JP7265624B2 - semiconductor film - Google Patents

Description

The present invention relates to an α-Ga ₂ O ₃ based semiconductor film.

In recent years, gallium oxide (Ga ₂ O ₃ ) has attracted attention as a semiconductor material. Gallium oxide is known to have five crystal forms _of α, β, γ, δ and _ε . It is very large and is expected to be used as a material for power semiconductors.

For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2014-72533) discloses a semiconductor comprising an underlying substrate having a corundum-type crystal structure, a semiconductor layer having a corundum-type crystal structure, and an insulating film having a corundum-type crystal structure. A device is disclosed, and an example is described in which an α-Ga ₂ O ₃ film is formed as a semiconductor layer on a sapphire substrate. Further, in Patent Document 2 (JP 2016-25256 A), an n-type semiconductor layer containing as a main component a crystalline oxide semiconductor having a corundum structure, and an inorganic compound having a hexagonal crystal structure as a main component A semiconductor device comprising a p-type semiconductor layer and an electrode is disclosed. In the example of Patent Document 2, an α-Ga ₂ O ₃ film having a metastable phase corundum structure as an n-type semiconductor layer and a hexagonal crystal structure as a p-type semiconductor layer are formed on a c-plane sapphire substrate. to fabricate a diode by forming an α-Rh ₂ O ₃ film having

By the way, the α-Ga ₂ O ₃ film has a corundum-type crystal structure, and the c-plane of the corundum-type crystal structure has three-fold symmetry. However, there is a problem that it occurs at the time and degrades the device characteristics. In this respect, a technique has been proposed for fabricating a film with a low content of rotational domains by introducing a buffer layer. For example, Patent Document 3 (Japanese Patent Laid-Open No. 2016-156073) describes a first layer mainly composed of an oxide having a corundum structure and a second layer mainly composed of an oxide containing aluminum. Alternately stacked quantum well structures are disclosed and said to be useful as buffer layers capable of reducing rotational domains and bowing. In addition, Patent Document 4 (Japanese Patent Application Laid-Open No. 2016-157878) describes a crystalline oxide semiconductor film that is mainly composed of an oxide semiconductor having a corundum structure and has a rotation domain content of 0.02% by volume or less. is disclosed, and it is also described that a quantum well structure having a configuration similar to that of Patent Document 3 is used as a buffer layer.

JP 2014-72533 A JP 2016-25256 A JP 2016-156073 A JP 2016-157878 A

However, in the conventional techniques disclosed in Patent Documents 3 and 4, when forming an α-Ga ₂ O ₃ film using a substrate with a diameter of 5.08 cm (2 inches) or more, the central portion of the film It has been difficult to form an α-Ga ₂ O ₃ -based semiconductor film that does not substantially contain rotational domains over a wide range from the edge to the outer periphery.

The present inventors have now been able to form an α-Ga ₂ O ₃ -based semiconductor film substantially free of rotational domains over a wide range from the center to the periphery of the film, thereby The inventors have found that the characteristics of a device fabricated using a ₂ O ₃ based semiconductor film can be made uniform.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an α-Ga ₂ O ₃ -based semiconductor film capable of uniforming device characteristics.

According to one aspect of the present invention, a semiconductor film whose main phase is a crystal having a corundum-type crystal structure composed of α-Ga ₂ O ₃ or α-Ga ₂ O ₃ -based solid solution,
The semiconductor film has a circular shape with a diameter of 5.08 cm (2 inches) or more,
When X-ray diffraction (XRD) φ scan measurement is performed on the (104) plane of the crystal at each of the center point X and the four peripheral points A, B, C and D on the surface of the semiconductor film, The ratio of the peak intensity of the secondary peak due to the rotation domain to the peak intensity of the main peak is 1.00% or less,
i) a straight line connecting the outer peripheral points A and C and a straight line connecting the outer peripheral points B and D intersect at right angles at the center point X; and ii) a semiconductor membrane, wherein each of the shortest distances of the perimeter points A, B, C and D from the outer edge of the semiconductor membrane is defined to be ⅕ of the radius of the semiconductor membrane.

According to another aspect of the present invention, there is provided a composite material comprising a circular support substrate with a diameter of 5.08 cm (φ2 inches) or more, and the semiconductor film formed on the support substrate. be done.

