U.S. patent application number 09/753590 was filed with the patent office on 2001-05-10 for semiconductor photonic device, method for making the same, and method for forming zno film.
This patent application is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Kadota, Michio.
Application Number | 20010000916 09/753590 |
Document ID | / |
Family ID | 16501851 |
Filed Date | 2001-05-10 |
United States Patent
Application |
20010000916 |
Kind Code |
A1 |
Kadota, Michio |
May 10, 2001 |
Semiconductor photonic device, method for making the same, and
method for forming ZnO film
Abstract
A semiconductor photonic device contains a substrate; a ZnO
buffer layer provided on the substrate; and a semiconductor
compound provided on the ZnO buffer layer and represented by
In.sub.xGa.sub.yAl.sub.zN wherein x+y+z=1, 0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1 and 0.ltoreq.z.ltoreq.1, wherein the ZnO buffer
layer has a lattice constant of about 5.2070 .ANG. or more in the
c-axis direction.
Inventors: |
Kadota, Michio; (Kyoto-shi,
JP) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Assignee: |
Murata Manufacturing Co.,
Ltd.
|
Family ID: |
16501851 |
Appl. No.: |
09/753590 |
Filed: |
January 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09753590 |
Jan 2, 2001 |
|
|
|
09342869 |
Jun 29, 1999 |
|
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Current U.S.
Class: |
257/43 ; 257/103;
257/97; 438/47 |
Current CPC
Class: |
H01L 33/007
20130101 |
Class at
Publication: |
257/43 ; 257/97;
257/103; 438/47 |
International
Class: |
H01L 021/00; H01L
033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 21, 1998 |
JP |
10-205125 |
Claims
What is claimed is:
1. A semiconductor photonic device comprising: a substrate; a ZnO
buffer layer on the substrate; and a semiconductor compound
represented by In.sub.xGa.sub.yAl.sub.zN wherein x+y+z=1,
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1 and 0.ltoreq.z.ltoreq.1 on
the ZnO buffer layer, wherein the ZnO buffer layer has a lattice
constant of about 5.2070 .ANG. or more in the c-axis direction.
2. A semiconductor photonic device according to claim 1, wherein
the ZnO buffer layer has a lattice constant of about 5.21 to 5.28
.ANG. in the c-axis direction.
3. A semiconductor photonic device according to claim 2, wherein
the ZnO buffer layer has a lattice constant of about 3.24 to 3.17
.ANG. in the a-axis direction.
4. A semiconductor photonic device according to claim 4, wherein
the substrate is glass or Si.
5. A semiconductor photonic device according to claim 4, wherein
the semiconductor compound is selected from the group consisting of
GaN, InGaN, InGaN, GaAlN and InGaAlN compounds.
6. A semiconductor photonic device according to claim 5, wherein
the semiconductor compound is selected from the group consisting of
GaN, InGaN, In.sub.0.2Ga.sub.0.8N, Al.sub.0.2Ga.sub.0.8N and
In.sub.0.2Ga.sub.0.2Al.sub.0.6N.
7. A semiconductor photonic device according to claim 1, wherein
the substrate is glass or Si.
8. A semiconductor photonic device according to claim 1, wherein
the semiconductor compound is selected from the group consisting of
GaN, InGaN, InGaN, GaAlN and InGaAlN compounds.
9. A method for making the semiconductor photonic device of claim 1
which comprises adjusting the lattice constant in the c-axis
direction of the ZnO buffer layer such that when the lattice
constant in the a-axis direction of the semiconductor compound is
smaller than the lattice constant in the a-axis direction of a ZnO
single crystal, the lattice constant in the c-axis direction of the
ZnO buffer layer is made larger than the lattice constant in the
c-axis direction of the ZnO single crystal, and when the lattice
constant in the a-axis direction of the semiconductor compound is
larger than the lattice constant in the a-axis direction of a ZnO
single crystal, the lattice constant in the c-axis direction of the
ZnO buffer layer is made smaller than the lattice constant in the
c-axis direction of the ZnO single crystal, whereby the lattice
constant in the a-axis direction of the ZnO buffer layer is made
nearly equal to the lattice constant in the a-axis direction of the
semiconductor compound.
10. A method for making the semiconductor photonic device according
to claim 9, wherein the ZnO buffer layer lattice constant is
adjusted to about 5.2070 .ANG. or more in the c-axis direction.
