U.S. patent application number 10/939689 was filed with the patent office on 2006-03-16 for gallium-nitride based light emitting diode light emitting layer structure.
Invention is credited to Fen-Ren Chien, Ru-Chin Tu, Tzu-Chi Wen, Liang-Wen Wu, Cheng-Tsang Yu.
Application Number | 20060054897 10/939689 |
Document ID | / |
Family ID | 36032961 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060054897 |
Kind Code |
A1 |
Yu; Cheng-Tsang ; et
al. |
March 16, 2006 |
Gallium-nitride based light emitting diode light emitting layer
structure
Abstract
A number of light-emitting layer structures for the GaN-based
LEDs that can increase the lighting efficiency of the GaN-based
LEDs on one hand and facilitate the growth of epitaxial layer with
better quality on the other hand are provided. The light-emitting
layer structure provided is located between the n-type GaN contact
layer and the p-type GaN contact layer. Sequentially stacked on top
of the n-type GaN contact layer in the following order, the
light-emitting layer contains a lower barrier layer, at least one
intermediate layer, and an upper barrier layer. That is, the
light-emitting layer contains at least one intermediate layer
interposed between the upper and lower barrier layers. When there
are multiple intermediate layers inside the light-emitting layer,
there is an intermediate barrier layer interposed between every two
immediately adjacent intermediate layers.
Inventors: |
Yu; Cheng-Tsang; (Wufong
Township, TW) ; Tu; Ru-Chin; (Tainan City, TW)
; Wu; Liang-Wen; (Banciao City, TW) ; Wen;
Tzu-Chi; (Tainan City, TW) ; Chien; Fen-Ren;
(Yonghe City, TW) |
Correspondence
Address: |
SUPREME PATENT SERVICES
P.O. BOX 2339
SARATOGA
CA
95070-0339
US
|
Family ID: |
36032961 |
Appl. No.: |
10/939689 |
Filed: |
September 11, 2004 |
Current U.S.
Class: |
257/79 ;
257/E33.008 |
Current CPC
Class: |
B82Y 20/00 20130101;
B82Y 10/00 20130101; H01L 33/06 20130101; H01L 33/32 20130101 |
Class at
Publication: |
257/079 |
International
Class: |
H01L 33/00 20060101
H01L033/00; H01L 31/12 20060101 H01L031/12; H01L 27/15 20060101
H01L027/15; H01L 29/26 20060101 H01L029/26 |
Claims
1. A light-emitting layer structure of a gallium-nitride (GaN)
based light emitting diode (LED), wherein said LED comprises a
sapphire substrate and comprises, on one side of said substrate
from bottom to top, a n-type GaN contact layer, a light-emitting
layer covering a part of an upper surface of said n-type GaN
contact layer; a p-type GaN contact layer covering said
light-emitting layer, a positive electrode covering said p-type GaN
contact layer, and a negative electrode covering another part of
said upper surface of said n-type GaN contact layer not covered by
said light-emitting layer, wherein said light-emitting layer,
sequentially from bottom to top, comprises: a lower barrier layer
made of un-doped aluminum-gallium-indium-nitride
(Al.sub.1-x-yGa.sub.xIn.sub.yN, 0.ltoreq.x,y.ltoreq.1,
x+y.ltoreq.1); at least an intermediate layer, wherein, when there
are more than one said intermediate layer, said intermediate layers
stack sequentially and an intermediate barrier layer made of
un-doped Al.sub.1-i-jGa.sub.iIn.sub.jN (0.ltoreq.i,j.ltoreq.1,
i+j.ltoreq.1) is interposed between every two immediately adjacent
said intermediate layers; and an upper barrier layer made of
un-doped Al.sub.1-p-qGa.sub.pIn.sub.qN (0.ltoreq.p,q.ltoreq.1,
p+q.ltoreq.1).