FIG. 2 is a diagram for explaining the positions of a central point X and four peripheral points A, B, C and D on the surface of the semiconductor film of the present invention; It is a schematic cross section which shows the structure of a mist CVD (chemical vapor deposition) apparatus. It is a schematic cross section showing the configuration of an aerosol deposition (AD) apparatus. 1 is a schematic cross-sectional view showing the layer structure of Schottky barrier diodes produced in Examples 1 to 9. FIG.

Semiconductor Film The semiconductor film according to the present invention has a main phase of crystals having a corundum type crystal structure, and the corundum type crystal structure is composed of α-Ga ₂ O ₃ or an α-Ga ₂ O ₃ solid solution. be. Therefore, the semiconductor film according to the present invention can be called an α-Ga ₂ O ₃ -based semiconductor film. The semiconductor film is circular with a size of 5.08 cm (2 inches) or more in diameter. Then, when X-ray diffraction (XRD) φ scan measurement is performed on the (104) plane of the crystal at each of the center point X and the four peripheral points A, B, C and D on the surface of the semiconductor film, The ratio of the peak intensity of the secondary peak due to the rotation domain to the peak intensity of the main peak is 1.00% or less. Like the semiconductor film 10 shown in FIG. 1, the outer points A, B, C and D are centered on i) a straight line connecting the outer points A and C and a straight line connecting the outer points B and D. and ii) perimeter points A, B, C and D are defined such that each shortest distance from the outer edge of the semiconductor film is 1/5 of the radius of the semiconductor film. Thus, the α-Ga ₂ O ₃ -based semiconductor film, in which the ratio of the peak intensity of the sub-peaks due to the rotating domains at five points sufficiently separated from each other is 1.00% or less, spreads from the center to the outer periphery of the film. It can be said that the semiconductor film does not substantially contain rotational domains (the content of rotational domains is extremely small) over a wide range, and the characteristics of devices manufactured using such a semiconductor film can be made uniform. “Homogenization of device characteristics” means that even when multiple devices are fabricated from different parts of the same semiconductor film, there is little variation in device characteristics among the resulting devices (devices are homogenized). It means that As described above, in the prior art, when forming an α-Ga ₂ O ₃ film using a substrate with a diameter of 5.08 cm (2 inches) or more, the thickness from the center to the outer periphery of the film is limited. Although it has been difficult to form an α-Ga ₂ O ₃ -based semiconductor film that does not substantially contain rotational domains over a wide range, the present invention solves this problem and makes it possible to uniform device characteristics. It is possible to provide an α-Ga ₂ O ₃ -based semiconductor film that is substantially free of rotational domains over such a wide range.

As described above, the semiconductor film of the present invention has a main phase of crystals having a corundum crystal structure. In the present specification, the phrase "a crystal having a corundum-type crystal structure as the main phase" means that a crystal having a corundum-type crystal structure is 80% by weight or more, preferably 90% by weight or more, more preferably 95% by weight of the semiconductor film. More preferably 97% by weight or more, particularly preferably 99% by weight or more, and most preferably 100% by weight. This corundum type crystal structure is composed of α-Ga ₂ O ₃ or α-Ga ₂ O ₃ solid solution. α-Ga ₂ O ₃ belongs to the trigonal crystal group, has a corundum-type crystal structure, and its c-plane has three-fold symmetry. The α-Ga ₂ O ₃ -based solid solution is a solid solution of other components in α-Ga ₂ O ₃ and maintains a corundum-type crystal structure. For example, the semiconductor film of the present invention contains α-Ga ₂ O ₃ , Cr ₂ O ₃ , Fe ₂ O ₃ , Ti ₂ O ₃ , V ₂ O ₃ , Ir ₂ O ₃ , Rh ₂ O ₃ , In ₂ O ₃ and Al _{2 O 3 .} All of these components have a corundum-type crystal structure, and lattice constants are relatively close to each other. Therefore, metal atoms of these components readily replace Ga atoms in solid solution. In addition, it is possible to control the bandgap, electrical properties, and/or lattice constant of the semiconductor film by dissolving these components. The solid solution amount of these components can be appropriately changed according to the desired properties.

