U.S. patent application number 11/511366 was filed with the patent office on 2007-08-02 for light emitting diode and method of manufacturing the same.
This patent application is currently assigned to Samsung Electro-Mechanics Co., Ltd.. Invention is credited to Jin-seo Im.
Application Number | 20070176191 11/511366 |
Document ID | / |
Family ID | 38321182 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070176191 |
Kind Code |
A1 |
Im; Jin-seo |
August 2, 2007 |
Light emitting diode and method of manufacturing the same
Abstract
A light emitting diode having high light extraction efficiency
and a method of manufacturing the same are provided. The LED
includes a semiconductor multiple layer including an active layer;
a transparent electrode layer formed on the semiconductor multiple
layer; and refraction field unit embedded in the transparent
electrode layer and formed of a material having a different
refractive index than the transparent electrode layer. The method
of manufacturing the LED includes: crystallizing and growing a
semiconductor multiple layer having an active layer on a substrate;
evaporating a first transparent electrode layer onto the
semiconductor multiple layer; forming a plurality of grooves in the
first transparent electrode layer by patterning and etching the
first transparent electrode layer; and evaporating a second
transparent electrode layer onto the first transparent electrode
layer at an angle to the grooves to form cavities filled with air
between the first transparent electrode layer and the second
transparent electrode layer.
Inventors: |
Im; Jin-seo; (Seoul,
KR) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
Samsung Electro-Mechanics Co.,
Ltd.
Suwon-si
KR
|
Family ID: |
38321182 |
Appl. No.: |
11/511366 |
Filed: |
August 29, 2006 |
Current U.S.
Class: |
257/98 ;
257/E33.068 |
Current CPC
Class: |
H01L 33/42 20130101;
H01L 2933/0083 20130101; H01L 33/44 20130101 |
Class at
Publication: |
257/98 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2006 |
KR |
10-2006-0009817 |
Claims
1. A light emitting diode (LED) comprising: a semiconductor
multiple layer comprising an active layer; a transparent electrode
layer formed on the semiconductor multiple layer; and a refraction
field unit embedded in the transparent electrode layer and formed
of a material having a different refractive index than the
transparent electrode layer.
2. The LED of claim 1, wherein the refraction field unit is formed
of a material having a lower refractive index than the transparent
electrode layer.
3. The LED of claim 2, wherein the transparent electrode layer is
formed of a material selected from the group consisting of ITO,
ZnO, and SnO.sub.2, and the refraction field unit is formed of a
material selected from the group consisting of SiO.sub.2, porous
SiO.sub.2, KDP, NH.sub.4H.sub.2PO.sub.4, CaCO.sub.3,
BaB.sub.2O.sub.4, NaF, and Al.sub.2O.sub.3.
4. The LED of claim 1, wherein the refraction field unit is formed
of a material having a higher refractive index than the transparent
electrode layer.
5. The LED of claim 4, wherein the transparent electrode layer is
formed of a material selected from the group consisting of ITO,
ZnO, and SnO.sub.2, and the refraction field unit is formed of a
material selected from the group consisting of SiC, LiNbO.sub.3,
LilO.sub.3, PbMoO.sub.4, Nb.sub.2O.sub.5, TiO.sub.2, and
ZrO.sub.2.
6. The LED of claim 1, wherein the refraction field unit comprises
a plurality of cavities filled with air.
7. The LED of claim 1, wherein the refraction field unit comprises
a plurality of refraction regions arranged at predetermined
intervals in the transparent electrode layer.
8. The LED of claim 7, wherein the interval of the refraction
regions is at least 0.5 times the wavelength of light generated by
the active layer.
9. A method of manufacturing an LED comprising: forming a
semiconductor multiple layer having an active layer on a substrate;
evaporating a first transparent electrode layer onto the
semiconductor multiple layer; forming a refraction layer on the
first transparent electrode layer by evaporating a material having
a different refractive index than the first transparent electrode
layer onto the first transparent electrode layer; forming
refraction field unit by patterning and etching the refraction
layer; and embedding the refraction field unit by evaporating a
second transparent electrode layer on the refraction field unit and
the first transparent electrode layer.
10. The LED of claim 9, wherein the refraction field unit comprises
a plurality of refraction regions arranged at predetermined
intervals in the transparent electrode layer.
11. The LED of claim 10, wherein the interval of the refraction
regions is at least 0.5 times the wavelength of light generated by
the active layer.
