U.S. patent application number 14/185132 was filed with the patent office on 2014-06-19 for p-algan layer and group iii nitride semiconductor light emitting device.
This patent application is currently assigned to DOWA ELECTRONICS MATERIALS CO., LTD.. The applicant listed for this patent is DOWA ELECTRONICS MATERIALS CO., LTD.. Invention is credited to Tetsuya MATSUURA, Yoshikazu OOSHIKA.
Application Number | 20140166943 14/185132 |
Document ID | / |
Family ID | 44145727 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140166943 |
Kind Code |
A1 |
OOSHIKA; Yoshikazu ; et
al. |
June 19, 2014 |
P-AlGAN LAYER AND GROUP III NITRIDE SEMICONDUCTOR LIGHT EMITTING
DEVICE
Abstract
A p-AlGaN layer doped with magnesium is provided that includes
an aluminum composition ratio x of 0.2 or more and less than 0.5
and a carrier concentration of 2.5.times.10.sup.17/cm.sup.3 or
more. A Group III nitride semiconductor light emitting device
including the p-Al.sub.xGa.sub.1-xN layer is also provided.
Inventors: |
OOSHIKA; Yoshikazu; (Tokyo,
JP) ; MATSUURA; Tetsuya; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DOWA ELECTRONICS MATERIALS CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
DOWA ELECTRONICS MATERIALS CO.,
LTD.
Tokyo
JP
|
Family ID: |
44145727 |
Appl. No.: |
14/185132 |
Filed: |
February 20, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13512747 |
Jun 8, 2012 |
|
|
|
PCT/JP2010/072728 |
Dec 10, 2010 |
|
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14185132 |
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Current U.S.
Class: |
252/512 |
Current CPC
Class: |
H01L 21/02579 20130101;
H01L 21/0262 20130101; H01L 33/325 20130101; C23C 16/303 20130101;
C23C 16/45523 20130101; H01L 33/007 20130101; H01L 21/02458
20130101; H01L 21/0254 20130101 |
Class at
Publication: |
252/512 |
International
Class: |
H01L 33/32 20060101
H01L033/32 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2009 |
JP |
2009-280963 |
Dec 9, 2010 |
JP |
2010-275128 |
Claims
1. A p-AlGaN layer doped with magnesium, the p-AlGaN layer having
an aluminum composition ratio x of 0.2 or more and less than 0.5
and a carrier concentration of 2.5.times.10.sup.17/cm.sup.3 or
more.
2. The p-AlGaN layer doped with magnesium according to claim 1,
which is manufactured by a process comprising the steps of: a first
step of supplying a Group V source gas at a Group V source gas flow
rate B.sub.1 (0<B.sub.1) and supplying a gas containing
magnesium at a Mg-containing gas flow rate C.sub.1 (0<C.sub.1)
while supplying a Group III source gas at a Group III source gas
flow rate A.sub.3 (0<A.sub.3); and a second step of supplying a
Group V source gas at a Group V source gas flow rate B.sub.2
(0<B.sub.2) and supplying a gas containing magnesium at a
Mg-containing gas flow rate C.sub.2 (0<C.sub.2) while supplying
a Group III source gas at a Group III source gas flow rate A.sub.2
(0<A.sub.2), wherein the first step and the second step are
performed to form the p-Al.sub.xGa.sub.1-xN layer, and the Group
III source gas flow rate A.sub.3 is a flow rate which allows only
initial growth nuclei of the p-Al.sub.xGa.sub.1-xN layer to grow
and satisfies A.sub.3.ltoreq.0.5A.sub.2.
3. The p-AlGaN layer doped with magnesium according to claim 2,
wherein the first step and the second step are repeated a plurality
of times to form the p-Al.sub.xGa.sub.1-xN layer.
4. The p-AlGaN layer doped with magnesium according to claim 1,
wherein the aluminum composition ratio x is 0.2 or more and less
than 0.3 and the carrier concentration is
5.times.10.sup.17/cm.sup.3 or more.
5. The p-AlGaN layer doped with magnesium according to claim 1,
wherein the aluminum composition ratio x is 0.3 or more and less
than 0.4 and the carrier concentration is
3.5.times.10.sup.17/cm.sup.3 or more.
6. The p-AlGaN layer doped with magnesium according to claim 1,
wherein the aluminum composition ratio x is 0.4 or more and less
than 0.5 and the carrier concentration is
2.5.times.10.sup.17/cm.sup.3 or more.
7. A Group III nitride semiconductor light emitting device
comprising the p-Al.sub.xGa.sub.1-xN layer according to claim
1.
8. A Group III nitride semiconductor light emitting device
comprising the p-Al.sub.xGa.sub.1-xN layer according to claim
4.
9. A Group III nitride semiconductor light emitting device
comprising the p-Al.sub.xGa.sub.1-xN layer according to claim
5.
10. A Group III nitride semiconductor light emitting device
comprising the p-Al.sub.xGa.sub.1-xN layer according to claim 6.
Description
INCORPORATION BY REFERENCE
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/512,747 filed on May 30, 2012, which in turn is a
National Phase of International Application No. PCT/JP2010/072728
filed on Dec. 10, 2010, which claims priority to Japanese Patent
Application No. 2010-275128 filed on Dec. 9, 2010 and Japanese
Patent Application No. 2009-280963 filed on Dec. 10, 2009. The
disclosures of the prior applications are hereby incorporated by
reference herein in their entireties.
TECHNICAL FIELD
[0002] The present invention relates to a p-AlGaN layer, and in
particular to a magnesium-doped p-AlGaN layer having constant
aluminum composition ratio. The present invention also relates to a
method of manufacturing the same, and a Group III nitride
semiconductor light emitting device using the same.
RELATED ART
[0003] In recent years, ultraviolet LEDs using Group III nitride
semiconductor devices are actively researched and developed since
they are expected to be used for back lights of liquid crystal
displays, excitation light sources of white LEDs for lighting and
sterilization, and medical uses, etc.
[0004] In general, the conductivity type of semiconductors is
determined depending on the kind of impurities added. By way of
example, when an AlGaN material is made to have p-type
conductivity, magnesium is typically used as an impurity. On this
occasion, the magnesium added serves as acceptors, and holes in
this AlGaN material serve as carriers.
[0005] However, when a semiconductor layer is thus formed by MOCVD
(metal organic chemical vapor deposition) using magnesium as an
impurity, a phenomenon called "doping delay" in which impurities
are not sufficiently introduced into the semiconductor layer in
growth would occur.
[0006] One of the reasons for this is that magnesium to be supplied
to the semiconductor layer would adhere to inner walls and the like
of a growth system and pipes in an initial stage of the growth of
the semiconductor layer and it would not be supplied sufficiently
to the semiconductor layer accordingly.
