U.S. patent application number 15/263000 was filed with the patent office on 2016-12-29 for light emitting diode having distributed bragg reflector.
The applicant listed for this patent is Seoul Viosys Co., Ltd.. Invention is credited to Jae Moo Kim, Kyoung Wan Kim, Ye Seul Kim, Jin Woong Lee, Sang Hyun Oh, Duk Il SUH, Yeo Jin Yoon.
Application Number | 20160380157 15/263000 |
Document ID | / |
Family ID | 45525830 |
Filed Date | 2016-12-29 |
United States Patent
Application |
20160380157 |
Kind Code |
A1 |
SUH; Duk Il ; et
al. |
December 29, 2016 |
LIGHT EMITTING DIODE HAVING DISTRIBUTED BRAGG REFLECTOR
Abstract
A light-emitting diode (LED) includes a light-emitting structure
arranged on a first surface of a substrate, the light-emitting
structure including a first conductivity-type semiconductor layer;
a second conductivity-type semiconductor layer, and an active layer
interposed between the first conductivity-type semiconductor layer
and the second conductivity-type semiconductor layer. The LED
includes a first distributed Bragg reflector arranged on a second
surface of the substrate opposite to the first surface, the first
distributed Bragg reflector including a first laminate structure
including alternately stacked SiO.sub.2 and Nb.sub.2O.sub.5 layers.
The first laminate structure of the first distributed Bragg
reflector is configured to reflect at least 90% of a first
wavelength range of blue light emitted from the light emitting
structure.
Inventors: |
SUH; Duk Il; (Ansan-si,
KR) ; Kim; Jae Moo; (Ansan-si, KR) ; Kim;
Kyoung Wan; (Ansan-si, KR) ; Yoon; Yeo Jin;
(Ansan-si, KR) ; Kim; Ye Seul; (Ansan-si, KR)
; Oh; Sang Hyun; (Ansan-si, KR) ; Lee; Jin
Woong; (Ansan-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seoul Viosys Co., Ltd. |
Ansan-si |
|
KR |
|
|
Family ID: |
45525830 |
Appl. No.: |
15/263000 |
Filed: |
September 12, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14608150 |
Jan 28, 2015 |
|
|
|
15263000 |
|
|
|
|
13760637 |
Feb 6, 2013 |
8963183 |
|
|
14608150 |
|
|
|
|
13100879 |
May 4, 2011 |
8373188 |
|
|
13760637 |
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Current U.S.
Class: |
257/98 |
Current CPC
Class: |
H01L 2224/48091
20130101; H01L 2924/181 20130101; H01L 2224/48247 20130101; H01L
2924/181 20130101; H01L 33/42 20130101; H01L 2224/73265 20130101;
H01L 33/38 20130101; H01L 33/50 20130101; H01L 33/10 20130101; H01L
2924/00014 20130101; H01L 2224/48257 20130101; H01L 2924/00012
20130101; H01L 2224/48091 20130101; H01L 33/46 20130101 |
International
Class: |
H01L 33/46 20060101
H01L033/46; H01L 33/42 20060101 H01L033/42; H01L 33/38 20060101
H01L033/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 28, 2010 |
KR |
10-2010-0072822 |
Aug 10, 2010 |
KR |
10-2010-0076914 |
Claims
1. A light-emitting diode (LED), comprising: a light-emitting
structure arranged on a first surface of a substrate, the
light-emitting structure comprising: a first conductivity-type
semiconductor layer; a second conductivity-type semiconductor
layer; and an active layer interposed between the first
conductivity-type semiconductor layer and the second
conductivity-type semiconductor layer; and a first distributed
Bragg reflector arranged on a second surface of the substrate
opposite to the first surface, the first distributed Bragg
reflector comprising a first laminate structure comprising
alternately stacked silicon dioxide (SiO.sub.2) and niobium
pentoxide (Nb.sub.2O.sub.5) layers, wherein the first laminate
structure of the first distributed Bragg reflector is configured to
reflect at least 90% of a first wavelength range of blue light
emitted from the light-emitting structure.
2. The LED of claim 1, wherein the first laminate structure of the
first distributed Bragg reflector is further configured to reflect
at least 90% of a second wavelength range of green light and at
least 90% of a third wavelength range of red light.
3. The LED of claim 1, wherein the first laminate structure of the
first distributed Bragg reflector comprises an uppermost layer and
a lowermost layer comprising SiO.sub.2.
4. The LED of claim 1, further comprising: a first electrode
connected to the first conductivity-type semiconductor layer; and a
second electrode connected to the second conductivity-type
semiconductor layer.
5. The LED of claim 4, further comprising: a metal layer located
under the first distributed Bragg reflector.
6. The LED of claim 4, further comprising: a second distributed
Bragg reflector arranged on the light-emitting structure, wherein
the light-emitting structure is interposed between the second
distributed Bragg reflector and the substrate.
7. The LED of claim 6, wherein the second distributed Bragg
reflector comprises a second laminate structure comprising
alternately stacked SiO.sub.2 and Nb.sub.2O.sub.5 layers.
8. The LED of claim 7, wherein the second laminate structure of the
second distributed Bragg reflector is configured to: allow a fourth
wavelength range of blue light generated in the active layer to
pass through the second Distributed Bragg reflector, and reflect a
fifth wavelength range of non-blue light.
