JP2003224071A - Manufacturing method for nitride based semiconductor and nitride semiconductor element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high quality nitride based semiconductor or an element constituted of the nitride based semiconductor not generating cracks on a Si substrate, and to provide the manufacturing method. <P>SOLUTION: An AlxGayInzN (0≤x≤1, 0≤y≤1, 0≤z≤1 and x+y+z=1) semiconductor layer 3 is grown by using an impurity added ZnO buffer layer 2 on a Si substrate 1. Thus, a columnar polycrystalline ZnO buffer layer for which the (c) axis orientatability is high and a grain size in a horizontal direction is small within the (C) plane is formed, and a nitride based semiconductor single crystal layer less influenced by heat distortion from the Si substrate is manufactured on it. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having an oscillation wavelength in the visible region to ultraviolet region, which is expected to be applied to the fields of high-density optical information processing and displays, and high-efficiency ultraviolet rays used for a solid light source for illumination The present invention relates to a nitride-based semiconductor device used for applications such as light emitting diodes and high frequency / high power transistors.

[0002]

2. Description of the Related Art Nitride semiconductors containing nitrogen (N) as a group V element have a short wavelength having an emission band in a wide wavelength range from the visible region to the ultraviolet region due to the size of the band gap and the breakdown voltage. It is regarded as a promising material for light emitting devices and high-power electronic devices. Above all, nitride-based semiconductors (Ga
N-based _{semiconductor: Al x Ga y In z N} (0 ≦ x, y, z ≦
1, x + y + z = 1)) has been actively researched, and blue light emitting diodes (LEDs) and green LEDs have been put to practical use. Moreover, in order to increase the capacity of the optical disk device, 400
A semiconductor laser having an oscillation wavelength in the nm band has been eagerly awaited, and a semiconductor laser made of a nitride-based semiconductor has attracted attention, and at present, it is about to reach a practical level.

In crystal growth of a nitride-based semiconductor, it is extremely difficult at present to produce a high-quality, large-diameter nitride-based semiconductor bulk crystal, so that sapphire and Si are used.
Metalorganic vapor phase epitaxy (M
Heteroepitaxy using a method such as the OVPE method) is performed. In heteroepitaxy, in order to suppress the occurrence of defects at the interface due to the mismatch of the lattice constant and the thermal expansion coefficient existing between various substrates and the nitride-based semiconductor, the temperature at which the nitride-based semiconductor is grown is usually set. A polycrystalline AlGaN-based buffer layer manufactured at a low growth temperature,
Alternatively, a method is disclosed in which a superlattice buffer layer made of AlN single crystal or GaN / AlN single crystal is deposited at a temperature at which a normal nitride-based semiconductor is grown, and stress generated between the substrate and the epicrystal is relaxed. Has been done.

In particular, if a high-quality nitride semiconductor can be formed on a Si substrate, very significant industrial effects such as cost and mass productivity are expected, and various efforts have been made.

[0005] For example, "Material Research"
rch Society Symposium Pro
ceedings Volume 449, p373
(1997 Material Research S
), a ZnO film is deposited on a (111) Si substrate by an electron beam evaporation method or a laser ablation MBE method, and then AlN is deposited by a MOVPE method.
A method of sequentially stacking GaN to obtain a GaN crystal is disclosed. In addition, “Proceedings of 61st JSAP Academic Lecture Meeting (September 2000, Hokkaido Institute of Technology) 4a-Y-
14 ”discloses a method of depositing polycrystalline ZnO having a columnar structure on a (001) Si substrate by using an RF magnetron sputtering method and then depositing polycrystalline GaN by using an ECR-MBE method. .

[0006]

However, comparing the coefficient of thermal expansion of Si with the coefficient of thermal expansion of a nitride semiconductor, the former is smaller, and the Si substrate is heated to grow a nitride semiconductor single crystal. When the temperature is lowered to room temperature after growth, tensile stress is applied to the nitride-based semiconductor crystal due to the thermal expansion irregularity, and the crystal is warped or cracked. Usually GaN
When is grown as a single crystal, cracks occur at about 1 μm.