2. The light-emitting layer structure of a GaN-based LED according
to claim 1, wherein said intermediate layer comprises, from bottom
to top, a first ultra-thin quantum-dot layer made of indium-nitride
(InN) and a quantum-well layer made of un-doped
Al.sub.1-m-nGa.sub.mIn.sub.nN (0.ltoreq.m,n.ltoreq.1,
m+n.ltoreq.1).
3. The light-emitting layer structure of a GaN-based LED according
to claim 2, wherein said intermediate layer further comprises a
second ultra-thin quantum-dot layer made of InN on top of said
quantum-well layer.
4. The light-emitting layer structure of a GaN-based LED according
to claim 2, wherein said upper, intermediate, and lower barrier
layers all have a thickness between 5 .ANG. and 300 .ANG., said
first ultra-thin quantum-dot layer has a thickness between 2 .ANG.
and 30 .ANG., and said quantum-well layer has a thickness between 5
.ANG. and 100 .ANG..
5. The light-emitting layer structure of a GaN-based LED according
to claim 3, wherein said upper, intermediate, and lower barrier
layers all have a thickness between 5 .ANG. and 300 .ANG., said
first and said second ultra-thin quantum-dot layers all have a
thickness between 2 .ANG. and 30 .ANG., and said quantum-well layer
has a thickness between 5 .ANG. and 100 .ANG..
6. The light-emitting layer structure of a GaN-based LED according
to claim 1, wherein said intermediate layer comprises, from bottom
to top, a first ultra-thin layer made of InN and a quantum-well
layer made of un-doped Al.sub.1-m-nGa.sub.mIn.sub.nN
(0.ltoreq.m,n.ltoreq.1, m+n.ltoreq.1).
7. The light-emitting layer structure of a GaN-based LED according
to claim 6, wherein said intermediate layer further comprises a
second ultra-thin layer made of InN on top of said quantum-well
layer.
8. The light-emitting layer structure of a GaN-based LED according
to claim 6, wherein said upper, intermediate, and lower barrier
layers all have a thickness between 5 .ANG. and 300 .ANG., said
first ultra-thin layer has a thickness between 2 .ANG. and 10
.ANG., and said quantum-well layer has a thickness between 5 .ANG.
and 100 .ANG..
9. The light-emitting layer structure of a GaN-based LED according
to claim 7, wherein said upper, intermediate, and lower barrier
layers all have a thickness between 5 .ANG. and 300 .ANG., said
first and said second ultra-thin layers all have a thickness
between 2 .ANG. and 10 .ANG., and said quantum-well layer has a
thickness between 5 .ANG. and 100 .ANG..
10. The light-emitting layer structure of a GaN-based LED according
to claim 1, wherein said intermediate layer is a super lattice well
layer comprising at least a first ultra-thin monolayer made of InN
and at least a second ultra-thin monolayer made of GaN,
sequentially stacked and interleaved with each other.
11. The light-emitting layer structure of a GaN-based LED according
to claim 10, wherein said first ultra-thin monolayers and said
second ultra-thin monolayers have identical number of layers, no
more than five layers respectively, and a thickness between 2 .ANG.
and 20 .ANG. for each individual layer.
12. The light-emitting layer structure of a GaN-based LED according
to claim 10, wherein said upper, intermediate, and lower barrier
layers all have a thickness between 5 .ANG. and 300 .ANG..
13. A light-emitting layer structure of a GaN-based LED, wherein
said LED comprises a sapphire substrate and comprises, on one side
of said substrate from bottom to top, a n-type GaN contact layer, a
light-emitting layer covering a part of an upper surface of said
n-type GaN contact layer, a p-type GaN contact layer covering said
light-emitting layer, a positive electrode covering said p-type GaN
contact layer, and a negative electrode covering another part of
said upper surface of said n-type GaN contact layer not covered by
said light-emitting layer, wherein said light-emitting layer,
sequentially from bottom to top, comprises: a lower barrier layer,
wherein said lower barrier layer is a super lattice barrier layer
comprising at least a fifth ultra-thin monolayer made of AlN and at
least a sixth ultra-thin monolayer made of GaN, sequentially
stacked and interleaved with each other; at least an intermediate
layer, wherein, when there are more than one said intermediate
layer, said intermediate layers stack sequentially and an
intermediate barrier layer, being a super lattice barrier layer
comprising at least a seventh ultra-thin monolayer made of In-doped
AlN and at least a eighth ultra-thin monolayer made of In-doped GaN
sequentially stacked and interleaved with each other, is interposed
between every two immediately adjacent said intermediate layers;
and an upper barrier layer, wherein said upper barrier layer is a
super lattice barrier layer comprising at least a ninth ultra-thin
monolayer made of AlN and at least a tenth ultra-thin monolayer
made of GaN, sequentially stacked and interleaved with each
other.