9. The LED of claim 6, further comprising a transparent conductive
layer interposed between the second conductivity-type semiconductor
layer and the second distributed Bragg reflector.
10. The LED of claim 9, the transparent conductive layer comprises
indium tin oxide (ITO) or zinc oxide (ZnO).
11. The LED of claim 6, wherein the second distributed Bragg
reflector covers at least a portion of the first conductivity-type
semiconductor layer and has an opening exposing the first
conductivity-type semiconductor layer.
12. A light-emitting diode (LED), comprising: a substrate
comprising a pattern on a first surface of the substrate; a
light-emitting structure disposed on the first surface of the
substrate, the light-emitting structure comprising: a first
conductivity-type semiconductor layer; a second conductivity-type
semiconductor layer; and an active layer disposed between the first
conductivity-type semiconductor layer and the second
conductivity-type semiconductor layer; a first electrode connected
to the first conductivity-type semiconductor layer; a second
electrode connected to the second conductivity-type semiconductor
layer; a first distributed Bragg reflector (DBR) disposed on a
second surface of the substrate opposite to the first surface; and
a second DBR disposed on the light-emitting structure having the
light-emitting structure disposed between the second DBR and the
substrate, the second DBR comprises a first opening exposing the
first electrode and a second opening exposing the second electrode,
wherein the first DBR and the second DBR comprise niobium pentoxide
(Nb.sub.2O.sub.5).
13. The LED of claim 12, wherein: the first DBR comprises a first
laminate structure comprising a plurality of silicon dioxide
(SiO.sub.2) layers and a plurality of Nb.sub.2O.sub.5 layers, the
first laminate structure is configured to reflect a first
wavelength range of blue light generated in the active layer.
14. The LED of claim 12, wherein the second DBR comprises a second
laminate structure comprising a plurality of SiO.sub.2 layers and a
plurality layers of Nb.sub.2O.sub.5 layers.
15. The LED of claim 12, wherein the second DBR covers a portion of
an upper surface of the first conductivity-type semiconductor
layer, a portion of a side surface of the second conductivity-type
semiconductor layer, and a portion of a side surface of the active
layer.
16. The LED of claim 12, wherein the second DBR has an opening
exposing the first conductivity-type semiconductor layer.
17. The LED of claim 16, wherein the first electrode is connected
to the first conductivity-type semiconductor layer through the
opening of the second DBR.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/608,150, filed on Jan. 28, 2015, which is a
continuation of U.S. patent application Ser. No. 13/760,637, filed
on Feb. 6, 2013, now issued as U.S. Pat. No. 8,963,183, which is a
divisional of U.S. patent application Ser. No. 13/100,879, filed on
May 4, 2011, now issued as U.S. Pat. No. 8,373,188, and claims
priority from and the benefit of Korean Patent Application No.
10-2010-0072822, filed on Jul. 28, 2010, and Korean Patent
Application No. 10-2010-0076914, filed on Aug. 10, 2010, all of
which are hereby incorporated by reference for all purposes as if
fully set forth herein.
BACKGROUND
[0002] Field
[0003] Exemplary embodiments of the present invention relate to a
light-emitting diode and, more particularly, to a light-emitting
diode having a distributed Bragg reflector.
[0004] Discussion of the Background
[0005] Gallium nitride (GaN)-based blue or ultraviolet (UV)
light-emitting diodes (LEDs) may be used in a wide range of
applications. In particular, various kinds of LED packages for
emitting light having mixed colors, for example, white light, have
been applied to backlight units, general lighting devices, and the
like.
[0006] Since optical power of the LED package may depend upon
luminous efficiency of an LED, numerous studies have focused on
development of LEDs having improved luminous efficiency. For
example, a metal reflector may be formed on a lower surface of a
transparent substrate such as a sapphire substrate to improve light
extraction efficiency of the LED.
[0007] FIG. 1 shows reflectivity of a sapphire substrate having an
aluminum layer formed on a lower surface thereof.
[0008] Referring to FIG. 1, a sapphire substrate having no aluminum
layer exhibits a reflectivity of about 20%, whereas the sapphire
substrate having an aluminum layer exhibits a reflectivity of about
80% over the entire visible spectrum.
[0009] FIG. 2 shows reflectivity of a sapphire substrate having a
distributed Bragg reflector formed by alternately stacking
TiO.sub.2/SiO.sub.2 on a lower surface thereof.
[0010] When the substrate is formed with the distributed Bragg
reflector instead of the aluminum layer, the substrate exhibits a
reflectivity approaching 100% for light in the blue wavelength
range, for example in a wavelength range of 400 nm to 500 nm and
having a peak wavelength of 460 nm, as shown in FIG. 2.
[0011] However, the distributed Bragg reflector may only increase
reflectivity in certain regions of the visible spectrum and may
exhibit significantly lower reflectivity in other regions. In other
words, as shown in FIG. 2, the reflectivity rapidly decreases at a
wavelength of about 520 nm or more and is less than 50% at a
wavelength of 550 nm or more.
