U.S. patent application number 13/468486 was filed with the patent office on 2012-08-30 for light-emitting semiconductor device using group iii nitrogen compound.
This patent application is currently assigned to Toyoda Gosei Co., Ltd.. Invention is credited to Makoto Asai, Hisaki Kato, Masayoshi Koike, Katsuhide Manabe, Michinari Sassa, Naoki Shibata, Shiro Yamazaki.
Application Number | 20120217510 13/468486 |
Document ID | / |
Family ID | 27465950 |
Filed Date | 2012-08-30 |
United States Patent
Application |
20120217510 |
Kind Code |
A1 |
Manabe; Katsuhide ; et
al. |
August 30, 2012 |
LIGHT-EMITTING SEMICONDUCTOR DEVICE USING GROUP III NITROGEN
COMPOUND
Abstract
A method of producing a light-emitting semiconductor device of a
group III nitride compound includes forming a high carrier
concentration N.sup.+-layer satisfying the formula
(Al.sub.x3Ga.sub.1-x3).sub.y3In.sub.1-y3N, wherein
0.ltoreq.x3.ltoreq.1, 0.ltoreq.y3.ltoreq.1 and
0.ltoreq.x3+y3.ltoreq.1, forming an emission layer of a group III
nitride compound semiconductor satisfying the formula,
Al.sub.x1Ga.sub.y1In.sub.1-x1-y1N, where 0.ltoreq.x1.ltoreq.1,
0.ltoreq.y1.ltoreq.1 and 0.ltoreq.x1+y1.ltoreq.1 on the high
carrier concentration layer N.sup.+-layer, and forming a P-layer of
a P-type conduction, on the emission layer, the P-layer including
aluminum gallium nitride satisfying the formula
Al.sub.x2Ga.sub.1-x2N, wherein 0.ltoreq.x2.ltoreq.1.
Inventors: |
Manabe; Katsuhide;
(Aichi-ken, JP) ; Kato; Hisaki; (Aichi-ken,
JP) ; Sassa; Michinari; (Aichi-ken, JP) ;
Yamazaki; Shiro; (Aichi-ken, JP) ; Asai; Makoto;
(Aichi-ken, JP) ; Shibata; Naoki; (Aichi-ken,
JP) ; Koike; Masayoshi; (Nakashima-gun, JP) |
Assignee: |
Toyoda Gosei Co., Ltd.
Aichi-ken
JP
|
Family ID: |
27465950 |
Appl. No.: |
13/468486 |
Filed: |
May 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12929231 |
Jan 10, 2011 |
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13468486 |
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12003173 |
Dec 20, 2007 |
7867800 |
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12929231 |
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11328079 |
Jan 10, 2006 |
7332366 |
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12003173 |
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11143664 |
Jun 3, 2005 |
7138286 |
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11328079 |
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09783035 |
Feb 15, 2001 |
7001790 |
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11143664 |
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09379621 |
Aug 24, 1999 |
6265726 |
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09783035 |
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08806646 |
Feb 26, 1997 |
6005258 |
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09379621 |
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08408164 |
Mar 21, 1995 |
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08806646 |
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Current U.S.
Class: |
257/76 ;
257/E33.025; 257/E33.028; 438/47 |
Current CPC
Class: |
H01L 33/007 20130101;
H01L 33/325 20130101; H01L 33/385 20130101; H01L 33/0025 20130101;
H01L 33/40 20130101; H01L 33/32 20130101; H01L 33/38 20130101; H01L
33/382 20130101 |
Class at
Publication: |
257/76 ; 438/47;
257/E33.028; 257/E33.025 |
International
Class: |
H01L 33/32 20100101
H01L033/32; H01L 33/40 20100101 H01L033/40 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 1994 |
JP |
76514/1994 |
Apr 28, 1994 |
JP |
113484/1994 |
Jul 28, 1994 |
JP |
197914/1994 |
Claims
1. A method of producing a light-emitting semiconductor device of a
group III nitride compound, said method comprising: forming a high
carrier concentration N.sup.+-layer satisfying formula
(Al.sub.x3Ga.sub.1-x3).sub.y3In.sub.1-y3N, wherein
0.ltoreq.x3.ltoreq.1, 0.ltoreq.y3.ltoreq.1, and
0.ltoreq.x3+y3.ltoreq.1; forming an emission layer of a group III
nitride compound semiconductor satisfying formula,
Al.sub.x1Ga.sub.y1In.sub.1-x1-y1N, where
0.ltoreq.x1.ltoreq.y1.ltoreq.1, 0.ltoreq.y1.ltoreq.1, and
0.ltoreq.x1+y1.ltoreq.1, on said high carrier concentration layer
N.sup.+-layer; and forming a P-layer of a P-type conduction, on
said emission layer, said P-layer comprising aluminum gallium
nitride satisfying formula Al.sub.x2Ga.sub.1-x2N, wherein
0.ltoreq.x2.ltoreq.1.
2. A semiconductor light emitting device, comprising: an n-type
clad layer consisting of a gallium nitride base compound
semiconductor; an active layer consisting of a gallium nitride
based compound semiconductor, said active layer comprising a
material having a band gap energy smaller than that of said n-type
clad layer; and a p-type clad layer consisting of a gallium nitride
based compound semiconductor, said p-type clad layer comprising a
material having a band gap energy greater than that of said active
layer, and sandwiching said active layer accompanying with said
n-type clad layer, wherein said materials of said n-type clad layer
and said p-type clad layer are selected as to make the band gap
energy of said n-type clad layer smaller than the band gap energy
of said p-type clad layer.
3. A semiconductor light emitting device, comprising: a substrate;
and GaN-type compound semiconductor layers stacked on the
substrate, the GaN-type layers including: at least one active
layer; at least one n-type layer; and at least one p-type layer,
wherein a band gap energy of the one n-type layer is smaller than a
band gap energy of the one p-type layer.
Description
[0001] The present applicant is a Divisional application of U.S.
patent application Ser. No. 12/929,231, filed on Jan. 10, 2011,
which is a Divisional application of U.S. patent application Ser.