14. The light-emitting layer structure of a GaN-based LED according
to claim 13, wherein said intermediate layer is a super lattice
well layer comprising at least a third ultra-thin monolayer made of
InN and at least a fourth ultra-thin monolayer made of GaN,
sequentially stacked and interleaved with each other.
15. The light-emitting layer structure of a GaN-based LED according
to claim 13, wherein said upper, intermediate, and lower barrier
layers all have a thickness between 5 .ANG. and 300 .ANG..
16. The light-emitting layer structure of a GaN-based LED according
to claim 14, wherein said third ultra-thin monolayers and said
fourth ultra-thin monolayers have identical number of layers, no
more than five layers respectively, and a thickness between 2 .ANG.
and 20 .ANG. for each individual layer.
17. The light-emitting layer structure of a GaN-based LED according
to claim 13, wherein said fifth ultra-thin monolayers and said
sixth ultra-thin monolayers have identical number of layers, no
more than five layers respectively, and a thickness between 2 .ANG.
and 20 .ANG. for each individual layer.
18. The light-emitting layer structure of a GaN-based LED according
to claim 13, wherein said seventh ultra-thin monolayers and said
eighth ultra-thin monolayers have identical number of layers, no
more than five layers respectively, and a thickness between 2 .ANG.
and 20 .ANG. for each individual layer.
19. The light-emitting layer structure of a GaN-based LED according
to claim 13, wherein said ninth ultra-thin monolayers and said
tenth ultra-thin monolayers have identical number of layers, no
more than five layers respectively, and a thickness between 2 .ANG.
and 20 .ANG. for each individual layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the gallium-nitride (GaN)
based light emitting diode (LED), and in particular to the
structure of the light-emitting layer of the GaN-based LED.
[0003] 2. The Prior Arts
[0004] LEDs have long been widely used as indicators or light
sources in various electronic consumer devices due to their
features including low power consumption, low heat dissipation, and
long operation life. In recent years, researches have been focused
on the development of LEDs with various colors and LEDs with high
luminance. Among these researches, highly efficient and illuminant
blue-light LEDs that can be put to practical use receive the most
attention. In October 1995, Nichia Corporation, Japan, announced
the successful production of highly illuminant blue-light LEDs
based on the indium-gallium-nitride (InGaN) material. This
breakthrough has led the world's optoelectronic industry to invest
tremendous capitals and resources in the gallium-nitride (GaN)
based, such as GaN, aluminum-gallium-nitride (AlGaN),
indium-gallium-nitride (InGaN), etc., LEDs.