11. A method for making the semiconductor photonic device according
to claim 10, wherein ZnO buffer layer is formed by sputtering and
the lattice constant in the c-axis direction of the ZnO buffer
layer is adjusted by controlling sputtering parameters of the ZnO
sputtering process.
12. A method for making the semiconductor photonic device according
to claim 11, wherein the sputtering parameter controlled is gas
flow rate or temperature or both.
13. A method for making the semiconductor photonic device according
to claim 9, wherein ZnO buffer layer is formed by sputtering and
the lattice constant in the c-axis direction of the ZnO buffer
layer is adjusted by controlling sputtering parameters of the ZnO
sputtering process.
14. A method for making the semiconductor photonic device according
to claim 13, wherein the sputtering parameter controlled is gas
flow rate or temperature or both.
15. A method for forming a ZnO film on a substrate comprising
forming said film by sputtering and adjusting the lattice constant
in the a-axis direction of the ZnO film by controlling the lattice
constant in the c-axis direction of the ZnO film.
16. A method for forming a ZnO film on a substrate according to
claim 15, wherein the sputtering parameter controlled is gas flow
rate or temperature or both.
17. A method for forming a ZnO film on a substrate according to
claim 16, wherein the ZnO lattice constant is adjusted to about
5.2070 .ANG. or more in the c-axis direction.
18. A method for forming a ZnO film on a substrate according to
claim 15, wherein the ZnO lattice constant is adjusted to about
5.2070 .ANG. or more in the c-axis direction.
Description
BACKGROUND OF THE INVENTION
1. 1. Field of the Invention
2. The present invention relates to a semiconductor photonic
device, a method for making the same, and a method for forming a
ZnO film. In particular, the present invention relates to a
semiconductor photonic device using a Group III-V compound, such as
GaN, InGaN, GaAlN or InGaAlN and a method for making the same.
Also, the present invention relates to a method for making a ZnO
film formed on a substrate, such as a Si substrate or a glass
substrate.
3. 2. Description of the Related Art
4. As materials for semiconductor photonic devices, such as
light-emitting diodes (LEDs) and semiconductor laser diodes (LDs)
which emit blue or ultraviolet light, Group III-V semiconductor
compounds represented by the general formula
In.sub.xGa.sub.yAl.sub.zN wherein x+y+z=1, 0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1, and 0.ltoreq.z.ltoreq.1 are known. Since the
semiconductor compounds are of direct transition type, they have
high luminescent efficiency. Furthermore, since the luminescent
wavelength can be controlled by the indium content, they have
attracted attention as materials for photonic devices.
5. Since it is difficult to make a large In.sub.xGa.sub.yAl.sub.zN
single crystal, a so-called heteroepitaxial growth process in which
an In.sub.xGa.sub.yAl.sub.zN film is grown on a substrate composed
of a different material is used in the production of the crystal
film, and it is typically grown on a C-plane sapphire substrate.
Because the C-plane sapphire substrate is expensive and there
exists a large lattice mismatch between the C-plane sapphire
substrate and the In.sub.xGa.sub.yAl.sub.zN film (for example, the
lattice mismatch rate for GaN ranges to 16.1%), many crystal
defects with a defect density of 10.sup.8/cm.sup.2 to
10.sup.11/cm.sup.2 are inevitably formed in the grown crystal, and
thus a high-quality crystal film having high crystallinity cannot
be formed.
6. In order to solve this problem, a proposed method for obtaining
a crystal with decreased defects by reducing lattice mismatch when
In.sub.xGa.sub.yAl.sub.zN is deposited on a C-plane sapphire
substrate is to provide a polycrystalline or amorphous AlN buffer
layer or a low-temperature-deposited GaN buffer layer on the
C-plane sapphire substrate. Since this method can reduce the
lattice mismatch not only between the C-plane sapphire substrate
and the buffer layer but also between the buffer layer and the
In.sub.xGa.sub.yAl.sub.zN, a crystal film with reduced defects can
be formed. The C-plane sapphire substrate used in this method,
however, is expensive and since the configuration is complicated,
higher production costs are unavoidable.
7. A SiC substrate has been studied and has small lattice mismatch
(for example, the lattice mismatch rate for GaN is 3.5%). The SiC
substrate, however, is considerably expensive compared to the
C-plane sapphire substrate (its price is approximately ten times
the price of the C-plane sapphire substrate).