No. 12/003,173 filed on Dec. 20, 2007, which is a Divisional
application of U.S. patent application Ser. No. 11/328,079 filed on
Jan. 10, 2006 now U.S. Pat. No. 7,332,366, which is a Divisional
application of U.S. patent application Ser. No. 11/143,664 filed on
Jun. 3, 2005 now U.S. Pat. No. 7,138,286, which in turn is a
Divisional application of U.S. patent application Ser. No.
09/783,035 filed on Feb. 15, 2001, now U.S. Pat. No. 7,001,790,
which in turn is a Divisional application of U.S. patent
application Ser. No. 09/379,621 filed on Aug. 24, 1999, now U.S.
Pat. No. 6,256,726, which in turn is a Divisional application of
U.S. patent application Ser. No. 08/806,646 filed on Feb. 26, 1997,
now U.S. Pat. No. 6,005,258, which in turn is a Continuation
application of U.S. patent application Ser. No. 08/408,164 filed
Mar. 21, 1995.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a light-emitting
semiconductor device that emits blue light and uses a group 111
nitrogen compound.
[0004] 2. Description of the Prior Art
[0005] It has been known that an aluminum gallium indium nitride
(AlGaInN) compound semiconductor may be used to obtain a
light-emitting diode (LED) which emits blue light. This
semiconductor device is useful because of its high luminous
efficiency resulting from direct electron transition and because of
its ability to emit blue light, which is one of the three primary
colors.
[0006] Irradiating an electron beam into an i-layer to which
magnesium (Mg) is doped and heat treatment is carried out enables
the i-layer to have a p-type layer of the AlGaInN semiconductor
device. As a result, a LED with a double hetero p-n junction
structure includes an aluminum gallium nitride (AlGaN) p-layer, a
zinc (Zn) doped indium gallium nitride (InGaN) emission layer and
an AlGaN n-layer, becomes useful instead of conventional LED of
metal insulator semiconductor (MIS) structure which includes an
n-layer and a semi-insulating i-layer.
[0007] The conventional LED with a double hetero p-n junction
structure is doped with Zn as an emission center. Luminous
intensity of this type of LED has been improved fairly. Still,
there exists a problem in luminous efficiency and further
improvement is necessary.
[0008] The emission mechanism of a LED with an emission layer doped
with only Zn, or only an acceptor impurity, as the emission center
is electron transition between conduction band and acceptor energy
levels. However, a large difference of their energy levels makes
recombination of electrons through deep levels dominant which deep
level recombination does not contribute to emission. This results
in lower luminous intensity. Further, the wavelength of light from
the conventional LED is about 380 to 440 nm, or shorter than that
of pure blue light.
[0009] Further, the emission layer doped with Zn as the emission
center exhibits semi-insulative characteristics. Its emission
mechanism is explained by recombination of an electron through
acceptor level injected from an n-layer and a hole injected from a
p-layer. However, the diffusion length of the hole is shorter than
that of the electron. It results in high ratio of holes
disappearing in a non-emission process before recombination of the
hole and electron occurs in the emission layer. This phenomenon
impedes higher luminous intensity.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to solve the above
problem and improve the luminous intensity of the LED of AlGaInN
semiconductor, or obtain enough spectrum to emit a purer blue
light.
[0011] According to the first aspect of the invention, there is
provided a light-emitting semiconductor device comprising:
[0012] an n-layer with n-type conduction of group II-nitride
compound semiconductor satisfying the formula
Al.sub.x3Ga.sub.y3In.sub.1-x3-y3N, inclusive of x3=0, y3=0 and
x3=y3=0,
[0013] a p-layer with p-type conduction of group III nitride
compound semiconductor satisfying the formula
Al.sub.x1Ga.sub.ylIn.sub.1-x1-y1N, inclusive of x1=0, y1=0 and
x1=y1=0,
[0014] an emission layer of group III nitride compound
semiconductor satisfying the formula
Al.sub.x2Ga.sub.y2In.sub.1-x2-y2 N, inclusive of x2=0, y2=0 and
x2=y2=0; the junction layer of the n-layer, the p-layer, and the
emission layer being any one of a homo-junction structure, a single
hetero-junction structure, and a double hetero-junction structure;
and
[0015] wherein the emission layer is formed between the n-layer and
the p-layer, and doped with both a donor and an acceptor
impurity.
[0016] It is preferable that the donor impurity is one of the group
IV elements and that the acceptor impurity is one of the group II
elements.
[0017] Preferable combinations of a donor and an acceptor impurity
include silicon (Si) and cadmium (Cd), silicon (Si) and zinc (Zn),
and silicon (Si) and magnesium (Mg), respectively.
[0018] The emission layer can be controlled to exhibit any one of
n-type conduction, semi-insulative, and p-type conduction depending
on the concentration ratio of a donor impurity and an acceptor
impurity doped thereto.
[0019] Further, the donor impurity can be one of the group VI
elements.
[0020] Further, it is desirable to design the composition ratio of
Al, Ga, and In in the n-layer, p-layer, and emission layer to meet
each of the lattice constants of the three layers to an
n.sup.+-layer of high carrier concentration on which the three
layers are formed.
[0021] Further, a double hetero-structure sandwiching of the
emission layer of p-type conduction by the n-layer and p-layer
improves luminous efficiency. Making the concentration of acceptor
impurity larger than that of the donor impurity and processing by
electron irradiation or heat treatment changes the emission layer
to exhibit p-type conduction. Magnesium, an acceptor impurity, is
especially efficient for obtaining p-type conduction.
[0022] Further, doping any combinations of the described acceptor
and donor impurity to an emission layer of p-type conduction also
improves luminous efficiency. The luminous mechanism doped with
acceptor and donor impurities is due to recombination of an
electron at donor level and a hole at the acceptor level. This
recombination occurs within the emission layer, so that luminous
intensity is improved.
[0023] Further, a double hetero-junction structure of a
triple-layer sandwiching the emission layer having a narrower bad
gap by the n-layer and p-layer having a wider band gap improves
luminous intensity. Since the emission layer and the p-layer
exhibit p-type conduction, valence bands of those layers are
successive even without applying external voltage. Consequently,
holes readily highly exist within the emission layer. In contrast,
conduction bands of the n-layer and the emission layer are not
successive without applying an external voltage. Applying a voltage
enables the conduction bands to be successive and electrons to be
injected deeper into the emission layer. Consequently, the number
of injected electrons into the emission layer increases ensuring
recombination with holes and a consequent improvement in luminous
intensity.
