U.S. patent application number 15/981864 was filed with the patent office on 2018-09-20 for nitride semiconductor structure.
This patent application is currently assigned to Genesis Photonics Inc.. The applicant listed for this patent is Genesis Photonics Inc.. Invention is credited to Yen-Lin Lai, Shen-Jie Wang.
Application Number | 20180269349 15/981864 |
Document ID | / |
Family ID | 50727077 |
Filed Date | 2018-09-20 |
United States Patent
Application |
20180269349 |
Kind Code |
A1 |
Lai; Yen-Lin ; et
al. |
September 20, 2018 |
NITRIDE SEMICONDUCTOR STRUCTURE
Abstract
A nitride semiconductor structure and a semiconductor light
emitting device including the same are revealed. The nitride
semiconductor structure includes a multiple quantum well structure
formed by a plurality of well layers and barrier layers stacked
alternately. One well layer is disposed between every two barrier
layers. The barrier layer is made of A.sub.xIn.sub.yGa.sub.1-x-yN
(0<x<1, 0<y<1, 0<x+y<1) while the well layer is
made of In.sub.zGa.sub.1-zN (0<z<1). Thereby quaternary
composition is adjusted for lattice match between the barrier
layers and the well layers. Thus crystal defect caused by lattice
mismatch is improved.
Inventors: |
Lai; Yen-Lin; (New Taipei
City, TW) ; Wang; Shen-Jie; (New Taipei City,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Genesis Photonics Inc. |
Tainan City |
|
TW |
|
|
Assignee: |
Genesis Photonics Inc.
Tainan City
TW
|
Family ID: |
50727077 |
Appl. No.: |
15/981864 |
Filed: |
May 16, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15499913 |
Apr 28, 2017 |
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15981864 |
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14732798 |
Jun 8, 2015 |
9640712 |
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15499913 |
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13963109 |
Aug 9, 2013 |
9076912 |
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14732798 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/12 20130101;
H01L 33/325 20130101; H01L 33/0025 20130101; H01L 33/06 20130101;
H01L 33/32 20130101; H01L 33/145 20130101 |
International
Class: |
H01L 33/00 20060101
H01L033/00; H01L 33/32 20060101 H01L033/32; H01L 33/14 20060101
H01L033/14; H01L 33/06 20060101 H01L033/06; H01L 33/12 20060101
H01L033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2012 |
TW |
101143101 |
Claims
1. A nitride semiconductor structure comprising: a first type doped
semiconductor layer; a second type doped semiconductor layer; a
light emitting layer disposed between the second type doped
semiconductor layer and the first type doped semiconductor layer,
the light emitting layer comprising a multiple quantum well (MQW)
structure, wherein the MQW structure comprises a plurality of
barrier layers and a plurality of well layers stacked alternately;
an InGaN based second type hole supply layer disposed between the
second type doped semiconductor layer and the light emitting layer;
and an AlGaN based second type carrier blocking layer disposed
between the second type doped semiconductor layer and the light
emitting layer, wherein the InGaN based second type hole supply
layer is doped with a second type dopant at a concentration larger
than 10.sup.18 cm.sup.-3 and carbon at a concentration between
10.sup.17 cm.sup.-3 and 10.sup.20 cm.sup.-3.
2. The nitride semiconductor structure as claimed in claim 1,
wherein a material of each of the barrier layers of the MQW
structure is doped with a first type dopant at a concentration
ranging from 10.sup.16 cm.sup.-3 to 10.sup.18 cm.sup.-3.
3. The nitride semiconductor structure as claimed in claim 1,
wherein a band gap of the InGaN based second type hole supply layer
is larger than a band gap of each of the well layers of the MQW
structure.
4. The nitride semiconductor structure as claimed in claim 1,
wherein the second type dopant in the InGaN based second type hole
supply layer is magnesium.
5. The nitride semiconductor structure as claimed in claim 1,
further comprising: an AlGaN based first type carrier blocking
layer, disposed between the first type doped semiconductor layer
and the light emitting layer.