8. Accordingly, production of a semiconductor photonic device using
an inexpensive Si or glass substrate has been desired. A possible
method is depositing a ZnO buffer layer on a Si or glass substrate,
and providing a GaN layer on the ZnO buffer layer followed by
forming an In.sub.xGa.sub.yAl.sub.zN semiconductor layer for
emitting light on the GaN layer (or providing an
In.sub.xGa.sub.yAl.sub.zN semiconductor layer containing a GaN
layer) Because the lattice constant in the a-axis direction
(hereinafter referred to as "a-constant") and the lattice constant
in the c-axis direction (herein after referred to as "c-constant")
of the ZnO single crystal are nearly equal to the a-constant and
the c-constant, respectively, of GaN, a GaN layer with reduced
lattice defects is considered to be formed. The ZnO crystal is
hexagonal and the crystal grows so that the c-axis direction is
perpendicular to the surface of the Si or glass substrate whereas
the a-axis direction is parallel to the surface of the Si or glass
substrate.
1TABLE 1 Crystal a-constant c-constant GaN 3.1860 .ANG. 5.1780
.ANG. ZnO 3.24982 .ANG. 5.20661 .ANG.
9. A device having a ZnO buffer layer provided on a Si substrate
has a substrate cost which is approximately one-tenth that of a
C-plane sapphire substrate and thus cost reduction can be achieved.
Since the Si substrate can have conductivity in contrast to
insulating characteristics of the C-plane sapphire, a p-type
electrode and a n-type electrode can be provided on the upper face
and the lower face and the device configuration can be
simplified.
10. A lattice mismatch rate of 2% is still present between the Zno
buffer layer formed on the Si substrate and GaN layer, as shown in
Table 1, although the rate is smaller than that in a combination of
GaN and a C-plane sapphire substrate or a SiC substrate. Thus,
defects formed by the lattice mismatch still remain.
SUMMARY OF THE INVENTION
11. The present invention is directed to solve the above-explained
technical problems. The semiconductor photonic device comprises: a
substrate; a ZnO buffer layer provided on the substrate; and a
semiconductor compound provided on the ZnO buffer layer and
represented by In.sub.xGa.sub.yAl.sub.zN wherein x+y+z=1,
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1 and 0.ltoreq.z.ltoreq.1,
wherein the ZnO buffer layer has a lattice constant of about 5.2070
.ANG. or more in the c-axis direction.
12. It is preferable that the ZnO buffer layer has a lattice
constant of about 5.21 to 5.28 .ANG. in the c-axis direction and a
lattice constant of about 3.24 to 3.17 .ANG. in the a-axis
direction.
13. The method for making a semiconductor photonic device which
comprises a semiconductor compound represented by
In.sub.xGa.sub.yAl.sub.zN wherein x+y+z=1, 0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1 and 0.ltoreq.z.ltoreq.1, comprises when the
lattice constant in the a-axis direction of the compound
semiconductor formed on the Zn buffer layer is smaller than the
lattice constant in the a-axis direction of a ZnO single crystal,
the lattice constant in the c-axis direction of a ZnO buffer layer
is adjusted so as to be larger than the lattice constant in the
c-axis direction of the ZnO single crystal, and when the lattice
constant in the a-axis direction of the semiconductor compound
formed on the Zn buffer layer is larger than the lattice constant
in the a-axis direction of the ZnO single crystal, the lattice
constant in the c-axis direction of the ZnO buffer layer is
adjusted so as to be smaller than the lattice constant in the
c-axis direction of the ZnO single crystal, so that the lattice
constant in the a-axis direction of the ZnO buffer layer is nearly
equal to the lattice constant in the a-axis direction of the
semiconductor compound.
14. The method forms a ZnO film on a substrate in which the lattice
constant in the a-axis direction of the ZnO film is controlled by
the lattice constant in the c-axis direction of the ZnO film.
15. For the purpose of illustrating the invention, there is shown
in the drawings several forms which are presently preferred, it
being understood, however, that the invention is not limited to the
precise arrangements and instrumentalities shown.
BRIEF DESCRIPTION OF THE DRAWINGS
16. FIG. 1 is a cross-sectional view of a configuration of a
semiconductor photonic device in accordance with an embodiment of
the present invention.
17. FIG. 2 is an outline view showing depositing a ZnO buffer layer
on a Si substrate using a sputtering system.
18. FIG. 3 is a graph showing the relationship between the
c-constant of a ZnO buffer layer formed on a Si substrate and the
gas flow rate ratio S(O.sub.2)/[S(Ar)+S(O.sub.2)].
19. FIG. 4 is a graph showing the relationship between the
a-constant and the c-constant of a ZnO buffer layer formed on a Si
substrate.