[0024] Other objects, features, and characteristics of the present
invention will become apparent upon consideration of the following
description in the appended claims with reference to the
accompanying drawings, all of which form a part of the
specification, and wherein referenced numerals designate
corresponding parts in the various figures.
BRIEF DESCRIPTION OF THE DRAWING
[0025] In the accompanying drawings:
[0026] FIG. 1 is a diagram showing the structure of the LED
embodied in Example 1;
[0027] FIGS. 2 through 7 are sectional views illustrating
successive steps of producing the LED embodied in Example 1;
[0028] FIG. 8 is a diagram showing the structure of the LED
embodied in Example 2;
[0029] FIG. 9 is a diagram showing the structure of the LED
embodied in Example 3;
[0030] FIG. 10 is a diagram showing the structure of the LED
embodied in Example 4;
[0031] FIG. 11 is a diagram showing the structure of the LED
embodied in Example 5;
[0032] FIGS. 12 and 13 are diagrams showing the structure of the
LED embodied in Example 6;
[0033] FIG. 14 is a diagram showing the structure of the LED
embodied in Example 7; and
[0034] FIGS. 15 and 16 are diagrams showing the structure of the
LED embodied in Example 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] The invention will be more fully understood by reference to
the following examples.
Example 1
[0036] FIG. 1 shows a LED 10 embodied in Example 1. It has a
sapphire (Al.sub.2O.sub.3) substrate 1 upon which the following
five layers are consecutively formed: an AlN buffer layer 2; a
silicon (Si) doped GaN n.sup.+-layer 3 of high carrier (n-type)
concentration; a Si-doped (Al.sub.x2Ga.sub.1-x2).sub.y2In.sub.1-y2N
n.sup.+-layer 4 of high carrier (n-type) concentration; a cadmium
(Cd) and Si-doped (Al.sub.x1Ga.sub.1-x1).sub.y1In.sub.1-ylN
emission layer 5; and a Mg-doped
(Al.sub.x2Ga.sub.1-x2).sub.y2In.sub.1-y2N p-layer 6. The AlN layer
2 has 500 .ANG. thickness. The GaN n.sup.+-layer 3 is about 2.0
.mu.m in thickness and has a 2.times.10.sup.18/cm.sup.3 electron
concentration. The n.sup.+-layer 4 is about 2.0 .mu.m in thickness
and has a 2.times.10.sup.18/cm.sup.3 electron concentration. The
emission layer 5 is about 0.5 .mu.m in thickness. The i-layer 6 is
about 1.0 .mu.m in thickness and has a 2.times.10.sup.17/cm.sup.3
hole concentration. Nickel electrodes 7 and 8 are connected to the
p-layer 6 and the n.sup.+-layer 4, respectively. They are
electrically insulated by a groove 9.
[0037] The LED 10 is produced by gaseous phase growth, called metal
organic vapor phase epitaxy referred to as MOVPE hereinafter.
[0038] The gases employed in this process are ammonia (NH.sub.3), a
carrier gas (H.sub.2 or N.sub.2), trimethyl gallium
(Ga(CH.sub.3).sub.3) (TMG hereinafter), trimethyl-1 aluminum
(Al(CH.sub.8).sub.3) (TMA hereinafter), trimethyl indium
(In(CH.sub.3).sub.3) (TMI hereinafter), dimethylcadmium
((Cd(CH.sub.3).sub.2) (DMCd hereinafter), silane (SiH.sub.4),
dlethylzinc ((C.sub.2H.sub.5).sub.2Zn) (DEZ hereinafter) and
biscyclopentadienyl magnesium (Mg(C.sub.5H.sub.5).sub.2)
(CP.sub.2Mg hereinafter).
[0039] The single crystalline sapphire substrate 1, whose main
surface `a` was cleaned by an organic washing solvent and heat
treatment, was placed on a susceptor in a reaction chamber for the
MOVPE treatment. Then the sapphire substrate 1 was etched at
1100.degree. C. by a vapor of H.sub.2 fed into the chamber at a
flow rate of 2 liter/min. under normal pressure for a period of 5
min.
[0040] On the etched sapphire substrate 1, a 500 .ANG. thick AlN
buffer layer 2 was epitaxially formed on the surface `a` under
conditions of lowering the temperature in the chamber to
400.degree. C., keeping the temperature constant, and supplying
H.sub.2, NH.sub.3 and TMA for a period of about 90 sec. at a flow
rate of 20 liter/min., 10 liter/min., and 1.8.times.10.sup.-5
mol/min., respectively. On the buffer layer 2, about a 2.2 .mu.m
thick Si-doped GaN n.sup.+-layer 3 of high carrier concentration
with an electron concentration of about 2.times.10.sup.18/cm.sup.3
was formed under conditions of keeping the temperature of the
sapphire substrate 1 at 1150.degree. C. and supplying H.sub.2,
NH.sub.3, TMG, and diluted silane to 0.86 ppm by H.sub.2 for thirty
minutes at a flow rate of liter/min., 10 liter/min.,
1.7.times.10.sup.-4 mol/min. and 200 ml/min., respectively.
[0041] The following manufacturing process provides for an emission
layer 5 as an active layer, an n.sup.+-layer 4 of high carrier
concentration, and a p-layer 6 as a clad layer; the LED 10 is
designed to emit at a 450 nm wavelength peak in the luminous
spectrum and have luminous centers of Cd and Si.
[0042] On the n.sup.+-layer 3, about a 0.5 .mu.m thick Si-doped
(Al.sub.0.47Ga.sub.0.53).sub.0.9In.sub.0.1N n.sup.+-layer 4 of high
carrier concentration with an electron concentration of
1.times.10.sup.18/cm.sup.3 was formed under conditions of keeping
the temperature of the sapphire substrate 1 at 850.degree. C. and
supplying N.sub.2 or H.sub.2, NH.sub.3, TMG, TMA, TMI, and diluted
silane to 0.86 ppm by H.sub.2 for 60 min. at a flow rate of
liter/min., 10 liter/min., 1.12.times.10.sup.-4 mol/min.,
0.47.times.10.sup.-4 mol/min., 0.1.times.10.sup.-4 mol/min. and
10.times.10.sup.-9 mol/min., respectively.