[0012] Accordingly, when an LED with the distributed Bragg
reflector is mounted on an LED package for emitting white light,
the distributed Bragg reflector of the LED may exhibit high
reflectivity with respect to light in the wavelength range of blue
light emitted from the LED, but may not exhibit effective
reflective characteristics with respect to light in the wavelength
ranges of green and/or red light, thereby restricting improvement
in light emission efficiency of the LED package.
[0013] A GaN-based semiconductor has an index of refraction of
about 2.4. Accordingly, there may be a difference in index of
refraction between the GaN-based semiconductor and external air or
a molding resin, so light generated in the active layer may be
trapped by the semiconductor layer and not be emitted to the
outside due to total internal reflection at an interface
therebetween.
SUMMARY
[0014] Exemplary embodiments of the present invention provide an
LED for an LED package to emit light having mixed colors, for
example, white light.
[0015] Exemplary embodiments of the present invention provide an
LED to improve light emission efficiency of an LED package.
[0016] Exemplary embodiments of the present invention provide an
LED to prevent optical loss inside the LED when light enters the
LED from outside of the LED.
[0017] Exemplary embodiments of the present invention provide an
LED to prevent optical loss caused by total internal
reflection.
[0018] Additional features of the invention will be set forth in
the description which follows, and in part will be apparent from
the description, or may be learned by practice of the
invention.
[0019] An exemplary embodiment of the present invention provides a
light-emitting diode including a light-emitting structure arranged
on a first surface of a substrate, the light-emitting structure
including a first conductivity-type semiconductor layer, a second
conductivity-type semiconductor layer, and an active layer
interposed between the first conductivity-type semiconductor layer
and the second conductivity-type semiconductor layer. The
light-emitting diode includes a first distributed Bragg reflector
arranged on a second surface of the substrate opposite to the first
surface, the first distributed Bragg reflector to reflect light
emitted from the light emitting structure. The first distributed
Bragg reflector has a reflectivity of at least 90% with respect to
light of a first wavelength in a blue wavelength range, light of a
second wavelength in a green wavelength range, and light of a third
wavelength in a red wavelength range. The first distributed Bragg
reflector has a laminate structure having an alternately stacked
SiO.sub.2 layer and an Nb.sub.2O.sub.5 layer.
[0020] An exemplary embodiment of the invention also discloses a
light emitting diode including a light-emitting structure arranged
on a first surface of a substrate, the light-emitting structure
including a first conductivity-type semiconductor layer, a second
conductivity-type semiconductor layer, and an active layer
interposed between the first conductivity-type semiconductor layer
and the second conductivity-type semiconductor layer. The
light-emitting diode includes an insulation layer arranged on the
light-emitting structure, a distributed Bragg reflector arranged on
a second surface of the substrate opposite to the first surface,
the distributed Bragg reflector to reflect light emitted from the
light-emitting structure, and a reflective metal layer, the
distributed Bragg reflector arranged between the substrate and the
reflective metal layer. The distributed Bragg reflector has a
reflectivity of at least 90% with respect to light of a first
wavelength in a blue wavelength range, light of a second wavelength
in a green wavelength range and light of a third wavelength in a
red wavelength range.
[0021] An exemplary embodiment of the present invention also
discloses a light-emitting diode including a substrate, a light
emitter arranged on a first surface of the substrate, and a
reflector arranged on a second surface of the substrate opposite to
the first surface, the reflector to reflect light emitted from the
light emitter. The reflector includes SiO.sub.2 layers and
Nb.sub.2O.sub.5 layers that are alternately arranged on each
other.
[0022] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention, and together with the description serve to explain
the principles of the invention.
[0024] FIG. 1 is a graph showing reflectivity of aluminum on a
sapphire substrate.
[0025] FIG. 2 is a graph showing reflectivity of a distributed
Bragg reflector on a sapphire substrate.
[0026] FIG. 3 is a sectional view of a light-emitting diode (LED)
having a distributed Bragg reflector according to an exemplary
embodiment of the present invention.
[0027] FIG. 4 is a graph showing optical absorption coefficients of
TiO.sub.2 and Nb.sub.2O.sub.5.
[0028] FIG. 5 is a graph showing a luminescence spectrum of a
yellow phosphor.
[0029] FIG. 6 is a graph showing a reflectance spectrum of a first
upper distributed Bragg reflector.
[0030] FIG. 7 is a sectional view of an LED package having an LED
according to an exemplary embodiment of the present invention.
[0031] FIG. 8 is a sectional view of an LED having a distributed
Bragg reflector according to an exemplary embodiment of the present
invention.
[0032] FIG. 9 is a graph showing a reflectance spectrum of a second
upper distributed Bragg reflector.
[0033] FIG. 10 is a sectional view of an LED having a distributed
Bragg reflector according to an exemplary embodiment of the present
invention.
[0034] FIG. 11 is a schematic sectional view of an electron beam
deposition apparatus, according to an exemplary embodiment of the
present invention.
[0035] FIG. 12 is a sectional view of a transparent conductive
layer according to an exemplary embodiment of the invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0036] The invention is described more fully hereinafter with
reference to the accompanying drawings, in which exemplary
embodiments of the invention are shown. This invention may,
however, be embodied in many different forms and should not be
construed as limited to the exemplary embodiments set forth herein.
