U.S. patent application number 17/096042 was filed with the patent office on 2022-01-13 for epitaxial light emitting structure and light emitting diode.
The applicant listed for this patent is XIAMEN SAN'AN OPTOELECTRONICS CO., LTD.. Invention is credited to CHUNG-YING CHANG, WEN-YU LIN, YUN-MING LO, CHIEN-YAO TSENG, MENG-HSIN YEH.
Application Number | 20220013685 17/096042 |
Document ID | / |
Family ID | |
Filed Date | 2022-01-13 |
United States Patent
Application |
20220013685 |
Kind Code |
A2 |
LIN; WEN-YU ; et
al. |
January 13, 2022 |
EPITAXIAL LIGHT EMITTING STRUCTURE AND LIGHT EMITTING DIODE
Abstract
An epitaxial light emitting structure includes n-type and p-type
semiconductor layers, and a light emitting component disposed
therebetween. The light emitting component includes a multiple
quantum well structure which contains a plurality of first periodic
layered elements, each of which includes first, second and third
layers alternately stacked on one another. For each of the first
periodic layered elements, the first, second and third layers
respectively have a first energy bandgap (Eg1), a second energy
bandgap (Eg2), and a third energy bandgap (Eg3) that satisfy a
relationship of Eg1<Eg2<Eg3. Also disclosed herein is a light
emitting diode which includes the aforementioned epitaxial light
emitting structure.
Inventors: |
LIN; WEN-YU; (Xiamen,
CN) ; YEH; MENG-HSIN; (Xiamen, CN) ; LO;
YUN-MING; (Xiamen, CN) ; TSENG; CHIEN-YAO;
(Xiamen, CN) ; CHANG; CHUNG-YING; (Xiamen,
CN) |
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Applicant: |
Name |
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State |
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Type |
XIAMEN SAN'AN OPTOELECTRONICS CO., LTD. |
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Prior
Publication: |
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Document Identifier |
Publication Date |
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US 20210066542 A1 |
March 4, 2021 |
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Appl. No.: |
17/096042 |
Filed: |
November 12, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/CN2018/087515 |
May 18, 2018 |
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17096042 |
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International
Class: |
H01L 33/04 20060101
H01L033/04; H01L 33/00 20060101 H01L033/00; H01L 33/32 20060101
H01L033/32 |
Claims
1. An epitaxial light emitting structure, comprising: an n-type
semiconductor layer; a p-type semiconductor layer; and a light
emitting component disposed between said n-type semiconductor layer
and said p-type semiconductor layer and including a multiple
quantum well structure which contains a plurality of first periodic
layered elements, wherein each of said first periodic layered
element includes a first layer, a second layer which is disposed on
said first layer, and a third layer which is disposed on said
second layer, said first layers, said second layers and said third
layers in said first periodic layered elements being alternately
stacked on one another; and wherein for each of said first periodic
layered elements, said first, second and third layers respectively
have a first energy bandgap (Eg1), a second energy bandgap (Eg2),
and a third energy bandgap (Eg3) that satisfy a relationship of
Eg1<Eg2<Eg3.
2. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, a difference between
the third energy bandgap (Eg3) and the second energy bandgap (Eg2)
is equal to or larger than 1.5 eV.
3. The epitaxial light emitting structure of claim 1, wherein said
first layers, said second layers, and said third layers in said
first periodical layered elements are alternately stacked on one
another in a direction away from said n-type semiconductor
layer.
4. The epitaxial light emitting structure of claim 1, wherein for
at least one of said first periodic layered elements, said first
layer includes a first lower sublayer and a first upper sublayer
which is disposed between said first lower sublayer and said second
layer, and which has an energy bandgap greater than an energy
bandgap of said first lower sublayer and smaller than that of the
second energy bandgap (Eg2).
5. The epitaxial light emitting structure of claim 1, wherein for
at least one of said first periodic layered elements, said second
layer includes a second lower sublayer and a second upper sublayer
which is disposed between said second lower sublayer and said third
layer, and which has an energy bandgap greater than an energy
bandgap of said second lower sublayer.
6. The epitaxial light emitting structure of claim 1, wherein for
at least one of said first periodic layered elements, said third
layer includes a third lower sublayer which has an energy bandgap
greater than the second energy bandgap (Eg2), and a third upper
sublayer which is disposed on said third lower sublayer opposite to
said second layer and which has an energy bandgap greater than that
of said third lower sublayer.
