U.S. patent application number 13/059031 was filed with the patent office on 2011-06-09 for method for fabricating ingan-based multi-quantum well layers.
This patent application is currently assigned to LATTICE POWER (JIANGXI) CORPORATION. Invention is credited to Wenqing Fang, Fengyi Jiang, Chunlan Mo, Li Wang.
Application Number | 20110133158 13/059031 |
Document ID | / |
Family ID | 41706801 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110133158 |
Kind Code |
A1 |
Jiang; Fengyi ; et
al. |
June 9, 2011 |
METHOD FOR FABRICATING INGAN-BASED MULTI-QUANTUM WELL LAYERS
Abstract
A method for fabricating quantum wells by using indium gallium
nitride (InGaN) semiconductor material includes fabricating a
potential well on a layered group III-V nitride structure at a
first predetermined temperature in a reactor chamber by injecting
into the reactor chamber an In precursor gas and a Ga precursor
gas. The method further includes, subsequent to the fabrication of
the potential well, terminating the Ga precursor gas, maintaining a
flow of the In precursor gas, and increasing the temperature in the
reactor chamber to a second predetermined temperature while
adjusting the In precursor gas flow rate from a first to a second
flow rate. In addition, the method includes annealing and
stabilizing the potential well at the second predetermined
temperature while maintaining the second flow rate. The method also
includes fabricating a potential barrier above the potential well
at the second predetermined temperature while resuming the Ga
precursor gas.
Inventors: |
Jiang; Fengyi; (Jiangxi,
CN) ; Wang; Li; (Jiangxi, CN) ; Mo;
Chunlan; (Jiangxi, CN) ; Fang; Wenqing;
(Jiangxi, CN) |
Assignee: |
LATTICE POWER (JIANGXI)
CORPORATION
Nanchang, Jiangxi
CN
|
Family ID: |
41706801 |
Appl. No.: |
13/059031 |
Filed: |
August 19, 2008 |
PCT Filed: |
August 19, 2008 |
PCT NO: |
PCT/CN2008/001488 |
371 Date: |
February 14, 2011 |
Current U.S.
Class: |
257/13 ;
257/E21.09; 257/E33.027; 438/478 |
Current CPC
Class: |
H01L 21/0262 20130101;
H01L 33/06 20130101; H01L 21/0254 20130101; H01L 33/007
20130101 |
Class at
Publication: |
257/13 ; 438/478;
257/E33.027; 257/E21.09 |
International
Class: |
H01L 33/06 20100101
H01L033/06; H01L 21/20 20060101 H01L021/20 |
Claims
1. A method for fabricating an active region comprising at least
one quantum well by using indium gallium nitride (InGaN)
semiconductor material, the method comprising: fabricating a
potential well on a layered group III-V nitride structure at a
first predetermined temperature in a reactor chamber by injecting
into the reactor chamber an In precursor gas and a Ga precursor
gas; subsequent to the fabrication of the potential well,
terminating the Ga precursor gas, maintaining a flow of the In
precursor gas, and increasing the temperature in the reactor
chamber to a second predetermined temperature while adjusting the
In precursor gas flow rate from a first to a second flow rate;
annealing and stabilizing the potential well at the second
predetermined temperature while maintaining the second flow rate;
and fabricating a potential barrier above the potential well at the
second predetermined temperature while resuming the Ga precursor
gas.
2. The method of claim 1, wherein the layered group III-V nitride
structure comprises a substrate, a buffer layer; and an n-type
semiconductor layer.
3. The method of claim 1, wherein the first predetermined
temperature is between 700.degree. C. and 950.degree. C.
4. The method of claim 1, wherein fabricating the potential well
involves maintaining the In and Ga precursor flows for 50 to 200
seconds.
5. The method of claim 1, wherein the In precursor gas is TMIn.
6. The method of claim 5, wherein fabricating the potential well
comprises injecting the TMIn gas at a flow rate that is between 160
and 360 sccm.
7. The method of claim 1, wherein the Ga precursor gas is TMGa, and
fabricating the potential well comprises injecting the TMGa gas at
a flow rate that is between 0.4 and 2.4 sccm.
8. The method of claim 1, wherein the second predetermined
temperature is between 850.degree. C. and 1050.degree. C.
9. The method of claim 1, wherein the first flow rate of the In
precursor gas is between 25 and 100 sccm.
10. The method of claim 1, wherein the second flow rate of the In
precursor gas is between 50 and 300 sccm.
11. The method of claim 1, wherein the increasing to the second
predetermined temperature is performed over 25 to 400 seconds.
12. A light-emitting device having an active region comprising at
least one quantum well based on InGaN semiconductor material, the
device comprising: a layered group III-V nitride structure; a
potential well on the layered group III-V nitride structure,
wherein the potential well is fabricated by: placing the layered
group III-V nitride structure in a reactor chamber at a first
predetermined temperature; injecting into the reactor chamber an In
precursor gas and a Ga precursor gas; subsequent to the fabrication
of the potential well, terminating the Ga precursor gas,
maintaining a flow of the In precursor gas, and increasing the
temperature in the reactor chamber to a second predetermined
temperature while adjusting the In precursor gas flow rate from a
first to a second flow rate; and annealing and stabilizing the
potential well at the second predetermined temperature while
maintaining the second flow rate; a barrier fabricated above the
potential well at a second predetermined temperature; and a group
III-V p-type nitride layer.
13. The device of claim 12, wherein the layered group III-V nitride
structure comprises a buffer layer; and an n-type semiconductor
layer.
14. The device of claim 12, wherein the first predetermined
temperature is between 700.degree. C. and 950.degree. C.
15. The device of claim 12, wherein injecting the In and Ga
precursor gas comprises maintaining the In and Ga precursor flows
for 50 to 200 seconds.
16. The device of claim 12, wherein the In precursor gas is
TMIn.
17. The device of claim 16, wherein injecting the In precursor gas
comprises injecting the TMIn gas at a flow rate that is between 160
and 360 sccm.
18. The device of claim 12, wherein the Ga precursor gas is TMGa,
and wherein injecting the Ga precursor gas comprises injecting the
TMGa gas at a flow rate that is between 0.4 and 2.4 sccm.
19. The device of claim 12, wherein the second predetermined
temperature is between 850.degree. C. and 1050.degree. C.
20. The device of claim 12, wherein the first flow rate of the In
precursor gas is between 25 and 100 sccm.
21. The device of claim 12, wherein the second flow rate of the In
precursor gas is between 50 and 300 sccm.
22. The device of claim 12, wherein the increasing to the second
predetermined temperature is performed over 25 to 400 seconds.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention relates to the manufacturing of
semiconductor light-emitting devices using indium gallium nitride
(InGaN) semiconductor material. More specifically, the present
invention relates to a technique for epitaxially growing
high-quality semiconductor material with a multi-quantum well (MQW)
structure.
[0003] 2. Related Art
[0004] Group III-V nitride compounds (e.g., GaN, InN, and AlN) and
alloy-compounds (e.g., AlGaN, InGaN, and AlGAlnN) have demonstrated
efficient luminescence in the blue-green spectrum. This efficiency
has been the driving force for their recent application in
light-emitting diodes (LEDs) and laser diodes, which in turn has
changed the market for color displays. Using group III-V nitride
materials for high-brightness LEDs has opened the door to many
applications previously deemed unfeasible, such as in traffic
lights and in flat-panel display as white light sources. In
addition, ultra-violet laser diodes using group III-V nitride
materials are now widely used in scientific instrumentation,
laboratories, and commercial products.
[0005] The active region of an LED is the area where light is
generated. It typically includes a multi-quantum well (MQW)
structure, which includes multiple periods of quantum well
structures. A single quantum well structure may include, for
example, an indium gallium nitride (InGaN)-based potential well
(well) sandwiched between potential barriers (barriers) based on
gallium nitride (GaN) or aluminum gallium nitride (AlGaN)
materials. Carriers are trapped in the well between the barriers.
An MQW structure allows higher carrier density and hence increases
the carrier recombination rate. The faster the carriers recombine,
the more efficient a light-emitting device becomes.
[0006] One of the factors that determine the color of the light
emitted by an LED is the concentration of indium (In) in the MQW
structure. Specifically, the color of the light emitted by an LED
can vary with different InGaN concentration or InGaN-to-GaN ratios
in the MQW structure. The higher the concentration of In or
InGaN-to-GaN ratio, the longer the wavelength of the visible light.
For instance, an LED emitting green light may exhibit a higher
concentration of In in the MQW structure than one emitting blue
light because the wavelength of green light is longer than that of
blue light. One of the challenges of producing light with longer
wavelengths is to increase the concentration of In in the MQW
structure while maintaining the quality of the MQW structure.
[0007] Typically, the LED-fabrication process involves subjecting
the structure to a relatively high temperature to obtain a
high-quality MQW structure. In a conventional method, the InGaN
well in an MQW structure is grown at a moderate temperature to
increase the concentration of In, and the temperature is
subsequently raised at least 100.degree. C. for the growth of GaN
barriers.
[0008] The temperature for fabricating an MQW structure is ideally
lower than 800.degree. C. to avoid the breaking of the
indium-nitrogen bond in the InGaN well. However, fabricating an MQW
structure at a lower temperature could result in a low-quality MQW
structure.
SUMMARY
[0009] One embodiment of the present invention provides a method
for fabricating an active region comprising at least one quantum
well by using indium gallium nitride (InGaN) semiconductor
material. The method includes fabricating a potential well on a
layered group III-V nitride structure at a first predetermined
temperature in a reactor chamber by injecting into the reactor
chamber an In precursor gas and a Ga precursor gas. The method
further includes, subsequent to the fabrication of the potential
well, terminating the Ga precursor gas, maintaining a flow of the
In precursor gas, and increasing the temperature in the reactor
chamber to a second predetermined temperature while adjusting the
In precursor gas flow rate from a first to a second flow rate. In
addition, the method includes annealing and stabilizing the
potential well at the second predetermined temperature while
maintaining the second flow rate. The method also includes
fabricating a potential barrier above the potential well at the
second predetermined temperature while resuming the Ga precursor
gas.
[0010] In a variation of this embodiment, the layered group III-V
nitride structure includes a substrate, a buffer layer; and an
n-type semiconductor layer.
[0011] In a variation of this embodiment, the first predetermined
temperature is between 700.degree. C. and 950.degree. C.
[0012] In a variation of this embodiment, fabricating the potential
well involves maintaining the In and Ga precursor flows for 50 to
200 seconds.
[0013] In a variation of this embodiment, the In precursor gas is
TMIn.
[0014] In a further variation, fabricating the potential well
includes injecting the TMIn gas at a flow rate that is between 160
and 360 sccm.
[0015] In a variation of this embodiment, the Ga precursor gas is
TMGa, and fabricating the potential well includes injecting the
TMGa gas at a flow rate that is between 0.4 and 2.4 sccm.
[0016] In a variation of this embodiment, the second predetermined
temperature is between 830.degree. C. and 1050.degree. C.
[0017] In a variation of this embodiment, the first flow rate of
the In precursor gas is between 25 and 100 sccm.
[0018] In a variation of this embodiment, the second flow rate of
the In precursor gas is between 50 and 300 sccm.
[0019] In a variation of this embodiment, the increasing to the
second predetermined temperature is performed over 25 to 400
seconds.
BRIEF DESCRIPTION OF THE FIGURES
[0020] The drawings accompanying and forming part of this
specification are included to depict certain aspects of the
invention. The invention may be better understood by reference to
one or more of these drawings in combination with the description
presented herein. It should be noted that the features illustrated
in the drawings are not necessarily drawn to scale.
[0021] FIG. 1 is a typical temperature vs. time diagram of a
process for growing a single InGaN/GaN quantum well structure.
[0022] FIG. 2 illustrates a cross-section view of an exemplary LED
which includes an InGaN/GaN MQW structure fabricated in accordance
with one embodiment.
[0023] FIG. 3 presents a flow chart illustrating a conventional
process for fabricating an active region of a GaN-based LED.
[0024] FIG. 4 presents a flow chart illustrating a process for
fabricating an active region of a GaN-based LED in accordance with
one embodiment.
DETAILED DESCRIPTION
[0025] The following description is presented to enable any person
skilled in the art to make and use the invention, and is provided
in the context of a particular application and its requirements.
Various modifications to the disclosed embodiments will be readily
apparent to those skilled in the art, and the general principles
defined herein may be applied to other embodiments and applications
without departing from the scope of the present invention. Thus,
the present invention is not limited to the embodiments shown, but
is to be accorded the widest scope consistent with the claims.
Overview
[0026] Embodiments of the present invention provide a method for
epitaxially fabricating a high-quality multi-quantum well (MQW)
structure using InGaN semiconductor material. Trimethylindium
(TMIn) is used as the source for In. A light-emitting diode (LED)
manufactured with the aforementioned MQW structure emits blue and
green lights with high luminance efficiency.
[0027] FIG. 1 is a typical temperature vs. time diagram of a
process for growing a single InGaN/GaN quantum well structure. This
process is divided into five periods, denoted as periods 110, 120,
130, 140, and 150, respectively. An InGaN well is grown during
period 110 at temperature t.sub.1. Subsequently, during period 120,
the temperature is raised from t.sub.1 to t.sub.2. The quantum well
grown in period 110 is then annealed and stabilized at temperature
t.sub.2 during period 130. Next, a GaN barrier is grown during
period 140 at temperature t.sub.2. The temperature is subsequently
lowered during period 150 in preparation of the growth of another
quantum well or other structures.
[0028] FIG. 2 illustrates a cross section view of an exemplary LED
which includes an InGaN/GaN MQW structure fabricated in accordance
with one embodiment. An LED 200 includes a substrate 210, a buffer
layer 220, a group III-V nitride n-type layer 230, an MQW active
region 240, and a group III-V nitride p-type layer 250. MQW active
region 240 includes a number (e.g., 4) of quantum wells. In one
embodiment, a respective quantum well includes an InGaN-based
potential well and a GaN-based potential barrier, which constitute
a period in MQW active region 240. MQW active region 240 is
fabricated using an In-rich fabrication method in accordance with
one embodiment.
[0029] FIG. 3 presents a flow chart illustrating a conventional
process for fabricating an active region of a GaN-based LED. The
fabrication process includes a number of operations (302-310). In
operation 302, a layered group III-V nitride structure is first
fabricated on a substrate in a reactor chamber. The layered
structure can include a buffer layer and a group III-V nitride
n-type layer.
[0030] An active region with one or more quantum wells is
fabricated on top of the n-type layer. Operations 304, 306, 308,
and 310, described below, illustrate a conventional process for
fabricating one quantum-well period. For an active region with n
quantum-well periods, these operations are repeated n times. Each
quantum-well period in an MQW structure can be grown under
substantially similar or different epitaxial conditions.
[0031] In operation 304, a potential well is fabricated in a
reactor chamber at a temperature higher than 720.degree. C. but
lower than 800.degree. C. for 150 seconds, which corresponds to
period 110 in FIG. 1. Note that nitrogen is used as the carrier gas
and TMIn and trimethylgallium (TMGa) are used as precursors. The
flow rate of TMIn is 260 standard cubic centimeters per minute
(sccm) and that of TMGa is 1.4 sccm.
[0032] In operation 306, the temperature in the reactor chamber is
gradually raised from 800.degree. C. to 950.degree. C., which
corresponds to period 120 in FIG. 1. The semiconductor material
remains in the chamber at 950.degree. C. for 100 seconds. After the
completion of the fabrication of the potential well, the precursor
flows are shut off, but the carrier gas flow remains on.
[0033] In operation 308, the temperature in the reactor chamber
remains at 950.degree. C. for approximately 60 seconds, which
corresponds to 130 in FIG. 1. This 60-second settling time
stabilizes the quantum well structure and prevents defect formation
in the structure.
[0034] In operation 310, a GaN barrier is epitaxially grown under
950.degree. C. for approximately 60 seconds. The flow of TMGa is
turned on and the flow rate is increased from 1.4 to 8 sccm. Note
that the active region fabricated using the conventional method
when forward-biased can produce visible light with a wavelength of
approximately 470 nm. The temperature is reduced when operation 310
is completed. After operations 304 to 310 are repeated for a
predetermined number of times, a group III-V p-type nitride layer
is then formed above the active region, and ohmic contacts are
constructed.
[0035] In the conventional method, the precursor flows are shut off
in operation 306, but the carrier gas flow remains on after the
completion of the fabrication of the potential well. Meanwhile,
during the annealing process, the fabricated InGaN semiconductor
material is exposed in a temperature that is 100.degree. C. higher
than the initial growth temperature. This higher temperature can
break the In--N bond in the potential well, which results in the
vaporization of In. Consequently, the concentration of In is
reduced. Although increasing the ratio of In to Ga can increase the
concentration of In, the effect is minimal, because during the
subsequent annealing process a substantial amount of In can still
escape from the grown potential well.
[0036] Embodiments of the present invention allow a high In
concentration to be maintained in an InGaN-based potential well. In
one embodiment, In is fabricated at a relatively low temperature.
The structure subsequently undergoes an annealing process in an
In-rich environment at a higher temperature. During the annealing
process, the precursor flow of TMIn remains on. The flow rate of
TMIn is predetermined based on the desired color of the emitted
light.
[0037] FIG. 4 presents a flow chart illustrating a process for
fabricating an active region of a GaN-based LED in accordance with
one embodiment. The fabrication process includes a number of
operations (402-410). In operation 402, a buffer layer and a group
III-V nitride n-type layer are grown in the same manner as shown in
FIG. 3. An active region with one or more quantum wells is formed
on top of the n-type layer. Operations 404, 406, 408, and 410,
described below, illustrate a process for fabricating one
quantum-well period. For an active region with n quantum-well
periods, these operations are repeated n times. Each quantum-well
period in an MQW structure can be grown under substantially similar
or different epitaxial conditions.
[0038] In operation 404, a potential well of an MQW structure is
fabricated at a first temperature for a period of time, using a
precursor gas that is rich in In (e.g., TMIn). In one embodiment,
the first temperature is higher than that in operation 304 of the
conventional method. As a result, the embodiments of present
invention yield a better-quality well, compared with that
fabricated using the conventional method.
[0039] In operation 406, the Ga precursor flow is stopped after the
well is fabricated. However, the In precursor flows continue while
the temperature in the reactor chamber is gradually increased to a
second temperature. In one embodiment, the flow rate of TMIn
increases gradually at a predetermined rate so as to reduce the
rate of the vaporization of In. In one embodiment, the flow rate
increases from 100 to 300 ml/min.
[0040] In operation 408, the semiconductor structure remains in the
reactor chamber at the second temperature for a period of time in
order for the fabricated material to anneal and stabilize. The TMIn
flow continues at a predetermined rate and the Ga precursor flow
remains off.
[0041] In operation 410, a potential barrier is grown at the second
temperature for a period of time. The TMGa flow is turned on and
the flow rate is set at a higher rate than that for fabricating the
well. The temperature in the reactor chamber is subsequently
lowered in preparation of the growth of the next quantum-well
period of other structures.
Example
[0042] An exemplary embodiment of fabricating an active region of a
GaN-based LED is presented. After a layered group III-V nitride
structure, including a group III-V nitride layer, is fabricated on
a substrate, an active region with five quantum wells is fabricated
on top of the n-type layer. Operations for growing a quantum-well
period, described below, are repeated five times.
[0043] An InGaN potential well of a MQW structure is epitaxially
grown in a reactor chamber at a growth temperature of approximately
830.degree. C. for approximately 150 seconds. The first temperature
is higher than that in a conventional method. This higher
temperature results in a better-quality quantum well, compared with
that fabricated using the conventional method. Nitrogen is used as
the carrier gas, and TMIn and TMGa are used as precursors. The flow
rate of TMIn is approximately 260 sccm and that of TMGa is
approximately 1.4 sccm.
[0044] The temperature in the reactor chamber is gradually raised
from 830.degree. C. to approximately 950.degree. C. The
semiconductor material remains in the chamber at 950.degree. C. for
approximately 100 seconds. The TMGa flow is shut off, but the flow
rate of TMIn is increased gradually from 50 to 150 seem so as to
reduce the rate of the vaporization of In.
[0045] The reactor chamber remains at 950.degree. C. for
approximately 60 seconds for the fabricated material to anneal and
stabilize. This 60-second settling time stabilizes the MQW
structure and prevents defect formation. The flow of TMIn continues
at 150 sccm while TMGa remains off.
[0046] After the completion of the InGaN potential well, a GaN
barrier is epitaxially grown at 950.degree. C. for approximately 60
seconds. The flow of TMGa is turned on and the flow rate is set at
8 sccm. The fabricated active region produces light with a
wavelength of approximately 470 nm and with a power output of 7 mW.
Subsequently, the temperature in the reactor chamber is lowered in
preparation for the growth of the next quantum-well period.
[0047] The invention is illustrated with different embodiments,
described in detail, and with examples for purposes of facilitating
the implementation of the different features or components of the
invention. However, it is not the intent of the inventors to limit
the application of the invention to the details shown. Modification
of the features or components of the invention can be made without
deviating from the spirit of the invention and thus still remains
within the scope of the appended claims.
* * * * *