20. FIG. 5 is an isometric view showing a configuration of a
semiconductor photonic device in accordance with another embodiment
of the present invention.
21. FIG. 6 is an isometric view showing a configuration of a
semiconductor photonic device in accordance with another embodiment
of the present invention.
22. FIG. 7 is a graph showing the relationship between the
a-constant and the composition of In.sub.xGa.sub.1-xN.
23. FIG. 8 is a graph showing the relationship between the
a-constant and the composition of In.sub.xGa.sub.1-xN.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
24. Direct control of the lattice constant in the a-axis direction
of the ZnO film deposited on a Si or glass substrate has been
considered to be difficult due to the effects of the lattice
constant of the substrate. In the method for forming the ZnO film
in accordance with the present invention, the lattice constant in
the a-axis direction of the ZnO film can be controlled by the
lattice constant in the c-axis direction of the ZnO film. The
lattice constant in the c-axis direction of the ZnO film can be
controlled by controlling parameters for depositing the ZnO
film.
25. This method is applicable to a method for making a
semiconductor photonic device using a semiconductor compound
represented by In.sub.xGa.sub.yAl.sub.zN wherein x+y+z=1,
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1 and 0.ltoreq.z.ltoreq.1.
If the lattice constant in the a-axis direction of the
semiconductor compound formed on a Zn buffer layer is smaller than
the lattice constant in the a-axis direction of a ZnO single
crystal, the lattice constant in the c-axis direction of a ZnO
buffer layer can be adjusted so as to be larger than the lattice
constant in the c-axis direction of the ZnO single crystal. In
contrast, if the lattice constant in the a-axis direction of the
semiconductor compound formed on the Zn buffer layer is larger than
the lattice constant in the a-axis direction of the ZnO single
crystal, the lattice constant in the c-axis direction of the ZnO
buffer layer can be adjusted so as to be smaller than the lattice
constant in the c-axis direction of the ZnO single crystal. Since
the lattice constant in the a-axis direction of the ZnO buffer
layer is close to the lattice constant in the a-axis direction of
the semiconductor compound, a semiconductor compound having high
crystallinity can be formed on the ZnO buffer layer.
26. As an actual application, a ZnO buffer layer having a lattice
constant in the c-axis direction of 5.2070 .ANG. or more is formed
on a substrate and a GaN layer is formed on the ZnO buffer layer in
a semiconductor photonic device using a semiconductor compound
represented by In.sub.xGa.sub.yAl.sub.zN wherein x+y+z=1,
0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1 and
0.ltoreq.z.ltoreq.1.
27. When the lattice constant in the c-axis direction of the Zno
buffer layer is controlled to be about 5.2070 .ANG. or more, the
lattice constant in the a-axis direction of the ZnO buffer layer
can be controlled to be smaller than the lattice constant in the
a-axis direction of the ZnO single crystal. Since the difference
between the lattice constant in the a-axis direction of the ZnO
buffer layer and the lattice constant of the GaN layer can be
reduced compared to conventional methods, the lattice mismatch
between the ZnO buffer layer and the GaN layer can be reduced.
28. When the lattice constant in the c-axis direction of the ZnO
buffer layer is in a range of about 5.21 to 5.28 .ANG., the lattice
constant in the a-axis direction is controlled to a range from
about 3.24 to 3.17 .ANG., which is closer to the lattice constant
of the GaN layer.
29. FIG. 1 shows a semiconductor photonic device 1 having a double
heterojunction configuration in accordance with an embodiment of
the present invention, and represents a light emitting diode or a
surface-emitting laser diode provided with an InGaN layer 6 as a
luminescent layer. In the semiconductor photonic device 1, a ZnO
buffer layer 3 having small specific resistivity is deposited on a
conductive Si substrate 2, and an n-type GaN layer 4, an n-type
AlGaN layer 5, an InGaN layer (luminescent layer) 6, a p-type AlGaN
layer 7 and a p-type GaN layer 8 are deposited on the ZnO buffer
layer 3 in that order. The n-type GaN layer 4, the n-type AlGaN
layer 5, the InGaN layer (luminescent layer) 6, the p-type AlGaN
layer 7 and the p-type GaN layer 8 form a double heterojunction
configuration. Furthermore, an n-type electrode 9 is provided on
the entire lower surface of the Si substrate 2 and a p-type
electrode 10 is partially provided on the upper surface of the
p-type GaN layer 8. When a voltage is applied between the p-type
electrode 10 and the n-type electrode 9, a current is injected into
the InGaN layer 6 from the p-type electrode 10 to emit light, and
the light emitted from the InGaN layer 6 emerges from the region
not provided with the p-type electrode 10 on the p-type GaN layer 8
toward the exterior.