[0007] On the other hand, Patent Document 1 discloses a technique
of preventing doping delay by supplying a magnesium-containing gas
into a growth system prior to the formation of the semiconductor
layer so that the amount of the above-described adherence is
saturated.
[0008] Beside such doping delay in an initial growth stage of a
semiconductor layer, doping delay is also known to occur after the
initial growth stage. One of the reasons is for example as follows.
For example, hydrogen atoms generated when a gas supplied into the
semiconductor layer in growth is partially introduced into crystals
are bound to nitrogen atoms in the crystals by hydrogen-bonding to
release electrons. Meanwhile, holes are released from magnesium
atoms which are p-type impurities disposed at lattice arrangements
where gallium atoms should originally be disposed. The released
electrons and the released holes are combined to electrically
compensate one another, which consequently prevents magnesium added
for achieving p-type conductivity from serving as acceptors. This
leads to decline in the carrier concentration in the semiconductor
layer.
[0009] Further, shorter wavelength ultraviolet LEDs increase demand
for Al.sub.xGa.sub.1-xN materials having a high aluminum
composition ratio and a wide band gap for use in an active layer. A
high aluminum composition ratio x increases ionization energy of
magnesium itself; therefore, it has been difficult to achieve high
carrier concentration.
[0010] Such decline in the carrier concentration increases
resistance, and this causes heat generation or the like, which
makes it impossible to obtain sufficient light output.
PRIOR ART DOCUMENT
Patent Document
[Patent Document 1] JP2007-42886 A
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0011] An object of the invention is to solve the above problems
and to provide a p-AlGaN layer achieving improved carrier
concentration and light output, a method of manufacturing the same,
and a Group III nitride semiconductor light emitting device using
the same.
Means for Solving the Problem
[0012] In order to achieve the above object, the present invention
primarily includes the following components.
[0013] (1) A method of manufacturing a p-AlGaN layer, the p-AlGaN
layer being one p-Al.sub.xGa.sub.1-xN layer (0.ltoreq.x<1) doped
with magnesium, which is formed by MOCVD, comprising the steps of:
a first step of supplying a Group V source gas at a Group V source
gas flow rate B.sub.1 (0<B.sub.1) and supplying a gas containing
magnesium at a Mg-containing gas flow rate C.sub.1 (0<C.sub.1)
while supplying a Group III source gas at a Group III source gas
flow rate A.sub.1 (0.ltoreq.A.sub.1); and a second step of
supplying a Group V source gas at a Group V source gas flow rate
B.sub.2 (0<B.sub.2) and supplying a gas containing magnesium at
a Mg-containing gas flow rate C.sub.2 (0<C.sub.2) while
supplying a Group III source gas at a Group III source gas flow
rate A.sub.2 (0<A.sub.2), wherein the first step and the second
step are repeated a plurality of times to form the
p-Al.sub.xGa.sub.1-xN layer, and the Group III source gas flow rate
A.sub.1 is a flow rate which allows no p-Al.sub.xGa.sub.1-xN layer
to grow and satisfies A.sub.1.ltoreq.0.5A.sub.2.
[0014] (2) A method of manufacturing a p-AlGaN layer, the p-AlGaN
layer being one p-Al.sub.xGa.sub.1-xN layer (023 x<1) doped with
magnesium, which is formed by MOCVD, comprising the steps of: a
first step of supplying a Group V source gas at a Group V source
gas flow rate B.sub.1 (0<B.sub.1) and supplying a gas containing
magnesium at a Mg-containing gas flow rate C.sub.1 (0<C.sub.1)
while supplying a Group III source gas at a Group III source gas
flow rate A.sub.3 (0<A.sub.3); and a second step of supplying a
Group V source gas at a Group V source gas flow rate B.sub.2
(0<B.sub.2) and supplying a gas containing magnesium at a
Mg-containing gas flow rate C.sub.2 (0<C.sub.2) while supplying
a Group III source gas at a Group III source gas flow rate A.sub.2
(0<A.sub.2), wherein the first step and the second step are
performed to form the p-Al.sub.xGa.sub.1-xN layer, and the Group
III source gas flow rate A.sub.3 is a flow rate which allows only
initial growth nuclei of the p-Al.sub.xGa.sub.1-xN layer to grow
and satisfies A.sub.3.ltoreq.0.5A.sub.2.
[0015] (3) A method of manufacturing a p-AlGaN layer, the p-AlGaN
layer being one p-Al.sub.xGa.sub.1-xN layer (0.ltoreq.x<1) doped
with magnesium, which is formed by MOCVD, comprising the steps of:
a first step of supplying a Group V source gas at a Group V source
gas flow rate B.sub.1 (0<B.sub.1) and supplying a gas containing
magnesium at a Mg-containing gas flow rate C.sub.1 (0<C.sub.1)
while supplying a Group III source gas at a Group III source gas
flow rate A.sub.3 (0<A.sub.3); and a second step of supplying a
Group V source gas at a Group V source gas flow rate B.sub.2
(0<B.sub.2) and supplying a gas containing magnesium at a
Mg-containing gas flow rate C.sub.2 (0<C.sub.2) while supplying
a Group III source gas at a Group III source gas flow rate A.sub.2
(0<A.sub.2), wherein the first step and the second step are
repeated a plurality of times to form the p-Al.sub.xGa.sub.1-xN
layer, and the Group III source gas flow rate A.sub.3 is a flow
rate which allows only initial growth nuclei of the
p-Al.sub.xGa.sub.1-xN layer to grow and satisfies
A.sub.3.ltoreq.0.5A.sub.2.
[0016] (4) The method of manufacturing a p-AlGaN layer according to
any one of (1) to (3) above, wherein the Group V source gas flow
rate B.sub.1 in the first step is equal to the Group V source gas
flow rate B.sub.2 in the second step, and/or the Mg-containing gas
flow rate C.sub.1 in the first step is equal to the Mg-containing
gas flow rate C.sub.2 in the second step.
[0017] (5) The method of manufacturing a p-AlGaN layer according to
any one of (1) to (4) above, wherein when a relationship between a
Group III source gas flow rate and a crystal growth rate is
evaluated from the crystal growth rate in the second step, the
Group III source gas flow rate in the first step is a flow rate
such that a growth rate of the p-Al.sub.xGa.sub.1-xN layer
corresponding to the flow rate is 0.03 nm/s or less.
[0018] (6) The method of manufacturing a p-AlGaN layer according to
any one of (1) to (5) above, wherein the aluminum composition ratio
x of the p-Al.sub.xGa.sub.1-xN layer is in the range of 0 to
0.8.
[0019] (7) A Group III nitride semiconductor light emitting device
comprising a p-Al.sub.xGa.sub.1-xN layer manufactured by the method
of manufacturing a p-AlGaN layer according to any one of (1) to (6)
above.