The semiconductor films of the present invention are circular in size with a diameter of 5.08 cm (2 inches) or greater, and may have a size of 10.0 cm or greater. Although the upper limit of the size of the semiconductor film is not particularly limited, it is typically 30.0 cm or less in diameter, more typically 20.0 cm or less in diameter. In this specification, the “circular shape” does not have to be a perfect circular shape, and may be a substantially circular shape that can be recognized as a generally circular shape as a whole. For example, a circular shape may be partially notched for specifying crystal orientation or for other purposes.

The semiconductor film of the present invention was subjected to X-ray diffraction (XRD) φ scan measurements on the (104) plane of the crystal at the central point X of the surface and each of the four peripheral points A, B, C and D. In this case, the ratio of the peak intensity of the secondary peak caused by the rotational domain to the peak intensity of the main peak is 1.00% or less, preferably 0.50% or less, and more preferably 0.10% or less. From the viewpoint of uniformity of device characteristics, the smaller the number of rotating domains, the better. Therefore, the lower limit of the peak intensity ratio of the sub-peaks caused by rotating domains is not particularly limited, and is ideally 0%.

In the semiconductor film of the present invention, the ratio of the peak intensity of the secondary peak due to the rotating domain to the peak intensity of the main peak measured at the center point X is _IX %, and the peripheral points A, B, C and D When the arithmetic mean value of the ratio of the peak _{intensity of} the secondary peak due to the rotation domain _to the peak intensity of the main peak measured in |I _X -I _M |≤0.10, more preferably |I _X -I _M |≤0.05, and most preferably |I _X -I _M |= 0 relationship is satisfied. These relationships mean that there is little difference in the content of rotational domains between the central portion and the outer peripheral portion of the semiconductor film, so that it is possible to more effectively achieve uniform device characteristics.

From the viewpoint of uniformity of device characteristics, the semiconductor film of the present invention preferably has an arithmetic mean value of 2.0 μm or more of the film thickness measured at the center point X and the outer peripheral points A, B, C and D, It is more preferably 3.0 μm or more, still more preferably 5.0 μm or more. When the film thickness is large in this way, it is possible to avoid the deterioration of device characteristics due to the occurrence of cracks during device fabrication, and it is possible to more effectively realize the uniformity of device characteristics. Conventionally, when an attempt is made to increase the film thickness, rotational domains are particularly likely to occur, making it difficult to achieve both an increase in film thickness and a reduction in the number of rotational domains. The film thickness can be increased without The upper limit of the film thickness is not particularly limited, and may be adjusted as appropriate from the viewpoint of cost and required properties. If a self-supporting semiconductor film is required, a thick film may be used. From this point of view, the thickness is, for example, 50 μm or more, or 100 μm or more, and there is no particular upper limit unless there is a cost limit.

The semiconductor film of the present invention preferably has a volume resistivity of 0.10 Ω cm or less, more preferably 0.0001 to 0.0001 to 0.0001 to 0.0001 to 0.0001. 0.10 Ω·cm, more preferably 0.0005 to 0.05 Ω·cm, particularly preferably 0.001 to 0.03 Ω·cm. Since the volume resistivity is low over a wide range from the central portion to the outer peripheral portion of the film, it is possible to more effectively achieve uniform device characteristics. Conventionally, when an attempt is made to lower the volume resistivity, rotation domains are particularly likely to occur, and it has been difficult to achieve both a reduction in volume resistivity and a reduction in rotation domains. volume resistivity can be lowered without

In the semiconductor film of the present invention, the maximum value R _max and the minimum value R _min of volume resistivity measured at the center point X and the peripheral points A, B, C and D are [(R _max −R _min )/R _max ]≦0.20, more preferably [(R _max −R _min )/R _max ]≦0.10, still more preferably [(R _max −R _min )/R _max ]≦0 .05, ideally satisfying the relationship [(R _max −R _min )/R _max ]=0. In this way, the variation in volume resistivity is small over a wide range from the central portion to the outer peripheral portion of the film, making it possible to more effectively achieve uniform device characteristics.