7. The epitaxial light emitting structure of claim 1, wherein said
multiple quantum well structure further contains at least one
second periodic layered element which includes a fourth layer and a
fifth layer.
8. The epitaxial light emitting structure of claim 7, wherein said
fourth layer and said fifth layer are made of different materials
that are independently selected from materials for making said
first layer, said second layer, and said third layer.
9. The epitaxial light emitting structure of claim 1, wherein a
number of said first periodic layered element in said multiple
quantum well structure ranges from 2 to 29.
10. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, the first energy
bandgap (Eg1) of said first layer ranges from 3.3 eV to 3.5 eV.
11. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, the second energy
bandgap (Eg2) of said second layer ranges from 3.55 eV to 3.90
eV.
12. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, a difference between
the second energy bandgap (Eg2) and the first energy bandgap (Eg1)
ranges from 0.25 eV to 0.30 eV.
13. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, said first layer has
a thickness ranging from 20 .ANG. to 150 .ANG..
14. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, said second layer has
a thickness ranging from 50 .ANG. to 300 .ANG..
15. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, said third layer has
a thickness not greater than 30 .ANG..
16. The epitaxial light emitting structure of claim 15, wherein the
thickness of said third layer ranges from 10 .ANG. to 15 .ANG..
17. The epitaxial light emitting structure of claim 1, wherein said
multiple quantum well structure of said light emitting component
has a total thickness ranging from 100 .ANG. to 3000 .ANG..
18. The epitaxial light emitting structure of claim 1, wherein each
of said n-type semiconductor layer, said light emitting component
and said p-type semiconductor layer is made of a nitride-based
semiconductor material.
19. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, said first layer is
made of In.sub.xGa.sub.1-xN, where 0.ltoreq.x.ltoreq.1.
20. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, said second layer is
made of In.sub.yAl.sub.zGa.sub.1-y-zN, where 0.ltoreq.y.ltoreq.1,
0.ltoreq.z<1 and y+z.ltoreq.1.
21. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, said second layer is
made of one of In.sub.yAl.sub.zGa.sub.1-y-zN and
Al.sub.zGa.sub.1-zN, where 0.ltoreq.y.ltoreq.0.02 and
0.06.ltoreq.z.ltoreq.0.12.
22. The epitaxial light emitting structure of claim 1, wherein for
each of said first periodic layered elements, said third layer of
said light emitting component is made of Al.sub.wGa.sub.1-wN, where
0<w.ltoreq.1.
23. The epitaxial light emitting structure of claim 22, wherein w
ranges from 0.95 to 1.
24. The epitaxial light emitting structure of claim 1, wherein said
third layer of said epitaxial light emitting layer is made of
AlN.
25. A light emitting diode, comprising an epitaxial light emitting
structure as claimed in claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part (CIP) application
of PCT International Application No. PCT/CN2018/087515, filed on
May 18, 2018. The entire content of the international patent
application is incorporated herein by reference.
FIELD
[0002] The disclosure relates to a light emitting diode including a
multiple quantum well structure having periodic layered elements
each in three layers.
BACKGROUND
[0003] A light emitting diode (LED) is a solid semiconductor light
emitting device and is operated by forming a p-n junction therein
to convert electrical energy into light energy. A conventional LED
includes an epitaxial structure which contains n-type and p-type
semiconductor layers, and a light emitting component disposed
therebetween. The light emitting component generally utilizes a
multiple quantum well (MQW) structure, which is made of
alternately-stacked two different semiconductor layers serving as a
well region and a barrier region, respectively. During operation, a
voltage is applied to the LED, and carriers, i.e., electron-hole
pairs, would be injected into the MQW structure by tunneling,
diffusion or thermionic emission. Most of the carriers are captured
to be confined in the well region, and recombine radiatively to
emit light. The wavelength of light emitted from the LED is
determined based on the energy bandgap of the material which forms
the well region. The luminance of the LED is related to internal
quantum efficiency and light extraction efficiency, and the
internal quantum efficiency can be increased by adjusting the
configuration of the MQW structure, such as well depth, thickness,
and composition.
SUMMARY
[0004] Therefore, an object of the disclosure is to provide an
epitaxial light emitting structure, and an LED including the
epitaxial light emitting structure that can alleviate at least one
of the drawbacks of the prior art.