[0043] On the n.sup.+-layer 4, about a 0.5 .mu.m thick Cd and
Si-doped(Al.sub.0.3Ga.sub.0.7).sub.0.94In.sub.0.06N emission layer
5 was formed under conditions of keeping the temperature of the
sapphire substrate 1 at 850.degree. C. and supplying N.sub.2 or
H.sub.2, NH.sub.3, TMG, TMA, TMI, DMCd, and diluted silane to 0.86
ppm by H.sub.2 for 60 min. at a flow rate of 20 liter/min., 10
liter/min., 1.53.times.10.sup.-4 mol/min., 0.47.times.10.sup.-4
mol/min., 0.02.times.10.sup.-4 mol/min., 2.times.10.sup.-7 mol/min.
and 10.times.10.sup.-9 mol/min., respectively. At this stage, the
layer 5 exhibited high resistivity. The impurity concentrations of
the Cd and the Si doped to the emission layer 5 were
5.times.10.sup.18/cm.sup.3 and 1.times.10.sup.18/cm.sup.3,
respectively.
[0044] On the emission layer 5, about a 1.0 .mu.m thick Mg-doped
(Al.sub.0.47Ga.sub.0.533).sub.0.9In.sub.0.1N p-layer 6 was formed
under conditions of keeping the temperature of the sapphire
substrate 1 at 1000.degree. C. and supplying N.sub.2 or H.sub.2,
NH.sub.3. TMG, TMA, TMI, and CP.sub.2Mg for 120 min. at a flow rate
of 20 liter/min., 10 liter/min., 1.12.times.10.sup.-4 mol/min.
0.47.times.10.sup.-4 mol/min., 0.1.times.10.sup.-4 mol/min. and
2.times.10.sup.-4 mol/min., respectively. Resistivity of the
p-layer 6 was 10.sup.8 .OMEGA.cm or more exhibiting insulative
characteristics. The impurity concentration of the Mg-doped into
the p-layer 6 was 1.times.10.sup.20/cm.sup.3.
[0045] Then, electron rays were uniformly irradiated into the
p-layer 6 using a reflective electron beam diffraction device. The
irradiation conditions were set at 10 KV for the accelerating
voltage, 1 .mu.A for the sample current, 0.2 mm/sec. for the speed
of the beam scanning, 60 .mu.m.phi. for the beam aperture, and at
5.0.times.10.sup.-5 Torr vacuum. This irradiation changed the
insulative p-layer 6 into a p-type conductive semiconductor with a
hole concentration of 2.times.10.sup.17/cm.sup.3 and a resistivity
of 2 .OMEGA.cm. Thereby, a wafer with multi-structural layers was
obtained as shown in FIG. 2.
[0046] The following FIGS. 3 to 7 show sectional views of an
individual element on the wafer. In actual practice and in
accordance with industry custom, a wafer with a large number of
elements thereon is treated by the following process and divided or
diced into individual elements.
[0047] A 2000 .ANG. thick SiO.sub.2 layer 11 was formed on the
p-layer 6 by sputtering. Then, the layer 11 was coated with a
photoresist layer 12. Two selected parts or areas of the
photoresist layer 12, named A and B, were removed by
photolithography as shown in FIG. 3. The part or area A is an
electrode forming part which corresponds to a place where a hole
15, shown in FIG. 5, is formed extending to and into the
n.sup.--layer 4 of high carrier concentration. The part or area B
corresponds to a place where a groove 9 shown in FIGS. 5 and 6 is
formed for insulating or electrically insulating the part or area A
from an electrode in contact with the p-layer 5.
[0048] As shown in FIG. 4, two parts of the SiO.sub.2 layer 11
which were not covered with the photoresist layer 12 were etched
off by an etching liquid such as hydrofluoric acid. Then, the
exposed part of the following successive three layers from the
surface of the device, the p-layer 6, the emission layer 5, and the
upper part of the n.sup.+-layer 4 of high carrier concentration,
were removed by dry etching, or supplying a high-frequency power
density of 0.44 W/cm.sup.2 and BCl.sub.3 gas of 10 ml/min. at a
vacuum degree of 0.04 Torr as shown in FIG. 5. After that, dry
etching with argon (Ar) was carried out on the device.
Consequently, a hole 15 for forming an electrode reaching the
n.sup.+-layer 4 of high carrier concentration and a groove 9 for
insulation are formed.
[0049] The SiO.sub.2 layer 11 remaining on the p-layer 6 was
removed by hydrofluoric acid as shown in FIG. 6. A nickel (Ni)
layer 13 was laminated on the entire surface of the device by vapor
deposition. Thus, the so-formed Ni layer 13 in the hole 15 is in
electrical contact with the n.sup.+-layer 4 of high carrier
concentration. A photoresist 14 was deposited on the Ni layer 13
and, then, was selectively etched off by photolithography as shown
in FIG. 7 leaving patterns of configuration for electrodes
connected to the n.sup.+-layer 4 of high carrier concentration and
the p-layer 6, respectively.
[0050] Using the photoresist 14 as a mask, the exposed part or area
of the Ni layer 13 from the photoresist 14 was etched off by an
etching liquid such as nitric acid. At this time, the nickel layer
13 laminated in the groove 9 was also removed completely. Then, the
photoresist layer 14 was removed by a photoresist removal liquid
such as acetone. There were formed two electrodes, the electrode 8
for the n.sup.+-layer 4 of high carrier concentration and the
electrode 7 for the p-layer 6. A wafer treated with the
above-mentioned process was divided or diced into each element
which shows a gallium nitride light-emitting diode with a p-n
junction structure as shown in FIG. 1.
[0051] The obtained LED 10 was found to have a luminous intensity
of 100 mcd and a wavelength of 450 nm by driving current of 20
mA.
[0052] The emission layer 5 preferably contains impurity
concentrations of Cd and Si within a range of
1.times.10.sup.17/cm.sup.3 to 1.times.10.sup.20/cm.sup.3,
respectively, in order to improve luminous intensity. It is further
desirable that the concentration of Si is smaller than that of Cd
by ten to fifty percent.