6. A nitride semiconductor structure comprising: a first type doped
semiconductor layer; a second type doped semiconductor layer; a
light emitting layer disposed between the second type doped
semiconductor layer and the first type doped semiconductor layer,
the light emitting layer comprising a multiple quantum well (MQW)
structure, wherein the MQW structure comprises a plurality of
barrier layers and a plurality of well layers stacked alternately;
an InGaN based second type hole supply layer disposed between the
second type doped semiconductor layer and the light emitting layer;
an AlGaN based first type carrier blocking layer disposed between
the first type doped semiconductor layer and the light emitting
layer; and an AlGaN based second type carrier blocking layer
disposed between the second type doped semiconductor layer and the
InGaN based second type hole supply layer, wherein the InGaN based
second type hole supply layer is doped with a second type dopant at
a concentration larger than 10.sup.18 cm.sup.-3 and carbon at a
concentration between 10.sup.17 cm.sup.-3 and 10.sup.20
cm.sup.-3.
7. The nitride semiconductor structure as claimed in claim 6,
wherein a material of each of the barrier layers of the MQW
structure is doped with a first type dopant at a concentration is
ranging from 10.sup.16 cm.sup.-3 to 10.sup.18 cm.sup.-3.
8. The nitride semiconductor structure as claimed in claim 6,
wherein a band gap of the InGaN based second type hole supply layer
is larger than a band gap of each of the well layers of the MQW
structure.
9. The nitride semiconductor structure as claimed in claim 6,
wherein the second type dopant in the InGaN based second type hole
supply layer is magnesium.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation application of and claims the
priority benefit of U.S. application Ser. No. 15/499,913, filed on
Apr. 28, 2017, now pending. The prior U.S. application Ser. No.
15/499,913 is a continuation application of and claims the priority
benefit of U.S. application Ser. No. 14/732,798, filed on Jun. 8,
2015, now patented. The prior U.S. application Ser. No. 14/732,798
is a continuation application of and claims the priority benefit of
U.S. application Ser. No. 13/963,109, filed on Aug. 9, 2013, now
patented, which claims the priority benefit of Taiwan application
serial no. 101143101, filed on Nov. 19, 2012. The entirety of each
of the above-mentioned patent applications is hereby incorporated
by reference herein and made a part of this specification.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to a nitride semiconductor
structure and a semiconductor light emitting device including the
same, especially to a nitride semiconductor structure that has a
multiple quantum well structure formed by quaternary AlGaInN
barrier layers and ternary InGaN well layers for reducing stress
coming from lattice mismatch. The thickness of the well layer is
ranging from 3.5 nm to 7 nm. At the same time, a better carrier
confinement is provided and the internal quantum efficiency is
improved. Thus the semiconductor light emitting device has a better
light emitting efficiency.
2. Description of Related Art
[0003] Generally, a nitride light emitting diode is produced by
forming a buffer layer on a substrate first. Then a n-type
semiconductor layer, a light emitting layer and a p-type
semiconductor layer are formed on the buffer layer in turn by
epitaxial growth. Next use photolithography and etching processes
to remove a part of the p-type semiconductor layer and a part of
the light emitting layer until a part of the n-type semiconductor
layer is exposed. Later a n-type electrode and a p-type electrode
are respectively formed on the exposed n-type semiconductor layer
and the p-type semiconductor layer. Thus, a light emitting diode
device is produced. The light emitting layer has a multiple quantum
well (MQW) structure formed by a plurality of well layers and
barrier layers disposed alternately. The band gap of the well layer
is lower than that of the barrier layer so that electrons and holes
are confined by each well layer of the MQW structure. Thus
electrons and holes are respectively injected from the n-type
semiconductor layer and the p-type semiconductor layer to be
combined with each other in the well layers and photons are
emitted.
[0004] In the MQW structure, there are about 1-30 layers of well
layers or barrier layers. The barrier layer is usually made of GaN
while the well layer is made of InGaN. However, there is about
10.about.15% lattice mismatch between GaN and InGaN that causes a
large stress in the lattice. Thus a piezoelectric field is induced
in the MQW structure by the stress. Moreover, during growth of
InGaN, the higher indium composition, the larger the piezoelectric
field generated. The piezoelectric field has a greater impact on
the crystal structure. The stress accumulated is getting larger
along with the increasing thickness during growth of InGaN. After
the crystal structure being grown over a critical thickness, larger
defects (such as V-pits) are present due to the stress, so that the
thickness of the well layer has a certain limit, generally about 3
nm.
