 and performs a wet etching process. Referring to FIG.
15, a first pattern 310 can be formed in a partial region of the
first conductivity type semiconductor layer 110. Referring to FIG.
16, using the first pattern 310 as a mask, the partial region of
the first conductivity type semiconductor layer 110 can be
dry-etched to form a first photonic crystal structure 115a with a
first period. Referring to FIG. 17, after the first pattern 310 is
removed, a second photonic crystal structure 115b with a second
period b can be formed in the partial region of the first
conductivity type semiconductor layer 110 having the first photonic
crystal structure 115a formed therein. In the embodiment 2, the
second photonic crystal structure may be formed also on the surface
of the first photonic crystal structure 115a.
[0063] The second period b may be smaller than the first period.
For example, if the first period is about 400 nm to about 3,000 nm,
the second period may be about 100 nm to about 800 nm.
[0064] Even if the mask of the first pattern 310 is removed and a
wet etching process is performed as shown in FIG. 16, the wet
etching of the N-type GaN mounting the first pattern 310 can be
somewhat delayed. The reason for this is that Ga ions accumulated
during the removal of the sapphire substrate by a laser lift-off
process interrupts the wet etching process. Thus, even if the first
pattern mask is removed, a surface roughness with a size of about
100 nm to about 300 nm may be formed at several points of the
photonic crystal surface. That is, the second photonic crystal
structure formed on the first photonic crystal structure 115a
corresponding to the first pattern 310 may have a finer second
period than the second photonic crystal structure formed between
the first photonic crystal structures 115a.
[0065] A mixed-period photonic crystal structure 115 may be
completed by the method of the embodiment 1 or 2. The GaN surface
supporting the mask of the first pattern 310 delays the wet etching
process, thereby forming a roughness of a fine second period with a
size of about 100 nm to about 300 nm. Therefore, through the wet
etching process, the surface roughness covers the entire photonic
crystal region, thus improving the light extraction efficiency.
[0066] FIGS. 18 and 19 are the GaN electron microscope surface
pictures when a wet etching process is performed immediately after
removal of a sapphire substrate, for example, a laser lift-off
process. FIGS. 20 and 21 are the GaN electron microscope surface
pictures when a wet etching process is performed after a dry
etching process for a portion of the GaN surface.
[0067] For example, in the case of a vertical type GaN LED
structure as in the embodiments 1 and 2, a wet etching process can
be performed on an n-type GaN layer 110 or an undoped-GaN layer 112
from which a sapphire substrate is removed. If a wet etching
process performed after removal of a substrate as shown in FIGS. 18
and 19, a wet etching process is not actively performed, except a
fine surface roughness, excluding a laser lift-off line.
[0068] On the other hand, if a wet etching process is performed
after Ga ions on the GaN surface are removed through a dry etching
process as shown in FIGS. 20 and 21, a roughness shape with
suitable sizes is uniformly formed on the surface, as can be seen
from the electron microscope pictures.
[0069] FIGS. 22 and 23 are the electron microscope surface pictures
when a dry etching process is performed using an etch mask and a
wet etching process is performed after removal of the etch
mask.
[0070] According to the embodiment, a fine surface roughness fills
the entire photonic crystal space as shown in FIGS. 22 and 23. In
no case, the photonic crystal structure is destroyed or covered by
the surface roughness, due to a difference in the wet etching
reaction depending on the exposure to the dry etching process.
[0071] According to the embodiment, a first photonic crystal is
formed through a lithography process and a dry etching process and
a second photonic crystal is formed through a wet etching process
to fabricate a mixed-period photonic crystal structure.
[0072] Also, the mixed-period photonic crystal structure can
increase the light extraction efficiency. That is, the mixed-period
photonic crystal structure according to the embodiment can provide
better light extraction efficiency characteristics than a
single-period photonic crystal structure or a light extraction
structure with surface roughness.
Embodiment 3
[0073] FIG. 24 is a sectional view of an LED according to an
embodiment 3.
[0074] Referring to FIG. 24, an LED according to an embodiment 3
may include: a light emitting structure including a second
conductivity type semiconductor layer 130, an active layer 120, and
a first conductivity type semiconductor layer 110; a conductive
substrate 100a formed on the light emitting structure; and a
mixed-period photonic crystal structure 115 formed in a partial
region of the conductive substrate 100a.