12. A method of manufacturing the LED of claim 6, the method
comprising: forming a semiconductor multiple layer having an active
layer on a substrate; evaporating a first transparent electrode
layer onto the semiconductor multiple layer; forming a plurality of
grooves in the first transparent electrode layer by patterning and
etching the first transparent electrode layer; and evaporating a
second transparent electrode layer onto the first transparent
electrode layer at an angle to the grooves to form refraction field
unit formed of cavities filled with air between the first
transparent electrode layer and the second transparent electrode
layer.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] This application claims the benefit of Korean Patent
Application No. 10-2006-0009817, filed on Feb. 1, 2006 in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
BACKGROUND OF THE DISCLOSURE
[0002] 1. Field of the Disclosure
[0003] The present disclosure relates to a light emitting diode and
a method of manufacturing the same, and more particularly, to a
light emitting diode including a transparent electrode with an
improved structure to improve the light extraction efficiency and a
method of manufacturing the light emitting diode.
[0004] 2. Description of the Related Art
[0005] A light emitting diode (LED) is formed of a light emitting
source using compound semiconductors such as GaAs, AlGaN, and
AlGaAs to generate various colors of light. Recently, with the
realization of highly efficient red, blue, green and white light
emitting diodes using nitride materials having excellent physical
and chemical characteristics, the application range of the light
emitting diodes has widened. LEDs can be more easily manufactured
and controlled than semiconductor lasers and have longer lifetimes
than fluorescent lamps, thus replacing fluorescent lamps as
illumination light sources of the next generation display
devices.
[0006] Examples of factors that determine the characteristics of
LEDs are color, brightness, and light intensity, which are
primarily determined by the compound semiconductor material used
for the LED devices. Also, the light generated by an active layer
of the LED must be effectively emitted to the outside, and this
depends on the structure and the material of a transparent
electrode or the package of the LED.
[0007] FIG. 1 is a cross-sectional view of a conventional LED.
Referring to FIG. 1, the LED includes a sapphire substrate 11, and
an n-type semiconductor layer 13, an active layer 15, a p-type
semiconductor layer 17, and a transparent electrode 19 sequentially
stacked on the sapphire substrate 17.
[0008] When a voltage is applied between the n-type semiconductor
layer 13 and the p-type semiconductor layer 17, holes from the
p-type semiconductor layer 17 and electrons from the n-type
semiconductor layer 13 combine in the active layer 15 to emit
light. The light is emitted through the transparent electrode 19 to
the outside.
[0009] However, in the structure illustrated in FIG. 1, light
extraction efficiency is low. Light extraction efficiency refers to
the ratio of emitted light to generated light in the active layer.
The low light extraction efficiency is caused by the difference
between the refractive indices of the semiconductor layers and the
surrounding material.
[0010] FIG. 2 illustrates the optical path of light emitted to the
outside in the LED of FIG. 1. When the light emitted by the active
layer is emitted to the outside, the light is refracted at a
boundary surface 19a between the transparent electrode 19 and the
outside. When light travels from the transparent electrode having a
high refractive index to the material having a low refractive index
at an incidence angle greater than a critical angle, light is
totally reflected at the boundary surface 19a. The critical angle
.theta..sub.C is given by Equation 1.
.theta..sub.C=sin.sup.-1(n.sub.2/n.sub.1) Equation 1
[0011] For example, when the transparent electrode 19 is formed of
ITO with a refractive index of 2, and the surrounding material is
air with a refractive index of 1, the critical angle is 30.degree..
That is, only light having an incidence angle of less than
30.degree. is emitted to the outside, and light having an incidence
angle of 30.degree. or greater is not emitted to the outside, thus
resulting in low light extraction efficiency.
SUMMARY OF THE DISCLOSURE
[0012] The present invention may provide a light emitting diode
with high light extraction efficiency and a method of manufacturing
the same.
[0013] According to an aspect of the present invention, there may
be provided a light emitting diode (LED) comprising: a
semiconductor multiple layer comprising an active layer; a
transparent electrode layer formed on the semiconductor multiple
layer; and a refraction field unit embedded in the transparent
electrode layer and formed of a material having a different
refractive index than the transparent electrode layer.