Rather, these exemplary embodiments are provided so that this
disclosure is thorough and will fully convey the scope of the
invention to those skilled in the art. In the drawings, the sizes
and relative sizes of layers and regions may be exaggerated for
clarity. Like reference numerals in the drawings denote like
elements.
[0037] 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.
[0038] FIG. 3 is a sectional view of a light emitting diode 20
having a distributed Bragg reflector 40 according to an exemplary
embodiment of the present invention.
[0039] Referring to FIG. 3, a light emitting diode 20 may include a
substrate 21, a light emitting structure 30, and a lower
distributed Bragg reflector 40. Further, the LED 20 may include a
buffer layer 23, a transparent electrode 31, a first electrode pad
33, a second electrode pad 35, a metal layer 45, and a first upper
distributed Bragg reflector 37.
[0040] The substrate 21 may be selected from any transparent
substrate, for example, a sapphire substrate or a SiC substrate.
The substrate 21 may have a pattern on an upper surface thereof,
for example a patterned sapphire substrate (PSS) having a pattern
on an upper surface thereof. The area of the substrate 21 may
determine the total area of a chip. The substrate 21 may have an
area of at least 90,000 .mu.m.sup.2. For example, the substrate 21
may have an area of at least 1 mm.sup.2.
[0041] The light emitting structure 30 is located on the substrate
21. The light emitting structure 30 includes a first
conductivity-type semiconductor layer 25, a second
conductivity-type semiconductor layer 29, and an active layer 27
interposed between the first and second conductivity-type
semiconductor layers 25 and 29. Herein, the first conductivity-type
and the second conductivity-type refer to opposite conductivity
types. For example, the first conductivity-type may be n-type and
the second conductivity-type may be p-type, or vice versa.
[0042] The first conductivity-type semiconductor layer 25, the
active layer 27, and the second conductivity-type semiconductor
layer 29 may be formed of, although not limited to, a GaN-based
compound semiconductor material, that is, (Al, In, Ga)N. The active
layer 27 is composed of elements to emit light at desired
wavelength, for example, UV or blue light. As shown, the first
conductivity-type semiconductor layer 25 and/or the second
conductivity-type semiconductor layer 29 have a single layer
structure or a multilayer structure. Further, the active layer 27
may have a single quantum well structure or a multi-quantum well
structure. The buffer layer 23 may be interposed between the
substrate 21 and the first conductivity-type semiconductor layer
25.
[0043] The first and second conductivity-type semiconductor layers
25 and 29 and the active layer 27 may be formed by metal organic
chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE),
and may be patterned to expose some regions of the first
conductivity-type semiconductor layer 25 by a photolithography and
etching process.
[0044] The transparent electrode layer 31 may be formed of, for
example, indium tin oxide (ITO) or Ni/Au on the second
conductivity-type semiconductor layer 29. The transparent electrode
layer 31 has a lower specific resistance than the second
conductivity-type semiconductor layer 29 and helps spread electric
current. The first electrode pad 33, for example, an n-electrode
pad, is formed on the first conductivity-type semiconductor layer
25, and the second electrode pad 35, for example, a p-electrode
pad, is formed on the transparent electrode layer 31. As shown, the
p-electrode pad 35 may be electrically connected to the second
conductivity-type semiconductor layer 29 through the transparent
electrode layer 31. Alternatively, the p-electrode pad 35 may
directly contact the second conductivity-type semiconductor layer
29.
[0045] The lower distributed Bragg reflector 40 is located under
the substrate 21. The lower distributed Bragg reflector 40 is
formed by alternately stacking layers having different indices of
refraction and has relatively high reflectivity, for example, a
reflectivity of at least 90%, not only with respect to light in the
blue wavelength range, for example, that is generated in the active
layer 27, but also with respect to light in the wavelength region
of yellow light or in the wavelength region of green and/or red
light. In addition, the lower distributed Bragg reflector 40 may
have a reflectivity of at least 90% for wavelengths in the range
of, for example, 400 nm to 700 nm.
[0046] The lower distributed Bragg reflector 40 has a relatively
high reflectivity over a wide wavelength range, and is formed by
controlling the optical thickness of each material layer
alternately stacked one above another. The lower distributed Bragg
reflector 40 may be formed by alternately stacking, for example, a
first layer formed of SiO.sub.2 and a second layer formed of
TiO.sub.2. The lower distributed Bragg reflector 40 may be formed
by alternately stacking a first layer formed of SiO.sub.2 and a
second layer formed of Nb.sub.2O.sub.5, to thereby form a laminate
structure.
[0047] U.S. patent application Ser. No. 12/917,937 discloses a
light emitting diode which includes a distributed Bragg reflector
having a reflectivity of at least 90% with respect to light in the
wavelength range of blue, green, and red light. That application
discloses a distributed Bragg reflector, which is formed by
alternately stacking layers having different indices of refraction,
for example, TiO.sub.2/SiO.sub.2 layers, to have high reflectivity
with respect to light not only in the blue wavelength range but
also in the green or red wavelength range. When curing an Ag epoxy
paste applied on the distributed Bragg reflector formed by
alternately stacking TiO.sub.2/SiO.sub.2 layers (41 layers), the
distributed Bragg reflector has a lower reflectivity than that of
the reflector before curing the Ag epoxy paste. The decrease in
reflectivity of the distributed Bragg reflector may be caused by
the relatively small number of layers constituting the distributed
Bragg reflector, which results in scattering light at an interface
between the distributed Bragg reflector and the Ag epoxy or optical
absorption by the Ag epoxy. To prevent the decrease in reflectivity
of the distributed Bragg reflector, the number of layers
constituting the distributed Bragg reflector may be increased.