30. In such a semiconductor photonic device 1 as described in the
conventional example, it is important to reduce lattice mismatch
between the ZnO buffer layer 3 formed on the Si substrate 2 and the
n-type GaN layer 4 as much as possible. Thus, the ZnO buffer layer
3 is formed as described below in this embodiment of the present
invention.
31. The ZnO buffer layer 3 is formed on the Si substrate 2 by a
sputtering process rather than an evaporation process, a CVD
process or an ion plating process. In a sputtering system 11 for
depositing the ZnO buffer layer 3, a cathode 13 and an anode 14 are
provided in a chamber 12, Zn or ZnO as a target 15 is provided on
the cathode 13 and the Si substrate 2 is placed on the anode 14.
Furthermore, a pipe 16 for introducing Ar gas, a pipe 17 for
introducing O.sub.2 gas and an exhaust duct 18 are provided with
the chamber 12. The flow rate of the Ar gas and the O.sub.2 gas can
be controlled by regulating valves 19 and 20. The sputtering system
11 has a temperature controlling unit (not shown in the drawing)
for controlling the substrate-heating temperature Tc constant.
32. The Ar gas and the O.sub.2 gas are introduced at given flow
rates into the chamber 12 while the gas in the chamber 12 is
exhausted through the exhaust duct so as to maintain the chamber at
a constant pressure. While the substrate is held at a constant
predetermined temperature, a radio frequency voltage is applied
between the anode 14 and the cathode 13 to generate plasma between
electrodes 13 and 14. Plasma ions 21 collide with the target to
discharge Zn or ZnO 22. ZnO discharged from the target or ZnO which
is formed by the reaction Zn discharged from the target with the
O.sub.2 gas is deposited on the surface of the Si substrate 2 to
form a polycrystalline ZnO buffer layer 3.
33. FIG. 3 shows the change in the c-constant of the ZnO buffer
layer 3 with respect to the ratio S(O.sub.2)/[S(Ar)+S (O.sub.2)]
wherein S(O.sub.2) is the flow rate of the O.sub.2 gas and S(Ar) is
the flow rate of the Ar gas when the ZnO buffer layer 3 is formed
on the surface of the Si substrate 2. The flow rate St in FIG. 3
indicates the total flow rate S(Ar)+S(O.sub.2) . FIG. 4 shows the
relationship between the a-constant and the c-constant of the ZnO
buffer layer 3 formed on the Si substrate 2.
34. Since the a-constant and the c-constant of the single crystal
ZnO is 3.24982 .ANG. and 5.20661 .ANG., respectively (the lattice
constants of the single crystal ZnO are shown by triangles in FIG.
4; refer to Table 1), and the a-constant of the GaN layer is 3.1860
.ANG. (the lattice constant of GaN is shown by a square in FIG. 4;
refer to Table 1), the a-constant of the ZnO buffer layer 3 can be
close to the a-constant of the GaN layer 4 rather than the single
crystal ZnO by controlling the c-constant of the ZnO buffer layer 3
to about 5.2070 .ANG. or more, according to FIG. 4. In particular,
the c-constant of the ZnO buffer layer 3 is controlled to be about
5.21 to 5.28 .ANG. so that the a-constant of the ZnO buffer layer 3
is about 3.17 to 3.24 .ANG. which is close to the a-constant of the
GaN layer 4. More particularly, the a-constant of the ZnO buffer
layer 3 can be substantially equal to the a-constant of the GaN
layer 4 when the c-constant of the ZnO buffer layer 3 is
approximately 5.26 .ANG..
35. The data shown in FIG. 3 demonstrates that the c-constant of
the ZnO buffer layer 3 can be controlled within the above-described
desired range when the gas flow rate St=S(Ar)+S(O.sub.2), the gas
flow rate ratio S(O.sub.2)/[S(Ar)+S(O.sub.2)] and the substrate
heating temperature Tc are controlled. In the sputtering system 11
used for obtaining the data in FIG. 3, for example, when the gas
flow rate St=S(Ar)+S(O.sub.2)=30 scam and when the substrate
heating temperature Ta=approximately 400.degree. C., the gas flow
rate ratio S(O.sub.2)/[S(Ar)+S(O.sub.2)] becomes approximately 50%.