[0005] FIG. 1 is a schematic diagram showing the structure of a
GaN-based LED according to prior arts. As shown in FIG. 1, the
conventional structure of a GaN-based LED contains a substrate 10
made of sapphire. Then, on one side of the sapphire substrate 10,
the GaN-based LED further contains a n-type GaN contact layer 11, a
InGaN light-emitting layer 12, and a p-type GaN contact layer 13,
sequentially stacked from bottom to top in this order. In addition,
there are a positive electrode 14 and a negative electrode 15
stacked upon the p-type GaN contact layer 13 and the n-type GaN
contact layer 11 respectively. Within this conventional GaN-based
LED structure, the light-emitting layer 12 usually has a
multi-quantum well (MQW) structure made of In.sub.xGa.sub.1-xN
(0.ltoreq.x.ltoreq.1). The electrons and holes are joined with each
other within the In.sub.xGa.sub.1-xN (0.ltoreq.x.ltoreq.1)
potential well and photons are thereby released. Please note that
the epitaxial growth of the In.sub.xGa.sub.1-xN
(0.ltoreq.x.ltoreq.1) requires a very high temperature to obtain
epitaxial layer with better quality. On the other hand, to increase
the possibility of forming the electron-hold pairs and thereby the
lighting efficiency, the growing temperature of the
In.sub.xGa.sub.1-xN (0.ltoreq.x.ltoreq.1) cannot be higher than
850.degree. C. so that multiple localized states can be formed from
the characteristics of the In.sub.xGa.sub.1-xN
(0.ltoreq.x.ltoreq.1) such as indium segregation and phase
separation. This is a dilemma requiring an appropriate
solution.
SUMMARY OF THE INVENTION
[0006] To overcome the foregoing disadvantages, the present
invention provides a number of light-emitting layer structures for
the GaN-based LEDs that can increase the lighting efficiency of the
GaN-based LEDs on one hand and facilitate the growth of epitaxial
layer with better quality on the other hand.
[0007] The light-emitting layer structure provided by the present
invention is located between the n-type GaN contact layer and the
p-type GaN contact layer. Sequentially stacked on top of the n-type
GaN contact layer in the following order, the light-emitting layer
contains a lower barrier layer, at least one intermediate layer,
and an upper barrier layer. That is, the light-emitting layer
contains at least one intermediate layer interposed between the
upper and lower barrier layers. When there are multiple
intermediate layers inside the light-emitting layer, there is an
intermediate barrier layer interposed between every two immediately
adjacent intermediate layers.
[0008] The upper and lower barrier layers have higher band gaps
than that of the intermediate layer so that the electrons and the
holes have a higher possibility joining with each other within the
intermediate layer, which in turn increase the lighting efficiency
of the GaN-based LED. The barrier layers have a thickness between 5
.ANG. and 300 .ANG., and a growing temperature between 400.degree.
C. and 1000.degree. C.
[0009] The foregoing and other objects, features, aspects and
advantages of the present invention will become better understood
from a careful reading of a detailed description provided herein
below with appropriate reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic diagram showing the structure of a
conventional GaN-based LED.
[0011] FIGS. 2(a), 2(b), and 2(c) are schematic diagrams showing
the GaN-based LED structures according to a first embodiment of the
present invention.
[0012] FIGS. 3(a), 3(b), and 3(c) are schematic diagrams showing
the GaN-based LED structures according to a second embodiment of
the present invention.
[0013] FIGS. 4(a) and 4(b) are schematic diagrams showing the
GaN-based LED structures according to a third embodiment of the
present invention.
[0014] FIGS. 5(a) and 5(b) are schematic diagrams showing the
GaN-based LED structures according to a fourth embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] FIGS. 2(a), 2(b), and 2(c) are schematic diagrams showing
the GaN-based LED structures according to a first embodiment of the
present invention. As shown in FIGS. 2(a), 2(b), and 2(c), the
GaN-based LED structures use sapphire as the substrate 20. Then,
sequentially from bottom to top on the sapphire substrate 20, the
GaN-based LED structures contain a n-type GaN contact layer 21, a
lower barrier layer 22 made of un-doped
aluminum-gallium-indium-nitride (Al.sub.1-x-yGa.sub.xIn.sub.yN,
0.ltoreq.x,y.ltoreq.1, x+y.ltoreq.1), at least an intermediate
layer 23, an upper barrier layer 24 made of un-doped
Al.sub.1-p-qGa.sub.pIn.sub.qN (0.ltoreq.p,q.ltoreq.1,
p+q.ltoreq.1), and a p-type GaN contact layer 25. The GaN-based LED
structures further contain a positive electrode 26 and a negative
electrode 27 on top of the p-type GaN contact layer 25 and the
n-type GaN contact layer 21 respectively.
[0016] As shown in FIG. 2(a), the intermediate layer 23 further
contains, from bottom to top, an ultra-thin quantum-dot layer 231
made of indium-nitride (InN) and a quantum-well layer 232 made of
un-doped Al.sub.1-m-nGa.sub.mIn.sub.nN (0.ltoreq.m,n.ltoreq.1,
m+n.ltoreq.1).
[0017] As shown in FIG. 2(b), the intermediate layer 23 can further
contain an optional InN ultra-thin quantum-dot layer 231' on top of
the un-doped Al.sub.1-m-nGa.sub.mIn.sub.nN (0.ltoreq.m,n.ltoreq.1,
m+n.ltoreq.1) quantum-well layer 232.
[0018] As shown in FIG. 2(c), when there are multiple intermediate
layers, every two immediately adjacent intermediate layers 23 and
23' have an intermediate barrier layer 28 made of un-doped
Al.sub.1-i-jGa.sub.iIn.sub.jN (0.ltoreq.i,j.ltoreq.1, i+j.ltoreq.1)
interposed therebetween.
[0019] The upper, intermediate, and lower barrier layers 24, 28,
and 22 all have a thickness between 5 .ANG. and 300 .ANG., and a
growing temperature between 400.degree. C. and 1000.degree. C. The
ultra-thin quantum-dot layers 231 and 231' have a thickness between
2 .ANG. and 30 .ANG., and a growing temperature between 400.degree.
C. and 1000.degree. C. The quantum-well layer 232 has a thickness
between 5 .ANG. and 100 .ANG.. Even though the quantum-well layer
and the barrier layers are all made of
aluminum-gallium-indium-nitrides, their compositions are not
required to be identical. That is, the (x, y), (p, q), (m, n), (i,
j) parameters in the foregoing molecular formulas are not
necessarily the same.
[0020] FIGS. 3(a), 3(b), and 3(c) are schematic diagrams showing
the GaN-based LED structures according to a second embodiment of
the present invention. The second embodiment and the foregoing
first embodiment of the present invention actually have identical
structures. The difference lies in the materials used for the
respective intermediate layers. As shown in FIG. 3(a), the
intermediate layer 33 further contains, from bottom to top, an
ultra-thin layer 331 made of InN and quantum-well layer 332 made of
un-doped Al.sub.1-m-nGa.sub.mIn.sub.nN (0.ltoreq.m,n.ltoreq.1,
m+n.ltoreq.1).
[0021] As shown in FIG. 3(b), the intermediate layer 33 can further
contain another optional InN ultra-thin layer 331' on top of the
un-doped Al.sub.1-m-nGa.sub.mIn.sub.nN (0.ltoreq.m,n.ltoreq.1,
m+n.ltoreq.1) quantum-well layer 332.
[0022] As shown in FIG. 3(c), when there are multiple intermediate
layers, every two immediately adjacent intermediate layers 33 and
33' must have an intermediate barrier layer 38 made of un-doped
Al.sub.1-i-jGa.sub.iIn.sub.jN (0.ltoreq.i,j.ltoreq.1, i+j.ltoreq.1)
interposed therebetween.
[0023] The upper, intermediate, and lower barrier layers 34, 38,
and 32 all have a thickness between 5 .ANG. and 300 .ANG., and a
growing temperature between 400.degree. C. and 1000.degree. C. The
ultra-thin layers 331 and 331' have a thickness between 2 .ANG. and
10 .ANG., and a growing temperature between 400.degree. C. and
1000.degree. C. The quantum-well layer 332 has a thickness between
5 .ANG. and 100 .ANG.. Even though the quantum-well layer and the
barrier layers are all made of aluminum-gallium-indium-nitrides,
their compositions are not required to be identical. That is, the
(x, y), (p, q), (m, n), (i, j) parameters in the foregoing
molecular formulas are not necessarily the same.