Meanwhile, an increase in the number of layers constituting the
distributed Bragg reflector may reduce an influence by the
condition of the interface between the distributed Bragg reflector
and the Ag epoxy, but may cause optical loss relating to an optical
absorption rate of each of the layers constituting the distributed
Bragg reflector, thereby causing a reduction in reflectivity.
[0048] Therefore, the LED according to exemplary embodiments of the
present invention may prevent optical loss relating to an increase
in the number of layers constituting the distributed Bragg
reflector by adopting Nb.sub.2O.sub.5 having a lower optical
absorption rate than TiO.sub.2 to form a distributed Bragg
reflector of SiO.sub.2/Nb.sub.2O.sub.5.
[0049] As the number of first and second layers stacked one above
another increases, it is possible to reduce influence by other
material layers adjoining a lower surface of the lower distributed
Bragg reflector 40. When a small number of layers are stacked, the
reflectivity of the lower distributed Bragg reflector 40 can be
lowered after an adhesive layer, for example, Ag epoxy pastes, is
cured. Therefore, the distributed Bragg reflector 40 may be
composed of fifty or more layers, that is, 25 pairs or more.
[0050] Further, as the number of first and second layers stacked
one above another increases, the optical absorption rate of the
material layers constituting the lower distributed Bragg reflector
40 increases, thereby causing a reduction in reflectivity. FIG. 4
shows variation of the absorption coefficients (K) of TiO.sub.2 and
Nb.sub.2O.sub.5 according to wavelength. TiO.sub.2 has an
absorption coefficient of zero at 600 nm or more and has an
absorption coefficient of about 0.2 with respect to light generated
in the active layer 27, for example, light in the blue wavelength
range. On the contrary, Nb.sub.2O.sub.5 has an absorption
coefficient of substantially zero in the visible spectrum.
Therefore, even when the lower distributed Bragg reflector 40 is
formed by alternately stacking SiO.sub.2/Nb.sub.2O.sub.5 to have a
large number of stacked layers, the lower distributed Bragg
reflector 40 may prevent optical loss caused by optical
absorption.
[0051] It is not necessary for the first layers or second layers to
have the same thickness. The thickness of the first layers or the
second layers is set to provide relatively high reflectivity not
only with respect to light generated in the active layer 27 but
also with respect to light having different wavelengths in the
visible spectrum. Further, the lower distributed Bragg reflector 40
may be formed by stacking a plurality of distributed Bragg
reflectors, each of which exhibits high reflectivity in a certain
wavelength range.
[0052] For example, for an LED package including an LED according
to an exemplary embodiment that emits white light, light having
different wavelengths from that of light emitted from the LED may
enter the LED package. In this case, the light having different
wavelengths can be reflected by the lower distributed Bragg
reflector 40, so that the LED package may have improved light
extraction efficiency.
[0053] Meanwhile, the uppermost and lowermost layers of the lower
distributed Bragg reflector 40 may be SiO.sub.2 layers. When the
SiO.sub.2 layers are stacked as the uppermost and lowermost layers
of the lower distributed Bragg reflector 40, the lower distributed
Bragg reflector 40 may be stably joined to the substrate 21 and can
be protected by the lowermost SiO.sub.2 layer.
[0054] Referring again to FIG. 3, the metal layer 45 may be located
under the lower distributed Bragg reflector 40. The metal layer 45
may be formed of a metallic material such as, for example,
aluminum. The metal layer 45 assists dissipation of heat from the
LED 20 during operation of the LED 20. Accordingly, the metal layer
45 may enhance heat dissipation of the LED 20.
[0055] Meanwhile, the first upper distributed Bragg reflector 37
may be located on the light emitting structure 30. As shown, the
first upper distributed Bragg reflector 37 may cover the
transparent electrode layer 31 and an exposed surface of the first
conductivity-type semiconductor layer 25.
[0056] The first upper distributed Bragg reflector 37 allows light
generated in the active layer 27 to pass therethrough while
reflecting light entering the LED 20 from outside, for example,
light emitted from the phosphors. Accordingly, the first upper
distributed Bragg reflector 37 allows light generated in the active
layer 27, such as blue light or light in the UV range, to pass
therethrough, and reflects light in the green to red wavelength
range, in particular, light in the yellow wavelength range.
[0057] FIG. 5 is a graph depicting luminescence spectrum of
phosphors used for a white light emitting diode package, and FIG. 6
is a graph depicting one example of a reflectance spectrum for the
first upper distributed Bragg reflector 37. As shown in FIG. 5, the
phosphors used for the LED package for emitting white light exhibit
a relatively high emission spectrum in the green to yellow
wavelength range. Thus, as shown in FIG. 6, the first upper
distributed Bragg reflector 37 may have a reflectance spectrum to
allow light emitted from the LED to pass therethrough while
reflecting light emitted from the phosphors, that is, light in the
green to yellow wavelength range. Such a first upper distributed
Bragg reflector 37 may be formed by alternately stacking material
layers having different indices of refraction, for example, a
SiO.sub.2 layer and a TiO.sub.2 layer or Nb.sub.2O.sub.5 layer,
thereby forming a laminate structure. Further, the first upper
distributed Bragg reflector 37 may be formed to have a desired
reflectance spectrum by setting optical thickness of each of the
layers.