[0053] In order to make the band gap of the emission layer smaller
than those of its respective adjacent two layers, i.e., the p-layer
6 and the n.sup.+-layer 4 of high carrier concentration, a double
hetero-junction structure was utilized for the LED 10 in this
embodiment. Alternatively, a single hetero-Junction structure can
be utilized.
[0054] Further, it is preferable that the composition ratio of Al,
Ga, and In in the respective three layers 4, 5, and 6 is
selectively designed to meet the lattice constants of their layers
4, 5, and 6 with the lattice constant of GaN in the n.sup.+-layer 3
of high carrier concentration as precisely as possible.
Example 2
[0055] FIG. 8 shows a LED 10 utilized in Example 2. The emission
layer 5 in Example 1 was doped with Cd and Si.
[0056] In this Example 2, an emission layer 5 is doped with Zn and
Si.
[0057] A manufacturing process of a sapphire substrate 1, the
formation of the AlN buffer layer 2 and the n.sup.+-layers 3 was
similar to that discussed in the previous example.
[0058] About a 0.5 .mu.m thick Si-doped
(Al.sub.0.3Ga.sub.0.7).sub.0.94In.sub.0.06N n.sup.+-layer 4 of high
carrier concentration with an electron concentration of
2.times.10.sup.19/cm.sup.3 was formed on the n.sup.+-layer 3 under
conditions of lowering the temperature in the chamber to
800.degree. C., keeping the temperature constant, and supplying
N.sub.2, NH.sub.3, TMG, TMA, TMI, and diluted silane to 0.86 ppm by
H.sub.2 for 120 min. at a flow rate of 20 liter/min., 10
liter/min., 1.12.times.10.sup.-4 mol/min., 0.47.times.10.sup.-4
mol/min., 0.1.times.10.sup.-4 mol/min., and 10.times.10.sup.-9
mol/min., respectively.
[0059] About a 0.5 .mu.m thick Si- and Zn-doped
(Al.sub.0.09Ga.sub.0.91).sub.0.99In.sub.0.01N emission layer 5 was
formed on the n.sup.+-layer 4 under conditions of lowering the
temperature in the chamber to 1150.degree. C., keeping it constant,
and supplying N.sub.2, NH.sub.3, TMG, TMA, TMI, diluted silane to
0.86 ppm by H.sub.2, and DEZ for 7 min. at a flow rate of 20
liter/min., 10 liter/min., 1.53.times.10.sup.-4 mol/min.,
0.47.times.10.sup.-4 mol/min., 0.02.times.10.sup.-4 mol/min. and
10.times.10.sup.-9 mol/min., and 2.times.10.sup.-4 mol/min.,
respectively.
[0060] The impurity concentration of the Zn- and Si-doped into the
emission layer 5 was 2.times.10.sup.18/cm.sup.3 and
1.times.10.sup.18/cm.sup.3, respectively.
[0061] About a 1.0 .mu.m thick Mg-doped
(Al.sub.0.3Ga.sub.0.7).sub.0.94In.sub.0.06N p-layer 6 was formed on
the emission layer 5 under conditions of lowering the temperature
in the chamber to 1100.degree. C., keeping the temperature
constant, and supplying N.sub.2, NH.sub.3, TMG, TMA, TMI, and
CP.sub.2Mg at a flow rate of 20 liter/min., 10 liter/min.,
1.12.times.10.sup.-4 mol/min., 0.47.times.10.sup.-4 mol/min.,
0.1.times.10.sup.-4 mol/min., and 2.times.10.sup.4 mol/min.,
respectively. The impurity concentration of Mg doped into the
p-layer 6 was 1.times.10.sup.20/cm.sup.3. At this stage, the
p-layer 6 remained insulative with a resistivity of 10.sup.8
.OMEGA.cm or more.
[0062] Then, the p-layer 6 was processed to have p-type conduction
by electron beam irradiation under the same conditions described in
Example 1. The subsequent process steps of forming the electrodes
are the same as that described in the previous example. The
so-obtained LED 10 was found to have a luminous intensity of 1000
mcd and a wavelength of 450 nm by driving current of 20 mA.
Example 3
[0063] FIG. 9 shows a structural view of a LED 10 embodied in
Example 3. The LED 10 in Example 3 was manufactured by additionally
doping Mg to the emission layer 5 of the LED in Example 2. Other
layers and electrodes were manufactured in the same way as those in
Example 2.
[0064] CP.sub.2Mg was fed at a flow rate of 2.times.10.sup.-4
mol/min. into a chamber in addition to the gasses employed in
Example 2 in order to manufacture the emission layer 5 in Example
3. The emission layer 5 was about 0.5 .mu.m thick comprising Mg,
Zn, and Si-doped (Al.sub.0.09Ga.sub.0.91).sub.0.99In.sub.0.01N. Its
resistivity was 10.sup.8 .OMEGA.cm remaining insulative. Impurity
concentration of Mg, Zn, and Si was 1.times.10.sup.19/cm.sup.3,
2.times.10.sup.18/cm.sup.3, and 1.times.10.sup.18/cm.sup.3,
respectively.
[0065] Then, both of the emission layer 5 and a p-layer 6 were
subject to electron beam irradiation with the electron beam
diffraction device under as same conditions as in Example 1. Thus,
the emission layer 5 and the p-layer 6 turned into layers
exhibiting p-type conduction with a hole concentration of
2.times.10.sup.17/cm.sup.3 and resistivity of 2 .OMEGA.cm.
Example 4
[0066] FIG. 10 shows a structural view of a LED 10 embodied in
Example 4. In this example, an emission layer 5 includes GaN and
had a single hetero-junction structure. Namely, one junction
comprises a heavily Si-doped n.sup.+-layer 4 of high carrier
concentration and a Zn- and Si-doped GaN emission layer 5, and
another junction includes the GaN emission layer 5 and a Mg-doped
Al.sub.0.1Ga.sub.0.9N p-layer 61 with p-type conduction. In this
example, the Mg-doped GaN p-layer 62 as a contact layer is formed
on the p-layer 61. An insulation groove 9 is formed through the
contact layer 62, the p-layer 61 and the emission layer 5.