[0014] According to an aspect of the present invention, there may
be provided a method of manufacturing an LED comprising: forming a
semiconductor multiple layer having an active layer on a substrate;
evaporating a first transparent electrode layer onto the
semiconductor multiple layer; forming a refraction layer on the
first transparent electrode layer by evaporating a material having
a different refractive index than the first transparent electrode
layer onto the first transparent electrode layer; forming
refraction field unit by patterning and etching the refraction
layer; and embedding the refraction field unit by evaporating a
second transparent electrode layer on the refraction field unit and
the first transparent electrode layer.
[0015] According to another aspect of the present invention, there
may be provided a method of manufacturing the LED of claim 6, the
method comprising: forming a semiconductor multiple layer having an
active layer on a substrate; evaporating a first transparent
electrode layer onto the semiconductor multiple layer; forming a
plurality of grooves in the first transparent electrode layer by
patterning and etching the first transparent electrode layer; and
evaporating a second transparent electrode layer onto the first
transparent electrode layer at an angle to the grooves to form
refraction field unit formed of air cavities filled with air
between the first transparent electrode layer and the second
transparent electrode layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The above and other features and advantages of the present
invention will be illustrated in detailed exemplary embodiments
thereof with reference to the attached drawings in which:
[0017] FIG. 1 is a cross-sectional view of a conventional light
emitting diode (LED);
[0018] FIG. 2 illustrates the optical path of light emitted in the
LED of FIG. 1;
[0019] FIG. 3 is a cross-sectional view of an LED according to an
embodiment of the present invention;
[0020] FIG. 4A is a schematic view illustrating the emission of
light when the refractive index of refraction field unit is less
than the refractive index of a transparent electrode layer in the
LED of FIG. 3;
[0021] FIG. 4B is a schematic view illustrating the emission of
light when the refractive index of refraction field unit is greater
than the refractive index of a transparent electrode layer in the
LED of FIG. 3;
[0022] FIG. 5 is a cross-sectional view of a comparative example
LED for comparison with the LED of FIG. 3;
[0023] FIG. 6 is a schematic view illustrating the optical path of
light in the LED of FIG. 5;
[0024] FIG. 7 is a graph of the increase rate of the light
extraction efficiencies of the LEDs of FIGS. 3 and 5;
[0025] FIGS. 8A through 8D are cross-sectional views illustrating a
method of manufacturing an LED according to an embodiment of the
present invention; and
[0026] FIGS. 9A through 9C are cross-sectional views illustrating a
method of manufacturing an LED according to another embodiment of
the present invention.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0027] The present invention will now be described more fully with
reference to the accompanying drawings, in which exemplary
embodiments of the invention are shown.
[0028] FIG. 3 is a cross-sectional view of a light emitting diode
(LED) according to an embodiment of the present invention.
Referring to FIG. 3, the LED includes a sapphire substrate 100, and
a semiconductor multiple layer 110 and a transparent electrode
layer 122 sequentially stacked on the sapphire substrate 100.
[0029] The semiconductor multiple layer 110 includes an n-type
semiconductor layer 113, an active layer 116, and a p-type
semiconductor layer 119. Each of the n-type semiconductor layer
113, the active layer 116, and the p-type semiconductor layer 119
may be formed of a compound semiconductor such as GaN.
[0030] Refraction field unit 125 is formed in the transparent
electrode layer 122 to improve the efficiency of light emitted to
the outside by refracting light generated by the active layer 116.
The refraction field unit 125 may be formed of a material having a
different refractive index than the transparent electrode layer or
may be cavities filled with air.
[0031] The transparent electrode layer 122 may be formed of a
material having high light transmittance with respect to light in
the visible spectrum and high electrical conductivity. For example,
indium tin oxide (ITO), tin oxide (SnO.sub.2), or zinc oxide (ZnO)
may be used.
[0032] When the light generated by the active layer 116 passes
through the transparent electrode layer 122 and is emitted to the
outside, the refraction field unit 125 increases the light
extraction efficiency by refracting the light generated by the
active layer 116, and thus, the refraction field unit 125 should be
formed of a material having a different refractive index than the
transparent electrode layer 122. Also, in order to increase this
effect, the difference between the refractive indices of the
refraction field unit 125 and the transparent electrode layer 122
can be great.
[0033] The refraction field unit 125 may be formed of a material
having a smaller refractive index than the transparent electrode
layer 122, for example, porous SiO.sub.2, KDP,
NH.sub.4H.sub.2PO.sub.4, CaCO.sub.3, BaB.sub.2O.sub.4, NaF, or
Al.sub.2O.sub.3. Also, the material forming the refraction field
unit 125 may have a greater refractive index than the transparent
electrode layer 122, and may be SiC, LiNbO.sub.3, LilO.sub.3,
PbMoO.sub.4, Nb.sub.2O.sub.5, TiO.sub.2, or ZrO.sub.2.