[0058] The first upper distributed Bragg reflector 37 may also be
formed to cover a mesa sidewall and may protect the LED 20 by
covering an upper surface of the LED 20 except for upper surfaces
of the electrode pads 33 and 35.
[0059] FIG. 7 is a sectional view of an LED package having the LED
20 mounted thereon according to an exemplary embodiment of the
present invention.
[0060] Referring to FIG. 7, the LED package includes a package body
60, leads 61a, 61b, the LED 20, and a molding member 63. The
package body 60 may be formed of a plastic resin.
[0061] The package body 60 has a mounting plane M for mounting the
LED 20 and a reflection plane R, from which light emitted from the
LED 20 is reflected. The LED 20 is mounted on the mounting plane M
and is electrically connected to the leads 61a, 61b via bonding
wires. The LED 20 may be bonded to the mounting plane M by
adhesives 62, which may be formed by curing, for example, Ag epoxy
pastes.
[0062] As described in FIG. 3, the LED 20 may include a lower
distributed Bragg reflector 40, a metal layer 45, and/or a first
upper distributed Bragg reflector 37.
[0063] The LED package emits mixed colors, for example, white
light. Therefore, the LED package may include phosphors for
wavelength conversion of light emitted from the LED 20. The
phosphors may be contained in the molding member 63, but are not
limited thereto.
[0064] Since the LED 20 includes the lower distributed Bragg
reflector 40, light subjected to wavelength conversion through the
phosphors and directed towards the mounting plane M through the LED
20 is reflected from the lower distributed Bragg reflector 40 to be
emitted outside. As a result, the LED package according to the
present exemplary embodiment has a relatively higher light emission
efficiency compared to a conventional LED package without a lower
distributed Bragg reflector.
[0065] In addition, when the LED 20 includes the first upper
distributed Bragg reflector 37, light emitted from the phosphors
can be reflected from the first upper distributed Bragg reflector
37. Accordingly, it is possible to prevent light emitted from the
phosphors from entering the LED 20 and thus causing optical
loss.
[0066] In the present exemplary embodiment, the LED package is
described as including the LED 20 and the phosphors to emit white
light, but the invention is not limited thereto. Various LED
packages for emitting white light are known in the art and the LED
20 according to the present exemplary embodiment may be applied to
any such LED package.
[0067] FIG. 8 is a sectional view of an LED having a distributed
Bragg reflector according to an exemplary embodiment of the present
invention.
[0068] Referring to FIG. 8, an LED 20a is generally similar to the
LED 20 described with reference to FIG. 3, except for second upper
distributed Bragg reflectors 39a and 39b respectively formed on
electrode pads 33 and 35. The second upper distributed Bragg
reflectors 39a and 39b are formed on upper surfaces of the
electrode pads 33 and 35, excluding regions for wire bonding (not
shown).
[0069] The second upper distributed Bragg reflectors 39a and 39b
reflect incident light from outside, specifically, light which has
a longer wavelength than that of light generated in the active
layer 27 and is in at least a part of the visible spectrum. The
second upper distributed Bragg reflectors 39a and 39b may reflect,
for example, light subjected to wavelength conversion by the
phosphors.
[0070] Since the electrode pads 33 and 35 may be formed of a light
absorbing metal, light generated in the active layer 27 is not
emitted outside through the electrode pads 33 and 35. Accordingly,
it is not necessary for the second upper distributed Bragg
reflectors 39a and 39b to allow the light generated in the active
layer 27 to pass therethrough. Such second upper distributed Bragg
reflectors 39a and 39b may be formed by alternately stacking
material layers having different indices of refraction, for example
a SiO.sub.2 layer and a TiO.sub.2 layer or Nb.sub.2O.sub.5 layer.
Further, the second upper distributed Bragg reflectors 39a and 39b
may be formed to have a desired reflectance spectrum by suitably
setting optical thickness of each of the layers.
[0071] FIG. 9 is a graph depicting one example of a reflectance
spectrum for the second upper distributed Bragg reflectors 39a and
39b.
[0072] Referring to FIG. 9, the second upper distributed Bragg
reflectors 39a and 39b exhibit relatively high reflectivity with
respect to light in the green to red wavelength range and may also
exhibit relatively high reflectivity with respect to light in the
blue wavelength range since it is not necessary to allow light in
the blue wavelength range to pass therethrough.
[0073] The LED 20a according to the present exemplary embodiment
may be mounted instead of the LED 20 on the LED package described
with reference to FIG. 7.
[0074] In the present exemplary embodiment, the LED 20a may further
include a first upper distributed Bragg reflector 37, as described
with reference to FIG. 3.
[0075] FIG. 10 is a sectional view of an LED 20b having a
distributed Bragg reflector 40 according to an exemplary embodiment
of the present invention.
[0076] Referring to FIG. 10, the LED 20b includes a substrate 21, a
light emitting structure 30, a distributed Bragg reflector 40, an
upper insulation layer 38, and a reflective metal layer 41.