[0020] (8) A p-AlGaN layer doped with magnesium, which has an
aluminum composition ratio x of 0.2 or more and less than 0.3 and a
carrier concentration of 5.times.10.sup.17/cm.sup.3 or more.
[0021] (9) A p-AlGaN layer doped with magnesium, which has an
aluminum composition ratio x of 0.3 or more and less than 0.4 and a
carrier concentration of 3.5.times.10.sup.17/cm.sup.3 or more.
[0022] (10) A p-AlGaN layer doped with magnesium, which has an
aluminum composition ratio x of 0.4 or more and less than 0.5 and a
carrier concentration of 2.5.times.10.sup.17/cm.sup.3 or more.
[0023] (11) A Group III nitride semiconductor light emitting device
comprising the p-Al.sub.xGa.sub.1-xN layer according to any one of
(8) to (10) above.
Effect of the Invention
[0024] The present invention can provide a p-AlGaN layer having a
carrier concentration and a light output which are improved by
forming one p-AlGaN layer doped with magnesium using MOCVD under
conditions where a Group III source gas is supplied in a first step
at a flow rate of 0 or at a flow rate equal to or less than a flow
rate of a Group III source gas supplied in a second step. The
present invention can also provide a method of manufacturing the
same and a Group III nitride semiconductor light emitting
device.
[0025] Further, the present invention can provide a p-AlGaN layer
achieving a carrier concentration and a light output which are
improved by repeating the first step and the second step a
plurality of times, a method of manufacturing the same, and a Group
III nitride semiconductor light emitting device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic view illustrating an example of an
MOCVD system for manufacturing a p-AlGaN layer in accordance with
the present invention.
[0027] FIG. 2 is a schematic cross-sectional view illustrating an
example of a growth furnace in an MOCVD system for manufacturing a
p-AlGaN layer in accordance with the present invention.
[0028] FIG. 3 shows XRD diffraction patterns of p-Al.sub.0.23
Ga.sub.0.77N layers in accordance with a method of the present
invention and a conventional method.
[0029] FIGS. 4(a) and 4(b) show TEM images of
p-Al.sub.0.23Ga.sub.0.77N layers in accordance with a method of the
present invention and a conventional method, respectively.
[0030] FIGS. 5(a) and 5(b) show differential interference contrast
micrographs of the outermost surfaces of p-Al.sub.0.23Ga.sub.0.77N
layers in accordance with a method of the present invention and a
conventional method, respectively.
[0031] FIG. 6 is a schematic cross-sectional view illustrating a
Group III nitride semiconductor light emitting device in accordance
with the present invention.
[0032] FIG. 7 shows a SIMS profile of a p-Al.sub.0.36Ga.sub.0.64N
layer in a light emitting device of Example 9.
[0033] FIG. 8 shows a SIMS profile of a p-Al.sub.0.36Ga.sub.0.64N
layer in a light emitting device of Comparative Example 6.
[0034] FIG. 9 is a graph showing collected carrier concentrations
calculated from specific resistance values of p-Al.sub.xGa.sub.1-xN
layers in accordance with a method of the present invention and a
conventional method.
BEST MODE FOR CARRYING OUT THE INVENTION
[0035] Next, embodiments of a method of manufacturing a p-AlGaN
layer in accordance with the present invention will be described
with reference to the drawings. FIG. 1 is a schematic
cross-sectional view illustrating an example of an MOCVD system for
manufacturing a p-AlGaN layer in accordance with the present
invention. This MOCVD system 100 includes a reaction furnace 103
having a first gas supply port 101 and a second gas supply port
102. The first gas supply port 101 supplies a carrier gas such as
hydrogen gas 104 and/or nitrogen gas 105, a Group III source gas
such as TMA (trimethylaluminium) 106 and TMG (trimethylgallium)
107, a magnesium-containing gas 108 as an impurity source gas,
and/or the like to the reaction furnace 103.
[0036] Meanwhile, the second gas supply port 102 supplies a carrier
gas such as hydrogen gas 104 and/or nitrogen gas 105, and a Group V
source gas 109 such as ammonia to the reaction furnace 103.
[0037] With respect to a method of manufacturing a p-AlGaN layer in
accordance with the present invention, magnesium-doped
p-Al.sub.xGa.sub.1-xN (0.ltoreq.x<1) having constant aluminum
composition ratio x is formed using such an MOCVD system 100
described above by a first step of supplying a Group V source gas
at a Group V source gas flow rate B.sub.1 (0<B.sub.1) and
supplying a gas containing magnesium at a Mg-containing gas flow
rate C.sub.1 (0<C.sub.1) while supplying a Group III source gas
at a Group III source gas flow rate A.sub.1 (0.ltoreq.A.sub.1); and
a second step of supplying a Group V source gas at a Group V source
gas flow rate B.sub.2 (0<B.sub.2) and supplying a gas containing
magnesium at a Mg-containing gas flow rate C.sub.2 (0<C.sub.2)
while supplying a Group III source gas at a Group III source gas
flow rate A.sub.2 (0.ltoreq.A.sub.2). The first step and the second
step are repeated a plurality of times to form the
p-Al.sub.xGa.sub.1-xN layer, and the Group III source gas flow rate
A.sub.1 is a flow rate which allows no p-Al.sub.xGa.sub.1-xN layer
to grow and satisfies A.sub.1.ltoreq.0.5A.sub.2. Thus, the carrier
concentration and light output of the p-AlGaN layer can be
improved.
[0038] Here, cases where "the Group III source gas flow rate
A.sub.1 is a flow rate which allows no p-AlGaN layer to grow" mean
cases where "the thickness of p-AlGaN is not enough to form a
substantial layer" to include such cases where no p-AlGaN is grown,
or where an initial crystal nucleus of p-AlGaN (for example, an
island-like crystal) is grown but the thickness is not enough to
form a substantial layer. Specifically, the case include a case
where A.sub.1 is a flow rate which allows no p-AlGaN to grow (at
least the cases where A.sub.1=0 apply to these) and cases where
A.sub.1 is a flow rate which allows only initial growth nuclei of
p-AlGaN to grow (at least the cases where A.sub.1>0 apply to
these). Such a Group III source gas flow rate A.sub.1 satisfies at
least the relation 0.ltoreq.A.sub.1.ltoreq.0.5A.sub.2. Further, the
first step serves to maintain the state where no layer is grown for
an intended period. On this occasion, the Group V source gas flow
rate B.sub.1 and the Mg-containing gas flow rate C.sub.1 are
preferably equal to or more than a flow rate which allows a layer
to grow as long as the Group III source gas is supplied. In other
words, B.sub.1.gtoreq.B.sub.2 and C.sub.1.gtoreq.C.sub.2 are
preferably satisfied. This is to prevent nitrogen leakage and
supply enough Mg into the system while the layer growth is
interrupted.