[0067] The LED 10 in this example has a sapphire substrate 1 upon
which the following five layers are consecutively formed: an AlN
buffer layer 2; a Si-doped GaN n.sup.+-layer 4 of high carrier
(n-type) concentration; a Zn and Si-doped GaN emission layer 5,
Mg-doped Al.sub.0.1Ga.sub.0.9N p-layer 61, and Mg-doped GaN contact
layer 62. The AlN layer 2 has a 500 .ANG. thickness. The GaN
n.sup.+-layer 4 has about a 4.0 .mu.m thickness and a
2.times.10.sup.18/cm.sup.3 electron concentration. The emission
layer 5 has about a 0.5 .mu.m thickness. The p-layer 61 has about a
0.5 .mu.m thickness and a 2.times.10.sup.17/cm.sup.3 hole
concentration. The contact layer 62 has about a 0.5 .mu.m thickness
and a 2.times.10.sup.17/cm.sup.3 hole concentration. Nickel
electrodes 7 and 8 are formed to connect to the contact layer 62
and the n.sup.+-layer 4 of high carrier concentration,
respectively. The two electrodes are electrically insulated by a
groove 9.
[0068] Here is explained a manufacturing process of the LED 10. The
sapphire substrate 1 and the AlN buffer layer 2 were prepared by
the same process described in detail in Example 1. On the AlN
buffer layer 2, about a 4.0 .mu.m thick Si-doped GaN n.sup.+-layer
4 of high carrier concentration with an electron concentration of
2.times.10.sup.18/cm.sup.3 was formed under conditions of lowering
the temperature in the chamber to 1150.degree. C., keeping the
temperature constant and supplying N.sub.2, NH.sub.3, TMG, and
diluted silane to 0.86 ppm by H.sub.2 for 60 min. at a flow rate of
20 liter/min., 10 liter/min., 1.7.times.10.sup.-4 mol/min.,
0.47.times.10.sup.-4 mol/min., 0.1.times.10.sup.-4 mol/min., and
10.times.10.sup.-9 mol/min., respectively.
[0069] The following manufacturing process and composition ratio
provide for the three layers, the emission layer 5 as an active
layer, the p-layer 62 as a clad layer, and the contact layer 62.
The LED is designed to have 430 nm wavelength at peak in the
luminous spectrum and have luminous centers of Zn and Si.
[0070] About a 0.5 .mu.m thick Zn- and Si-doped GaN emission layer
5 was formed on the n.sup.+-layer 4 under conditions of lowering
the temperature in the chamber to 1000.degree. C., keeping it
constant and supplying N.sub.2 or H.sub.2, NH.sub.3, TMG, DMZ, and
diluted silane to 0.86 ppm by H.sub.2 for 8 min. at a flow rate of
20 liter/min., 10 liter/min., 1.53.times.10.sup.-4 mol/min.,
2.times.10.sup.-7 mol/min., and 10.times.10.sup.-9 mol/min.,
respectively.
[0071] About a 0.5 .mu.m thick Mg-doped Al.sub.0.1Ga.sub.0.9N
p-layer 61 was formed on the emission layer 5 under conditions of
lowering the temperature in the chamber to 1000.degree. C., keeping
the temperature constant and supplying N.sub.2 or H.sub.2,
NH.sub.3, TMG, TMA, and CP.sub.2Mg for 7 min. at a flow rate of 20
liter/min., 10 liter/min., 1.12.times.10.sup.-4 mol/min.,
0.47.times.10.sup.-4 mol/min., and 2.times.10.sup.-7 mol/min.,
respectively. At this stage, the p-layer 61 remained insulative
with a resistivity of 10.sup.8 .OMEGA.cm or more. The impurity
concentration of the Mg-doped into the p-layer 61 was
1.times.10.sup.19/cm.sup.3.
[0072] Then, about a 0.5 .mu.m thick Mg-doped GaN contact layer 62
was formed on the p-layer 61 under conditions of lowering the
temperature in the chamber to 1000.degree. C., keeping the
temperature constant and supplying N.sub.2 or H.sub.2, NH.sub.3,
TMG, and CP.sub.2Mg for 10 min. at a flow rate of 20 liter/min., 10
liter/min., 1.12.times.10.sup.-4 mol/min., and 2.times.10.sup.-4
mol/min., respectively. At this stage, the Mg-doped contact layer
62 remained insulative with a resistivity of 10.sup.8 .OMEGA.cm or
more. The impurity concentration of the Mg-doped into the contact
layer 62 was 1.times.10.sup.20/cm.sup.3.
[0073] Then, the p-layer 61 and contact layer 62 were uniformly
irradiated by an electron beam under the same conditions as
described in Example 1. Consequently, the p-layer 61 and contact
layer 62 are processed to exhibit p-type conduction with a
2.times.10.sup.17/cm.sup.3 hole concentration and 2 .OMEGA.cm or
more resistivity. The subsequent process steps of forming the
electrodes is the same as that described in the previous example.
As a result, the LED 10 having a single hetero-junction structure
is obtained whose emission layer is doped with Zn as an acceptor
and Si as a donor impurity. Alternatively, doping Mg and
irradiating electrons into the emission layer 5 can be used to
obtain an emission layer 5 with p-type conduction.
Example 5
[0074] FIG. 11 shows a LED 10 embodied in this example. Three
layers, a p-layer 61, an emission layer 5, and an n.sup.+-layer 4,
are unique to Example 5. The p-layer 61 is formed of Mg-doped
Al.sub.x1Ga.sub.1-x1N. The emission layer 5 is Zn- and Si-doped
Al.sub.x2Ga.sub.1-x2N. The n.sup.+-layer 4 of high carrier
concentration is Si-doped Al.sub.x3Ga.sub.1-x3N. Other layers and
electrodes are formed the same as those described in Example 4. The
composition ratio of x1, x2 and x3 in each layer is designed to
make the band gap of the emission layer 5 smaller than those of the
n.sup.+-layer 4 and p-layer 61 forming a double hetero-junction
structure or a single hetero-junction structure. Thanks to this
structure, carriers are confined in the emission layer 5
contributing to higher luminous intensity. The emission layer 5 can
exhibit any one of semi-insulative, p-type conductivity, or n-type
conductivity.