The semiconductor film of the present invention can contain a Group 14 element as a dopant. Here, the group 14 element is a group 14 element according to the periodic table formulated by IUPAC (International Union of Pure and Applied Chemistry), specifically carbon (C), silicon (Si), germanium (Ge ), tin (Sn), and lead (Pb). The content of the dopant (group 14 element) in the semiconductor film is preferably 1.0×10 ¹⁶ to 1.0×10 ²¹ /cm ³ , more preferably 1.0×10 ¹⁷ to 1.0×10 ¹⁹ /cm 3 . ^cm3 . It is preferable that these dopants are homogeneously distributed in the film and that the dopant concentrations on the front surface and the back surface of the semiconductor film are approximately the same. Conventionally, when a dopant is added, rotational domains are particularly likely to occur, making it difficult to achieve both dopant addition and rotational domain reduction. However, according to the semiconductor film of the present invention, the dopant is added without such problems. can do.

The semiconductor film of the present invention may be in the form of a self-supporting film alone, or may be formed on a supporting substrate. In the latter case, the semiconductor film of the present invention is preferably formed on a circular support substrate having a diameter of 5.08 cm (2 inches) or more. That is, according to a preferred aspect of the present invention, there is provided a composite material comprising a circular support substrate with a diameter of 5.08 cm (2 inches) or more, and a semiconductor film formed on the support substrate. . The size of the support substrate may be 10.0 cm or more, similar to the size of the semiconductor film, and the upper limit is not particularly limited. 0 cm or less.

The supporting substrate is preferably a substrate having a corundum structure and being biaxially oriented along the c-axis and the a-axis (biaxially oriented substrate). By using a biaxially oriented substrate having a corundum structure as the supporting substrate, it is possible to use the semiconductor film also as a seed crystal for heteroepitaxial growth. The biaxially oriented substrate may be a polycrystal, a mosaic crystal (a collection of crystals with slightly different crystal orientations), or a single crystal such as sapphire or Cr ₂ O ₃ . As long as it has a corundum structure, it may be composed of a single material or a solid solution of a plurality of materials. The main components of the supporting substrate are α-Cr ₂ O ₃ , α-Fe ₂ O ₃ , α-Ti ₂ O ₃ , α-V ₂ O ₃ , α-Rh ₂ O ₃ and α-Al ₂ O ₃ or α-Al ₂ O ₃ , α-Cr ₂ O ₃ , α-Fe 2 O 3 , α-Ti ₂ O ₃ , α- _{V 2 O 3 and} α-Rh ₂ O Solid solutions containing two or more selected from the group consisting of ₃ are preferred. Among them, sapphire (α-Al ₂ O ₃ single crystal) is particularly preferable in terms of excellent thermal conductivity and easy commercial availability of large-area, high-quality substrates, and α-Cr ₂ from the viewpoint of reducing crystal defects. Solid solutions of O ₃ or α-Cr ₂ O ₃ with foreign materials are particularly preferred.

In addition, as a support substrate and a seed crystal for heteroepitaxial growth, on a corundum single crystal such as sapphire and Cr ₂ O ₃ , a material having a corundum type crystal structure having a longer a-axis length and / or c-axis length than sapphire. Composite base substrates with structured alignment layers can also be used. The alignment layer is a material selected from the group consisting of α-Cr ₂ O ₃ , α-Fe ₂ O ₃ , α-Ti ₂ O ₃ , α-V ₂ O ₃ and α-Rh ₂ O ₃ or α - two selected from the group consisting of Al ₂ O ₃ , α-Cr ₂ O ₃ , α-Fe ₂ O ₃ , α-Ti ₂ O ₃ , α-V ₂ O ₃ and α-Rh ₂ O ₃ Including solid solutions containing the above.

Alternatively, the semiconductor film formed over the base substrate for film formation may be separated and transferred to another supporting substrate. The material of the other support substrate is not particularly limited, but a suitable material may be selected from the viewpoint of material properties. For example, from the viewpoint of thermal conductivity, metal substrates such as Cu, ceramic substrates such as SiC and AlN, and the like are preferable. It is also preferable to use a substrate having a coefficient of thermal expansion of 6 to 13 ppm/K at 25 to 400.degree. By using a supporting substrate having such a coefficient of thermal expansion, it is possible to reduce the difference in thermal expansion from the semiconductor film, and as a result, it is possible to suppress the occurrence of cracks in the semiconductor film and film peeling due to thermal stress. An example of such a support substrate is a substrate composed of a Cu—Mo composite metal. The composite ratio of Cu and Mo can be appropriately selected in consideration of thermal expansion coefficient matching with the semiconductor film, thermal conductivity, electrical conductivity, and the like.