[0039] Further, when two kinds of gases, TMA (trimethylaluminium)
and TMG (trimethylgallium) for example, are supplied as Group III
source gases, the Group III source gas flow rate A.sub.1 represents
the total flow rate of these gases.
[0040] Note that "the aluminum composition ratio is constant" means
that the aluminum composition ratio x of the layer which is grown
in each of the second steps does not change irrespective of the
repeat count of the first step and the second step. Specifically,
this means that the gas flow rate A.sub.1 in each repetition is an
equal flow rate. However, in measuring the aluminum quantity by
SIMS, in terms of the analysis principle, the aluminum composition
ratio varies in the depth direction. Further, the aluminum
composition ratio may be fluctuated in the layer or aluminum may be
distributed in the plane, due to the system in epitaxial growth.
Such phenomena can be accepted because they are caused also in
conventional methods. Note that the aluminum composition in the
present invention is a value measured at the substrate center.
[0041] FIG. 3 is an x-ray diffraction (XRD) image of a
p-Al.sub.0.23Ga.sub.0.77N layer (supply of the Group III source gas
is modulated: mode of the present invention) manufactured by a
method in accordance with the present invention and a
p-Al.sub.0.23Ga.sub.0.77N layer (Group III source gas without
supply modulation: conventional mode) manufactured by a
conventional method. Table 1 shows representative values of XRD
intensity corresponding to Miller indices [002] and [102] which
provide indications of crystal quality. The former represents
"tilt" with respect to the growth axis direction of an initial
growth nucleus, while the latter represents the degree of "twist"
with respect to the growth in-plane direction. FIGS. 4(a) and 4(b)
show transmission electron microscope (TEM) images of
p-Al.sub.0.23Ga.sub.0.77N layers in accordance with a method of the
present invention and a conventional method, respectively. FIGS.
5(a) and 5(b) show electron diffraction patterns of the outermost
surfaces of p-Al.sub.0.23Ga.sub.0.77N layers in accordance with a
method of the present invention and a conventional method,
respectively.
TABLE-US-00001 TABLE 1 XRD [002] [102] Invention mode 195 456
Conventional mode 234 442
[0042] As shown in FIG. 3 and FIGS. 4(a) and 4(b), a method of the
present invention is equivalent to a conventional method in
macroscopic XRD spectra, and no periodic perturbation in crystal
growth was observed in the microscopic TEM images and the electron
diffraction patterns. Thus, only one single crystal layer is found
to be grown in either case. Note that while XRD spectra of FIG. 3
have two peaks caused by components of different axes at
approximately 75.degree. in the conventional mode, these peaks are
lost in the method of the present invention. Further, the
representative value corresponding to Miller index [002] shown in
Table 1 is reduced. Thus, the present invention is found to
contribute to the improvement in crystallinity. Note that Table 1
shows that the component "twist" with respect to the growth
in-plane direction of the initial growth nucleus differs little,
while the "tilt" with respect to the growth axis direction is
reduced. This suggests that the components of different axes are
reduced, and the orientation of the initial growth nuclei in the
growth direction is improved.
[0043] A method of manufacturing a p-AlGaN layer in accordance with
the present invention will be described. First, as shown in FIG. 2,
a base substrate 111 is placed on a susceptor 110 in the reaction
furnace 103. Examples of the base substrate 111 include a GaN
substrate, a sapphire substrate, and an AlN template substrate in
which an AlN layer is provided on a sapphire substrate.
Alternatively, such a substrate on which a semiconductor layer is
stacked may be used.
[0044] Next, in a first step, a carrier gas such as hydrogen gas
104 and/or nitrogen gas 105 and a Group V source gas 109 such as
ammonia are supplied from the second gas supply port 102 into this
reaction furnace 103. Further, a Group III source gas is supplied
from the first gas supply port 101 into this reaction furnace 103
at a flow rate which does not result in layer growth or at a flow
rate which causes only initial nucleus growth. Along with these
source gases, a magnesium-containing gas 108 is supplied. The Group
V source gas 109 here is supplied to control decline in partial
pressure of nitrogen in the reaction furnace 103 and to protect the
outer most surface where crystal growth occurs. Note that
CP.sub.2Mg (bis-cyclopentadienyl magnesium) or the like can be used
as the magnesium-containing gas 108.
[0045] After a predetermined time, in a second step, a Group III
source gas is supplied from the first gas supply port 101 at a flow
rate which results in layer growth. Along with this source gas, a
magnesium-containing gas 108 is supplied. Concurrently, a Group V
source gas 109 is supplied from the second gas supply port 102 at a
flow rate which results in layer growth. Note that the above
"predetermined period of time" for maintaining the first step is
preferably about 5 seconds or more and 60 seconds or less. When the
predetermined period is too short, the effects of the present
invention cannot be obtained sufficiently. Otherwise when the
predetermined time is too long, Mg is introduced excessively, which
would make Mg cause defects to deteriorate the crystallinity or
reduce carrier concentration in subsequent crystal growth.
[0046] In a method of manufacturing a p-AlGaN layer in accordance
with the present invention, the p-Al.sub.xGa.sub.1-xN layer
(0.ltoreq.x<1) doped with magnesium is formed using MOCVD by a
first step of supplying a Group V source gas at a Group V source
gas flow rate B.sub.1 (0<B.sub.1) and supplying a gas containing
magnesium at a Mg-containing gas flow rate C.sub.1 (0<C.sub.1)
while supplying a Group III source gas at a Group III source gas
flow rate A.sub.3 (0<A.sub.3); and a second step of supplying a
Group V source gas at a Group V source gas flow rate B.sub.2
(0<B.sub.2) and supplying a gas containing magnesium at a
Mg-containing gas flow rate C.sub.2 (0<C.sub.2) while supplying
a Group III source gas at a Group III source gas flow rate A.sub.2
(0<A.sub.2). The first step and the second step are performed to
form the p-Al.sub.xGa.sub.1-xN layer, and the Group III source gas
flow rate A.sub.3 is a flow rate which allows only initial growth
nuclei of the p-Al.sub.xGa.sub.1-xN layer to grow and satisfies
A.sub.3.ltoreq.0.5A.sub.2. With such a method, surfaces of the
reaction furnace 103 and the pipes and the like can be previously
coated with adequate magnesium. This makes it possible to suppress
reduction in the magnesium concentration of the AlGaN layer in
initial growth, namely, doping delay. Here, the flow rate which
allows only initial nuclei to grow refers to a flow rate which
leads to a state where for example, island-like initial crystal
nuclei are formed but the thickness is not enough to form a
substantial layer. Such a Group III source gas flow rate A.sub.3
satisfies at least the relation 0<A.sub.3.ltoreq.0.5A.sub.2.