[0075] The embodiment 3 may use the technical features of the
embodiments 1 and 2. The embodiment 3 can be a vertical type LED
structure where a light emitting structure including a first
conductivity type semiconductor layer 110, an active layer 120, and
a second conductivity type semiconductor layer 140 is formed on a
conductive substrate 110a, wherein the substrate need not be
removed during the fabrication process.
[0076] That is, the embodiment 3 can use a conductive substrate and
forms a mixed-period photonic crystal structure 115 on a portion of
the conductive substrate.
[0077] A method for fabricating an LED according to the embodiment
3 will be described with reference to FIG. 24. A description of an
overlap with the embodiments 1 and 2 will be omitted for
conciseness.
[0078] Referring to FIG. 24, a conductive substrate 100a is
prepared. The conductive substrate 100a can be high in electric
conductivity and can be transparent in the range of visible rays.
The conductive substrate 100a may be formed of gallium nitride
(e.g., GaN), gallium oxide (e.g., Ga.sub.2O.sub.3), zinc oxide
(ZnO), silicon carbide (SiC), or metal oxide.
[0079] Like the embodiments 1 and 2, a light emitting structure
including a first conductivity type semiconductor layer 110, an
active layer 120, and a second conductivity type semiconductor
layer 140 is formed on the conductive substrate 100a.
[0080] A portion of the bottom of the conductive substrate 100a can
be removed. For example, a polishing process may be performed to
reduce the thickness of the bottom layer of the conductive
substrate 100a. The thickness of the conductive substrate 100a
after the polishing process may vary according to the application
product of a desired device. For example, the conductive substrate
100a with a thickness of about 400 .mu.m to about 500 .mu.m can be
polished to a thickness of about 70 .mu.m to about 100 .mu.m, to
which the embodiment is not limited.
[0081] When a nitride semiconductor thin layer can be formed on the
conductive substrate 100a at high temperatures by means of a thin
layer growth equipment, the surface crystal quality of the bottom
surface of the conductive substrate 100a may degrade due to high
thin layer growth temperatures and reactive gases. Thus, polishing
the bottom layer of the conductive substrate 100a can improve the
electrical characteristics of the device.
[0082] Like the embodiment 1 or 2, a mixed-period photonic crystal
structure 115 may be formed in a partial region of the conductive
substrate 100a.
[0083] A first electrode 150 may be formed in the remaining region
of the conductive substrate 100a, except the partial region having
the mixed-period photonic crystal structure 115 formed therein.
Embodiment 4
[0084] FIG. 25 is a sectional view of an LED according to an
embodiment 4.
[0085] Referring to FIG. 25, an LED according to an embodiment 4
may include: a nonconductive substrate 100; a light emitting
structure formed on the nonconductive substrate 100 and including a
first conductivity type semiconductor layer 110, an active layer
120, and a second conductivity type semiconductor layer 140; and a
mixed-period photonic crystal structure 115 formed in a partial
region of the second conductivity type semiconductor layer 140. A
second electrode 170 may be formed on the second conductivity type
semiconductor layer 140, and a first electrode 160 may be formed on
the first conductivity type semiconductor layer 110.
[0086] The embodiment 4 may use the technical features of the
embodiments 1 to 3. The embodiment 4 can have a horizontal type LED
structure and may include a mixed-period photonic crystal structure
115 on the second conductivity type semiconductor layer 140.
[0087] Any reference in this specification to "one embodiment," "an
embodiment," "example embodiment," etc., means that a particular
feature, structure, or characteristic described in connection with
the embodiment is included in at least one embodiment of the
invention. The appearances of such phrases in various places in the
specification are not necessarily all referring to the same
embodiment. Further, when a particular feature, structure, or
characteristic is described in connection with any embodiment, it
is submitted that it is within the purview of one skilled in the
art to effect such feature, structure, or characteristic in
connection with other ones of the embodiments.
[0088] Although embodiments have been described with reference to a
number of illustrative embodiments thereof, it should be understood
that numerous other modifications and embodiments can be devised by
those skilled in the art that will fall within the spirit and scope
of the principles of this disclosure. More particularly, various
variations and modifications are possible in the component parts
and/or arrangements of the subject combination arrangement within
the scope of the disclosure, the drawings and the appended claims.
In addition to variations and modifications in the component parts
and/or arrangements, alternative uses will also be apparent to
those skilled in the art.
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