Thus, the c-constant of the ZnO buffer layer 3 can be controlled to
be approximately 5.262 .ANG., and the corresponding a-constant can
be controlled to be near the a-constant, 3.1860 .ANG., of the GaN
layer 4.
36. The relationship between the c-constant and the a-constant of
the ZnO buffer layer 3 is impartial although the relationship
between the c-constant of the ZnO buffer layer 3 and the control
parameters of the film deposition system varies with the type of
the system. Thus, the a-constant of the ZnO buffer layer 3 can be
made close to the a-constant of the GaN layer 4 by properly
controlling the parameters of the deposition system so that the
c-constant of the Zno buffer layer 3 is a desired value.
37. (Second Embodiment)
38. The present invention is also applicable to devices other than
the semiconductor photonic device having the double heterojunction
configuration of the InGaN layer 6 as shown in FIG. 1. For example,
as a semiconductor photonic device 31 shown in FIG. 5, a ZnO buffer
layer 33 may be deposited on a Si substrate 32, an n-type GaN layer
34 and a p-type GaN layer 35 may be deposited, an n-type electrode
36 may be formed on the lower surface of the Si substrate 32 and a
p-type electrode 27 and may be formed on the p-side GaN layer 35.
Also, a luminescent device may have a configuration in which a ZnO
buffer layer, a low-temperature-deposited GaN buffer layer, an
n-type GaN layer and a p-type GaN layer are deposited on a glass
substrate, although not shown in the drawing.
39. (Third Embodiment)
40. The device may be a semiconductor photonic device 41 such as a
laser diode or an edge emitting type light emitting diode, as shown
in FIG. 6, in which a ZnO buffer layer 43 is formed on a Si
substrate 42, an n-type GaN clad layer 44, a p-type GaN active
layer 45, a p-type GaN clad layer 46 are deposited, a SiO.sub.2
film 47 is formed on the region other than the center of the p-type
GaN clad layer 46, a p-type electrode 48 is provided over the
SiO.sub.2 film 47 and the p-type GaN clad layer 46, and an n-type
electrode 49 is provided on the lower surface of the Si substrate
42.
41. (Fourth Embodiment)
42. Although GaN is formed on a ZnO film in the above embodiments,
the present invention is also applicable to a case in which InGaN,
InAlGaN, or AlGaN is directly deposited on a ZnO film. For example,
since the a-constant of In.sub.0.2Ga.sub.0.8N is approximately 3.26
.ANG., which is derived from the relationship between the
a-constant and the composition of In.sub.xGa.sub.1-xN shown in FIG.
7, the a-constant of the ZnO film can be close to the a-constant of
the In.sub.0.2Ga.sub.0.8N when the c-constant of the Zno film is
5.155 .ANG. to 5.205 .ANG., according to the graph shown in FIG.
4.
43. (Fifth Embodiment)
44. Since the a-constant of Al.sub.0.2Ga.sub.0.8N is approximately
3.176 .ANG., which is derived from the relationship between the
a-constant and the composition of Al.sub.xGa.sub.1-xN shown in FIG.
8, the a-constant of the ZnO film can be close to the a-constant of
the Al.sub.0.2Ga.sub.0.8N when the c-constant of the ZnO film is
5.27 .ANG. to 5.28 .ANG., according to the graph shown in FIG.
4.
45. (Sixth Embodiment)
46. Since the a-constant of In.sub.0.2Al.sub.0.2Ga.sub.0.6N is
approximately 3.245 .ANG., which is derived from the relationship
between the a-constant and the composition of
In.sub.xAl.sub.yGa.sub.2N (wherein x+y+z=1) shown in FIG. 9, the
a-constant of the ZnO film can be closed to the a-constant of the
In.sub.0.2Al.sub.0.2Ga.sub.0.6N when the c-constant of the ZnO film
is 5.19 .ANG. to 5.22 .ANG., according to the graph shown in FIG.
4. In this embodiment, a case wherein x=0.2, y=0.2, and z=0.6 is
described. An optimized c-axis length of ZnO is derived from the
graphs shown in FIGS. 4 and 9 in any other case and control is
performed so as to achieve the optimized value.
47. While preferred embodiments of the invention have been
disclosed, various modes of carrying out the principles disclosed
herein are contemplated as being within the scope of the following
claims. Therefore, it is understood that the scope of the invention
is not to be limited except as otherwise set forth in the
claims.
* * * * *