Note that in the present invention, the growth of only initial
growth nuclei can be confirmed by observing the surface of a
substrate of which growth is interrupted after the first step with
the use of a metallurgical microscope or a SEM to find island-like
initial growth nuclei dispersed on the substrate surface.
[0047] Further, when two kinds of gases, TMA (trimethylaluminium)
and TMG (trimethylgallium) for example, are supplied as Group III
source gases, the Group III source gas flow rate A.sub.3 represents
the total flow rate of these gases.
[0048] The Group V source gas flow rate B.sub.1 in the first step
is preferably equal to the Group V source gas flow rate B.sub.2 in
the second step, and/or the Mg-containing gas flow rate C.sub.1 in
the first step is preferably equal to the Mg-containing gas flow
rate C.sub.2 in the second step. That is, it is preferable that the
flow rate A.sub.1 or A.sub.3 of the Group III source gas in the
first step is different from the flow rate A.sub.2 of the Group III
source gas in the second step while the Group V source gas flow
rate is constant.
[0049] The adherence of magnesium to the surface of the AlGaN layer
in growth makes predominant the growth in lateral directions, and
reduces the crystal growth rate in the growth axis direction. This
increases the frequency of regional growth of initial nuclei
(three-dimensional); thus, the effective surface area is increased,
and the frequency of magnesium introduction is improved by
suppressing the migration of atoms. Therefore, forcible
introduction of magnesium by the physical adherence, and
improvement in the frequency of magnesium introduction due to the
reduction in the growth rate improve the magnesium concentration of
the AlGaN layer.
[0050] Further, since this effect is temporary, the above first
step and the second step are repeated a plurality of times, so that
the magnesium concentration of the AlGaN layer can be maintained at
a constant high concentration. For example, even when a p-AlGaN
layer having the aluminum composition ratio of 0.15 or more, which
reduces the magnesium concentration due to the increase of the
ionization energy of magnesium itself is formed, a p-AlGaN layer
having higher magnesium concentration than conventional can be
manufactured.
[0051] Furthermore, in a method of manufacturing a p-AlGaN layer in
accordance with the present invention, one p-AlGaN layer doped with
magnesium is formed particularly using the above-mentioned MOCVD
system 100 by previously performing a step of supplying a Group III
source gas at a flow rate reduced to a level that allows only
initial nuclei to grow and supplying a Group V source gas and a gas
containing magnesium before the step of supplying a gas containing
magnesium along with the Group III and Group V source gases at flow
rates which allow crystals to grow. Thus, the magnesium doping
level in the p-AlGaN layer can be maintained.
[0052] As initial nuclei have portions containing sufficient Mg,
which have been forcibly formed in the initial growth, the source
materials to be supplied later are predominantly diffused in
lateral directions and their crystal growth rates in the growth
axis direction are reduced accordingly. In other words, the
diffused molecules are introduced into step ends at a higher rate,
which promotes the formation of a flat layer (surfactant effect).
However, this effect is temporary and initial growth nuclei causing
irregularities begin to form again after the step flow growth
(growth in lateral directions) continued for a while. This involves
increase in the surface area to suppress in-plane diffusion of Mg
itself, and the introduction frequency of Mg into the layer is
improved, which consequently improves the magnesium concentration
in the AlGaN layer.
[0053] Thus, according to the present invention, a step of
supplying the Group III gas at a flow rate reduced to a level that
allows only initial nuclei to grow and supplying the Group V source
gas and the gas containing magnesium is provided, so that
introduction of Mg can be improved and the crystallinity can be
improved by growth in lateral directions.
[0054] The Group III source gas flow rate (A.sub.1 or A.sub.3) in
the first step is different from the Group III source gas flow rate
A.sub.2 in the second step, and the Group III source gas flow rate
in the first step is preferably 1/2 or less, more preferably 1/4 or
less the Group III source gas flow rate A.sub.2 in the second step.
In particular, the relationship between the Group III source gas
flow rate and the crystal growth rate is evaluated from the
thickness of a layer grown per unit time in a range where crystal
growth can be observed (namely, crystal growth rate) (for example,
the relationship between a plurality of pairs of Group III source
gas flow rates and crystal growth rates in a flow rate range of 10
sccm to 30 sccm is linearized). When the Group III source gas flow
rate (A.sub.1 or A.sub.3) in the first step is extrapolated from
this relationship, the flow rate is preferably such that the
crystal growth rate of the p-Al.sub.xGa.sub.1-xN layer that
corresponds to the flow rate (A.sub.1 or A.sub.3) in the first step
is 0.03 nm/s or less, more preferably 0.01 nm/s to 0.03 nm/s based
on the computation. Note that the figure of the Group III source
gas flow rate in the first step and the second step (the ratio of
Ga and Al) may not necessarily show the multiple proportion
relationship. Specifically, the Al composition of the initial
growth nuclei created in the first step may not necessarily be the
same as the Al composition of the initial growth nuclei created in
the second step. This is for making the initial growth nuclei
created in the first step contain Mg at a maximum and for improving
the crystallinity of a crystal film formed in the second step,
thereby maximizing the effect of the present invention. Note that
although the Al compositions are different, the crystal layers
obtained in the mode of the present invention can be deemed to have
constant Al composition because an initial growth nuclei created in
the first step has negligible thickness as compared to the crystal
film formed in the second step. In addition, when the computational
growth rate is 0.01 nm/s to 0.03 nm/s, the Group III source
material is less probable to be present in the substrate surface;
for example, only island-like initial growth nuclei are created.
Thus, the thickness does not increase enough to form a substantial
layer even over a long period of time. Note that if the Group III
source gas flow rate in the first step is computationally a flow
rate such that the crystal growth rate is less than 0.01 nm/s, the
decomposition of the initial growth nuclei becomes predominant over
its growth. Thus, p-AlGaN is not grown.
[0055] The flow rate of the Group III source gas which allows only
initial nuclei to grow cannot be specified definitely because it
varies depending on the shape, temperature, and the Group V source
gas flow rate of the MOCVD system. However, the Group III source
gas flow rate (A.sub.1 or A.sub.3) in the first step is preferably,
for example, 1 sccm to 10 sccm while the Group III source gas flow
rate A.sub.2 in the second step is 20 sccm to 50 sccm. Further, the
Group V source gas flow rates B.sub.1 and B.sub.2 in the first step
and the second step may be, for example, 5 slm to 50 slm (standard
liter per minute). Further, the Mg-containing gas flow rates
C.sub.1 and C.sub.2 in the first step and the second step may be,
for example, 20 seem to 200 sccm.