Example 6
[0075] FIG. 12 shows a LED 10 embodied in this example. Three
layers, a p-layer 61, an emission layer 5, and an n.sup.+-layer 4,
are unique to Example 6. The p-layer 61 formed of Mg-doped
Al.sub.x1Ga.sub.1-x1N. The emission layer 5 is formed of Zn- and
Si-doped Ga.sub.yIn.sub.1-yN. The n.sup.+-layer 4 of high carrier
concentration is formed of Si-doped Al.sub.x2Ga.sub.1-x2N. Other
layers and electrodes are formed the same as those described in
Example 4. The composition ratio of x1, x2, and x3 in each layer is
designed to make the band gap of the emission layer 5 smaller than
those of the n.sup.+-layer 4 and p-layer 61 forming a double
hetero-junction structure or a single hetero-junction structure.
Thanks to this structure, carriers are confined in the emission
layer 5 contributing to higher luminous intensity. The emission
layer 5 can exhibit any one of semi-insulative, p-type
conductivity, or n-type conductivity.
[0076] The LED 10 in this example has a sapphire substrate 1 which
has the following five layers are consecutively formed thereon: an
AlN buffer layer 2; a Si-doped Al.sub.x2Ga.sub.1-x2N n.sup.+-layer
4 of high carrier (n-type) concentration; a Zn- and Si-doped
Ga.sub.0.94In.sub.0.06N emission layer 5. Mg-doped
Al.sub.0.1Ga.sub.0.9N p-layer 61 of p-type, and an Mg-doped GaN
contact layer 62 of p-type. The AlN layer 2 has a 500 .ANG.
thickness. The Al.sub.x2Ga.sub.1-x2N n.sup.+-layer 4 has about a
4.0 .mu.m thickness and a 2.times.10.sup.18/cm.sup.3 electron
concentration. The emission layer 5 has about 0.5 .mu.m thickness.
The p-layer 61 has about a 0.5 .mu.m thickness and a
2.times.10.sup.17/cm.sup.3 hole concentration. The contact layer 62
has about a 0.5 .mu.m thickness and a 2.times.10.sup.17/cm.sup.3
hole concentration. Nickel electrodes 7 and 8 are formed to connect
to the contact layer 62 and n.sup.+-layer 4 of high carrier
concentration, respectively. The two electrodes are electrically
insulated by a groove 9.
[0077] A manufacturing process for the LED 10 of FIG. 12 is as
follows. The sapphire substrate 1 and the AlN buffer layer 2 were
prepared by the same process described in detail in Example 1. On
the AlN buffer layer 2, about a 4.0 .mu.m thick Si-doped
Al.sub.x2Ga.sub.1-x2N n.sup.+-layer 4 of high carrier concentration
with an electron concentration of 2.times.10.sup.18/cm.sup.3 was
formed under conditions of lowering the temperature in the chamber
to 1150.degree. C., keeping it constant, and supplying N.sub.2,
NH.sub.3, TMG, TMA, and diluted silane to 0.86 ppm by H.sub.2 for
60 min. at a flow rate of 20 liter/min., 10 liter/min.,
1.12.times.10.sup.-4 mol/min., 0.47.times.10.sup.-4 mol/min., and
10.times.10.sup.-9 mol/min., respectively.
[0078] Following manufacturing process and composition ratio for
the three layers, the emission layer 5 as an active layer, the
p-layer 61 as a clad layer, and the contact layer 62, show an
example where the LED 10 is designed to have 450 nm wavelength at
peak in luminous spectrum and have luminous centers of Zn and
Si.
[0079] About a 0.5 .mu.m thick Zn- and Si-doped
Ga.sub.0.94In.sub.0.06N emission layer 5 was formed on the
n.sup.+-layer 4 under conditions of raising the temperature in the
chamber to 850.degree. C., keeping it constant, and supplying
N.sub.2 or H.sub.2. NH.sub.3, TMG, TMI, DMZ and, silane for 60 min.
at a flow rate of 20 liter/min., 10 liter/min.,
1.53.times.10.sup.-4 mol/min., 0.02.times.10.sup.-4 mol/min.,
2.times.10.sup.-7 mol/min., and 10.times.10.sup.-9 mol/min.,
respectively.
[0080] About a 0.5 .mu.m thick Mg-doped Al.sub.0.1Ga.sub.0.9N
p-layer 61 was formed on the emission layer 5 under conditions of
raising the temperature in the chamber to 1000.degree. C., keeping
the temperature constant and supplying N.sub.2 or H.sub.2,
NH.sub.3, TMG, TMA, and CP.sub.2Mg for 7 min. at a flow rate of 20
liter/min., 10 liter/min., 1.12.times.10.sup.-4 mol/min.,
0.47.times.10.sup.-4 mol/min., and 2.times.10.sup.-7 mol/min.,
respectively. At this stage, the p-layer 61 remained insulative
with a resistivity of 10.sup.8 .OMEGA.cm or more. The impurity
concentration of the Mg doped into the p-layer 61 was
1.times.10.sup.19/cm.sup.3.
[0081] Then, about a 0.5 .mu.m thick Mg-doped GaN contact layer 62
was formed on the p-layer 61 under conditions of keeping the
temperature in the chamber at 1000.degree. C. and supplying N.sub.2
or H.sub.2, NH.sub.3, TMG, and CP.sub.2Mg for 10 min. at a flow
rate of 20 liter/min., 10 liter/min., 1.12.times.10.sup.-4
mol/min., and 2.times.10.sup.-4 mol/min., respectively. At this
stage, the Mg-doped contact layer 62 remained insulative with a
resistivity of 10.sup.8 .OMEGA.cm or more. The impurity
concentration of the Mg doped into the contact layer 62 was
1.times.10.sup.20/cm.sup.3.
[0082] Then, the p-layer 61 and contact layer 62 were uniformly
irradiated by an electron beam with the same conditions described
in Example 1. Consequently, the p-layer 61 and contact layer 62 are
processed to exhibit p-type conduction with a
2.times.10.sup.17/cm.sup.3 hole concentration and a 2-cm
resistivity. The subsequent process steps of forming the electrodes
is the same as that described in the previous example.
[0083] In Examples 1 to 6, the emission layer 5 can exhibit any one
of semi-insulation, p-type conductivity, or n-type conductivity.