Further, the LED 20b may include a buffer layer 23, a transparent
electrode 31, a first electrode pad 33, and a second electrode pad
35.
[0077] The substrate 21, the light emitting structure 30, the
distributed Bragg reflector 40, the buffer layer 23, the
transparent electrode layer 31, the first electrode pad 33, and the
second electrode pad 35 have similar configurations to those of the
LED 20 described with reference to FIG. 3, and detailed
descriptions thereof will be omitted herein.
[0078] The reflective metal layer 41 is located under the
distributed Bragg reflector 40. The reflective metal layer 41 has
high reflectivity and may be, for example, an aluminum layer or a
silver (Ag) layer. The reflective metal layer 41 reflects incident
light having a large angle of incidence and passing through the
distributed Bragg reflector 40. Further, a protective layer 43 may
be located under the reflective metal layer 41. The protective
layer 43 covers the reflective metal layer 41 to prevent
deformation of the reflective metal layer 41 due to oxidation or
diffusion of the reflective metal layer 41. The protective layer 43
may be formed of a metal or an insulation material. The protective
layer 43 may be formed of a metal to improve dissipation of heat
from the LED.
[0079] The upper insulation layer 38 may be located on the light
emitting structure 30. The upper insulation layer 38 covers the
light emitting structure 30 to protect the light emitting structure
30 from external environmental factors. As shown, the upper
insulation layer 38 may cover the transparent electrode layer 31.
Further, the upper insulation layer 38 may cover a mesa sidewall
and an exposed surface of the first conductivity-type semiconductor
layer 25 formed by mesa etching.
[0080] The upper insulation layer 38 may be formed of a transparent
material, for example SiO.sub.2, which allows light generated in
the active layer 27 to pass therethrough. In addition, the upper
insulation layer 38 may be a refractive index-grading layer, the
index of refraction of which decreases in a gradual or stepwise
manner in a direction away from the light emitting structure 30.
For example, the refractive index-grading layer may be formed by
sequentially depositing a relatively high density layer and a
relatively low density layer through variation of process
parameters, such as deposition rate, temperature, pressure,
reaction gas flux, and plasma power, when forming the upper
insulation layer 38 using a chemical vapor deposition (CVD)
process. Since the index of refraction of the upper insulation
layer 38 gradually decreases towards an outside surface in a
direction away from the light emitting structure 30, it is possible
to reduce total internal reflection of light which is emitted
through the upper insulation layer 38.
[0081] The transparent electrode layer 31 may be formed of, for
example, indium tin oxide (ITO) or ZnO on the second
conductivity-type semiconductor layer 29. The transparent electrode
layer 31 may be interposed between the second conductivity-type
semiconductor layer 29 and the upper insulation layer 38. The
transparent electrode layer 31 has a lower specific resistance than
the second conductivity-type semiconductor layer 29, thereby
assisting current spreading. The transparent electrode layer 31 may
be formed by thermal deposition, electron beam deposition, ion
beam-assisted deposition, or sputtering. Here, the transparent
electrode layer 31 may be a low refractive index layer having a
relatively low index of refraction or may be a refractive
index-grading layer, the index of refraction of which decreases in
a gradual or stepwise manner in a direction away from the second
conductivity-type semiconductor layer 29.
[0082] The LED 20b according to the present exemplary embodiment
may be mounted instead of the LED 20 on the LED package described
with reference to FIG. 7. As described in FIG. 10, the LED 20b
includes the distributed Bragg reflector 40, the reflective metal
layer 41, and the upper insulation layer 38. In addition, when the
upper insulation layer 38 and/or the transparent electrode layer 31
are the refractive index-grading layers, the LED 20b may exhibit
further improved light extraction efficiency, thereby further
reducing optical loss inside the LED 20b. Further, the upper
insulation layer 38 may be formed on the first and second electrode
pads 33 and 35, similar to as described above with reference to the
second upper distributed Bragg reflector 39a and 39b in FIG. 8.
[0083] FIG. 11 is a schematic sectional view of an electron beam
deposition apparatus 50 for forming a transparent conductive layer
(not shown) having a relatively low index of refraction.
[0084] Referring to FIG. 11, the electron beam deposition apparatus
includes a vacuum chamber 51, a substrate holder 55, a rotator 52,
a shaft 53, an electron beam evaporator 57, and a source 59, in
which the vacuum chamber 51 is formed with a gas inlet 51a and a
gas outlet 51b.
[0085] The substrate 10 has a second conductivity-type
semiconductor layer 29, which is formed by growing semiconductor
layers on a substrate 21 such as a sapphire substrate. The
substrate 10 is disposed on the substrate holder 55. Generally, a
plurality of substrates 10 is arranged on the substrate holder 55
and each of the substrates 10 is disposed such that an upper
surface of the substrate faces the source 59. In other words, the
source 10 is disposed on a line perpendicular to the surface of the
substrate 10 and extending to the center of the substrate 10. The
substrate holder 55 may have a concave shape to allow each of the
substrates 10 to be disposed at a normal position (indicated by a
dotted line) with respect to the source 59. Further, the substrate
holder 55 may be rotated by the rotator 52. Namely, the rotator 52
rotates the shaft 53, which in turn rotates the substrate holder
55. As the substrate holder 55 is rotated as described above, the
transparent electrode layer may be uniformly deposited on the
substrate 10, in particular, on the plurality of substrates 10.