ZnO has a lattice constant close to that of GaN.
Although it is considered to be promising as a buffer layer, if the crystallinity is improved by increasing the orientation of ZnO, the thermal strain of the Si substrate is directly applied to GaN, and the problem of cracks cannot be avoided. For example, in the conventional technique, as shown in FIG. 3, a columnar polycrystalline ZnO buffer layer 6 is deposited on a (111) Si substrate 1, and GaN is deposited on the ZnO buffer layer 6.
Initially grown nuclei 7 are deposited and then grown to obtain a GaN layer 8. In this method, in order to improve the c-axis orientation in the direction perpendicular to the substrate, it is necessary to heat the substrate at a high temperature such that ZnO is not decomposed and evaporated. In this case, the substrate is heated to a considerable extent (the thickness of the columnar polycrystal). Ga of the Ga
In each of the N initial growth nuclei 7, the coherency with the Si substrate 1 is increased through the ZnO buffer layer 6,
Eventually, the thermal strain of the Si substrate 1 will be applied to the GaN layer 8, and the GaN layer 8 will be cracked.

The present invention has been made in view of the above problems, and it is an S-type substrate of a different type, particularly excellent in mass productivity and productivity.
Provided are a method and a structure for producing a high quality nitride-based semiconductor single crystal layer without cracks on an i substrate.

[0009]

According to the method of manufacturing a nitride semiconductor of the present invention, an Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0) is formed by using an impurity-doped ZnO buffer layer on a Si substrate.
≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) based semiconductor is characterized by growing. In particular, the feature is that the impurities are composed of at least one of In, Ga, and Al. By adding impurities to the ZnO buffer layer, the columnar shape is excellent in c-axis orientation but has a small degree of lateral growth, that is, a columnar shape with a large vertical / horizontal ratio, as compared with the case of using a conventional ZnO buffer layer without adding impurities. Polycrystalline Zn
An O buffer layer is obtained, which prevents thermal strain of the substrate from being added to the GaN on the ZnO buffer layer. Further, the coefficient of thermal expansion of the Si substrate is larger than that of ZnO, and the columnar polycrystalline ZnO buffer layer having a high c-axis orientation and a large aspect / width ratio causes compressive strain. The large lattice constant of ZnO will be reduced in the C-plane, and it will be closer to the bulk lattice constant of GaN. Therefore, by utilizing this effect, the lattice mismatch between GaN and ZnO is avoided. In this case, ZnO doped with impurities
By using the buffer layer to suppress the lateral growth of the columnar polycrystalline ZnO buffer layer, the domain size of ZnO having high single crystallinity is reduced.
Avoid applying thermal strain from the i-substrate through the buffer to GaN.

The nitride semiconductor device of the present invention is S
Al _x Gay _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ formed using an impurity-doped ZnO buffer layer on an i substrate
1, 0 ≦ z ≦ 1, x + y + z = 1) based semiconductor.

Further, in the method for manufacturing a nitride-based semiconductor of the present invention, Al _x Ga _y In _z N (0 ≦ x ≦ 1,0 ≦ y is used by using an Al ₂ O ₃ buffer layer doped with impurities on a Si substrate. ≦ 1,
0 ≦ z ≦ 1, x + y + z = 1) -based semiconductor is grown. In particular, it is characterized in that the impurities are composed of at least Si or Ge. A columnar polycrystalline Al ₂ O ₃ buffer layer having a high c-axis orientation and a large aspect ratio is formed by adding impurities, and Si is formed on the GaN layer on the columnar polycrystalline Al ₂ O ₃ buffer layer.
Preventing thermal strain from the substrate is described in the above Z
It is similar to the nO buffer layer. Further, contrary to the case of the ZnO buffer layer, the coefficient of thermal expansion of the Si substrate is smaller than that of Al ₂ O ₃ , and the c-axis orientation is high and the longitudinal / longitudinal
Because results in tensile strain to a large columnar polycrystalline Al ₂ O ₃ buffer layer of the lateral ratio, small Al ₂ O ₃ compared to GaN
The lattice constant of is to be increased in the C-plane, and
Since it is close to the bulk lattice constant of N, the lattice mismatch between GaN and Al ₂ O ₃ is avoided by utilizing this effect. In this case, the Al ₂ O ₃ buffer layer doped with impurities is used to suppress the lateral growth of the columnar polycrystalline Al ₂ O ₃ buffer layer, thereby reducing the domain size of Al ₂ O ₃ having high single crystallinity. Therefore, thermal strain from the Si substrate is prevented from being applied to GaN through the buffer.