[0005] Moreover, in the MQW structure, band gap is tilted or
twisted due to effects of a strong polarization field. Thus
electrons and holes are separated and confined on opposite sides of
the well layer, which leads to decrease the overlapping of the wave
function of the electron hole pairs and further to reduce both
radiative recombination rate and internal quantum efficiency of
electron hole pairs.
SUMMARY OF THE INVENTION
[0006] A nitride semiconductor structure comprising a first type
doped semiconductor layer; a light emitting layer, comprising a
multiple quantum well (MQW) structure; an AlGaN based second type
carrier blocking layer; and a second type doped semiconductor
layer, wherein the AlGaN based second type carrier blocking layer
is disposed between the second type doped semiconductor layer and
the light emitting layer, and the light emitting layer is disposed
between the AlGaN based second type carrier blocking layer and the
first type doped semiconductor layer, and the MQW structure
comprises a plurality of AlInGaN based barrier layers and a
plurality of InGaN based well layers stacked alternately.
[0007] A nitride semiconductor structure comprising: a first type
doped semiconductor layer; a light emitting layer, comprising a
multiple quantum well (MQW) structure; a InGaN based hole supply
layer; and a second type doped semiconductor layer, wherein the
light emitting layer is disposed between the first type doped
semiconductor layer and the InGaN based hole supply layer, and the
InGaN based hole supply layer is disposed between the light
emitting layer and the second type doped semiconductor layer, and
the MQW structure comprises a plurality of AlInGaN based barrier
layers and a plurality of InGaN based well layers stacked
alternately, and the band gap of the hole supply layer is larger
than that of the InGaN based well layers.
[0008] A nitride semiconductor structure comprising: a first type
doped semiconductor layer; a AlGaN based first type carrier
blocking layer; a light emitting layer, comprising a multiple
quantum well (MQW) structure; a AlGaN based second type carrier
blocking layer; and a second type doped semiconductor layer,
wherein the light emitting layer is disposed between the first type
doped semiconductor layer and the second type doped semiconductor
layer, the AlGaN based first type carrier blocking layer is
disposed between the first type doped semiconductor layer and the
light emitting layer, the AlGaN based second type carrier blocking
layer is disposed between the second type doped semiconductor layer
and the light emitting layer, and the MQW structure comprises a
plurality of AlInGaN based barrier layers and a plurality of InGaN
based well layers stacked alternately.
[0009] By the quaternary AlGaInN barrier layers and the ternary
InGaN well layers, the stress caused by lattice mismatch is
improved and the piezoelectric field in the MQW structure is
further reduced effectively. Thus inhibition of the piezoelectric
effect and improvement of internal quantum efficiency are achieved.
Therefore the semiconductor light emitting device gets a better
light emitting efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The structure and the technical means adopted by the present
invention to achieve the above and other objects can be best
understood by referring to the following detailed description of
the preferred embodiments and the accompanying drawings,
wherein
[0011] FIG. 1 is a schematic drawing showing a cross section of an
embodiment of a nitride semiconductor structure according to the
present invention;
[0012] FIG. 2 is a schematic drawing showing a cross section of an
embodiment of a semiconductor light emitting device including a
nitride semiconductor structure according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] In the following embodiments, when it is mentioned that a
layer of something or a structure is disposed over or under a
substrate, another layer of something, or another structure, that
means the two structures, the layers of something, the layer of
something and the substrate, or the structure and the substrate can
be directly or indirectly connected. The indirect connection means
there is at least one intermediate layer disposed therebetween.
[0014] Referring to FIG. 1, a first type doped semiconductor layer
3 and a second type doped semiconductor layer 7 are disposed over a
substrate 1. A light emitting layer 5 is disposed between the first
type doped semiconductor layer 3 and the second type doped
semiconductor layer 7. The light emitting layer 5 has a multiple
quantum well (MQW) structure. The MQW structure includes a
plurality of well layers 51 and barrier layers 52 stacked
alternately. One well layer 51 is disposed between every two
barrier layers 52. The barrier layer 52 is made of quaternary
AlxInyGa1-x-yN (0<x<1, 0<y<1, 0<x+y<1) and the
well layer 51 is made of material In.sub.zGa.sub.1-zN
(0<z<1). The thickness of the well layer 51 is ranging from
3.5 nm to 7 nm, preferably from 4 nm to 5 nm. The thickness of the
barrier layer 52 is ranging from 5 nm to 12 nm. The barrier layer
52 is doped with a first type dopant (such as silicon or germanium)
at a concentration ranging from 10.sup.16 cm.sup.-3 to 10.sup.18
cm.sup.-3 so as to reduce carrier screening effect and increase
carrier-confinement.