When the concentration of the Zn-doped to the emission layer 5 is
higher than that of the Si, the layer 5 exhibits semi-insulative
characteristics. When the concentration of the Zn is smaller than
that of the Si, the emission layer 5 exhibits n-type
conduction.
[0084] In order to improve the luminous intensity, the impurity
concentration of Zn and Si doped to the emission layer 5 is
preferably in the 1.times.10.sup.17/cm.sup.3 to
1.times.10.sup.20/cm.sup.3 range, respectively. The concentration
is more preferably in the 1.times.10.sup.18/cm.sup.3 to
1.times.10.sup.19/cm.sup.3 range. It is not preferable that the
impurity concentration be lower than 1.times.10.sup.18/cm.sup.3,
because the luminous intensity of the LED decreases as a result. It
is not desirable that the impurity concentration is higher than
1.times.10.sup.19/cm.sup.3, because poor crystallinity occurs. It
is preferable that the concentration of Si is ten to one-tenth as
that of Zn. The most preferable concentration of Si is in the one
to one-tenth range or closer to one-tenth to Zn.
[0085] In Examples 1 to 6, Cd, Zn, and Mg were employed as acceptor
impurities and Si as a donor impurity. Alternatively, beryllium
(Be) and mercury (Hg) can be used as an acceptor impurity.
Alternatively, carbon (C), germanium (Ge), tin (Sn), lead (Pb),
sulfur (S), selenium (Se), and tellurium (Te) can be used as a
donor impurity.
[0086] Electron irradiation was used in Examples 1 to 6 in order to
process an emission layer 5 to exhibit p-type conduction.
Alternatively, annealing, heat processing in the atmosphere of
N.sub.2 plasma gas and laser irradiation can be used.
Example 7
[0087] FIG. 14 shows a structural view of a LED 10 embodied in
Example 7. The LED 10 in this example was manufactured by
additionally doping Mg to the emission layer 5 of the LED 10 in
Example 1. Other layers and electrodes were manufactured the same
way as those described in Example 1.
[0088] CP.sub.2Mg was fed at a flow rate of 2.times.10.sup.-7
mol/min. into a chamber in addition to gasses employed in Example 1
in order to manufacture the emission layer 5 in Example 7. The
emission layer 5 was about a 0.5 .mu.m thick including Mg-, Cd-,
and Si-doped (Al.sub.0.09Ga.sub.0.91).sub.0.99In.sub.0.01N
remaining high insulative. Impurity concentration of the Mg. Cd and
Si was 1.times.10.sup.20/cm.sup.3, 5.times.10.sup.18/cm.sup.3, and
1.times.10.sup.18/cm.sup.3, respectively.
[0089] Then, electron beam was uniformly irradiated on both of the
emission layer 5 and p-layer 6 with an electron diffraction device
under the same conditions as in Example 1. The emission layer 5 and
p-layer 6 came to exhibit p-type conduction with a hole
concentration of 2.times.10.sup.17/cm.sup.3 and a resistivity of 2
.OMEGA.cm.
Example 8
[0090] FIGS. 15 and 16 show structural views of a LED 10 embodied
in Example 8. The LED 10 in this example was manufactured by
additionally doping Mg and irradiating electrons into the emission
layer 5 of the LED 10 in Example 6. The emission layer 5 of Example
8 includes Mg-, Zn-, and Si-doped Ga.sub.yIn.sub.1-yN exhibiting
p-type conduction. Other layers and electrodes were manufactured
the same way as those described in Example 1.
[0091] FIG. 16 shows an example where the LED 10 is designed to
have a 450 nm wavelength at peak in the luminous intensity. The
manufacturing process and composition equation of the three layers,
the emission layer 5 as an active layer, the p-layer 61 as a clad
layer and the contact layer 62 are described hereinafter.
[0092] The CP.sub.2Mg was fed at a flow rate of 2.times.10.sup.-4
mol/min. into a chamber in addition to gasses employed in Example 6
in order to manufacture the emission layer in Example 8. The
emission layer 5 was about a 0.5 .mu.m thick including Mg-, Zn-,
and Si-doped Ga.sub.0.94In.sub.0.06N remaining highly
insulative.
[0093] Then, the emission layer 5, p-layer 61 and contact layer 61
were uniformly irradiated by an electron diffraction device under
the same conditions as those described in Example 1. This
irradiation changed the emission layer 5, p-layer 61, and contact
layer 62 into layers exhibiting p-type conduction with a hole
concentration of 2.times.10.sup.17/cm.sup.3 and a resistivity of 2
.OMEGA.cm.
[0094] In Examples 7 and 8, the impurity concentration of Zn and Si
doped into the emission layer 5 are preferably in the
1.times.10.sup.17/cm.sup.3 to 1.times.20.sup.20/cm.sup.3 range,
respectively. The concentration is more preferably in the
1.times.10.sup.18/cm.sup.3 to 1.times.10.sup.19/cm.sup.3 range. It
is not preferable that the impurity concentration be lower than
1.times.10.sup.18/cm.sup.3, because luminous intensity of the LED
decreases as a result. It is not desirable that the impurity
concentration be higher than 1.times.10.sup.19/cm.sup.3, because
poor crystallinity occurs. It is further preferable that the
concentration of Si be ten to one-tenth as same as that of Zn. The
most preferable concentration of Si is in the two to one-tenth
range.
[0095] In Examples 7 and 8, Cd, Zn and Mg were employed as acceptor
impurities and Si as a donor impurity. Alternatively, beryllium
(Be) and mercury (Hg) can be used as an acceptor impurity.
Alternatively, carbon (C), germanium (Ge), tin (Sn), lead (Pb),
sulfur (S), selenium (Se) and tellurium (Te) can be used as a donor
impurity.
[0096] Electron irradiation was used in Examples 7 and 8 in order
to change layers to have p-type conduction. Alternatively,
annealing, heat process in the atmosphere of N.sub.2 plasma gas,
laser irradiation and any combination thereof can be used.
[0097] While the invention has been described in connection with
what are presently considered to be the most practical and
preferred embodiments, it is to be understood that the invention is
not to be limited to the disclosed embodiments, but on the
contrary, is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims.
* * * * *