[0056] In either case where no Group III source gas is flown
(A.sub.1=0 sccm) or where the Group III source gas is flown to
allow only initial nuclei to grow (A.sub.1, A.sub.3=1 seem to 10
sccm) in the first step, the magnesium concentration of the AlGaN
layer can be maintained at a high, constant concentration by
repeating the first step and the second step a plurality of times.
However, it is more preferable to allow initial nuclei to grow
because the effect of improving crystallinity can be achieved more
easily.
[0057] A p-AlGaN layer having high magnesium concentration and
improved crystallinity can be manufactured by the above methods of
the present invention.
[0058] Further, the aluminum composition ratio of the p-AlGaN layer
may be 0 to 0.8. Note that the aluminum composition ratio x can be
found by measuring the emission wavelength of photoluminescence and
converting the emission wavelength of photoluminescence using
Bowing parameters described in Yun F. etal, J. Appl. Phys. 92, 4837
(2002).
[0059] Subsequently, embodiments of a Group III nitride
semiconductor light emitting device of the present invention will
be described with reference to the drawings. A Group III nitride
semiconductor light emitting device 200 in accordance with the
present invention may have a structure including an AlN template
substrate having an AlN strain buffer layer 202 on a sapphire
substrate 201; and a superlattice strain buffer layer 203, an
n-AlGaN layer 204, a light emitting layer 205, a p-AlGaN blocking
layer 206, a p-AlGaN guide layer 207, a p-AlGaN cladding layer 208,
and a p-GaN contact layer 209 on the AlN template substrate. These
p-AlGaN layers can be grown by the above methods of manufacturing a
p-AlGaN layer in accordance with the present invention.
[0060] Further, according to the methods of manufacturing a p-AlGaN
layer in accordance with the present invention, a p-AlGaN layer
having a carrier concentration of 5.times.10.sup.17/cm.sup.3 or
more and preferably 1.times.10.sup.18/cm.sup.3 or less can be
obtained as a magnesium-doped p-Al.sub.xGa.sub.1-xN layer having a
constant aluminum composition ratio when the aluminum composition
ratio x is 0.2 or more and less than 0.3. Further, when the
aluminum composition ratio x is 0.3 or more and less than 0.4, a
p-AlGaN layer having a carrier concentration of
3.5.times.10.sup.17/cm.sup.3 or more and preferably
5.times.10.sup.17/cm.sup.3or less can be obtained. Furthermore,
when the aluminum composition ratio x is 0.4 or more and less than
0.5, a p-AlGaN layer having a carrier concentration of
2.5.times.10.sup.17/cm.sup.3 or more and preferably
3.5.times.10.sup.17/cm.sup.3 or less can be obtained.
[0061] Note that FIGS. 1 to 6 show examples of representative
alternative embodiments, and the present invention is not limited
to these embodiments.
EXAMPLE
Example 1
[0062] In Example 1, after an AlN template substrate having a
strain buffer layer was placed in a growth furnace shown in FIG. 1
and FIG. 2 and the temperature was increased to 1050.degree. C. at
10 kPa, a first step and a second step were alternately repeated
120 times. In each of the first steps, while Group III source gases
(TMG flow rate: 4 sccm, TMA flow rate: 5 sccm) were flown, a
carrier gas (mixture of N.sub.2 and H.sub.2, flow rate: 50 slm), a
Group V source gas (NH.sub.3, flow rate: 15 slm), and a CP.sub.2Mg
gas (flow rate: 50 sccm) were supplied for 15 seconds (supply time
t.sub.1). In each of the subsequent second steps, only the flow
rates of the Group III source gases were changed to a TMG flow rate
of 20 sccm and a TMA flow rate of 25 sccm, and the Group III source
gases, the carrier gas, the Group V source gas, and the CP.sub.2Mg
gas were supplied for 60 seconds (supply time t.sub.2). Thus, a
p-Al.sub.0.23Ga.sub.0.77N layer having a thickness of 1080 nm was
formed. (Note that the unit "sccm" of the above flow rates
expresses the amount (cm.sup.3) of gas flown per minute at 1 atm
(atmospheric pressure: 1013 hPa) at 0.degree. C.) Note that in the
first step, initial growth nuclei were grown, but a layer was not
grown. The crystal growth rate in the second step was 0.15 nm/s.
The computational growth rate corresponding to the Group III source
gas flow rate in the first step was 0.03 nm/s.
Example 2
[0063] In Example 2, a p-Al.sub.0.23Ga.sub.0.77N layer having a
thickness of 1080 nm was formed by a similar method to Example 1
except for that the supply time t.sub.2 was 30 seconds, and the
repeat count was 240.
Example 3
[0064] In Example 3, a p-Al.sub.0.23Ga.sub.0.77N layer having a
thickness of 1080 nm was formed by a similar method to Example 1
except for that the supply time t.sub.2 was 45 seconds, and the
repeat count was 180.
Example 4
[0065] In Example 4, a p-Al.sub.0.23Ga.sub.0.77N layer having a
thickness of 1080 nm was formed by a similar method to Example 1
except for that the supply time t.sub.2 was 120 seconds, and the
repeat count was 60.
Example 5
[0066] In Example 5, a p-Al.sub.0.23Ga.sub.0.77N layer having a
thickness of 1080 nm was formed by a similar method to Example 1
except for that the supply time t.sub.2 was 7200 seconds, and the
repeat count was one.
Reference Example
[0067] In Reference Example, a p-Al.sub.0.23Ga.sub.0.77N layer
having a thickness of 1080 nm was formed by a similar method to
Example 5 except for that no Group III source gas was flown and no
initial growth nucleus was grown in the first step.
Comparative Example 1
[0068] In Comparative Example 1, a p-Al.sub.0.23Ga.sub.0.77N layer
having a thickness of 1080 nm was formed by a similar method to
Example 1 except for that the supply time t.sub.1 was 0 second, the
supply time t.sub.2 was 7200 seconds, and the repeat count was
one.
[0069] (Evaluation 1)
[0070] After each of the forgoing Examples 1 to 5, Reference
Example, and Comparative Example 1; annealing was performed at
800.degree. C. for 5 minutes in a nitrogen atmosphere using a lamp
annealing furnace. Then, the in-plane specific resistance of the
p-AlGaN layers was measured using an eddy current sheet resistance
measurement system (MODEL 1318 manufactured by Lehighton
Electronics, inc). The results of evaluating carrier concentrations
calculated from the specific resistances under conditions where the
activation depth is 0.5 .mu.m and the mobility is 5 are shown in
Table 2.
TABLE-US-00002 TABLE 2 Supply Supply Thickness Total Carrier
concen- p-AlGaN Al time time Repeat per thickness of Specific
tration calculated single film composition t.sub.1 t.sub.2 count r
repetition single film resistance from Specific layer ratio
(second) (second) (number) (nm) layer (nm) (.OMEGA. .times. cm)
resistance (/cm.sup.3) Example 1 0.23 15 60 120 9 1080 1.7 7.35
.times. 10.sup.17 Example 2 0.23 15 30 240 4.5 1080 2.19 5.70
.times. 10.sup.17 Example 3 0.23 15 45 180 6 1080 2 6.24 .times.
10.sup.17 Example 4 0.23 15 120 60 18 1080 2.67 4.67 .times.
10.sup.17 Example 5 0.23 15 7200 1 1080 1080 2.7 4.63 .times.
10.sup.17 Reference 0.23 15 7200 1 1080 1080 2.73 4.58 .times.
10.sup.17 Example Comparative 0.23 0 7200 1 1080 1080 2.75 4.53
.times. 10.sup.17 Example 1
[0071] Table 2 shows that the specific resistances in Examples 1 to
5 were reduced as compared with Comparative Example 1, therefore
Examples 1 to 5 in accordance with the present invention have an
effect of increasing carrier concentration as compared with
Comparative Example 1.
Example 6
[0072] In Example 6, after an AlN template substrate having a
strain buffer layer was placed in a growth furnace shown in FIG. 1
and FIG. 2 and the temperature was increased to 1050.degree. C. at
10 kPa, a first step and a second step were alternately repeated
120 times. In each of the first steps, while a Group III source gas
(TMG flow rate: 5 sccm) was flown, a carrier gas (mixture of
N.sub.2 and H.sub.2, flow rate: 50 slm), a Group V source gas
(NH.sub.3, flow rate: 15 slm), and a CP.sub.2Mg gas (flow rate: 50
sccm) were supplied for 15 seconds (supply time t.sub.1). In each
of the subsequent second steps, only the flow rate of the Group III
source gas was changed to a TMG flow rate of 20 sccm, and the Group
III source gas, the carrier gas, the Group V source gas, and the
CP.sub.2Mg gas were supplied for 60 seconds (supply time t.sub.2).
Thus, a p-GaN layer having a thickness of 1080 nm was formed. Note
that in the first step, initial growth nuclei were grown, but a
layer was not grown. The crystal growth rate in the second step was
0.15 nm/s. The computational growth rate corresponding to the Group
III source gas flow rate in the first step was 0.02 nm/s.
Example 7
[0073] In Example 7, after an AlN template substrate having a
strain buffer layer was placed in a growth furnace shown in FIG. 1
and FIG. 2 and the temperature was increased to 1050.degree. C. at
10 kPa, a first step and a second step were alternately repeated
120 times. In each of the first steps, while Group III source gases
(TMG flow rate: 2 sccm, TMA flow rate: 5 sccm) were flown, a
carrier gas (mixture of N.sub.2 and H.sub.2, flow rate: 50 slm), a
Group V source gas (NH.sub.3, flow rate: 15 slm), and a CP.sub.2Mg
gas (flow rate: 50 sccm) were supplied for 15 seconds (supply time
t.sub.1). In each of the subsequent second steps, only the flow
rates of the Group III source gases were changed to a TMG flow rate
of 20 sccm and a TMA flow rate of 45 sccm, and the Group III source
gases, the carrier gas, the Group V source gas, and the CP.sub.2Mg
gas were supplied for 60 seconds (supply time t.sub.2). Thus, a
p-Al.sub.0.36Ga.sub.0.64N layer having a thickness of 1080 nm was
formed. Note that in the first step, initial growth nuclei were
grown, but a layer was not grown. The crystal growth rate in the
second step was 0.15 nm/s. The computational growth rate
corresponding to the Group III source gas flow rate in the first
step was 0.02 nm/s.
Example 8
[0074] In Example 8, a p-Al.sub.0.43Ga.sub.0.57N layer having a
thickness of 1080 nm was formed by a similar method to Example 7
except for the following: in each of the first steps, while Group
III source gases (TMG flow rate: 2 sccm, TMA flow rate: 6 sccm)
were flown, a carrier gas (mixture of N.sub.2 and H.sub.2, flow
rate: 50 slm), a Group V source gas (NH.sub.3, flow rate: 15 slm)
and a CP.sub.2Mg gas (flow rate: 50 seem) were supplied for 15
seconds (supply time t.sub.1); in each of the subsequent second
steps, only the flow rates of the Group III source gases were
changed to a TMG flow rate of 20 sccm and a TMA flow rate of 65
sccm, and the Group III source gases, the carrier gas, the Group V
source gas, and the CP.sub.2Mg gas were supplied for 60 seconds
(supply time t.sub.2); and the first step and the second step were
alternately repeated. Note that in the first step, initial growth
nuclei were grown, but a layer was not grown. The crystal growth
rate in the second step was 0.15 nm/s. The computational growth
rate corresponding to the Group III source gas flow rate in the
first step was 0.02 nm/s.
Comparative Example 2
[0075] In Comparative Example 2, a p-GaN layer having a thickness
of 1080 nm was formed by a similar method to Example 6 except for
that the supply time t.sub.1 was 0 second, the supply time t.sub.2
was 7200 seconds, and the repeat count was one.
Comparative Example 3
[0076] In Comparative Example 3, a p-Al.sub.0.23Ga.sub.0.77N layer
having a thickness of 1080 nm was formed by a similar method to
Example 1 except for that the supply time t.sub.1 was 0 second, the
supply time t.sub.2 was 7200 seconds, and the repeat count was
one.
Comparative Example 4
[0077] In Comparative Example 4, a p-Al.sub.0.36Ga.sub.0.64N layer
having a thickness of 1080 nm was formed by a similar method to
Example 7 except for that the supply time t.sub.1 was 0 second, the
supply time t.sub.2 was 7200 seconds, and the repeat count was
one.
Comparative Example 5
[0078] In Comparative Example 5, a p-Al.sub.0.43Ga.sub.0.57N layer
having a thickness of 1080 nm was formed by a similar method to
Example 8 except for that the supply time t.sub.1 was 0 second, the
supply time t.sub.2 was 7200 seconds, and the repeat count was
one.
Example 9
[0079] As shown in FIG. 6, a superlattice strain buffer layer
(AlN/GaN, thickness: 600 nm), an n-Al.sub.0.23Ga.sub.0.77N layer
(thickness: 1300 nm), a light emitting layer (AlInGaN, thickness:
150 nm), a p-Al.sub.0.36Ga.sub.0.64N blocking layer (thickness: 20
nm), a p-Al.sub.0.23Ga.sub.0.77N cladding layer (thickness: 180
nm), and a p-GaN contact layer (thickness: 20 nm) were grown on an
AlN template substrate having an AlN strain buffer layer on a
sapphire substrate by MOCVD process to produce a Group III nitride
semiconductor light emitting device.
[0080] Here, the p-Al.sub.0.36Ga.sub.0.64N blocking layer was
formed by a similar method to Example 7 except for that the supply
time t.sub.1 was 15 seconds, the supply time t.sub.2 was 45
seconds, and the repeat count was three.
Example 10
[0081] In Example 10, as shown in FIG. 6, a superlattice strain
buffer layer (AlN/GaN, thickness: 600 nm), an
n-Al.sub.0.23Ga.sub.0.77N layer (thickness: 1300 nm), a light
emitting layer (AlInGaN, thickness: 150 nm), a
p-Al.sub.0.43Ga.sub.0.57N blocking layer (thickness: 20 nm), a
p-Al.sub.0.23Ga.sub.0.77N cladding layer (thickness: 180 nm), and a
p-GaN contact layer (thickness: 20 nm) were grown on an AlN
template substrate having an AlN strain buffer layer on a sapphire
substrate by MOCVD process to produce a Group III nitride
semiconductor light emitting device.
[0082] Here, the p-Al.sub.0.43Ga.sub.0.57N blocking layer was
formed by a similar method to Example 8 except for that the supply
time t.sub.1 was 10 seconds, the supply time t.sub.2 was 45
seconds, and the repeat count was three.
Comparative Example 6
[0083] In Comparative Example 6, a Group III nitride semiconductor
light emitting device having a p-Al.sub.0.36Ga.sub.0.44N blocking
layer was produced by a similar method to Example 9 except for that
the supply time t.sub.1 was 0 second, the supply time t.sub.2 was
135 seconds, and the repeat count was one.
Comparative Example 7
[0084] In Comparative Example 7, a Group III nitride semiconductor
light emitting device having a p-Al.sub.0.43Ga.sub.0.57N blocking
layer was produced by a similar method to Example 10 except for
that the supply time t.sub.1 was 0 second, the supply time t.sub.2
was 135 seconds, and the repeat count was one.
[0085] (Evaluation 2)
[0086] The results of measuring the magnesium concentration of the
p-AlGaN blocking layers in the light emitting devices of Example 9
and Comparative Example 6 using a SIMS (secondary ion mass
spectrometer) are shown in FIG. 7 and FIG. 8, respectively.
[0087] Further, as in Evaluation 1, the carrier concentrations were
calculated from the specific resistance of the p-AlGaN single film
layers. The results are shown in Table 3 and FIG. 9.
TABLE-US-00003 TABLE 3 Supply Supply Thickness Total Carrier
concen- p-AlGaN Al time time Repeat per thickness of Specific
tration calculated single film composition t.sub.1 t.sub.2 count r
repetition single film resistance from Specific layer ratio
(second) (second) (number) (nm) layer (nm) (.OMEGA. .times. cm)
resistance (/cm.sup.3) Example 6 0 15 60 120 9 1080 0.113 1.10
.times. 10.sup.19 Example 1 0.23 15 60 120 9 1080 1.7 7.35 .times.
10.sup.17 Example 7 0.36 15 60 120 9 1080 2.76 4.52 .times.
10.sup.17 Example 8 0.43 15 60 120 9 1080 4.47 2.79 .times.
10.sup.17 Comparative 0 0 7200 1 1080 1080 0.146 8.57 .times.
10.sup.18 Example 2 Comparative 0.23 0 7200 1 1080 1080 2.75 4.53
.times. 10.sup.17 Example 3 Comparative 0.36 0 7200 1 1080 1080
3.62 3.45 .times. 10.sup.17 Example 4 Comparative 0.43 0 7200 1
1080 1080 5.42 2.30 .times. 10.sup.17 Example 5
[0088] Table 3 shows that the magnesium concentrations in Examples
6, 1, 7, and 8 in accordance with the present invention are higher
than those of Comparative Examples 2, 3, 4, and 5 involving the
same Al compositions, respectively. This also leads to increase in
the effective carrier concentration, which consequently reduces the
specific resistance.
[0089] (Evaluation 3)
[0090] Further, the emission EL outputs of back side of the light
emitting devices of the above Examples 9, 10, and Comparative
Examples 6 and 7 were measured using a multichannel spectrometer
(C10082CAH manufactured by Hamamatsu Photonics K.K.). The results
are shown in Table 4.
TABLE-US-00004 TABLE 4 p-AlGaN Supply Supply Thickness Total
blocking layer Al time time Repeat per thickness of EL in Light
composition t.sub.1 t.sub.2 count r repetition single film output
emitting device ratio (second) (second) (number) (nm) layer (nm)
(.mu.W) Example 9 0.36 15 45 3 6.67 20 33.1 Example 10 0.43 10 45 3
6.67 20 25 Comparative 0.36 0 135 1 20 20 15.5 Example 6
Comparative 0.43 0 135 1 20 20 6.9 Example 7
[0091] Table 4 shows that the EL output of Example 9 in accordance
with the present invention is significantly improved as compared
with Comparative Example 6. Further, the effect of improved output
can also be confirmed in Example 10 involving a higher Al
composition ratio as compared with Comparative Example 7. These
results are considered due to the improvement in energization
accompanying the increase in the carrier concentration as apparent
from Table 4.
INDUSTRIAL APPLICABILITY
[0092] According to the present invention, a p-AlGaN layer having a
carrier concentration and a light output which are improved by
forming one p-AlGaN layer doped with magnesium using MOCVD under
conditions where a Group III source gas is supplied in a first step
at a flow rate of 0 or at a flow rate equal to or less than a flow
rate of a Group III source gas supplied in a second step can be
provided. The present invention can also provide a method of
manufacturing the same and a Group III nitride semiconductor light
emitting device.
[0093] Further, the present invention can provide a p-AlGaN layer
achieving a carrier concentration and a light output which are
improved by repeating the first step and the second step a
plurality of times, a method of manufacturing the same, and a Group
III nitride semiconductor light emitting device.
EXPLANATION OF REFERENCE NUMERALS
[0094] 100: MOCVD system [0095] 101: First gas supply port [0096]
102: Second gas supply port [0097] 103: Growth furnace [0098] 104:
Hydrogen gas [0099] 105: Nitrogen gas [0100] 106: TMA [0101] 107:
TMG [0102] 108: CP.sub.2Mg [0103] 109: Ammonia [0104] 110:
Susceptor [0105] 111: Base substrate [0106] 112: AlGaN layer [0107]
200: Group III nitride semiconductor light emitting device [0108]
201: Base substrate [0109] 202: AlN strain buffer layer [0110] 203:
Superlattice strain buffer layer [0111] 204: N-nitride
semiconductor layer [0112] 205: Light emitting layer [0113] 206:
P-AlGaN blocking layer [0114] 207: P-AlGaN guide layer [0115] 208:
P-AlGaN cladding layer [0116] 209: P-GaN contact layer
* * * * *