[0015] Moreover, a hole supply layer 8 is disposed between the
light emitting layer 5 and the second type doped semiconductor
layer 7. The hole supply layer 8 is made of In.sub.xGa.sub.1-xN
(0<x<1) and is doped with a second type dopant (such as
magnesium or zinc) at a concentration larger than 10.sup.18 cm
.sup.-3. The hole supply layer 8 is also doped with a Group IV A
element whose concentration is ranging from 10.sup.17 cm.sup.-3 to
10.sup.20 cm .sup.-3. The optimal Group IV A element is carbon. The
pentavalent nitrogen is replaced by carbon, so that the hole supply
layer 8 has higher concentration of holes and more holes are
provided to enter the light emitting layer 5. Thus the
electron-hole recombination is increased. The band gap of the hole
supply layer 8 is larger than that of the well layer 51 of MQW
structure, so that the holes are allowed to enter the well layers
and the electrons will not escape into the second type doped
semiconductor layer 7.
[0016] Furthermore, a first type carrier blocking layer 4 made of
material Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the
light emitting layer 5 and the first type doped semiconductor layer
3 while a second type carrier blocking layer 6 made of
Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the hole
supply layer 8 and the second type doped semiconductor layer 7. Due
to the property that the band gap of AlGaN containing aluminum is
larger than that of the GaN, not only the range of band gap of the
nitride semiconductor is increased, the carriers are confined in
the MQW structure. Thus the electron-hole recombination rate is
increased and the light emitting efficiency is improved.
[0017] In addition, a buffer layer 2 made of Al.sub.xGa.sub.1-xN
(0<x<1) is disposed between the substrate 1 and the first
type doped semiconductor layer 3. The buffer layer 2 is for
improving lattice mismatch caused by the first type doped
semiconductor layer 3 grown on the heterogeneous substrate 1. The
materials for the buffer layer 2 can also be GaN, InGaN, SiC, ZnO,
etc. The buffer layer is produced by a low-temperature epitaxial
growth at the temperature ranging from 400 degrees Celsius
(.degree. C.) to 900.degree. C.
[0018] While in use, the material for the substrate 1 can be
sapphire, silicon, SiC, ZnO or GaN, etc. The first type doped
semiconductor layer 3 is made of Si-doped or Ge-doped GaN-based
materials while the second type doped semiconductor layer 7 is made
of Mg-doped or Zn-doped GaN-based materials. The first type doped
semiconductor layer 3 and the second type doped semiconductor layer
7 are produced by the method such as metalorganic chemical vapor
deposition (MOCVD). As to the well layer 51 and the barrier layer
52, they are produced by metal organic chemical vapor deposition or
molecular beam epitaxy (MBE) deposition of gas mixture of a lower
alkyl group-indium and gallium compound. The barrier layers 52 are
deposited at the temperature ranging from 850.degree. C. to
1000.degree. C. while the well layers 51 are formed at the
temperature ranging from 500.degree. C. to 950.degree. C. The
AlGaInN barrier layers 52 and the InGaN well layers 51 of the MQW
structure have the same element-indium so that the lattice constant
of the barrier layers 52 and the lattice constant of the well
layers 51 are similar. Thus not only crystal defects caused by
lattice mismatch between conventional InGaN well layers and GaN
barrier layers can be improved, the stress caused by lattice
constant mismatch between materials is also improved. The thickness
of the well layer 51 of the nitride semiconductor structure is
ranging from 3.5 nm to 7 nm, preferably from 4 nm to 5 nm.
