JP3534879B2 - Semiconductor device using three-dimensional quantum confinement - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a quantum mechanical effect due to a quantum box structure which three-dimensionally confine quantum confinement. In the present specification, the quantum box means one having a structure capable of performing quantum confinement three-dimensionally, and not only one having a box shape, but also another shape such as an elliptic sphere. Also includes.

With the progress of semiconductor processes, nanoscale thin film growth technology and microfabrication technology have come to be used for manufacturing semiconductor devices. The thin film growth technology and the microfabrication technology have increased the degree of circuit integration, and have put into practical use strained quantum well lasers and the like utilizing the quantum mechanical effect.

[0003]

2. Description of the Related Art It has been pointed out that a conventional semiconductor device has a limit of degree of integration due to a limit of fine processing by a photolithography technique and heat generation caused by movement of many electrons. Further, the demands on the characteristics of the semiconductor laser have become strict, and in recent years, a semiconductor laser capable of operating stably against a large temperature change has been demanded. It is difficult for strained quantum well lasers to meet this strict requirement.

It is considered that these requirements are theoretically solved by a quantum box structure that performs quantum confinement in three dimensions. Only two electrons (sometimes several) can enter one quantum box. The density of states is localized in a wave vector, ideally in a delta function. For example, in an optical semiconductor device, a highly efficient optical modulator can be manufactured due to its delta function density of states. With respect to the semiconductor laser as well, it is considered that since the temperature distribution of carriers is suppressed, the differential gain is improved and the temperature characteristics can be improved.

As a method for realizing a quantum box structure, various methods which have further developed conventional fine processing techniques have been proposed. For example, a method using lithography using an electron beam, a method of forming a quantum box structure near the top of a pyramid-shaped crystal stacked on a mask pattern, a method of utilizing lateral growth in the initial stage of growth on a sloping substrate, and an STM technique. Is a method based on atomic manipulation applied to.

[0006]

In order to take advantage of the quantum mechanical effect peculiar to the quantum box structure, it is important to make the size of the quantum box uniform up to the atomic scale. However, it is difficult to suppress variations in processing size to the atomic scale because the crystal is artificially processed by the method of forming a quantum box, which is a development of the conventional fine processing technology.

Further, the apparatus is complicated and requires a multi-step processing process, which is not suitable for industrial production. Further, due to the multi-step processing process, deterioration of crystal quality due to inclusion of impurities, generation of crystal defects such as dislocations and atomic vacancies is unavoidable.

An object of the present invention is to provide a semiconductor device having a quantum box structure which can be manufactured by a relatively simple manufacturing process.

[0009]

The semiconductor device of the present invention comprises:
A substrate having a semiconductor surface, a buffer layer formed on the semiconductor surface and made of a semiconductor crystal having an in-plane lattice distortion, and arranged in a scattered manner on the buffer layer,
A microcrystal body made of a semiconductor crystal having a lattice strain in the in-plane direction, wherein one of the lattice strain of the buffer layer and the lattice strain of the microcrystal body is extension strain and the other is contraction strain.

Further, it covers the surface on which the microcrystalline body is arranged and has the same lattice strain as that of the microcrystalline body among extension strain and shrinkage strain, and the magnitude thereof is larger than the lattice strain of the microcrystalline body. A semiconductor layer made of a small semiconductor crystal may be formed.

Another semiconductor device according to the present invention is a substrate having a semiconductor surface, a buffer layer formed on the semiconductor surface and made of a semiconductor crystal under in-plane stress, and a buffer layer on the buffer layer. And a microcrystal body made of a semiconductor crystal, which is arranged in a scattered manner in the in-plane direction stress, and in-plane direction stress in the buffer layer and in-plane direction stress in the microcrystal body. One is compressive stress and the other is tensile stress.

Furthermore, the same stress as that of the microcrystalline body is applied to the inside of the microcrystalline body covering the surface on which the microcrystalline body is arranged, and the magnitude thereof is larger than the stress in the microcrystalline body. You may form the semiconductor layer which consists of a small semiconductor crystal.

Another semiconductor device of the present invention is the first semiconductor device when no distortion occurs.
A substrate having a semiconductor surface made of a semiconductor crystal having a lattice constant of, a buffer layer made of a semiconductor crystal having a second lattice constant when the semiconductor surface is free of strain, and a buffer layer formed on the buffer layer. A microcrystal body made of a semiconductor crystal arranged in a dot shape and having a third lattice constant in the absence of strain, wherein the first lattice constant is the second lattice constant or the third lattice constant. It is a medium size.

Further, a semiconductor layer made of a semiconductor crystal having a lattice constant between the first lattice constant and the third lattice constant in the absence of strain is formed so as to cover the surface on which the microcrystalline body is arranged. Good.

[0015]

When a buffer layer having a lattice mismatch is deposited on the semiconductor surface, strain occurs in the buffer layer. This strain is relaxed in the buffer layer as the distance from the semiconductor surface increases. That is, the lattice constant of the buffer layer approaches the lattice constant when there is no strain.

When a semiconductor crystal lattice-mismatched with the upper surface of the buffer layer is deposited on this, if the lattice mismatch exceeds the elastic limit in the growth plane, microcrystals having a strain larger than that of the surroundings are scattered. The semiconductor layer containing the microcrystals is deposited, or the microcrystalline bodies are scattered in a scattered manner. Since the size of the microcrystalline body is a quantum size, when the bandgap of the microcrystalline body is smaller than the surrounding bandgap, the microcrystalline body functions as a quantum box.

When the lattice constant of the semiconductor surface is between the strain-free lattice constant of the microcrystalline body and the lattice constant of the buffer layer without strain, the lattice mismatch between the microcrystalline body and the buffer layer surface. The match is greater than the lattice mismatch between the microcrystal and the semiconductor surface. At this time, with respect to the lattice strain of the buffer layer and the lattice strain of the microcrystalline body, if one is extension strain, the other is contraction strain. In addition, if one of the in-plane stress in the buffer layer and the in-plane stress in the microcrystal body is a compressive stress, the other becomes a tensile stress.

When microcrystals are formed on the buffer layer,
Since the lattice mismatch becomes larger than in the case where the microcrystalline body is directly formed on the semiconductor surface, the internal strain of the microcrystalline body becomes large. It is considered that when the internal strain of the microcrystalline body becomes large, many smaller microcrystalline bodies are formed. In addition,
This could be confirmed by experiments.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the previous proposal disclosed by the inventors of the present invention in Japanese Patent Application No. 6-222107 will be described with reference to FIG.

FIG. 7 shows a sectional view of a semiconductor laminated structure having a quantum box structure according to the above proposal. A GaAs buffer layer 32, an InGaAs layer 33, and a GaAs cap layer 34 are epitaxially grown on a GaAs substrate 31. The InGaAs layer 33 is formed on the buffer layer 32 under an InGaAs growth condition of a composition having a lattice mismatch that exceeds the elastic limit in the growth plane.

The inventors of the present invention have confirmed that InG
It has been found that, when the aAs layer is epitaxially grown, the microcrystals 35 having a different composition from the surroundings are formed in scattered points. The microcrystalline body 35 has a flat spherical shape crushed in the thickness direction. Microcrystal 35 and I around it
From the composition of the nGaAs layer 33, it was found that strain was concentrated in the microcrystalline body 35 and the strain around it was relatively small.

It is considered that the formation of the microcrystalline body 35 in the InGaAs layer 33 stabilizes the entire strain energy. If the energy gap of the microcrystalline body 35 is smaller than the energy gap of the peripheral region,
The microcrystal body 35 serves as a quantum box that performs quantum confinement three-dimensionally.

The microcrystals 35 are not formed by artificial processing, but are self-formed so as to maintain a physical energy balance. Therefore, the size thereof is substantially uniform, and the crystallinity around the microcrystalline body 35 is also kept extremely good.

In the above proposal, the quantum box can be self-formed, but in order to obtain a more remarkable quantum effect, it is desired to further reduce the size of the quantum box. At this time, in order to prevent the in-plane occupation rate of the quantum boxes from decreasing, it is necessary to increase the density of the quantum boxes. Hereinafter, an embodiment of the present invention will be described in which the size of the quantum box can be reduced without reducing the in-plane occupancy of the quantum box.

FIG. 1 schematically shows a cross-sectional view of a semiconductor laminated structure according to an embodiment of the present invention and lattice constants of the respective layers when there is no strain. On the GaAs substrate 1, as shown in the left diagram of FIG.
nGaAsP buffer layer 2, InGaAsP lower layer 3, I
The nGaAs quantum box layer 4 and the InGaAsP upper layer 5 are laminated in this order. In the InGaAs quantum box layer 4,
Quantum boxes 4a are formed in a dotted pattern.

InGaAsP buffer layer 2, InGaA
sP lower layer 3, InGaAs quantum box layer 4, and InGaA
The film thickness of the sP upper layer 5 is 500 nm and 100 n, respectively.
m, 10 nm, and 100 nm.

Each layer is formed by metal organic vapor phase epitaxy (MOVP).
It was epitaxially grown in E). InGa
AsP buffer layer 2, InGaAsP lower layer 3 and InG
Trimethylindium (TMI), triethylgallium (TEG), as a source gas at the time of depositing the aAsP upper layer 5,
Using phosphine (PH ₃ ) and arsine (AsH ₃ ), trimethylindiumdimethylethylamine adduct (In (C
_{H 3) 3 N (CH 3} ) 2 (C 2 H 5)), was used trimethylgallium (TMG) and arsine.

FIG. 2 shows the in-plane diameter of the quantum box 4a with respect to the strain amount of the buffer layer of the semiconductor laminated structure shown in FIG. The horizontal axis represents the strain amount of the buffer layer 2 in%, and the vertical axis represents the in-plane diameter of the quantum box 4a in nm. The strain amount of the buffer layer is a lattice constant of the GaAs substrate 1 is a, InGaAs
When the lattice constant of the P buffer layer 2 without strain is b,
It was defined as (ba) / a. The diameter of the quantum box was observed with a transmission electron microscope (TEM).

When the strain amount of the buffer layer 2 is 0, the diameter of the quantum box is about 22 nm. When the strain amount increases in the positive direction, the diameter of the quantum box increases, and when the strain amount is 0.7%, the diameter of the quantum box becomes about 32 nm. When the strain amount increases in the negative direction, the diameter of the quantum box decreases, and the strain amount becomes −0.
At 8%, the quantum box diameter is about 16 nm.

The reason why the diameter of the quantum box becomes smaller when the strain amount of the buffer layer increases in the negative direction and becomes larger when the strain amount increases in the positive direction is considered as follows.

When the strain amount is negative, extension strain occurs in the in-plane direction of the buffer layer 2. GaA in the buffer layer 2
s The strain gradually relaxes as the distance from the surface of the substrate 1 increases. Therefore, the lattice constant of the upper surface of the buffer layer 2 approaches the lattice constant when there is no strain, and becomes smaller than the lattice constant of the GaAs substrate 1.

The InGaAsP lower layer 3 has such a composition that it has a lattice constant in the absence of strain, which is between the lattice constants of the InGaAs quantum box layer 4 and the InGaAsP buffer layer 2. The strain is gradually relaxed also in the InGaAsP lower layer 3, and the lattice constant of the upper surface of the InGaAsP lower layer 3 is GaA.
It is smaller than the lattice constant of the s substrate 1.

The lattice constant of the InGaAs quantum box layer 4 is Ga.
Since it is larger than the lattice constant of As, the mismatch between the lattice constant of the upper surface of the InGaAsP lower layer 3 and the lattice constant of InGaAs is larger than that of GaAs and InGaAs. Since the lattice mismatch becomes large, a larger strain energy is generated in the InGaAs quantum box layer 4. It is considered that the size of the quantum box 4a becomes smaller in order to reduce the strain energy.

On the contrary, when the strain amount of the buffer layer 2 is increased in the positive direction, the lattice constants of the upper surface of the buffer layer 2 and the lower surface of the InGaAsP lower layer 3 become larger than the lattice constant of the GaAs substrate 1. Therefore, the mismatch between the lattice constant of the upper surface of the InGaAsP lower layer 3 and the lattice constant of InGaAs becomes small. Therefore, it is considered that the quantum box 4a becomes large.

The right diagram of FIG. 1 shows the lattice constant of each layer when the strain amount of the buffer layer 2 is negative and there is no strain. The horizontal axis is GaAs
The relative value of the lattice constant with the lattice constant of the substrate 1 as a reference (0) is shown on an arbitrary scale. The relative value of the lattice constant of the InGaAsP buffer layer 2 without strain is negative, and the lattice constant of the InGaAsP lower layer 3 without strain is an intermediate value between the lattice constant of the GaAs substrate 1 and the lattice constant of the buffer layer 2. . InGa
The relative value of the lattice constant of the As quantum box layer 4 when there is no strain is positive.

If the relative value of the lattice constant of the InGaAs quantum box layer 4 without strain is negative, by making the relative value of the lattice constant of the InGaAsP buffer layer without strain positive, the InGaAs quantum box layer It is possible to increase the lattice mismatch between the InGaAsP lower layer 3 and the InGaAsP lower layer 3.

As described above, the buffer layer is provided between the substrate and the quantum box layer, and the relative value of the lattice constant of the buffer layer without strain is opposite in sign to the relative value of the lattice constant of the quantum box layer without strain. The lattice mismatch between the quantum box layer and the surface of the layer below it can be increased. From the above consideration, it is considered that the in-plane diameter of the quantum box can be reduced when the lattice mismatch becomes large. In order to obtain the effect of reducing the in-plane diameter of the quantum box, the strain in the in-plane direction of the buffer layer is preferably 1 × 10 ⁻³ or more.

In this case, with respect to the lattice strain of the buffer layer and the lattice strain of the quantum box layer, if one is an extension strain, the other is a contraction strain, and the strains are in mutually opposite directions. In addition, if one of the in-plane stress in the buffer layer and the in-plane stress in the quantum box layer is a compressive stress, the other is a tensile stress.

FIG. 3 shows a quantum box 4a having the laminated structure shown in FIG.
3 shows the dependence of the emission wavelength of photoluminescence (PL) on the buffer layer strain amount. The horizontal axis represents the strain amount of the buffer layer in%, and the vertical axis represents the emission wavelength in μm. In addition,
Kr laser light having a wavelength of 6471Å was used as the excitation light.

When the strain amount of the buffer layer is 0, the emission wavelength is about 1.3 μm. When the amount of strain in the buffer layer increases in the negative direction, the emission wavelength becomes shorter, and the amount of strain is -0.8%.
At that time, it becomes about 1.16 μm. When the amount of strain in the buffer layer increases in the positive direction, the emission wavelength becomes longer, and the amount of strain becomes 0.
It becomes about 1.46 μm at 75%.

As the quantum box becomes smaller, the spacing between the electron energy levels in the quantum box becomes wider and the emission wavelength becomes shorter. Therefore, also from FIG. 3, it is suggested that the quantum box becomes smaller when the strain amount of the buffer layer increases in the negative direction.

FIG. 4 shows a quantum box 4a having the laminated structure shown in FIG.
3 shows the dependence of PL emission intensity on the buffer layer strain relaxation amount. The abscissa represents the strain relaxation amount of the buffer layer in the unit of%, and the ordinate represents the PL emission intensity on an arbitrary scale.

Here, the strain relaxation amount of the buffer layer is GaA.
When the lattice constant of the s substrate 1 is a, the lattice constant of the buffer layer 2 without strain is b ₀ , and the lattice constant of the upper surface of the buffer layer 2 is b ₁ , | a−b ₁ | / | a−b ₀ | Was defined. That is, when the strain relaxation amount is 0%, the lattice constant on the upper surface of the buffer layer is the same as the lattice constant of the GaAs substrate 1, and when the strain relaxation amount is 100%, the lattice constant on the upper surface of the buffer layer is the same as that of the buffer layer. It is the same as the lattice constant when strained.

The symbols  and  in the figure indicate the cases where the strain amounts of the buffer layer 2 are −0.8% and −0.3%, respectively. The strain relaxation amount was controlled by changing the thickness of the buffer layer, and measured by examining the X-ray diffraction of the asymmetric crystal plane.

As shown in FIG. 4, as the strain relaxation amount of the buffer layer increases, the PL intensity also increases. It is considered that this is because the crystallinity of the quantum boxes is improved or the distribution density of the quantum boxes is increased. Therefore, when the quantum box is used as the emission center, it is preferable to increase the strain relaxation amount of the buffer layer.

In the above embodiment, the InGaAsP buffer layer 2 and the InGaAsP quantum box layer 4 are arranged between the InGaAsP buffer layer 2 and the InGaAsP quantum box layer 4.
Although the case where the lower layer 3 is inserted has been described, the InGaAs quantum box layer may be directly formed on the InGaAsP buffer layer 2. In addition, the InGaAsP buffer layer 2 and InGa
A plurality of layers may be inserted between the layer and the As quantum box layer 4.

In the above embodiment, GaAs is used as the substrate,
InGaAsP for the buffer layer and InGaAs for the quantum box layer
However, other semiconductor crystals may be used. For example, other III-V group compound semiconductors or semiconductors composed of group IV elements such as Si, Ge and SiGe may be used. Alternatively, a GaAs layer grown at a low temperature may be used as the buffer layer. GaAs
Ga grown at low temperature deviates from stoichiometry
The As layer grows. Therefore, it is possible to form a GaAs layer having a lattice constant different from that of normal GaAs.

Although FIG. 1 shows the case where the quantum box 4a is formed at the same time as the quantum box layer 4, a semiconductor crystal may grow on the semiconductor surface in an island shape. FIG. 5 shows a cross-sectional view of the semiconductor laminated structure when the quantum boxes are grown in an island shape. A buffer layer 2 is formed on a semiconductor substrate 1, and an island-shaped microcrystalline body 6 is grown on the buffer layer 2. The island-shaped grown microcrystals also act as quantum boxes if their size is small enough to cause quantum effects. The microcrystalline body 6 may be embedded with another semiconductor layer. At this time, lattice strain may or may not exist in the other semiconductor layers.

FIG. 6 is a sectional view of a semiconductor laser device to which the laminated structure according to the above-mentioned embodiment is applied. On a n-type GaAs substrate 20, a 500 nm-thick n-type In _0.2 Ga _0.8
P buffer layer 21, 500 nm thick n-type In _0.3 Ga
_0.7 P buffer layer 22, 50 nm thick n-type GaAs
_0.7 P _0.3 clad layer 23, 10 nm thick intrinsic GaA
s _0.7 P _0.3 guide layer 24, intrinsic InGaAs active layer 2
5, 10 nm thick intrinsic GaAs _0.7 P _0.3 guide layer 2
6. A p-type GaAs _0.7 P _0.3 clad layer 27 having a thickness of 50 nm and a p-type In _0.3 Ga _0.7 P contact layer 28 having a thickness of 500 nm are laminated in this order.

Since the lattice constant of the InGaP buffer layer 21 without strain is smaller than that of GaAs,
Tensile strain occurs in the P buffer layer 21. Conversely, In
Since the lattice constant of the GaAs active layer 25 without strain is larger than that of GaAs, compressive strain occurs. As described above, strains in opposite directions are generated in the InGaP buffer layer 21 and the InGaAs active layer 25.

A quantum box 25a is formed in the active layer 25 due to the lattice mismatch between the GaAsP guide layer 24 and the InGaAs active layer 25. This lattice mismatch is caused by InG
Since it is larger than the lattice mismatch between the aAs active layer 25 and the GaAs substrate, a smaller quantum box 25a is formed. The electrons and holes injected into the active layer 25 enter the quantum box having a small band gap and occupy the energy state of the quantum box. When the electron-hole pair recombines in the quantum box 25a and the energy state becomes empty, other electrons and holes enter the quantum box 25a.

As described above, the electron-hole pairs are recombined in the quantum box to emit light, so that a semiconductor laser having excellent temperature characteristics can be realized. Further, the upper surface of the InGaP buffer layer 21 has a lattice constant smaller than that of GaAs. Therefore, it becomes possible to use a semiconductor crystal having a lattice constant smaller than that of GaAs for the cladding layer. Generally, in a III-V compound semiconductor crystal, the band gap increases as the lattice constant decreases.

Therefore, it becomes possible to use a semiconductor crystal having a large band gap as the cladding layer. When the band gap of the clad layer becomes large, the light can be confined more efficiently, so that improvement in the laser emission efficiency can be expected.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0055]

As described above, according to the present invention,
It becomes possible to self-assemble small quantum boxes with high density. When this quantum box is applied to a semiconductor laser device, a semiconductor laser device having excellent temperature characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a semiconductor laminated structure according to an example of the present invention, and a graph showing relative values of lattice constants of each layer when there is no strain.

2 shows the in-plane diameter of the quantum box in the laminated structure shown in FIG.
It is a graph shown with respect to the amount of strains of a buffer layer.

FIG. 3 is a graph showing the PL emission wavelength from the quantum box in the laminated structure shown in FIG. 1 against the strain amount of the buffer layer.

FIG. 4 is a graph showing the PL emission intensity from the quantum box in the laminated structure shown in FIG. 1 against the strain relaxation amount of the buffer layer.

FIG. 5 is a cross-sectional view of a semiconductor laminated structure when quantum boxes are grown in an island shape.

FIG. 6 is a sectional view of a semiconductor laser device according to an embodiment of the present invention.

FIG. 7 is a cross-sectional view of a semiconductor laminated structure proposed by the inventors of the present application.

[Explanation of symbols]

1 GaAs substrate 2 InGaAsP buffer layer 3 InGaAsP lower layer 4 InGaAs quantum box layer 4a quantum box 5 InGaAsP upper layer 6 Microcrystal 20 n-type GaAs substrate 21, 22 n-type InGaP buffer layer 23 n-type GaAsP clad layer 24, 26 GaAsP guide layer 25 InGaAs active layer 27 p-type GaAsP clad layer 28 p-type InGaP contact layer 31 GaAs substrate 32 GaAs buffer layer 33 InGaAs layer 34 GaAs cap layer 35 quantum box

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-231084 (JP, A) JP-A-5-62896 (JP, A) JP-A-8-88345 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 29/06

Claims (8)

(57) [Claims] 1. A substrate having a semiconductor surface, a buffer layer formed on the semiconductor surface and made of a semiconductor crystal having in-plane lattice strain, and arranged on the buffer layer in a scattered manner. A semiconductor device having a microcrystalline body made of a semiconductor crystal having in-plane lattice strain, wherein one of the lattice strain of the buffer layer and the lattice strain of the microcrystalline body is extension strain and the other is contraction strain. 2. The surface on which the microcrystalline body is arranged is covered, and the strain has the same lattice strain as that of the microcrystalline body among extension strain and shrinkage strain, and its magnitude is the lattice strain of the microcrystalline body. The semiconductor device according to claim 1, further comprising a semiconductor layer made of a semiconductor crystal smaller than a size. 3. A substrate having a semiconductor surface, a buffer layer formed on the semiconductor surface and made of a semiconductor crystal to which a stress in an in-plane direction is applied, and dot-shaped arrangements on the buffer layer. , Having a microcrystalline body made of a semiconductor crystal to which stress in the in-plane direction is applied, one of the in-plane direction stress in the buffer layer and the in-plane direction stress in the microcrystal body is a compressive stress, The other is a semiconductor device that has tensile stress. 4. The surface of the microcrystalline body is covered with a stress that is the same as the microcrystalline body of the compressive stress and the tensile stress, and the magnitude of the stress is the stress in the microcrystalline body. The semiconductor device according to claim 3, further comprising a semiconductor layer made of a semiconductor crystal smaller than that. 5. A substrate having a semiconductor surface made of a semiconductor crystal having a first lattice constant when unstrained, and a buffer formed on the semiconductor surface and made of a semiconductor crystal having a second lattice constant when unstrained. Layer and the buffer layer, and the third layer is arranged in a scattered manner on the buffer layer when there is no strain.
And a microcrystal body made of a semiconductor crystal having a lattice constant of, wherein the first lattice constant is an intermediate size between the second lattice constant and the third lattice constant. 6. A semiconductor layer formed of a semiconductor crystal that covers a surface on which the microcrystalline body is arranged and that has a lattice constant intermediate between the first lattice constant and the third lattice constant when no strain is applied. The semiconductor device according to claim 5. 7. The buffer layer and the microcrystalline body are II
The semiconductor device according to claim 1, which is made of an IV group compound semiconductor. 8. The semiconductor device according to claim 1, wherein the semiconductor surface is made of a III-V group compound semiconductor.