[0005] According to one aspect of the disclosure, the epitaxial
light emitting structure includes an n-type semiconductor layer, a
p-type semiconductor layer, and a light emitting component disposed
therebetween. The light emitting component includes a multiple
quantum well structure which contains a plurality of first periodic
layered elements. Each of the first periodic layered element
includes a first layer, a second layer disposed on the first layer,
and a third layer disposed on the second layer. The first layers,
the second layers and the third layers in the first periodic
layered elements are alternately stacked on one another. For each
of the first periodic layered elements, the first, second and third
layers respectively have a first energy bandgap (Eg1), a second
energy bandgap (Eg2), and a third energy bandgap (Eg3) that satisfy
a relationship of Eg1<Eg2<Eg3.
[0006] According to another aspect of the disclosure, an light
emitting diode includes the aforementioned epitaxial light emitting
structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Other features and advantages of the disclosure will become
apparent in the following detailed description of the embodiments
with reference to the accompanying drawings, of which:
[0008] FIG. 1 is a schematic view illustrating a first embodiment
of an epitaxial light emitting structure according to the
disclosure;
[0009] FIG. 2 is a schematic view illustrating an embodiment of a
light emitting diode (LED) according to the disclosure;
[0010] FIG. 3 is a schematic view illustrating a comparative
embodiment with respect to the first embodiment;
[0011] FIGS. 4A and 4B are transmission electron microscopy (TEM)
images of the first embodiment;
[0012] FIG. 5 is an energy dispersive X-ray (EDX) elemental line
profile of the first embodiment;
[0013] FIG. 6 is a scatter plot illustrating light output power
(abbreviated as LOP) of the LEDs of Experimental sample 1 (i.e.,
E1a and E1b) and Comparative sample 1 (i.e., C1a and C1b) at
different peak wavelengths;
[0014] FIG. 7 is a schematic view illustrating a second embodiment
of the epitaxial light emitting structure according to the
disclosure;
[0015] FIG. 8 is a schematic view illustrating a third embodiment
of the epitaxial light emitting structure according to the
disclosure;
[0016] FIG. 9 is a schematic view illustrating a fourth embodiment
of the epitaxial light emitting structure according to the
disclosure; and
[0017] FIG. 10 is a schematic view illustrating a fifth embodiment
of the epitaxial light emitting structure according to the
disclosure.
DETAILED DESCRIPTION
[0018] Before the disclosure is described in greater detail, it
should be noted that where considered appropriate, reference
numerals or terminal portions of reference numerals have been
repeated among the figures to indicate corresponding or analogous
elements, which may optionally have similar characteristics.
[0019] Referring to FIG. 1, a first embodiment of an epitaxial
light emitting structure 100 according to this disclosure includes
an n-type semiconductor layer 110, a p-type semiconductor layer
140, and a light emitting component 120 disposed therebetween.
[0020] The n-type semiconductor layer 110 and the p-type
semiconductor layer 140 may be independently made of a
nitride-based semiconductor material, and each has an energy
bandgap greater than that of the light emitting component 120. In
certain embodiments, the n-type semiconductor layer 110 and the
p-type semiconductor layer 140 is made of an aluminum gallium
nitride (AlGaN)-based material or a GaN-based material.
[0021] The epitaxial light emitting structure 100 may further
include a p-type electron blocking layer 130 formed between the
light emitting component 120 and the p-type semiconductor layer
140. The p-type electron blocking layer 130 is made of an aluminum
nitride-based semiconductor material and has an energy bandgap
greater than that of the p-type semiconductor layer 140. The
electron blocking layer 130 may be formed as a single layer
structure or a multiple layered structure (such as a superlattice
structure).
[0022] The light emitting component 120 includes a multiple quantum
well (MQW) structure which contains a plurality of (i.e., at least
two) first periodic layered elements (A). The light emitting
component 120 is made of a nitride-based material, such as an
unintentionally doped nitride-based material. A number of the first
periodic layered element (A) in the MQW structure may range from 2
to 29.
[0023] Each of the first periodic layered element (A) includes a
first layer 121, a second layer 122 which is disposed on the first
layer 121, and a third layer 123 which is disposed on the second
layer 122. The first layers 121, the second layers 122 and the
third layers 123 in the first periodic layered elements (A) are
alternately stacked on one another.