[0019] Moreover, the piezoelectric field in the MQW structure is
effectively reduced because that the quaternary AlGaInN barrier
layers 52 and InGaN well layers 51 can improve the stress caused by
lattice mismatch. Thus the tilted and twisted energy band is
improved in a certain degree. Therefore the piezoelectric effect is
reduced effectively and the internal quantum efficiency is
increased.
[0020] The above nitride semiconductor structure is applied to
semiconductor light emitting devices. Referring to FIG. 2, a cross
section of a semiconductor light emitting device including the
nitride semiconductor structure of an embodiment according to the
present invention is revealed. The semiconductor light emitting
device includes at least: a substrate 1, a first type doped
semiconductor layer 3 disposed over the substrate 1 and made of
Si-doped or Ge-doped GaN based materials, a light emitting layer 5
disposed over the first type doped semiconductor layer 3 and having
a multiple quantum well (MQW) structure, a second type doped
semiconductor layer 7 disposed over the light emitting layer 5 and
made of Mg-doped or Zn-doped GaN based materials, a first type
electrode 31 disposed on and in ohmic contact with the first type
doped semiconductor layer 3, and a second type electrode 71
disposed on and in ohmic contact with the second type doped
semiconductor layer 7.
[0021] The MQW structure includes a plurality of well layers 51 and
barrier layers 52 stacked alternately. One well layer 51 is
disposed between every two barrier layers 52. The barrier layer 52
is made of material Al.sub.xIn.sub.yGa.sub.1-x-yN and x and y
satisfy the conditions: 0<x<1, 0<y<1, and 0<x+y<1
while the well layer 51 is made of material In.sub.zGa.sub.1-zN and
0<z<1. The thickness of the well layer 51 is ranging from 3.5
nm to 7 nm, preferably from 4 nm to 5 nm.
[0022] The first type electrode 31 and the second type electrode 71
are used together to provide electric power and are made of (but
not limited to) the following materials: titanium, aluminum, gold,
chromium, nickel, platinum, and their alloys. The manufacturing
processes are well-known to people skilled in the art.
[0023] Moreover, a first type carrier blocking layer 4 made of
material Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the
light emitting layer 5 and the first type doped semiconductor layer
3 while a second type carrier blocking layer 6 made of material
Al.sub.xGa.sub.1-xN (0<x<1) is disposed between the light
emitting layer 5 and the second type doped semiconductor layer 7.
Due to the property that the band gap of AlGaN containing aluminum
is larger than that of GaN, not only the range of the band gap of
the nitride semiconductor is increased, the carriers are also
confined in the MQW structure. Thus the electron-hole recombination
rate is increased and the light emitting efficiency is further
improved.
[0024] A buffer layer 2 made of Al.sub.xGa.sub.1-xN (0<x<1)
is disposed between the substrate 1 and the first type doped
semiconductor layer 3 so as to improve lattice constant mismatch
caused by the first type doped semiconductor layer 3 grown on the
heterogeneous substrate 1. The buffer layer 2 can also be made of
material including GaN, InGaN, SiC, ZnO, etc.
[0025] In summary, due to that both quaternary AlGaInN barrier
layers 52 and ternary InGaN well layers 51 have the same
element-indium, the quaternary composition of the semiconductor
light emitting device of the present invention can be adjusted and
improved for providing a lattice matching composition that allows
the barrier layers 52 and the well layers 51 to have similar
lattice constants. Thus not only crystal defects caused by lattice
mismatch between conventional InGaN well layers and GaN barrier
layers can be improved, the stress caused by lattice mismatch is
also improved. The thickness of the well layer 51 of the nitride
semiconductor structure is ranging from 5 nm to 7 nm, preferably
from 4 nm to 5 nm. Moreover, the addition of more aluminum (Al) in
the barrier layer 52 provides a better carrier confinement and
electrons and holes are effectively confined in the well layer 51.
Thereby the internal quantum efficiency is increased and the
semiconductor light emitting device provides a better light
emitting efficiency.
[0026] Furthermore, the quaternary AlGaInN barrier layers and the
ternary InGaN well layers can improve the stress caused by lattice
mismatch and further reduce the piezoelectric field in the MQW
structure effectively. Thus the piezoelectric effect is inhibited
and the internal quantum efficiency is improved. Therefore, the
semiconductor light emitting device gets a better light emitting
efficiency.
[0027] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details, and
representative devices shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *