U.S. patent application number 13/582235 was filed with the patent office on 2012-12-27 for semiconductor device and method of producing the same.
This patent application is currently assigned to DOWA ELECTRONICS MATERIALS CO., LTD.. Invention is credited to Tetsuya Matsuura, Yoshikazu Ooshika.
Application Number | 20120326209 13/582235 |
Document ID | / |
Family ID | 44542381 |
Filed Date | 2012-12-27 |
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United States Patent
Application |
20120326209 |
Kind Code |
A1 |
Ooshika; Yoshikazu ; et
al. |
December 27, 2012 |
SEMICONDUCTOR DEVICE AND METHOD OF PRODUCING THE SAME
Abstract
To provide a semiconductor device including a functional
laminate having flatness and crystallinity improved by effectively
passing on the crystallinity and flatness improved in a buffer to
the functional laminate, and to provide a method of producing the
semiconductor device; in the semiconductor device including the
buffer and the functional laminate having a plurality of nitride
semiconductor layers, the functional laminate includes a first
n-type or i-type Al.sub.xGa.sub.1-xN layer (0.ltoreq.x<1) on the
buffer side, and an Al.sub.zGa.sub.1-zN adjustment layer containing
p-type impurity, which has an approximately equal Al composition to
the first Al.sub.xGa.sub.1-xN layer (x-0.05.ltoreq.z.ltoreq.x+0.05,
0.ltoreq.z<1) is provided between the buffer and the functional
laminate.
Inventors: |
Ooshika; Yoshikazu; (Tokyo,
JP) ; Matsuura; Tetsuya; (Tokyo, JP) |
Assignee: |
DOWA ELECTRONICS MATERIALS CO.,
LTD.
Tokyo
JP
|
Family ID: |
44542381 |
Appl. No.: |
13/582235 |
Filed: |
March 1, 2011 |
PCT Filed: |
March 1, 2011 |
PCT NO: |
PCT/JP2011/055172 |
371 Date: |
August 31, 2012 |
Current U.S.
Class: |
257/183 ;
257/E21.09; 257/E29.081; 438/478 |
Current CPC
Class: |
H01L 21/0254 20130101;
H01L 29/7787 20130101; H01L 21/02389 20130101; H01L 29/66462
20130101; H01L 33/04 20130101; H01L 21/02458 20130101; H01L 33/007
20130101; H01S 2301/173 20130101; H01L 29/2003 20130101; H01L 33/12
20130101; H01L 33/32 20130101; H01S 5/32341 20130101; H01L 21/02507
20130101 |
Class at
Publication: |
257/183 ;
438/478; 257/E29.081; 257/E21.09 |
International
Class: |
H01L 29/267 20060101
H01L029/267; H01L 21/20 20060101 H01L021/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 2010 |
JP |
2010-044520 |
Claims
1. A semiconductor device comprising a buffer and a functional
laminate including a plurality of nitride semiconductor layers, on
a substrate, wherein the functional laminate includes a first
n-type or i-type Al.sub.xGa.sub.1-xN layer (0.ltoreq.x<1) on the
buffer side, and an Al.sub.zGa.sub.1-zN adjustment layer containing
p-type impurity, which has an approximately equal Al composition to
the first Al.sub.xGa.sub.1-xN layer (x-0.05.ltoreq.z.ltoreq.x+0.05,
0.ltoreq.z<1) is provided between the buffer and the functional
laminate.
2. The semiconductor device according to claim 1, wherein the
substrate is an AlN template substrate.
3. The semiconductor device according to claim 1, wherein the
buffer includes an Al.sub..alpha.Ga.sub.1-.alpha.N layer
(0.ltoreq..alpha..ltoreq.1) at least on the functional laminate
side, and difference between an Al composition .alpha. of the
Al.sub..alpha.Ga.sub.1-.alpha.N layer and an Al composition x of
the first Al.sub.xGa.sub.1-xN layer is 0.1 or more.
4. The semiconductor device according to claim 1, wherein the first
Al.sub.xGa.sub.1-xN layer is n-type, and the functional laminate
includes at least a light emitting layer and a second
Al.sub.yGa.sub.1-yN layer (0.ltoreq.y<1) in this order on the
first Al.sub.xGa.sub.1-xN layer.
5. The semiconductor device according to claim 1, wherein an i-type
Al.sub.wGa.sub.1-wN layer (x-0.05.ltoreq.w.ltoreq.x+0.05,
0.ltoreq.w<1) not doped with impurity is further provided
between the Al.sub.zGa.sub.1-zN adjustment layer containing p-type
impurity and the first Al.sub.xGa.sub.1-xN layer.
6. The semiconductor device according to claim 5, wherein the
Al.sub.zGa.sub.1-zN adjustment layer containing p-type impurity and
the i-type Al.sub.wGa.sub.1-wN layer not doped with impurity
satisfy the relationship of z<w.
7. The semiconductor device according to claim 1, wherein a
thickness of the Al.sub.zGa.sub.1-zN adjustment layer containing
p-type impurity is in a range of 100 nm to 1500 nm.
8. The semiconductor device according to claim 1, wherein the
Al.sub.zGa.sub.1-zN adjustment layer containing p-type impurity is
doped with Mg, and the Mg concentration is in a range of
5.times.10.sup.16/cm.sup.3 to 2.times.10.sup.20/cm.sup.3.
9. The semiconductor device according to claim 1, wherein a
concentration of O contained in the first Al.sub.xGa.sub.1-xN layer
is less than 2.times.10.sup.18/cm.sup.3.
10. The semiconductor device according to claim 1, wherein the
buffer includes a superlattice strain buffer layer having a
superlattice structure formed by alternately stacking
Al.sub..beta.Ga.sub.1-.beta.N layers (0.ltoreq..beta..ltoreq.0.3)
and AlN layers.
11. A method of producing a semiconductor device, wherein a buffer,
an Al.sub.zGa.sub.1-zN adjustment layer containing p-type impurity
(x-0.05.ltoreq.z.ltoreq.x+0.05, 0.ltoreq.z<1), and a functional
laminate including an i-type or n-type Al.sub.xGa.sub.1-xN layer
(0.ltoreq.x<1) are sequentially formed on a substrate.
Description
TECHNICAL FIELD
[0001] The present invention relates to a semiconductor device and
a method of producing the semiconductor device. The present
invention particularly relates to a semiconductor device such as
ultraviolet light emitting diodes, electronic devices, and to a
method of producing the same.
RELATED ART
[0002] In recent years, ultraviolet LEDs (light emitting diodes)
that can be favorably used in the fields of sterilization, water
purification, medical treatment, illumination, high-density optical
recording, and the like and high electron mobility transistors
(HEMTs) which have a device structure formed using an AlGaN based
thin film as a material are known. Further, for such ultraviolet
LEDs and HEMTs having a device structure formed using an
AlGaN-based thin film, various approaches have been made to obtain
high quality AlGaN-based thin films.
[0003] In general, an ultraviolet LED has a functional laminate
having a structure in which a light emitting layer is interposed
between an n-type nitride semiconductor layer and a p-type nitride
semiconductor layer. In order to relax strain due to difference in
lattice constant between the nitride semiconductor layers and a
substrate, a functional laminate is generally formed on the
substrate with a buffer interposed therebetween. HEMTs have a
functional laminate including an i-type channel layer and an n-type
electron supply layer that are formed of nitride semiconductor
layers. In order to reduce strain due to difference in lattice
constant between the nitride semiconductor layers and the
substrate, the functional laminate is also generally formed over
the substrate with a buffer interposed therebetween.
[0004] Patent Document 1 discloses a nitride semiconductor
substrate in which a first semiconductor layer (buffer) mainly
containing AlN or AlGaN that is doped with a lateral growth
promoting substance is formed on a substrate directly or with one
or a plurality of nitride semiconductor layers mainly containing
AlN or AlGaN interposed therebetween, and a functional laminate
including a nitride semiconductor layer is formed thereon.
According to this technique, lateral growth is promoted in the
buffer, accompanied by promotion of coupling of dislocations, which
allows the threading dislocation in a buffer surface to be
reduced.
PRIOR ART DOCUMENT
Patent Document
[0005] Patent Document 1: Japanese Patent Application Publication
No. JP2005-235908
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0006] In Patent Document 1, a typical AlN low-temperature
deposited buffer layer is formed between a buffer and an n-type
A.sub.0.4Ga.sub.0.6N layer. However, the relation of the Al
compositions between the AlN low-temperature deposited buffer layer
and the n-type Al.sub.0.4Ga.sub.0.6N layer is not considered.
Further, the AlN low-temperature deposited buffer layer reduces the
effect of promoting lattice relaxation in the buffer provided
thereunder; thus, crystallinity improvement due to lateral growth
was not sufficient.
[0007] In addition, in a case where, on a buffer, a nitride
semiconductor layer having a different composition from the buffer
is formed as a functional laminate, problems of lattice mismatch
between the nitride semiconductor layer of the functional laminate
and the buffer has not been noted.
[0008] An object of the invention is to solve the above problems
and provide a semiconductor device in which the crystal quality
improved in a buffer is effectively passed on to a functional
laminate to improve flatness and crystallinity of the functional
laminate. Another object of the invention is to provide a method of
producing the semiconductor device.
Means for Solving the Problem
[0009] The inventors of the present invention have made various
studies to achieve the above objects to consequently find that the
crystallinity and flatness improved in a buffer can be effectively
passed on to a functional laminate by providing an
Al.sub.zGa.sub.1-zN adjustment layer between the buffer on a
substrate and an n-type Al.sub.xGa.sub.1-xN layer in a functional
laminate having, for example, the n-type Al.sub.xGa.sub.1-xN layer
(0.ltoreq.x<1), a light emitting layer, and a p-type
Al.sub.yGa.sub.1-yN layer (0.ltoreq.y.ltoreq.1) from the buffer
side. Note that the Al.sub.zGa.sub.1-zN adjustment layer
(0.ltoreq.z<1) is containing p-type impurity, and the Al
composition z is within the range of .+-.0.05 from the Al
composition x of the n-type Al.sub.xGa.sub.1-xN layer in the
functional laminate closest on the buffer side. Thus, they
accomplished the present invention.
[0010] The present invention is based on the above findings, and
its constituent features are as follows.
[0011] (1) A semiconductor device comprising a buffer and a
functional laminate including a plurality of nitride semiconductor
layers, on a substrate,
[0012] wherein the functional laminate includes a first n-type or
i-type Al.sub.xGa.sub.1-xN layer (0.ltoreq.x<1) on the buffer
side, and
[0013] an Al.sub.zGa.sub.1-zN adjustment layer containing p-type
impurity, which has an approximately equal Al composition to the
first Al.sub.xGa.sub.1-xN layer (x-0.05.ltoreq.z.ltoreq.x++0.05,
0.ltoreq.z<1) is provided between the buffer and the functional
laminate.
[0014] (2) The semiconductor device according to (1) above, wherein
the substrate is an AlN template substrate.
[0015] (3) The semiconductor device according to (1) or (2),
wherein the buffer includes an Al.sub..alpha.Ga.sub.1-.alpha.N
layer (0.ltoreq..alpha..ltoreq.1) at least on the functional
laminate side, and difference between an Al composition .alpha. of
the Al.sub..alpha.Ga.sub.1-.alpha.N layer and an Al composition x
of the first Al.sub.xGa.sub.1-xN layer is 0.1 or more.
[0016] (4) The semiconductor device according to any one of (1) to
(3) above, wherein
[0017] the first Al.sub.xGa.sub.1-xN layer is n-type, and
[0018] the functional laminate includes at least a light emitting
layer and a second Al.sub.yGa.sub.1-yN layer (0.ltoreq.y<1) in
this order on the first Al.sub.xGa.sub.1-xN layer.
[0019] (5) The semiconductor device according to any one of (1) to
(4) above, wherein an i-type Al.sub.wGa.sub.1-wN layer
(x-0.05.ltoreq.w.ltoreq.x+0.05, 0.ltoreq.w.ltoreq.1) not doped with
impurity is further provided between the Al.sub.zGa.sub.1-zN
adjustment layer containing p-type impurity and the first
Al.sub.xGa.sub.1-xN layer.
[0020] (6) The semiconductor device according to (5) above, wherein
the Al.sub.zGa.sub.1-zN adjustment layer containing p-type impurity
and the i-type Al.sub.wGa.sub.1-wN layer not doped with impurity
satisfy the relationship of z<w.
[0021] (7) The semiconductor device according to any one of (1) to
(6) above, wherein a thickness of the Al.sub.zGa.sub.1-zN
adjustment layer containing p-type impurity is in a range of 100 nm
to 1500 nm.
[0022] (8) The semiconductor device according to any one of (1) to
(7) above, wherein the Al.sub.zGa.sub.1-zN adjustment layer
containing p-type impurity is doped with Mg, and the Mg
concentration is in a range of 5.times.10.sup.16/cm.sup.3 to
2.times.10.sup.20/cm.sup.3.
[0023] (9) The semiconductor device according to any one of (1) to
(8) above, wherein a concentration of O contained in the first
Al.sub.xGa.sub.1-xN layer is less than
2.times.10.sup.18/cm.sup.3.
[0024] (10) The semiconductor device according to any one of (1) to
(9) above, wherein the buffer includes a superlattice strain buffer
layer having a superlattice structure formed by alternately
stacking Al.sub..beta.Ga.sub.1-.beta.N layers
(0.ltoreq..beta..ltoreq.0.3) and AlN layers.
[0025] (11) A method of producing a semiconductor device, wherein a
buffer, an Al.sub.zGa.sub.1-zN adjustment layer containing p-type
impurity (x-0.05.ltoreq.z.ltoreq.x+0.05, 0.ltoreq.z<1), and a
functional laminate including an i-type or n-type
Al.sub.xGa.sub.1-xN layer (0.ltoreq.x<1) are sequentially formed
on a substrate.
Effect of the Invention
[0026] The present invention can provide a semiconductor device
having a functional laminate excellent in flatness and
crystallinity and a method of producing the semiconductor device.
The flatness and crystallinity improved in a buffer can be
effectively passed on to the functional laminate by providing an
Al.sub.zGa.sub.1-zN adjustment layer between the buffer on a
substrate and a first n-type or i-type Al.sub.xGa.sub.1-xN layer in
the functional laminate having an n-type Al.sub.xGa.sub.1-xN layer
(0.ltoreq.x<1). The Al.sub.zGa.sub.1-zN adjustment layer
(0.ltoreq.z<1) is containing p-type impurity, and the Al
composition z is within the range of .+-.0.05 from the Al
composition x of the first Al.sub.xGa.sub.1-xN layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic cross-sectional view of a
semiconductor device 100 in accordance with the present
invention.
[0028] FIG. 2 is a schematic cross-sectional view showing a layered
structure in a production of a semiconductor device 100 according
to the present invention.
[0029] FIGS. 3(a) and 3(b) are 1000.times. photomicrographs of
surfaces in Experimental Examples 1 and 2, respectively.
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] Embodiments of a semiconductor device in accordance with the
present invention will be described with reference to the
drawings.
[0031] FIG. 1 is a schematic cross-sectional view showing an
example of the semiconductor device 100 in accordance with the
present invention.
[0032] The semiconductor device 100 in accordance with the present
invention includes a buffer 2 and a functional laminate 3 having a
plurality of nitride semiconductor layers on a substrate 1 as shown
in FIG. 1. The semiconductor device 100 is characterized in that
the functional laminate 3 has a first n-type or i-type
A.sub.xGa.sub.1-xN layer (0.ltoreq.x<1) 4 (n-type in FIG. 1) on
the buffer 2 side, and an Al.sub.zGa.sub.1-zN adjustment layer
(x-0.05.ltoreq.z.ltoreq.x+0.05, 0.ltoreq.z<1) 5 (hereinafter
also referred to simply as "adjustment layer 5") is provided
between the buffer 2 and the functional laminate 3. The adjustment
layer 5 contains p-type impurity, and has an approximately equal Al
composition to the first Al.sub.xGa.sub.1-xN layer 4. With such a
structure, flatness and crystallinity improved in the buffer 2 can
be effectively passed on to the functional laminate 3, which
results in preferable flatness and crystallinity of the functional
laminate 3. Note that the functional laminate 3 refers to a portion
serving as a device, in which for example electric current flows,
in a semiconductor device such as an LED or an HEMT, and the
function of a device is not imparted to the adjustment layer 5 even
if the adjustment layer 5 is adjacent to the first
Al.sub.xGa.sub.1-xN layer (0.ltoreq.x<1) 4.
[0033] The Al.sub.zGa.sub.1-zN adjustment layer 5 containing p-type
impurity is provided between the buffer 2 and the n-type
Al.sub.xGa.sub.1-xN layer 4, which can particularly prevent
impurities such as oxygen (O) from diffusing into the functional
laminate 3 from the substrate 1; as a result, the light output can
be improved. Further, since the adjustment layer 5 contains p-type
impurity, lateral growth in the adjustment layer 5 is promoted, and
the flatness of the adjustment layer 5 can be improved, which
consequently improves the flatness of layers thereon. Further, the
Al composition z of the Al.sub.zGa.sub.1-zN adjustment layer 5
containing p-type impurity is set within the range of .+-.0.05 from
the Al composition x of the n-type Al.sub.xGa.sub.1-xN layer 4, so
that the crystallinity and flatness improved in the buffer 2 and
the p-type Al.sub.zGa.sub.1-zN adjustment layer 5 can be
effectively passed on to the n-type Al.sub.xGa.sub.1-xN layer 4 and
even to the layers provided thereon. Thus, the semiconductor device
100 of the present invention can achieve high light output.
[0034] Here, the p-type impurity is preferably Mg, Zn, Ca, or Be,
more preferably Mg or Zn, and Mg is highly preferred. In terms of
the segregation effect for nitride semiconductors, Mg, Zn, Ca, or
Be can be used as the p-type impurity. Mg or Zn is preferred as a
lateral crystal growth promoting substance for promoting the
crystal growth of AlGaN or GaN in the lateral direction. Among
them, Mg hardly diffuses into other layers, which makes it highly
preferable as a lateral crystal growth promoting substance.
Further, the Al.sub.zGa.sub.1-zN adjustment layer containing p-type
impurity may be not only a p-type Al.sub.zGa.sub.1-zN adjustment
layer obtained by activation of p-type impurity but alternatively
an Al.sub.zGa.sub.1-zN adjustment layer doped with p-type impurity
not subjected to an activation process.
[0035] It is preferable that the first Al.sub.xGa.sub.1-xN layer 4
is n-type, and the functional laminate 3 has at least a light
emitting layer 6 and a second p-type Al.sub.yGa.sub.1-yN layer
(0.ltoreq.y<1) 7 in this order on the first Al.sub.xGa.sub.1-xN
layer 4. With the thus formed light emitting device, the flatness
and crystallinity improved in the buffer 2 can be effectively
passed on to the functional laminate 3, in particular to the light
emitting layer 6 in the functional laminate 3; thus, the functional
laminate 3 can have preferable flatness and crystallinity, and
light output can be improved.
[0036] Further, an i-type Al.sub.wGa.sub.1-wN layer
(0.ltoreq.w<1) 8 not doped with impurity (hereinafter also
referred to as "undoped" Al.sub.wGa.sub.1-wN layer 8) having an
approximately equal Al composition to the first Al.sub.xGa.sub.1-xN
layer 4 is preferably provided in addition between the adjustment
layer 5 and the first Al.sub.xGa.sub.1-xN layer 4. Moreover, the Al
composition w of this undoped Al.sub.wGa.sub.1-wN layer 8 is
preferably within the range of .+-.0.05 from the Al composition x
of the first Al.sub.xGa.sub.1-xN layer 4. This is for effectively
passing on the crystallinity and flatness improved in the
adjustment layer 5 to the first Al.sub.xGa.sub.1-xN layer 4 and
even to layers thereon; further preventing the diffusion of the
above impurities; and avoiding thyristor effects due to pn junction
in a case where the first Al.sub.xGa.sub.1-xN layer 4 is
n-type.
[0037] More preferably, x-0.05.ltoreq.z<w.ltoreq.x+0.05 may be
taken. Strain due to lattice constant difference between a layer in
the buffer 2 on the closest side to the functional laminate 3 and
the first Al.sub.xGa.sub.1-xN layer 4 (lattice constant difference
between x and a to be described) can be more appropriately reduced
due to the relationship between the Al.sub.zGa.sub.1-zN adjustment
layer 5 containing p-type impurity and the i-type
Al.sub.wGa.sub.1-wN layer 8. With the relation
x-0.05.ltoreq.z<w.ltoreq.x+0.05, upper layers have higher Al
composition and consequently have a relatively small lattice
constant, so that tensile stress is applied by lower layers to the
layers stacked thereabove. In other words, tensile stress is
applied in the crystal growth of the i-type Al.sub.wGa.sub.1-wN
layer 8. Therefore, crystal growth of the i-type
Al.sub.wGa.sub.1-wN layer 8 not doped with p-type impurity itself
can additionally have an effect of promoting lateral growth, and
the effect of maintaining the improved flatness can be further
enhanced by the i-type Al.sub.wGa.sub.1-wN layer 8. However, when
the composition difference from x is more than 0.05, cracks would
occur or flatness would be affected by strain due to the difference
in the lattice constant.
[0038] The i-type AlGaN layer not doped with impurity here refers
to a layer which is not designed to be doped with specific impurity
(also referred to as "undoped layer"). Ideally, a semiconductor
preferably contains no impurity; however, a semiconductor with low
carrier density (for example, less than 5.times.10.sup.16/cm.sup.3)
can be referred to as i-type as long as it does not electrically
serve as a p-type or n-type semiconductor.
[0039] The thickness of the adjustment layer 5 is preferably in the
range of 100 nm to 1500 nm, more preferably 100 nm to 300 nm. When
the thickness is less than 100 nm, sufficient surface flatness
would not be achieved; when the thickness is more than 1500 nm,
cracks would occur in the surface of the adjustment layer; and when
the thickness is more than 300 nm, cracks would occur in the
functional laminate.
[0040] The adjustment layer 5 is doped with magnesium (Mg), and its
Mg concentration is preferably in the range of
5.times.10.sup.16/cm.sup.3 to 2.times.10.sup.20/cm.sup.3. When Mg
is used as p-type impurity, the lateral growth of the adjustment
layer 5 is promoted to help promotion of planarization. When the Mg
concentration is less than 5.times.10.sup.16/cm.sup.3, sufficient
surface flatness would not be achieved. Further, when the Mg
concentration is more than 2.times.10.sup.20/cm.sup.3, the Mg
concentration is supersaturated to cause segregation, which would
significantly impair the flatness of the surface.
[0041] The concentration of oxygen (O) contained in the first
Al.sub.xGa.sub.1-xN layer 4 is preferably less than
2.times.10.sup.18/cm.sup.3, more preferably
1.times.10.sup.18/cm.sup.3 or less. Oxygen contained in the n-type
Al.sub.xGa.sub.1-xN layer 4 has been mixed in, for example when a
layer is stacked on the substrate 1 with oxygen in the atmosphere
being attached thereto and the oxygen is diffused into the upper
layer. The oxygen causes reduction in the power output of light
emitting devices; therefore, the concentration is preferably even
lower.
[0042] The buffer 2 serves to reduce dislocation or strain resulted
from the lattice mismatch or thermal expansion difference between
the substrate 1 and the functional laminate 3, and it can be
selected from known buffers depending on the type of the substrate
1 and the functional laminate 3. The present invention is
advantageous in a case where the Al compositions of layers in the
buffer 2 and the functional laminate 3 that are most close to each
other are different, and particularly in a case where the
difference of the Al compositions is 0.1 or more. Specifically, the
difference between the Al composition .alpha. of the
Al.sub..alpha.Ga.sub.1-.alpha.N layer (0.ltoreq..alpha..ltoreq.1)
in the buffer 2 on the closest side to the functional laminate 3
and the Al composition x of the first Al.sub.xGa.sub.1-xN layer 4
is preferably 0.1 or more.
[0043] The buffer 2 may be a single layer or a multilayer, but a
superlattice is preferably used. Further, the buffer 2 more
preferably includes a superlattice strain buffer layer having a
superlattice structure formed by alternately stacking
Al.sub..beta.Ga.sub.1-.beta.N layers (0.ltoreq..beta..ltoreq.0.3)
2a and AlN layers 2b. The Al.sub..beta.Ga.sub.1-.beta.N layers
(0.ltoreq..beta..ltoreq.0.3) 2a are preferred to be p-type. This is
for reducing lattice mismatch and improving the flatness. Note that
the layered structure of the superlattice strain buffer layer is
partially omitted in the figure. Although not shown in the figure,
an AlN layer having a thickness ranging from 500 nm to 1500 nm
epitaxially grown on the substrate 1 using a known technique such
as MOCVD, MOVPE, HVPE, or MBE, for example, may be provided as an
initial layer between the substrate 1 and the superlattice strain
buffer layer.
[0044] For the thickness of the layers forming the superlattice
strain buffer layer, the thickness of the p-type
Al.sub..beta.Ga.sub.1-.beta.N layers 2a may be for example, 0.1 nm
to 3 nm, preferably 2 nm or less, while the thickness of the AlN
layers 2b may be for example, 0.1 nm to 9 nm, preferably 0.9 nm to
9 nm. Further, as to the number of the stacked p-type
Al.sub..beta.Ga.sub.1-.beta.N layers 2a and AlN layers 2b, the
number of the pairs of the p-type Al.sub..beta.Ga.sub.1-.beta.N
layers 2a and AlN layers 2b can be, for example 20 to 70,
preferably 20 to 50. Such a number of stacked layers can
sufficiently suppress the occurrence of dislocation. Assuming that
the superlattice strain buffer layer is AlGaN, the Al composition
is generally calculated from the Al composition and the thickness
of each layer. It should be noted that the Al composition of the
surfaces of the buffer 2 facing to the functional laminate 3 does
not refer to the calculated Al composition of the superlattice, but
to the practical Al composition of the surfaces irrespective of the
thickness.
[0045] Note that in the superlattice strain buffer layer, the AlN
layers 2b made of AlN are thicker (the ratio of the AlN layers 2b
is higher) on the substrate 1 side, and the ratio of the AlN layers
2b with respect to the p-type Al.sub..beta.Ga.sub.1-.beta.N layers
2a preferably decreases gradually to the side of the n-type
Al.sub.xGa.sub.1-xN layer 4. With such a structure, the
crystallinity of the n-type Al.sub.xGa.sub.1-xN layer 4 can be
further improved.
[0046] Further, the superlattice strain buffer layer is not
substantially electrically conductive as a whole (for example, the
specific resistance measured by a sheet resistance measuring
apparatus is 10 .OMEGA.cm/square or more), and the impurity
concentration of the whole superlattice strain buffer layer
measured by SIMS is preferably 1.times.10.sup.18 cm.sup.-3 or less,
more preferably 7.times.10.sup.17 cm.sup.-3 or less. When the
impurity concentration is more than 1.times.10.sup.18 cm.sup.-3,
thyristor failure would occur in the nitride semiconductor
device.
[0047] In general, doping of AlN layers with p-type impurity is
difficult and involves deterioration of crystallinity; therefore,
the AlN layers are designed not to be doped with p-type impurity.
In contrast, since the superlattice strain buffer layer of the
present invention is not required to be electrically conductive,
the amount of impurities in the AlN layers 2b is preferably much
smaller than the normal impurity doping amount, excluding
unavoidable impurity diffused from the p-type
Al.sub..beta.Ga.sub.1-.beta.N layers 2a.
[0048] Here, layers having a low Al content: an Al composition
.beta. ranging 0.ltoreq..beta..ltoreq.0.3, which further contain
p-type impurity, can be used as the p-type
Al.sub..beta.Ga.sub.1-.beta.N layers 2a. Note that, as the p-type
impurity, for example Mg, Zn, Ca, or Be can be used. The p-type
impurity can be contained in the Al.sub..beta.Ga.sub.1-.beta.N
layers 2a by supplying the p-type impurity simultaneously with a
source gas in the formation of the Al.sub..beta.Ga.sub.1-.beta.N
layers 2a and alternatively by intermittently supplying the p-type
impurity onto the AlN layers 2b, then forming the
Al.sub..beta.Ga.sub.1-.beta.N layers 2a, and diffusing the p-type
impurity into the Al.sub..beta.Ga.sub.1-.beta.N layers 2a. The
concentration of the p-type impurity in the p-type
Al.sub..beta.Ga.sub.1-.beta.N layers 2a may be, for example,
5.times.10.sup.16/cm.sup.3 or more and less than
2.times.10.sup.20/cm.sup.3, preferably 7.times.10.sup.17/cm.sup.3
to 1.7.times.10.sup.19/cm.sup.3, more preferably
7.times.10.sup.18/cm.sup.3 to 1.7.times.10.sup.19/cm.sup.3.
[0049] In addition, a known substrate that is different kind from
Group III nitride on which a Group III nitride can be grown can be
used as the substrate 1. An AlN template substrate in which a
single crystal AlN layer 1b is grown directly on a sapphire base
substrate 1a, and an AlGaN template substrate in which a single
crystal AlGaN layer 1b is directly grown on a sapphire base
substrate 1a are preferable. A Si substrate is also preferred.
[0050] The inventors found that when an AlN template substrate is
used, the above attachment of oxygen (O) in the atmosphere more
easily occurs as compared with the case of using a sapphire
substrate, and rise in the concentration of oxygen in the
functional laminate 3 due to the attached oxygen is required to be
suppressed. Then, with respect to a semiconductor device of the
present invention, they found that the diffusion of the oxygen (O)
into the functional laminate 3 can be effectively suppressed by
providing the Al.sub.zGa.sub.1-zN adjustment layer 5 containing
p-type impurity. The layer containing p-type impurity, which has an
adequate thickness is considered to suppress the diffusion of
oxygen (O).
[0051] Si or the like is preferably used as n-type impurity in the
n-type Al.sub.xGa.sub.1-xN layer 4. A layer made of
Al.sub..gamma.In.sub..delta.Ga.sub.1-.gamma.-.delta.N (where
0.ltoreq..gamma..ltoreq.1, 0.ltoreq..delta..ltoreq.1,
0.ltoreq..gamma.+.delta..ltoreq.1) can be used as the light
emitting layer 6. Mg, Zn, Ca, Be, or the like is preferably used as
p-type impurity in the p-type Al.sub.yGa.sub.1-yN layer 7. The
thickness of the layers may be, for example, as follows: the n-type
Al.sub.xGa.sub.1-xN layer 4: 1300 nm to 1400 nm, the light emitting
layer 6: 50 nm to 80 nm, and the p-type Al.sub.yGa.sub.1-yN layer
7: 200 nm to 300 nm. Note that these layers can be formed by
epitaxial growth using known techniques.
[0052] Further, as shown in FIG. 1, a p-side electrode 9 can be
provided on the p-type Al.sub.yGa.sub.1-yN layer 7, and an n-side
electrode 10 can be provided on the partially exposed n-type
Al.sub.xGa.sub.1-xN layer 4. A NiAu electrode obtained by
sequentially vapor-depositing a Ni-containing film and an
Au-containing film by vacuum vapor deposition, for example, may be
used as the p-side electrode 9. A TiAl electrode obtained by
sequentially vapor-depositing a Ti-containing film and an
Al-containing film by vacuum vapor deposition, for example, may be
used as the n-side electrode 10.
[0053] Next, an embodiment of a method of producing a semiconductor
device according to the present invention will be described with
reference to the drawings.
[0054] FIG. 2 schematically shows an example of a layered structure
of a semiconductor device 100 in accordance with the present
invention at a stage of production.
[0055] The method of producing the semiconductor device 100 in
accordance with the present invention is characterized by
sequentially forming a buffer 2, an Al.sub.zGa.sub.1-zN adjustment
layer (x-0.05.ltoreq.z.ltoreq.x+0.05, 0.ltoreq.z<1) 5 containing
p-type impurity, and a functional laminate 3 containing an i-type
or n-type Al.sub.xGa.sub.1-xN layer (0.ltoreq.x<1) 4, on a
substrate 1 for example by MOCVD, as shown in FIG. 2. With such a
structure, flatness and crystallinity improved in the buffer can be
effectively passed on to the functional laminate, so that a
semiconductor device having the functional laminate with favorable
flatness and crystallinity can be provided.
[0056] Next, when the semiconductor device is a light emitting
device, as shown in FIG. 1, at least a p-type Al.sub.yGa.sub.1-yN
layer 7 and a light emitting layer 6 (and part of an n-type
Al.sub.xGa.sub.1-xN layer 4) which have been formed on the
adjustment layer 5 are etched by dry etching to partially expose
the n-type Al.sub.xGa.sub.1-xN layer 4 on the light emitting layer
6 side (in the upper part of FIG. 1). Then, finally, a p-side
electrode 9 and an n-side electrode 10 are formed by vacuum vapor
deposition to electrically connect the n-type Al.sub.xGa.sub.1-xN
layer 4 and the p-type Al.sub.yGa.sub.1-yN layer 7. Thus, a
semiconductor device 100 shown in FIG. 1 can be obtained.
[0057] Since p-type impurity is contained in the adjustment layer 5
of the thus produced semiconductor device 100, lateral crystal
growth of the adjustment layer 5 is promoted, so that the flatness
and crystallinity of the adjustment layer 5 is improved.
Accordingly, the flatness and crystallinity of the n-type
Al.sub.xGa.sub.1-xN layer 4 formed on the adjustment layer 5 is
also improved, which consequently improves the flatness and
crystallinity of the light emitting layer 6 and the p-type
Al.sub.yGa.sub.1-yN layer 7 thereon. Thus, a semiconductor device
100 with high light output can be obtained.
[0058] The n-type Al.sub.xGa.sub.1-xN layer 4 of a nitride
semiconductor device of the present invention may be a laminate of
an n-cladding layer and an n-contact layer. Meanwhile, the p-type
Al.sub.yGa.sub.1-yN layer 7 may be a laminate of a p-cladding layer
and a p-contact layer.
[0059] The case where the first Al.sub.xGa.sub.1-xN layer is n-type
has been described above; however, the present invention can also
be applied to cases where the first Al.sub.xGa.sub.1-xN layer is
undoped i-type. When the first Al.sub.xGa.sub.1-xN layer is i-type,
for example, this i-type Al.sub.xGa.sub.1-xN layer is used as a
channel layer, and an n-type AlGaN-based layer provided thereon as
an electron supply layer, and three electrodes of a source, a gate,
and a drain are provided thereon to obtain an electronic device
having a HEMT structure.
[0060] The above description merely shows examples of embodiments
of the present invention, and the present invention is not limited
to the embodiments. For example, the above AlGaN layer may be a
layer into which In, B, or the like is inevitably mixed at
approximately 1% or less.
EXAMPLES
[0061] Here, to show the advantage of the adjustment layer 5 in the
present invention containing p-type impurity, the fact that
significantly favorable flatness can be achieved in a case of
forming p-type AlGaN on AlN as compared with a case of forming an
n-type or i-type AlGaN layer will be shown experimentally.
Experimental Example 1
[0062] A Mg-doped p-type Al.sub.0.31Ga.sub.0.69N layer (thickness:
1000 nm, doped with Mg, Mg concentration:
1.times.10.sup.19/cm.sup.3) was grown on an AlN template substrate
by MOCVD.
Experimental Example 2
[0063] A Si-doped n-type Al.sub.0.31Ga.sub.0.69N layer (thickness:
1000 nm, doped with Si, Si concentration:
4.times.10.sup.18/cm.sup.3) was grown on an AlN template substrate
by MOCVD.
Experimental Example 3
[0064] An undoped i-type Al.sub.0.31Ga.sub.0.69N layer (thickness:
1000 nm) was grown on an AlN template substrate by MOCVD.
[0065] (Evaluation 1)
[0066] Surfaces of the Mg-doped AlGaN layer in Experimental Example
1 above, the n-type AlGaN layer in Experimental Example 2 above,
and the i-type AlGaN layer in Experimental Example 3 above were
observed using an optical microscope and an atomic force microscope
(AFM) to evaluate the flatness of the surfaces using the arithmetic
mean roughness Ra obtained by the AFM measurement.
[0067] FIGS. 3(a) and 3(b) are micrographs, taken through an
optical microscope (1000.times.), of the surfaces in Experimental
Examples 1 and 2, respectively. As evident from the micrographs, no
step was seen in Experimental Example 1, while steps were observed
in the same field of view in Experimental Example 2. This reveals
that Experimental Example 1 in which the Mg-doped
Al.sub.0.31Ga.sub.0.69N layer was grown on the substrate achieved a
flatter surface than Experimental Example 2 in which the n-type
Al.sub.0.31Ga.sub.0.69N layer was grown on the substrate. Steps
were also found in the surface of Experimental Example 3 similarly
to Experimental Example 2.
[0068] Further, from the results of the AFM measurements, the
arithmetic mean roughness Ra was as follows: Experimental Example
1: Ra=0.74 nm, Experimental Example 2; Ra=6.32 nm, and Experimental
Example 3: Ra=5.94 nm. This shows that Experimental Example 1
achieved a significantly flatter surface as compared with
Experimental Examples 2 and 3.
[0069] The above shows that when the n-type AlGaN layer having a
very different Al composition from AlN was formed on AlN,
irregularities were formed on the surface of the n-type AlGaN
layer. Meanwhile, when the Mg-doped AlGaN layer having a very
different Al composition from AlN was formed on AlN, the surface of
the Mg-doped AlGaN layer was flat. Note that the flatness of the
surface of the undoped i-type AlGaN layer was also impaired to an
extent similar to the n-type AlGaN layer in the case where the
i-type AlGaN layer was grown directly on AlN.
Example 1
[0070] An AlN layer (thickness: 27 nm) was stacked as an initial
layer by MOCVD on an AlN template substrate, and then a buffer
(superlattice strain buffer layer), a p-type
Al.sub.0.31Ga.sub.0.69N adjustment layer (thickness: 100 nm, Mg
concentration: 1.times.10.sup.18/cm.sup.3) doped with Mg as a
substance for promoting planarization, an undoped i-type
Al.sub.0.35Ga.sub.0.65N layer (thickness: 300 nm) were epitaxially
grown thereon in this order. Further, an n-type
Al.sub.0.35Ga.sub.0.65N layer (thickness: 1300 nm, doped with Si,
Si concentration: 1.times.10.sup.19/cm.sup.3), a light emitting
layer (multiple quantum well structure with an emission wavelength
of 325 nm, total thickness: 64.5 nm), and a p-type
Al.sub.0.32Ga.sub.0.68N layer (thickness: 280 nm, doped with Mg, Mg
concentration: 1.5.times.10.sup.19/cm.sup.3) were epitaxially grown
in this order to form a functional laminate. Thus, an epitaxial
laminate was formed on the substrate. Specifically, in this
example, z=0.31, w=x=0.35, and y=0.32 were satisfied and z was
within the range of .+-.0.05 from x; w was equal to x; and
z<w.
[0071] Note that the superlattice strain buffer layer had a
structure in which a superlattice laminate I having 20 pairs of
alternately stacked AlN layers (thickness: 9 nm) and GaN layers
(thickness: 2.1 nm), a superlattice laminate II having 30 pairs of
alternately stacked AlN layers (thickness: 2.7 nm) and GaN layers
(thickness: 2.1 nm), and a superlattice laminate III having 50.5
pairs of alternately stacked AlN layers (thickness: 0.9 nm) and GaN
layers (thickness: 2.1 nm) ("50.5 pairs" implies that both the
first layer and the last layer in the laminate were AlN layers)
were sequentially stacked. The GaN layers were doped with Mg.
[0072] Here, the layer in the buffer (superlattice strain buffer
layer) on the closest side of the functional laminate was an AlN
layer. The difference (.alpha.-x) between the Al composition
.alpha. of the buffer on the functional laminate side (the AlN
layer) and the Al composition x of the functional laminate on the
buffer side (n-type Al.sub.0.35Ga.sub.0.65N layer), the AlN layer
and the n-type Al.sub.0.35Ga.sub.0.65N layer being opposite to each
other, was 1.0-0.35=0.65, and was more than 0.1. Assuming that the
superlattice laminate III was AlGaN, the total Al composition .eta.
is calculated as 0.9 nm/2.1 nm=0.43. The production conditions of
the superlattice strain buffer layer and the p-type
Al.sub.0.31Ga.sub.0.69N layer are shown in Table 1.
TABLE-US-00001 TABLE 1 Al Compo- TMG TMA NH.sub.3 Cp.sub.2Mg Device
structure sition (sccm) (sccm) (slm) (sccm) Mg-doped
Al.sub.0.31Ga.sub.0.69N 0.31 15 30 10 25 layer Superlattice
Superlattice 0 20 -- 10 25 strain buffer laminate III 1 -- 10 0.5
-- layer Superlattice 0 20 -- 10 25 laminate II 1 -- 10 0.5 --
Superlattice 0 20 -- 10 25 laminate I 1 -- 10 0.5 --
Comparative Example 1
[0073] An epitaxial laminate was formed in a manner similar to
Example 1 except for that the p-type Al.sub.0.31Ga.sub.0.69N
adjustment layer doped with Mg was not formed.
Example 2
[0074] An epitaxial laminate was formed in a manner similar to
Example 1 except for that the Al composition of the undoped i-type
AlGaN layer was w=0.29 and the Al composition of the n-type AlGaN
layer in the functional laminate was x=0.29. Since z=0.31, z is
within the range of .+-.0.05 from x in this example, but
z>w.
Example 3
[0075] An epitaxial laminate was formed in a manner similar to
Example 1 except for that the undoped i-type
Al.sub.0.35Ga.sub.0.65N layer was not formed. In this example,
z=0.31 and x=0.35.
Comparative Example 2
[0076] An epitaxial laminate was formed in a manner similar to
Example 3 except for that the Al composition of the p-type AlGaN
adjustment layer was z=0.19. In this comparative example, x=0.35
without change, so that z is out of the range of .+-.0.05 from
x.
Comparative Example 3
[0077] An epitaxial laminate was formed in a manner similar to
Example 3 except for that the Al composition of the p-type AlGaN
adjustment layer was z=0.41. In this comparative example, x=0.35
without change, so that z is out of the range of +0.05 from x.
[0078] (Evaluation 2)
[0079] Samples of Examples 1-3 and Comparative Examples 1-3 above
at a stage where the functional laminate had been formed were
analyzed by an X-ray diffractometer to find half widths of the
peaks corresponding to the (0002) plane and the (10-12) plane. The
results are shown in Table 2. Note that the smaller the half width
is, the better the crystallinity is. With respect to the sample of
Comparative Example 2, the half width could not have been measured
since the surface of the functional laminate was cracked.
TABLE-US-00002 TABLE 2 Half width (arcsec) (0002) (10-12)
Comparative Example 1 368 683 Example 1 334 528 Example 2 343 542
Example 3 355 619 Comparative Example 2 Cracked Comparative Example
3 366 663
[0080] (Evaluation 3)
[0081] With respect to the samples of Examples 1-3 and Comparative
Examples 1-3 above, the growth surface was scribed with a diamond
pen; Indium dots were physically pressed on a point where the
n-type AlGaN layer was exposed and a point 1.5 mm apart from this
exposed point. Thus, a simple nitride semiconductor device using
the formed two points as an n-type electrode and a p-type electrode
was manufactured. Then, probes were put on those points; light was
output from the rear surface after a DC current of 20 mA was
applied; and the light was guided to a multi-channel spectrometer
through an optical fiber. The peak intensity of the spectrum was
converted to output power to obtain the light output power Po. The
emission wavelength was 327 nm in each of the cases. The results
are shown in Table 3. Note that the sample of Comparative Example 2
did not emit light.
TABLE-US-00003 TABLE 3 Light output (mW) Comparative Example 1 0.2
Example 1 2.1 Example 2 1.7 Example 3 1.1 Comparative Example 2 No
light output Comparative Example 3 0.3
[0082] (Evaluation 4)
[0083] With respect to the samples of Examples 1-3 and Comparative
Examples 1-3, the reflectance of the surface after the growth of
the AlGaN adjustment layer doped with Mg, during the growth of the
i-type AlGaN layer growth, during the growth of the n-type AlGaN
layer forming the functional laminate, and during the growth of the
light emitting layer was measured, which were normalized with the
reflectance of the surface after the growth of the superlattice
strain buffer layer.
[0084] In order to measure the reflectance of a surface of a wafer
being grown, a xenon lamp light source and optical system members
which enable irradiation of the wafer through a furnace window were
prepared. The wafer was irradiated with the source light, and the
reflected light guided through the optical fiber from a light
receiving portion was measured by a spectrophotometer. The optical
axis was adjusted by using a previously polished sapphire
substrate, and the reflection intensity was measured. Relative
reflection intensity was determined from the reflectance of the
sapphire substrate and the reflectance of the samples at each
growth stage. When the sample is grown with its surface being flat,
in other words, with the flatness of the surface being high, light
passes along the optical axis from the light source to the light
receiving portion; therefore, the light intensity of the received
light is shown as a constant value. However, when the sample is
grown with its surface being rough, light is scattered on the
wafer; therefore, the intensity of light to be received becomes
lower as compared with the case of flat surface. With this
measurement system, the in-situ surface condition of the wafer just
being grown can be measured in the form of the light intensity over
time, and the change in the surface condition of the wafer during
growth can be followed. In this measurement, based on the relative
intensity with respect to sapphire which was determined in the
growth of the superlattice strain buffer layer, the relative
intensity of each growth layer with respect to sapphire was
normalized with the relative intensity of the superlattice strain
buffer layer. The results are shown in Table 4. The measurement
could not be performed on the sample of Comparative Example 2
because of cracks.
TABLE-US-00004 TABLE 4 Compar- Compar- Compar- ative ative ative
Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 1 ple 2 ple 3 ple 2
ple 3 Light 0.58 1.20 1.01 0.79 Un- 0.59 emitting measur- layer
able N-type 0.66 0.93 0.86 0.76 0.67 AlGaN layer I-type 0.66 0.93
0.86 AlGaN layer P-type 0.95 0.95 0.95 0.95 AlGaN layer Super- 1.00
1.00 1.00 1.00 1.00 lattice strain buffer layer
[0085] As seen in Table 4, in Comparative Examples 1 and 3, the
reflectance was not maintained after the growth of the superlattice
strain buffer layer, and the reflectance was reduced as upper
layers were stacked. Meanwhile, in Examples 1-3, the reflectance
was maintained even after the growth of the superlattice strain
buffer layer than Comparative Examples 1 and 3. This is considered
because the flatness and crystallinity improved in the buffer were
effectively passed on to the functional laminate through the p-type
Al.sub.0.31Ga.sub.0.69N adjustment layer.
[0086] Note that the intensity of the light emitting layer in
Example 1 was 1.2 because the Al composition of the light emitting
layer was low and the refractive index thereof was high, which
accordingly increased the difference between the refractive indices
of the light emitting layer and the ambient gas in the furnace
(refractive index of a mixture of N.sub.2 and H.sub.2, which was
almost equal to the refractive index of the atmosphere) to increase
the reflectance. On the other hand, in Comparative Examples 1 and
3, the reflectance of the light emitting layer was lower than that
of the n-type AlGaN layer, which was resulted from the reduction in
the reflectance evidently due to surface roughness.
[0087] (Evaluation 5)
[0088] The impurity concentration of the samples of Example 1 and
Comparative Example 1 above was measured by SIMS.
[0089] The oxygen (O) concentration of the n-type
Al.sub.0.35Ga.sub.0.65N layer and the light emitting layer in
Example 1 was 1.times.10.sup.18/cm.sup.3, while the oxygen (O)
concentration of those in Comparative Example 1 was
8.times.10.sup.18/cm.sup.3. The oxygen (O) concentration of the
n-type AlGaN layer and the light emitting layer in Examples 2 and 3
was also approximately equal to that in Example 1 and was less than
2.times.10.sup.18/cm.sup.3. Therefore, the p-type AlGaN adjustment
layer of the present invention reduced the concentration of oxygen
(O) in the layers to be stacked afterwards to less than
2.times.10.sup.18/cm.sup.3, which contributed to the improvement in
the light output.
[0090] The above results show that with respect to a semiconductor
device in accordance with the present invention, the flatness and
crystallinity improved in the buffer were passed on to the
Al.sub.0.31Ga.sub.0.69N adjustment layer containing p-type impurity
to approximate the Al composition of the adjustment layer to the Al
composition of the AlGaN layer thereon. Accordingly, the flatness
and crystallinity were passed on to the i-type or n-type
Al.sub.0.35Ga.sub.0.65N, and further to the whole functional
laminate. Thus, the light output of the device was demonstrated to
be improved. Still further, comparing Example 1 and Example 3, it
was found that an i-type Al.sub.wGa.sub.1-wN layer not being doped
with impurity is preferably provided in addition; meanwhile,
comparing Example 1 and Example 2, z<w is more preferable.
[0091] It is evident that a high output light emitting device can
be obtained by fabricating a semiconductor device by then partially
exposing the n-type AlGaN layer forming the functional laminate
obtained in this example by dry etching, for example, forming an
n-side electrode on the n-type AlGaN layer, and forming a p-side
electrode on the p-type AlGaN layer.
[0092] In cases where an AlGaN layer is grown directly on AlN as in
Experimental Example 2 and Experimental Example 3, the surface
flatness is affected. It was found that the surface of the AlGaN
layer can be planarized by providing an AlGaN adjustment layer
containing p-type impurity of the present invention therebetween
with an appropriate Al composition, and that this further
contributes to the improvement in crystallinity.
[0093] Use of an adjustment layer of the present invention makes it
possible to improve flatness and crystallinity of a nitride
semiconductor layer provided thereon, and this can be applied to
electronic devices such as HEMTs and the like without limitation to
light emitting devices. Specifically, for example when a
superlattice buffer and a non-doped channel layer has an AlGaN
layer containing p-type impurity, which has an approximately equal
Al composition to the channel layer therebetween, the flatness and
crystallinity improved in the buffer can be effectively passed on,
and the flatness and crystallinity of the channel layer and layers
provided thereon can be improved.
INDUSTRIAL APPLICABILITY
[0094] The present invention can provide a semiconductor device
having a functional laminate excellent in flatness and
crystallinity and a method of producing the semiconductor device.
The flatness and crystallinity improved in a buffer can be
effectively passed on to the functional laminate by providing an
Al.sub.zGa.sub.1-zN adjustment layer between the buffer on a
substrate and a first n-type or i-type Al.sub.xGa.sub.1-xN layer in
the functional laminate having an n-type Al.sub.xGa.sub.1-xN layer
(0.ltoreq.x<1). The Al.sub.zGa.sub.1-zN adjustment layer
(0.ltoreq.z<1) is containing p-type impurity, and the Al
composition z is within the range of .+-.0.05 from the Al
composition x of the first Al.sub.xGa.sub.1-xN layer.
EXPLANATION OF REFERENCE NUMERALS
[0095] 100: Semiconductor device [0096] 1: Substrate [0097] 1a:
Sapphire substrate [0098] 1b: AlN or AlGaN layer [0099] 2: Buffer
layer [0100] 2a: P-type Al.sub..beta.Ga.sub.1-.beta.N layer [0101]
2b: AlN layer [0102] 3: Functional laminate [0103] 4: N-type
Al.sub.xGa.sub.1-xN layer [0104] 5: P-type impurity containing
Al.sub.zGa.sub.1-zN adjustment layer [0105] 6: Light emitting layer
[0106] 7: P-type Al.sub.yGa.sub.1-yN layer [0107] 8: I-type
Al.sub.wGa.sub.1-wN layer not doped with impurity [0108] 9: P-side
electrode [0109] 10: N-side electrode
* * * * *