[0024] For each of the first periodic layered elements (A), the
first, second and third layers 121, 122, 123 respectively have a
first energy bandgap (Eg1), a second energy bandgap (Eg2), and a
third energy bandgap (Eg3) that satisfy a relationship of
Eg1<Eg2<Eg3. With the first and second layers 121, 122
respectively serving as a well region and a barrier region which
are alternately stacked, carriers (i.e., electron-hole pairs)
injected into the light emitting component 120 can be confined
therein, so as to increase the concentration of the electron-hole
pairs and the possibility of recombination, thereby improving the
emission efficiency of the epitaxial light emitting structure 100.
With the third layer 123 being disposed on the second layer 122 to
form an additional potential barrier, an improved confinement of
the electron-hole pairs can be achieved. The third energy bandgap
(Eg3) of the third layer 123 showing a potential barrier spike in a
bandgap diagram of the epitaxial light emitting structure 100 may
prevent the carriers from overflowing, which may occur in a tilted
energy band due to application of an external bias to the epitaxial
light emitting structure 100, so as to increase the efficiency of
radial recombination and brightness of the epitaxial light emitting
structure 100.
[0025] Moreover, a material having a larger energy bandgap
indicates that the material exhibits a proper insulation property.
The third layer 123 formed with an appropriate thickness in each of
the first periodic layered elements (A) may block a reverse
current, and reduces current leakage so as to decrease an aging
time of the epitaxial light emitting structure 100. In this
embodiment, for each of the first periodic layered elements (A),
the third layer 123 has a thickness not greater than 30 .ANG., such
as 10 .ANG. to 15 .ANG.. When the third layer 123 has a too small
thickness (such as lower than 10 .ANG., e.g., from 5 .ANG. to lower
than 10 .ANG.), less carriers are confined in the epitaxial light
emitting structure 100. On the other hand, the third layer 123
having a thickness greater than 30 .ANG. may have poor
conductivity, and thus light emitting performance of the light
emitting component 120 may be reduced and the external bias applied
thereto will be increased during operation.
[0026] By controlling the second energy bandgap (Eg2) to be lower
than the third energy bandgap (Eg3), the stress in the MQW
structure can be well modulated. For each of the first periodic
layered elements (A), a difference between the third energy bandgap
(Eg3) and the second energy bandgap (Eg2) is equal to or larger
than 1.5 eV, so as to effectively confine the carriers and reduce
overflow thereof.
[0027] The epitaxial light emitting structure 100 is adapted for
use in a GaN-based light emitting diode (LED), and is configured to
emit a light having an emission wavelength that ranges from 210 nm
to 420 nm. The light may include, but is not limited to, a UVC
radiation having a peak wavelength ranging from 210 nm to 280 nm, a
UVB radiation having a peak wavelength ranging from 280 nm to 320
nm, and a UVA radiation having a peak wavelength ranging from 320
nm to 420 nm. In certain embodiments, the epitaxial light emitting
structure 100 is configured to emit ultraviolet (UV) light which
has an emission wavelength ranging from 350 nm to 370 nm. For each
of the first periodic layered elements (A), the first layer 121 may
be made of one of AlGaN, GaN and InGaN. With different contents of
aluminum (Al) or indium (In) doped in the first layer 121, light
having varied wavelengths can be provided. In general, the first
layer 121 including a higher Al content provides a light having a
shorter wavelength, and the first layer 121 including a higher In
content provides a light having a longer wavelength. The first,
second and third layers 121, 122, 123 in each of the first periodic
layered elements (A) may be made of one of the following
combinations: AlGaN/AlGaN/AlN, GaN/AlGaN/AlN, InGaN/AlGaN/AlN,
InGaN/InAlGaN/AlN and InGaN/GaN/AlN.
[0028] In this embodiment, to generate a UVA radiation having a
peak wavelength ranging from 360 nm to 420 nm, the first layer 121
of each of the first periodic layered elements (A) is made of
In.sub.xGa.sub.1-xN, where 0.ltoreq.x.ltoreq.1. In other
embodiments, x ranges from 0 to 0.1. The numeral x can be varied to
adjust the emission wavelength of the light, in which a larger x
generates a shorter emission wavelength, while a smaller x
generates a longer emission wavelength. That is, the In content in
the first layer 121 can be varied to control the first energy
bandgap (Eg1), thereby adjusting the emission wavelength of the
light. For example, the peak wavelength is 365 nm when x is
approximately 0.005, the peak wavelength ranges from 385 nm to 395
nm when x ranges from 0.03 to 0.05, and the peak wavelength is 400
nm when x is approximately 0.08. The second layer 122 of each of
the first periodic layered elements (A) is made of
In.sub.yAl.sub.zGa.sub.1-y-zN, where 0.ltoreq.y<1,
0.ltoreq.z<1 and y+z.ltoreq.1. For example, the second layer 122
may be made of InAlGaN or AlGaN. In one aspect, the second layer
122 is made of Al.sub.zGa.sub.1-zN, where 0.ltoreq.y.ltoreq.0.02
and 0.06.ltoreq.z.ltoreq.0.12. The third layer 123 of each of the
first periodic layered elements (A) is made of Al.sub.wGa.sub.1-wN,
where 0<w.ltoreq.1. In one aspect, the third layer 123 is made
of Al.sub.wGa.sub.1-wN, where 0.95.ltoreq.w.ltoreq.1. For example,
the third layer 123 may be made of AlN. The Al and In contents of
the second layer 122 may be varied to adjust the second energy
bandgap (Eg2), and the Al content of the third layer 123 may be
varied to adjust the third energy bandgap (Eg3). For each of the
first periodic layered elements (A), the first energy bandgap (Eg1)
of the first layer 121 ranges from 3.3 eV to 3.5 eV, such as 3.3 eV
to 3.4 eV. The first layer 121 may have a thickness lower than 300
.ANG.. The second energy bandgap (Eg2) of the second layer 122
ranges from 3.55 eV to 3.9 eV, such as 3.59 eV to 3.70 eV. The
second layer 122 may have a thickness lower than 300 .ANG.. The
third energy bandgap (Eg3) of the third layer 123 is 6.2 eV. The
third layer 123 may have a thickness ranging from 10 .ANG. to 15
.ANG.. It is noted that when the first layer 121 is made of
In.sub.xGa.sub.1-xN, where 0<x.ltoreq.0.1, and the third layer
123 is made of Al.sub.wGa.sub.1-wN, where 0<w.ltoreq.1, a large
energy bandgap difference would be generated between the first
layer 121 and the third layer 123, causing a large lattice mismatch
therebetween, and such lattice mismatch may become more serious as
the In content of the first layer 121 or the Al content of the
third layer 123 increases. In addition, since the first layer 121
made of InGaN needs to be grown under a relatively low growth
temperature, the growth temperature of the third layer 123 made of
AlN is also low. Therefore, the thickness of the third layer 123 is
controlled to be lower than 30 .ANG., so as to reduce lattice
mismatch and improve crystal quality, thereby improving emission
efficiency of the LED.
[0029] The MQW structure in an LED made of nitride-based
semiconductor materials mainly adopts In and Al doping materials to
obtain well layers and barrier layers. The lattice constant of InN,
GaN and AlN has a relationship of InN>GaN>AlN. In this
embodiment, each of the first periodic layered elements (A) of the
MQW structure includes three layers having a stepped variation of
the lattice constant, i.e., InGaN (the first layer 121)>InAlGaN
or AlGaN (the second layer 122)>AlGaN or AlN (the third layer
123), such that lattice mismatch between these layers in the MQW
structure can be reduced and the stress generated therein may also
be effectively released so as to improve crystal quality. As
compared to the first embodiment of the MQW structure shown in FIG.
1 (i.e., the first layers 121, the second layers 122, and the third
layers 123 are alternately stacked on one another in a direction
away from the n-type semiconductor layer 110), a comparative
embodiment with respect to the first embodiment is shown in FIG. 3,
in which the first layers 121, the third layers 123, and the second
layers 122 in such order in the first periodical layered elements
(A) are alternately stacked on one another in the direction away
from the n-type semiconductor layer 110. That is, for each of the
first periodic layered elements (A), the third layer 123 is
disposed between the first layer 121 and the second layer 122.
Since a large energy bandgap difference is present between the
first layer 121 and the third layer 123, the hole mobility in the
comparative embodiment is smaller than that of the first
embodiment. The stress released in the comparative embodiment is
also less than that in the first embodiment due to a relatively
large stress difference between the first layer 121 and the third
layer 123.
[0030] The epitaxial light emitting structure 100 of this
disclosure may be formed on a growth substrate by metal organic
chemical vapor deposition (MOCVD), and then transferred to a
supporting substrate 200, thereby obtaining an LED 10 of this
disclosure (see FIG. 2), which has a vertical structure (i.e.,
vertical LED). Alternatively, the LED may also be a horizontal LED
or a flip-chip LED.
[0031] Referring to FIG. 2, the vertical LED 10 includes the
epitaxial light emitting structure 100 as mentioned above, in which
the p-type semiconductor layer 140 faces the supporting substrate
200, and the n-type semiconductor layer 110 has a light exit
surface. The epitaxial light emitting structure 100 may be formed
with at least one hole that extends through the p-type
semiconductor layer 140, the p-type electron blocking layer 130 and
the light emitting component 120, and that terminates at and
exposes the n-type semiconductor layer 110. The vertical LED 10 may
further include a first metal layer 160, an insulating layer 170
and a second metal layer 180 that are formed between the supporting
substrate 200 and the epitaxial light emitting structure 100.
Specifically, the first metal layer 160 is disposed on the p-type
semiconductor layer 140 opposite to the light emitting component
120, and may include a metal reflective material for reflecting the
light emitted from the light emitting component 120. The insulating
layer 170 covers the first metal layer 160 and a side wall of the
epitaxial light emitting structure 100 exposed from the hole. The
second metal layer 180 is disposed on the insulating layer 170
opposite to the first metal layer 160 and fills the hole to contact
the n-type semiconductor layer 110. The second metal layer 180 may
include a metallic adhesive material for bonding to the supporting
substrate 200. The vertical LED 10 may further include a first
electrode 210 that is electrically connected to the first metal
layer 160, and a second electrode 220 that is disposed on the
supporting substrate 200 opposite to the second metal layer
180.
[0032] Two UV vertical LED samples emitting light that has a peak
wavelength ranging from 365 nm to 370 nm, i.e., Experimental sample
1 (E1) and Comparative sample 1 (C1), are prepared (each having a
size of 325 .mu.m.times.325 .mu.m). Specifically, Experimental
sample 1 (E1) has an epitaxial light emitting structure 100 of the
first embodiment as shown in FIG. 1, which was first grown on a
sapphire substrate and then transferred to a supporting substrate
made of silicon. Each of the n-type semiconductor layer 110, the
p-type electron blocking layer 130 and the p-type semiconductor 140
is made of AlGaN. With regard to the light emitting component 120,
the multiple quantum well structure contains five of the first
periodic layered elements (A), each including the first layer 121
made of In.sub.0.05Ga.sub.0.95N and having an average thickness of
76 .ANG., the second layer 122 made of Al.sub.0.08Ga.sub.0.92N and
having an average thickness of 177 .ANG., and the third layer 123
made of AlN and having an average thickness of 10 .ANG. (see TEM
images shown in FIGS. 4A and 4B). In certain embodiments, the
multiple quantum well structure of the light emitting component 120
has a total thickness ranging from 100 .ANG. to 3000 .ANG..
Referring further to FIG. 5, an EDX elemental line profile of the
light emitting component 120 of the first embodiment indicates
variation of Al, Ga and N contents in each of the first periodic
layered elements (A), as well as the distribution and relative
thickness of each of the first, second and third layers 121, 122,
123.
[0033] Comparative sample 1 (C1) has an epitaxial light emitting
structure similar to that of E1, except that the third layer is
omitted in each of the first periodic layered elements (A). That
is, the MQW structure of C1 contains five of the conventional
periodic layered elements, each of which merely includes the first
layer 121 made of In.sub.0.05Ga.sub.0.95N and having an average
thickness of 76 .ANG., and the second layer 122 made of
Al.sub.0.08Ga.sub.0.92N and having an average thickness of 177
.ANG..
[0034] Since a circular carrier plate is used for growing the
epitaxial light emitting structure by MOCVD, the epitaxial light
emitting structure formed in different positions on the circular
carrier plate may have different growth qualities. Therefore, two
LEDs of E1, i.e., E1a and E1b respectively grown at positions a and
b on the circular carrier plate, and two LEDs of C1 (i.e., C1a and
C1b) respectively grown at positions a and b on the circular
carrier plate were subjected to determination of light output power
under a current of 150 mA.
[0035] As shown in FIG. 6, although the LEDs of E1a, E1b, C1a and
C1b emit light having a similar wavelength range (i.e., from 365 nm
to 370 nm), the light output power of the LEDs of E1a and E1b are
higher than that of C1a and C1b, which indicates that luminance of
the LEDs according to this disclosure can be greatly enhanced. The
LEDs of E1a and E1b were also subjected to a test for a hot/cold
(H/C) factor determination at 25.degree. C. and at 85.degree. C.
The LEDs of E1a and E1b have a H/C factor ranging from 78% to 80%,
which is higher than that of a conventional LEDs (i.e., H/C factor
lower than 70%).
[0036] Therefore, the LED of this disclosure can exhibit an
enhanced luminance stability during operation in a thermal
state.
[0037] Each of the LEDs of E1a, E1b, C1a and C1b was subjected to
an aging test described as follows. To be specific, each LED was
lit up for 48 hours or 96 hours under a current of 150 mA, at a
junction temperature of 125.degree. C. and at an environmental
temperature of 65.degree. C. Then, a reverse bias of 5 V was
applied to each LED to determine leakage current therein, so as to
measure an initial light output power (LOP.sub.i), an aged light
output power (LOP.sub.48/96), an aged forward voltage
(Vf.sub.48/96) and an aged reverse current (IR.sub.48/96) of each
LED. A decay rate of light, a change of the forward voltage
(.DELTA.Vf) between an initial forward voltage (Vf.sub.i) (i.e.,
when the LED was not lit up) and the aged forward voltage, and
leakage current, i.e., a change of the reverse current (.DELTA.IR)
between an initial reverse current (IR.sub.i) and the aged reverse
current, were respectively calculated based on the formulas
below:
Decay rate of
light=(LOP.sub.48/96/LOP.sub.i).times.100%.DELTA.f=Vf.sub.48/96-Vf.sub.i;
.DELTA.IR=IR.sub.48/96-IR.sub.i.
[0038] When the .DELTA.IR is smaller, the light emitting component
120 has better quality and current flow through the p-n junction of
the light emitting component 120 under the reverse bias is less,
indicating the LED exhibits a more stabilized reverse
characteristic during operation.
TABLE-US-00001 TABLE 1 Decay rate of Change of forward light (%)
voltage .DELTA.Vf (V) .DELTA.IR Sample 48 hr 96 hr 48 hr 96 hr 48
hr 96 hr E1a 95.80 94.84 -0.014 -0.002 0.92 1.38 E1b 96.18 93.96
-0.012 0.059 0.93 1.40 C1a 95.10 93.65 -0.019 -0.004 1.24 1.80 C1b
96.18 95.79 -0.027 0.016 1.67 2.67
[0039] As shown in Table 1, the decay rate of light and the
.DELTA.IR in E1a and E1b are less than those in C1a and C1b, which
indicates that the LED of this disclosure, which includes a
plurality of the third layers 123 in the epitaxial light emitting
structure 100, can reduce current leakage and exhibit improved
durability.
[0040] Referring to FIG. 7, a second embodiment of the epitaxial
light emitting structure 100 according to this disclosure is
similar to the first embodiment except that in the second
embodiment, the MQW structure further contains at least one second
periodic layered element (B) which includes a fourth layer 124 and
a fifth layer 125. The fourth layer 124 and the fifth layer 125 may
be made of different materials that are independently selected from
materials for making the first layer 121, the second layer 122, and
the third layer 123. For example, the fourth layer 124 and the
fifth layer 125 may be respectively made of materials for making
the first layer 121 and the second layer 122.
[0041] In this embodiment, the first periodic layered elements (A)
are disposed on the p-type electron blocking layer 130 opposite to
the p-type semiconductor layer 140, and the at least one second
periodic layered element (B) is disposed between the n-type
semiconductor layer 110 and the first periodic layered elements
(A). The first, second and third layers 121, 122 and 123 in each of
the first periodic layered elements (A) are respectively made of
InGaN, AlGaN and AlN. The fourth and fifth layers 124, 125 in each
of the second periodic layered elements (B) may be respectively
made of materials for making the first and second layers 121, 122
(i.e., InGaN and AlGaN). The number of the first periodic layered
elements (A) is more than 2, such as from 2 to 29. The number of
the second periodic layered elements (B) ranges from 1 to 28.
[0042] In a variation of the second embodiment, the at least one
second periodic layered element (B) is disposed on the p-type
electron blocking layer 130 opposite to the p-type semiconductor
layer 140, and the first periodic layered elements (A) are disposed
between the n-type semiconductor layer 110 and the second periodic
layered elements (B).
[0043] Referring to FIG. 8, a third embodiment of the epitaxial
light emitting structure 100 according to this disclosure is
similar to the first embodiment except that in the third
embodiment, for at least one of the first periodic layered elements
(A), the first layer 121 includes a first lower sublayer 1211 and a
first upper sublayer 1212 which is disposed between the first lower
sublayer 1211 and the second layer 122. The first upper sublayer
1212 has an energy bandgap that is greater than an energy bandgap
of the first lower sublayer 1211 and that is smaller than that of
the second energy bandgap (Eg2). In this embodiment, the first
lower sublayer 1211 is made of In.sub.x1Ga.sub.1-x1N and the first
upper sublayer 1212 is made of In.sub.x2Ga.sub.1-x2N, where x1 and
x2 independently range from 0 to 0.03, and x1 is greater than
x2.
[0044] Referring to FIG. 9, a fourth embodiment of the epitaxial
light emitting structure 100 according to this disclosure is
similar to the first embodiment except that in the fourth
embodiment, for at least one of the first periodic layered elements
(A), the second layer 122 includes a second lower sublayer 1221 and
a second upper sublayer 1222 which is disposed between the second
lower sublayer 1221 and the third layer 123. The second upper
sublayer 1222 has an energy bandgap greater than an energy bandgap
of the second lower sublayer 1221. In this embodiment, the second
lower sublayer 1221 and the second upper sublayer 1222 are made of
In.sub.yAl.sub.zGa.sub.1-y-zN with different In and Al contents,
where y ranges from 0 to 0.002 and z ranges from 0.06 to 0.12.
[0045] Referring to FIG. 10, a fifth embodiment of the epitaxial
light emitting structure 100 according to this disclosure is
similar to the second embodiment except that in the fifth
embodiment, for at least one of the first periodic layered elements
(A), the third layer 123 includes a third lower sublayer 1231 and a
third upper sublayer 1232 which is disposed on the third lower
sublayer 1231 opposite to the second layer 122. The third lower
sublayer 1231 has an energy bandgap greater than the second energy
bandgap (Eg2), and the third upper sublayer 1232 has an energy
bandgap greater than that of the third lower sublayer 1231. A
difference between the energy bandgap of the third lower sublayer
1231 and the second energy bandgap (Eg2) is equal to or larger than
1.5 eV. The third lower sublayer 1231 and the third upper sublayer
1232 are made of AlGaN and AlN, respectively.
[0046] In conclusion, by forming an additional barrier layer (i.e.,
the third layer 123) having a relatively high energy bandgap on the
conventional MQW structure having alternately stacked first and
second layers 121, 122 that serves as the well and barrier regions,
the epitaxial light emitting structure 100 of this disclosure can
exert an additional confinement effect for carriers. Since the
energy bandgap of the third layer 123 is greater than those of the
first and second layer 121, 122, when the energy band is tilted
under an external bias applied to the epitaxial light emitting
structure 100 of the LED 10, a potential barrier spike can be
generated to prevent carrier overflow, thereby increasing
efficiency of radial recombination and luminance of the LED of this
disclosure.
[0047] In the description above, for the purposes of explanation,
numerous specific details have been set forth in order to provide a
thorough understanding of the embodiments. It will be apparent,
however, to one skilled in the art, that one or more other
embodiments maybe practiced without some of these specific details.
It should also be appreciated that reference throughout this
specification to "one embodiment," "an embodiment," an embodiment
with an indication of an ordinal number and so forth means that a
particular feature, structure, or characteristic may be included in
the practice of the disclosure. It should be further appreciated
that in the description, various features are sometimes grouped
together in a single embodiment, figure, or description thereof for
the purpose of streamlining the disclosure and aiding in the
understanding of various inventive aspects, and that one or more
features or specific details from one embodiment may be practiced
together with one or more features or specific details from another
embodiment, where appropriate, in the practice of the
disclosure.
[0048] While the disclosure has been described in connection with
what are considered the exemplary embodiments, it is understood
that this disclosure is not limited to the disclosed embodiments
but is intended to cover various arrangements included within the
spirit and scope of the broadest interpretation so as to encompass
all such modifications and equivalent arrangements.
* * * * *