[0086] In the present exemplary embodiment, the substrate 10 may
also be disposed at an angle with respect to the source 59 instead
of being disposed at a normal position (indicated by a dotted
line). Namely, the source 59 is deviated from the line
perpendicular to the surface of the substrate 10 and extending to
the center of the substrate 10. When the plurality of substrates 10
is disposed in the deposition apparatus, each of the substrates 10
may be disposed at an identical angle with respect to the source
59.
[0087] When a transparent electrode layer is deposited on the
substrate 10 by evaporating the source 59 with an electron beam,
the transparent electrode layer is deposited in a slanted direction
on the substrate 10 instead of being deposited perpendicular to the
substrate 10. As a result, as compared with the case where the
transparent electrode layer is deposited on substrate 10 at the
normal position, the transparent electrode layer has a low density,
so that the index of refraction of the transparent electrode layer
may be decreased. Accordingly, it is possible to reduce optical
loss relating to total internal reflection at an interface between
the transparent electrode layer and air or between the transparent
electrode layer and the upper insulation layer 38.
[0088] In addition, in the present exemplary embodiment, the
transparent electrode layer may be asymmetrically deposited on the
substrate 10 by stopping rotation of the substrate 10 or changing a
rotational condition of the substrate 10, which is rotated by the
rotator 52. Accordingly, it is possible to deposit a transparent
electrode layer which has a low index of refraction.
[0089] In the present exemplary embodiment, the electron beam
deposition apparatus 50 has been illustrated for deposition of the
transparent electrode layer. However, thermal deposition and ion
beam-assisted deposition may also be performed under the condition
that the substrate 10 is disposed at an angle with respect to the
target or that the rotational speed of the substrate is adjusted.
In addition, deposition of the transparent electrode layer having a
low index of refraction using sputtering may also be performed,
with the substrate disposed at an angle with respect to the
target.
[0090] FIG. 12 is a sectional view of an example of the transparent
electrode layer 31 according to the exemplary embodiment of the
present invention described above with reference to FIGS. 10 and
11.
[0091] Referring to FIG. 12, a transparent electrode layer 31a of
the present exemplary embodiment is similar to the transparent
electrode layer 31 described with reference to FIG. 10 except that
the transparent electrode layer 31a is a refractive index-grading
layer. Specifically, the transparent electrode layer 31a is a
refractive index-grading layer, the index of refraction of which
decreases in a gradual or stepwise manner in a direction away from
the second conductivity-type semiconductor layer 29.
[0092] The transparent electrode layer 31a may be formed by thermal
deposition, electron beam deposition, ion beam-assisted deposition,
or sputtering. In this case, the transparent electrode layer 31a
may be formed as the refractive index-grading layer by sequentially
depositing a relatively high density layer and a relatively low
density layer through variation of process parameters, such as
deposition rate, temperature, pressure, reaction gas flux, and
plasma power. Since the index of refraction of the transparent
electrode layer 31a gradually decreases towards an outside from the
second conductivity-type semiconductor layer 29, it is possible to
reduce total internal reflection of light emitted through the
second conductivity-type semiconductor layer 29.
[0093] As such, according to the exemplary embodiments of the
present invention, the LED may include a distributed Bragg
reflector exhibiting relatively high reflectivity with respect to
light over a wide wavelength range of the visible spectrum, thereby
improving light emission efficiency of an LED package for emitting
mixed colors, for example, white light. In addition, the LED may
reduce optical absorption of the distributed Bragg reflector by
alternately stacking SiO.sub.2/Nb.sub.2O.sub.5 to form the
distributed Bragg reflector, thereby increasing the number of
layers constituting the distributed Bragg reflector while
maintaining high reflectivity after mounting the LED in the LED
package. Further, the LED may include a metal layer under the
distributed Bragg reflector, thereby improving dissipation of heat
from the LED. Further, the LED may include an upper distributed
Bragg reflector on the light emitting structure or on an upper
surface of an electrode pad, thereby reducing optical loss of light
which enters the LED from outside. Furthermore, the LED may include
a reflective metal layer and a protective layer on a lower surface
of the distributed Bragg reflector, thereby preventing deformation
of the distributed Bragg reflector and the reflective metal layer
when the LED is mounted on the package. In addition, an upper
insulation layer and/or a transparent conductive layer may be a
refractive index-grading layer, thereby improving light extraction
efficiency of the LED.
[0094] Although the invention has been illustrated with reference
to some exemplary embodiments in conjunction with the drawings, it
will be apparent to those skilled in the art that various
modifications and changes can be made to the invention without
departing from the spirit and scope of the invention. Further, it
should be understood that some features of a certain embodiment may
also be applied to other embodiments without departing from the
spirit and scope of the invention. Therefore, it should be
understood that the embodiments are provided by way of illustration
only and are given to provide complete disclosure of the invention
and to provide thorough understanding of the invention to those
skilled in the art. Thus, it is intended that the invention covers
the modifications and variations provided they fall within the
scope of the appended claims and their equivalents.
* * * * *