[0034] The refraction field unit 125 includes a plurality of
refraction regions 126 and refraction regions 126 are arranged at
regular intervals, T. However, the arrangement may also be
irregular.
[0035] A resin layer 128 may be formed as a capping layer on the
transparent electrode layer 122.
[0036] FIGS. 4A and 4B illustrate the principle of increasing the
light extraction efficiency of the light emitting diode according
to an embodiment of the present invention. The light generated by
the active layer 116 passes through the transparent electrode layer
122 and is emitted to the outside, and since the light having an
incidence angle of less than the critical angle .theta..sub.c is
not totally reflected, the light can be emitted to the outside.
Also, in case that the incidence angle .theta..sub.i1 is greater
than the critical angle .theta..sub.C, since the incidence angle
.theta..sub.i2 of light at the boundary surface 122a becomes
smaller than the incidence angle .theta..sub.i1 when the light
reaches the boundary surface 122a passing through the refraction
field unit 125, the light is more likely to be emitted to the
outside instead of being totally reflected.
[0037] FIG. 4A is a schematic view illustrating light passing
through the refraction field unit 125 when the refractive index of
the refraction field unit 125 is less than the refractive index of
the transparent electrode layer 122. The light having an incidence
angle of .theta..sub.i1 has an incidence angle of 90-.theta..sub.i1
at a lateral surface 126a of one of the refraction regions 126. The
refraction angle of the light at the lateral surface 126a is
90-.theta..sub.2, which is greater than 90-.theta..sub.i1 when the
refractive index of the refraction field 126 is less than the
refractive index of the transparent electrode layer 122. That is,
.theta..sub.2 is smaller than .theta..sub.i1. Also, the incidence
angle at an upper surface 126b of the refraction field 126 is
.theta..sub.2, and the refraction angle is .theta..sub.i2, which is
smaller than .theta..sub.2.
[0038] Thus, the incidence angle .theta..sub.i2 at the boundary
surface 122a is smaller than the incident angle .theta..sub.i1.
When the incidence angle .theta..sub.i2 is smaller than the
critical angle .theta..sub.C, the light can be emitted to the
outside, thereby increasing the overall amount of the light emitted
to the outside.
[0039] FIG. 4B illustrates the light passing through the refraction
field unit 125 when the refractive index of the refraction field
unit 125 is greater than the refractive index of the transparent
electrode layer 122. Light having an incidence angle .theta..sub.i1
greater than the critical angle .theta..sub.C passes through a
surface 126c and a surface 126d of the refraction region 126 and is
refracted, and thus the incidence angle .theta..sub.i2 at the
boundary surface 122a can be smaller than the critical angle
.theta..sub.C, thereby increasing the amount of the light emitted
to the outside.
[0040] FIG. 5 is a cross-sectional view of a conventional LED for
comparison with the LED of the above described embodiment of the
present invention. Referring to FIG. 5, the LED includes a sapphire
substrate 51, and an n-type semiconductor layer 53, an active layer
55, a p-type semiconductor layer 57, a transparent electrode layer
59, and a resin layer 61 sequentially stacked on the sapphire
substrate 51. A concavo-convex structure is formed on an upper
surface of the transparent electrode layer 59 and has a period,
T.
[0041] FIG. 6 is a schematic view illustrating the optical path of
light in the LED of FIG. 5. Referring to FIG. 6, when light having
an incidence angle .theta..sub.i passes through a lateral wall 59a
on which a concavo-convex structure is formed and is emitted to the
outside, the incidence angle .theta..sub.i of the light with
respect to the lateral wall 59a is 90-.theta..sub.i. Thus the light
can be emitted to the outside when 90-.theta..sub.i is smaller than
the critical angle, in addition to the case when the incidence
angle .theta..sub.i is smaller than the critical angle
.theta..sub.C, thereby improving the light extraction
efficiency.
[0042] FIG. 7 is a graph of the results of a simulation of the
increase rate of the light extraction efficiencies of the LEDs
illustrated in FIGS. 3 and 5.
[0043] Referring to FIG. 7, the increase rate of the light
extraction efficiency is plotted against T/.lamda., wherein T
denotes the period T of the refraction field unit 125 (see FIG. 3)
or the concavo-convex structure(see FIG. 5), and .lamda. denotes
the wavelength of the light generated by the active layer. The
increase rate is to the conventional LED (see FIG. 1). The dotted
line denotes the results obtained from the comparative example LED
of FIG. 5 and the solid line denotes results obtained from the LED
according to an embodiment of the present invention illustrated in
FIG. 3.
[0044] The simulation was conducted while increasing the value of
T/.lamda.. The transparent electrode layer was formed of ITO, and
the refraction field unit was air cavities. That is, the refractive
index of the transparent electrode layer was 2, and the refractive
index of the refraction field unit was 1.
[0045] The maximum increase rate of the light extraction efficiency
of the LED according to an embodiment of the present embodiment is
40% and is greater than the comparative example, too. In the
comparative example of the conventional LED, when the transparent
electrode 59 (see FIG. 5) is etched to form the concavo-convex
structure, the transparent electrode may be damaged by the etching,
and thus the quality of the electrode may be reduced in that the
transparency of the transparent electrode layer may be decreased or
the resistance thereof may be increased, and thus, the LED
according to an embodiment of the present embodiment is improved
and is advantageous relative to the comparative example LED.
[0046] In both cases, the increase rate of the light extraction
efficiency increases as the value of T/.lamda. increases and
saturates at a predetermined value of T/.lamda.. When T/.lamda. is
between 0 and 1, the light extraction efficiency increases quickly,
and thereafter the light extraction efficiency is saturated. The
light extraction efficiency of the LED according to an embodiment
of the present invention is about 20% or higher than that of the
conventional LED when T/.lamda. is greater than 0.5.
[0047] The simulation results are related to limited parameters and
simulation can also be conducted with respect to other parameters,
thereby enabling one to choose a structure for improving the light
extraction efficiency. For example, the size of the refraction
field unit 125 (see FIG. 3) or specific position of the transparent
electrode layer 122 (see FIG. 3) may be determined.
[0048] FIGS. 8A through 8D are cross-sectional views illustrating a
method of manufacturing an LED according to an embodiment of the
present invention.
[0049] First, referring to FIG. 8A, an n-type semiconductor layer
213, an active layer 216, and a p-type semiconductor layer 219 are
formed on a sapphire substrate 200, and a first transparent
electrode layer 222 is evaporated onto the p-type semiconductor
layer 219.
[0050] Next, referring to FIG. 8B, a refraction layer 224 having a
different refractive index than the first transparent electrode
layer 222 is evaporated onto the first transparent electrode layer
222. Then, referring to FIG. 8C, the refraction field unit 225 is
formed using a patterning process and an etching process.
[0051] Referring to FIG. 8D, a second transparent electrode layer
228 is evaporated onto the first transparent electrode layer 222 on
which the refraction field unit 225 is formed, thereby embedding
the refraction field unit 225 into the first transparent electrode
layer 222 and the second transparent electrode layer 228, thus
completing the LED.
[0052] FIGS. 9A through 9C are cross-sectional views illustrating a
method of manufacturing an LED according to another embodiment of
the present invention.
[0053] Referring to FIG. 9A, an n-type semiconductor layer 313, an
active layer 316, and a p-type semiconductor layer 319 are formed
on a sapphire substrate 300, and then a first transparent electrode
layer 322 is evaporated onto the p-type semiconductor layer 319.
Next, referring to FIG. 9B, grooves 324 are formed in the
evaporated first transparent electrode layer 322 using a patterning
process and an etching process. Then, referring to FIG. 9C, a
second transparent electrode layer 328 is evaporated using an
e-beam evaporator. An arrow A denotes the direction in which an
electron beam is evaporated. When the electron beam is evaporated
at an angle to the grooves 324, a self-shadowing region where the
electron beam is not incident is formed in the grooves 324.
Accordingly, the grooves 324 are not filled with the second
transparent electrode layer 328, and thus, an LED with air cavities
as refraction field unit 325 is manufactured.
[0054] As described above, the LED according to the present
invention includes a refraction field unit formed of a material
having a different refractive index than the transparent electrode
layer inside the transparent electrode layer and thus the light
extraction efficiency of the light generated by the semiconductor
active layer is high. Also, since the transparent electrode layer
does not include a concavo-convex structure, there is no danger of
the transparent electrode layer being damaged by etching, thereby
ensuring a high transparency and a low resistance of the
transparent electrode layer.
[0055] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims.
* * * * *