[0024] FIGS. 4(a) and 4(b) are schematic diagrams showing the
GaN-based LED structures according to a third embodiment of the
present invention. The third embodiment and the previous two
embodiments of the present invention actually have identical
structures. The difference lies in the materials used for the
respective intermediate layers. As shown in FIG. 4(a), the
intermediate layer 43 is a supper lattice well layer further
containing at least an InN ultra-thin monolayer 431 and a GaN
ultra-thin monolayer 432. Within the intermediate layer 43, the
monolayers are sequentially stacked and interleaved with each
other. For one example, from the lower barrier layer 42 up, there
are InN ultra-thin monolayer 431, GaN ultra-thin monolayer 432,
then another InN ultra-thin monolayer 431', and then another GaN
ultra-thin monolayer 432', and so on. For another example, from the
lower barrier layer 42 up, there are GaN ultra-thin monolayer 432,
InN ultra-thin monolayer 431, then another GaN ultra-thin monolayer
432', and then another InN ultra-thin monolayer 431', and so on.
The monolayers all have a thickness between 2 .ANG. and 20 .ANG.,
and a growing temperature between 400.degree. C. and 1000.degree.
C. Within the intermediate layer 43, there are at least one InN
ultra-thin monolayer 431 and one GaN ultra-thin monolayer 432,
making the total number of monolayers at least two. On the other
hand, within the intermediate layer 43, there are at most five InN
ultra-thin monolayers 431 and five GaN ultra-thin monolayers 432,
making the total number of monolayers at most ten.
[0025] As shown in FIG. 4(b), when there are multiple intermediate
layers, every two immediately adjacent intermediate layers 43 and
43' must have an intermediate barrier layer 48 made of un-doped
Al.sub.1-i-jGa.sub.iIn.sub.jN (0.ltoreq.i,j.ltoreq.1, i+j.ltoreq.1)
interposed therebetween.
[0026] The upper, intermediate, and lower barrier layers 44, 48,
and 42 all have a thickness between 5 .ANG. and 300 .ANG., and a
growing temperature between 400.degree. C. and 1000.degree. C. Even
though the barrier layers are all made of
aluminum-gallium-indium-nitrides, their compositions are not
required to be identical. That is, the (x, y), (p, q), (i, j)
parameters in the foregoing molecular formulas are not necessarily
the same.
[0027] FIGS. 5(a) and 5(b) are schematic diagrams showing the
GaN-based LED structures according to the fourth embodiment of the
present invention. The fourth embodiment and the third embodiment
of the present invention actually have identical structures. The
difference lies in the materials used for the upper, intermediate,
and lower barrier layers. As shown in FIGS. 5(a) and 5(b), each
barrier layer has a structure identical to that of the intermediate
layer 43. Specifically, each barrier layer is a supper lattice
barrier layer further containing at least an In-doped, AlN
ultra-thin monolayer 531 and an In-doped, GaN ultra-thin monolayer
532. Within each the barrier layer, the monolayers are sequentially
stacked and interleaved with each other, similar to the
intermediate layer 43. The monolayers all have a thickness between
2 .ANG. and 20 .ANG., and a growing temperature between 400.degree.
C. and 1000.degree. C. Within each barrier layer, there are at
least one AlN ultra-thin monolayer 531 and one GaN ultra-thin
monolayer 532, making the total number of monolayers at least two.
On the other hand, within each barrier layer, there are at most
five AlN ultra-thin monolayer 531 and five GaN ultra-thin monolayer
532, making the total number of monolayers at most ten. The upper,
intermediate, and lower barrier layers 54, 58, and 52 may contain
different numbers of monolayers respectively. However, the barrier
layers all have a thickness between 5 .ANG. and 300 .ANG., and a
growing temperature between 400.degree. C. and 1000C.
[0028] Although the present invention has been described with
reference to the preferred embodiments, it will be understood that
the invention is not limited to the details described thereof.
Various substitutions and modifications have been suggested in the
foregoing description, and others will occur to those of ordinary
skill in the art. Therefore, all such substitutions and
modifications are intended to be embraced within the scope of the
invention as defined in the appended claims.
* * * * *