The nitride semiconductor device of the present invention is S
Al was formed with Al ₂ O ₃ buffer layer doped impurity i on the substrate _{x Ga y In z N (0} ≦ x ≦ 1,0 ≦ y ≦
1, 0 ≦ z ≦ 1, x + y + z = 1) based semiconductor.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

The method for growing a nitride-based semiconductor of the present invention is not limited to the metal organic chemical vapor deposition (MOVPE) method, but may be a hydride vapor phase epitaxy method (H-VPE method) or a molecular beam epitaxy method (MBE method). ), Etc., can be applied to all the methods proposed so far for growing a nitride semiconductor layer. In addition, in the MOVPE growth method, the growth pressure ranges from reduced pressure to atmospheric pressure and pressure (760 Torr or more) (1
(Torr = 133.322 Pa), any pressure may be used, and the pressure may be switched to an optimum pressure in each layer. The carrier gas for supplying the raw material to the substrate is at least a gas containing an inert gas such as nitrogen or hydrogen.

The nitride-based semiconductor in the present invention is a semiconductor containing nitrogen as a group V element, and can be applied, for example, when the group V element contains P or As in addition to N.

Example 1 Using a ZnO buffer layer doped with impurities on the Si substrate of the present invention, Al _x Ga _y In _z N
(0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z =
1) A method for growing a system semiconductor will be described.

As shown in FIG. 1, a ZnO: Al buffer layer 2 is deposited to a thickness of 10 nm on a (111) Si substrate 1 by a sputtering method. Next, using the MOVPE method, AlG
The aInN layer 3 is grown. The ZnO: Al buffer layer 2 is sputtered by introducing an Al-doped ZnO target using a magnetron sputtering device by introducing a mixed gas of Ar and O ₂ . Substrate temperature is about 30
It is 0 ° C. In addition, the AlGaInN layer 3 is a low pressure MOVP.
Using method E, when heating the substrate from room temperature,
The growth starts from 0 ° C., and the AlGaI
The above A at a higher temperature depending on the composition of the nN layer 3
A single crystal of the lGaInN layer 3 is grown. For example AlGa
Approx. 1080 ° C for N layer and 800 ° C for InGaN layer
Grows at the substrate temperature of. The reason for growing from about 400 ° C. is to avoid thermal decomposition of the ZnO: Al buffer layer 2, and when the substrate temperature is about 400 ° C. or higher, the ZnO: A
The l buffer layer 2 is rapidly decomposed and the buffer layer disappears.
When depositing the ZnO: Al buffer layer 2, for example, several atomic layers of an AlN film may be sputtered as a protective film against thermal decomposition.

Next, the effectiveness of the ZnO buffer layer doped with impurities will be described.

As shown in FIG. 2 (a), a ZnO: Al buffer layer 2 is deposited on a (111) Si substrate 1. In this case, the substrate temperature is controlled at about 300 ° C. This is (1
11) To improve the orientation of <111> direction obtained from the Si substrate 1, and to increase the c-axis orientation of hexagonal ZnO on the (111) Si substrate 1 to form AlGaIn
The purpose is to align the c-axis orientation of the N-based semiconductor crystal. In order to make the c-axis orientation uniform, it is desirable to raise the substrate temperature, and after the substrate temperature during sputtering or after sputtering, heat treatment is performed in, for example, an atmosphere containing oxygen as a main component to form the ZnO: Al buffer layer 2 You may make the c-axis orientation uniform. In particular, the reason for adding Al impurities to ZnO is to reduce the lateral grain size in the C-plane of columnar polycrystalline ZnO, and the detailed mechanism has not been clarified at present, but ZnO is added by adding impurities.
The wettability of the nuclei on the substrate during sputtering is improved, the number of independent nuclei increases, and the polycrystallinity increases, and the relaxation of crystals occurs as a result of impurities, so that a large single crystal grows in the lateral direction. Mechanisms such as difficulty can be considered. According to the experiments conducted by the inventors, the average grain size in the lateral direction in the C plane is plotted against the deposition temperature (or the heat treatment temperature after deposition) of the ZnO: Al buffer layer 2 as shown in FIG. By adding impurities, the average grain size was reduced to about half as compared with the conventional method that does not do. As described above, in the temperature range in which ZnO is not decomposed, the higher the substrate temperature is, the more the c-axis orientation is improved. Therefore, it is desirable to deposit or heat-treat the ZnO: Al buffer layer 2 at 250 to 350 ° C. On the ZnO: Al buffer layer 2 thus obtained, M
When GaN is grown by OVPE, GaN initial growth nuclei 4 are formed corresponding to the buffer layer having a small grain size, and smaller nuclei are formed as compared with the conventional method. As a result, when the GaN initial growth nuclei are small, the thermal strain applied due to the thermal expansion mismatch with the Si substrate is small, so the thermal strain applied to the GaN layer 5 shown in FIG. A GaN layer with few cracks was obtained.
FIG. 5 shows that the impurity concentration is 10 ¹⁶ cm ⁻³ or less, that is, almost no impurities are added to the ZnO buffer layer (no impurities are added at all, or some impurities are added but negligible). ) A graph in which the crack density in GaN having a film thickness of about 5 μm is set to 1 and the density is plotted against the impurity addition concentration is shown. It was found that the crack density decreased as the impurity concentration increased.

In this embodiment, the case where Al impurities are added to the ZnO buffer layer has been described, but other Ga, In
Similar effects can be obtained with n-type impurities such as N, p-type impurities such as N, and other impurities. In particular, in the case of n-type impurities, as will be described later, it is effective when providing an n-electrode on an n-type Si substrate in a nitride-based semiconductor device using an n-type Si substrate, and a high-quality nitride-based nitride-based This is a method for producing a nitride-based semiconductor element that is excellent not only in obtaining a semiconductor but also in mass productivity and productivity.

Further, in this embodiment, ZnO doped with impurities is used.
Although the sputtering method has been described as the method for forming the buffer layer, it goes without saying that any conventionally used film forming method such as an electron beam evaporation method or an ECR-MBE method can be applied.

An example in which the method of the present invention is applied to a nitride semiconductor laser will be described with reference to FIG.

First, Z is formed on a (111) n-Si substrate 71.
For the substrate on which the nO: Al buffer layer 72 is deposited, n?
AlGaN cladding layer 73, n? AlGaInN optical guide layer 74, GaInN-based multiple quantum well (MQW) active layer 75, p-AlGaN cap layer 76, p? AlGaI
nN optical guide layer 77, p-AlGaN cladding layer 78,
p? After sequentially growing the AlGaInN contact layer 79, the p-AlGaN cladding layer 78, p? AlGaI
The nN contact layer 79 is processed into a ridge stripe shape,
Both sides of the ridge are covered with a SiO ₂ insulating film 81 to form a current injection region. The stripe width is about 3-5 microns. P? Of the opening of the insulating film 81? A p-electrode 80 is provided on the surface of the AlGaInN contact layer 79 and part of the insulating film 81. An n electrode 82 is formed on the back surface of the (111) n-Si substrate 71. This element (excluding substrate)
Has a total film thickness of about 5 μm.

Conventionally, when the above-mentioned device structure is formed on a Si substrate, the total film thickness is limited to less than 1 μm due to the restriction of crack generation due to thermal strain. In order to realize the optical confinement necessary for the guide, the limitation of the film thickness becomes a big problem and it is impossible to obtain a high quality laser device.

The device obtained by this method can obtain a sufficient film thickness for a laser device, and a nitride semiconductor laser which oscillates in a wavelength band of 400 nm having an extremely high quality on a Si substrate becomes possible. . The device had few cracks and defects and high reliability, and a life of 10,000 hours or more was obtained at 60 ° C. and 30 mW.

In the present embodiment, the nitride semiconductor laser has been described. However, if a high quality nitride semiconductor can be realized on Si, it is possible to operate at high frequency, high output and high temperature by utilizing the physical properties of the nitride semiconductor. It is needless to say that the present invention can be applied to a FET, a bipolar transistor, or a nitride-based semiconductor element such as a light emitting diode or a light source for illumination that utilizes the emission characteristics in the ultraviolet region. Further, by integrating Si and the nitride-based semiconductor, the effect of integration can be naturally realized.

In this embodiment, (111) of the Si substrate is used.
The surface has been described, but S having a slightly tilted surface orientation
It is also effective for i-boards. Further, a method of selectively providing a metal or dielectric film on a Si substrate or a GaN film on the Si substrate for the purpose of reducing crystal defects, or using selective lateral growth on a substrate having a processed groove formed by etching or the like. Can also be applied.

Further, according to the present invention, after a high quality nitride semiconductor is grown, the Si substrate and the impurity-added ZnO buffer layer are removed by etching or the like to obtain a substrate composed of only the nitride semiconductor. It can also be applied to the manufacturing method.

(Example 2) Another method for growing a high-quality nitride semiconductor on a Si substrate will be described.

As shown in FIG. 6, an Al ₂ O ₃ : Si buffer layer 9 having a film thickness of 1 is formed on the (111) Si substrate 1 by the sputtering method.
Deposit 0 nm. Next, using the MOVPE method, AlGa
The InN layer 10 is grown. Al ₂ O ₃ : Si buffer layer 9
Is sputtered by introducing a mixed gas of Ar and O ₂ into a Si-doped Al ₂ O ₃ target using a magnetron sputtering device. Substrate temperature is about 5
It is 00 ° C. Next, the AlGaInN layer 10 is depressurized MO.
Using the VPE method, a single crystal of the AlGaInN layer 3 is grown at a high temperature according to the composition of the AlGaInN layer 10. For example, in the AlGaN layer, at about 1080 ° C., I
The nGaN layer grows at a substrate temperature of about 800 ° C. Al
_{Since the 2} O ₃ : Si buffer layer 9 is more thermally stable than the ZnO: Al buffer layer of Example 1, the above Al ₂ O ₃ : Si buffer layer 9 is:
After depositing the Si buffer layer 9, Al is formed using the MOVPE method.
When the GaInN layer 10 is grown, it has an advantage that thermal decomposition of the buffer layer due to substrate heating can be avoided, and it is also advantageous for heat treatment in an atmosphere containing oxygen as a main component in order to improve the c-axis orientation.

The reason why Si impurities are added to the Al ₂ O ₃ buffer layer is the same as in the ZnO buffer layer of Example 1, and a columnar polycrystalline buffer layer having a high c-axis orientation and a small lateral grain size is prepared. This is because. The difference from the ZnO buffer layer is that Al ₂ O ₃ has a larger coefficient of thermal expansion than Si, so that tensile strain is added to Al ₂ O ₃ and
_{Since the} lattice constant of ₂ O _{3 in} the c-plane is expanded, Ga
The lattice mismatch between N and Al ₂ O ₃ is reduced, and a higher quality nitride semiconductor layer can be obtained.

Similar to the first embodiment, Al is formed on the Si substrate.
_{When a} laser device composed of a nitride semiconductor layer was manufactured using a ₂ O ₃ : Si buffer layer, a high quality laser having the same characteristics as in Example 1 was obtained. The device has few cracks and defects and high reliability.
A life of 10,000 hours or more was obtained at 0 mW.

It was confirmed that other impurities added to the Al ₂ O ₃ buffer layer also had the same effect on Group IV elements such as Ge.

It is needless to say that the method of depositing the impurity-added Al ₂ O ₃ buffer layer is not limited to the case of this embodiment, and any other commonly used method may be used.

[0035]

As described above, according to the method for manufacturing a nitride-based semiconductor of the present invention, it is possible to avoid applying thermal strain from the Si substrate to the nitride-based semiconductor layer, and it is difficult to realize the conventional method. It is possible to realize a high-quality nitride-based semiconductor single crystal layer having a uniform film thickness, and to manufacture a nitride-based semiconductor element having excellent mass productivity and productivity.

Further, according to the nitride-based semiconductor device structure of the present invention, it is possible to realize a laser having a film thickness sufficient to form an optical waveguide structure without causing cracks or defects on a Si substrate. Without limitation, a low cost nitride semiconductor device can be realized.

[Brief description of drawings]

FIG. 1 is a structural cross-sectional view of a nitride semiconductor showing a first embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of a nitride-based semiconductor showing a first embodiment of the present invention.

FIG. 3 is a manufacturing process diagram of a conventional nitride-based semiconductor

FIG. 4 is a diagram showing an effect of one embodiment of the present invention.

FIG. 5 is a diagram showing an effect of one embodiment of the present invention.

FIG. 6 is a structural cross-sectional view of a nitride-based semiconductor showing a second embodiment of the present invention.

FIG. 7 is a cross-sectional view of a nitride semiconductor device showing the first embodiment of the present invention.

[Explanation of symbols]

1 Si substrate 2 ZnO: Al buffer layer 3 AlGaInN layer 4 GaN initial growth nucleus 5 GaN layer 6 ZnO buffer layer 7 GaN initial growth nucleus 8 GaN layer 9 Al2O3: Si buffer layer 10 AlGaInN layer 71 n-Si substrate 72 ZnO: Al Buffer layer 73 n-AlGaN cladding layer 74 n-AlGaInN optical guide layer 75 GaInN-based multiple quantum well active layer 76 p-AlGaN cap layer 77 p-AlGaInN optical guide layer 78 p-AlGaN cladding layer 79 p-AlGaInN contact layer 80 p Electrode 81 SiO ₂ 82 n-electrode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasutoshi Kawaguchi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 4G077 AA03 BE11 DB08 EB01 ED06                       EF02 HA02 TB05 TC13 TK01                 4K030 AA11 BA02 BA08 BA11 BA38                       BB02 CA04 DA02 FA10 HA04                       JA10 LA18                 5F045 AA04 AB14 AF03 AF13 BB12                       BB13 CA12 DA53                 5F052 JA07 KA01                 5F073 AA45 AA55 AA74 CA07 CB04                       CB07 EA29

Claims (8)

[Claims] 1. Al _x Gay _y In _z N (0≤x≤1,0≤y using a ZnO buffer layer doped with impurities on a Si substrate.
≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) system semiconductor is grown, The manufacturing method of the nitride system semiconductor characterized by the above-mentioned. 2. The method for producing a nitride-based semiconductor according to claim 1, wherein the impurity is composed of at least In, Ga or Al. 3. An Al _x Ga _y In _z N (0 ≦ x ≦) formed by using an impurity-doped ZnO buffer layer on a Si substrate.
1,0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) based semiconductor device. 4. The Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1 according to claim 3, wherein the impurities are composed of at least In, Ga or Al. , 0 ≦ z
≦ 1, x + y + z = 1) based semiconductor device. 5. An Al _x Ga _y In _z N (0≤x≤1,0≤ using an Al ₂ O ₃ buffer layer doped with impurities on a Si substrate.
y ≦ 1,0 ≦ z ≦ 1, x + y + z = 1) -based semiconductor is grown, and a method for manufacturing a nitride-based semiconductor. 6. The method for manufacturing a nitride-based semiconductor according to claim 5, wherein the impurities are composed of at least one of Si and Ge. 7. An Al _x Ga _y In _z N (0 ≦ x formed by using an Al ₂ O ₃ buffer layer doped with impurities on a Si substrate.
≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1, x + y + z = 1) based semiconductor device. 8. The Al _{x according} to claim 7, wherein the impurities are composed of at least one of Si and Ge.
_{Ga y In z N (0 ≦} x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1,
x + y + z = 1) type semiconductor device.