Method for producing a semiconductor film The semiconductor film of the present invention uses a sapphire substrate or a composite base substrate as a base substrate, and an α-Ga ₂ O ₃ -based material is formed thereon (in the case of a composite base substrate, on an orientation layer). It can be manufactured by A known method can be used for forming the semiconductor layer, but preferred examples include the mist CVD method (mist chemical vapor deposition method), the HVPE method (halide vapor phase epitaxy method), and the MBE method (molecular beam epitaxy method). ), and the mist CVD method or the HVPE method is particularly preferred. An α-Ga ₂ O ₃ -based semiconductor film that does not substantially contain a rotating domain over a wide range from the center to the outer periphery of the film is formed while rotating the sapphire substrate or using a composite underlying substrate. It can be realized by

That is, when a sapphire substrate is used as the base substrate, film formation is performed while rotating the substrate 36 in the in-plane direction, as in the apparatus shown in FIG. 2, which will be described later. At this time, by setting appropriate conditions, it is possible to prevent the rotation domain from being included even with a larger substrate size and film thickness. By spinning the substrate to create centrifugal force, the airflow near the substrate 36 can be conveniently controlled to provide film uniformity.

On the other hand, when a composite underlying substrate is used as the underlying substrate, it is not always necessary to rotate the substrate while forming the film, but the substrate may be rotated. In any case, by setting appropriate rotation conditions and/or film formation conditions, it is possible to eliminate rotation domains even with a larger substrate size, thicker film thickness, or lower resistivity.

The mist CVD method, which is one of the particularly preferable film forming methods, will be described below.

In the mist CVD method, a raw material solution is atomized or dropletized to generate mist or droplets, the mist or droplets are transported to a film formation chamber equipped with a substrate using a carrier gas, and the mist or droplets are generated in the film formation chamber. It is a method of thermally decomposing and chemically reacting droplets to form and grow a film on a substrate. It does not require a vacuum process and can produce a large amount of samples in a short time. FIG. 2 shows an example of a mist CVD apparatus. The mist CVD apparatus 20 shown in FIG. 2 includes a mist generation chamber 22 for generating mist M from a carrier gas G and a raw material solution L, and a semiconductor film 38 formed by spraying the mist M onto a substrate 36 through thermal decomposition and chemical reaction. and a film forming chamber 30 for forming a film. The mist generating chamber 22 includes a carrier gas inlet 24 through which carrier gas G is introduced, an ultrasonic vibrator 26 provided in the mist generating chamber 22, and a film forming chamber 30 through which the mist M generated in the mist generating chamber 22 is introduced. and a duct 28 for conveying to. A raw material solution L is accommodated in the mist generating chamber 22 . The ultrasonic vibrator 26 is configured to apply ultrasonic vibration to the raw material solution L to generate the mist M together with the carrier gas G. As shown in FIG. The film forming chamber 30 includes a nozzle 32 for blowing the mist M introduced through the duct 28 onto the substrate 36, a rotating stage 34 to which the substrate 36 is fixed, and a rotating stage provided near the back surface of the rotating stage 34. A heater 42 for heating the substrate 34 and the substrate 36 and an exhaust port 44 for discharging the carrier gas G are provided. The rotating stage 34 is configured to be rotatable in the in-plane direction when spraying the mist M onto the substrate 36 . By forming the semiconductor film 38 while rotating the substrate 36 with such a configuration, even when the semiconductor film 38 is formed using a substrate having a diameter of 5.08 cm (2 inches) or more, the center portion of the film can be It is possible to form an α-Ga ₂ O ₃ -based semiconductor film substantially free of rotational domains over a wide range up to the outer periphery.

The raw material solution L used in the mist CVD method is not limited as long as it is a solution from which an α-Ga ₂ O ₃ -based semiconductor film can be obtained. Examples include those obtained by dissolving an organic metal complex or a halide in a solvent. Examples of organometallic complexes include acetylacetonate complexes. Moreover, when a dopant is added to the semiconductor layer, a dopant component solution may be added to the raw material solution. Furthermore, an additive such as hydrochloric acid may be added to the raw material solution. Water, alcohol, or the like can be used as the solvent.

Next, the obtained raw material solution L is atomized or dropletized to generate a mist M or droplets. A preferred example of a method of atomizing or forming droplets is a method of vibrating the raw material solution L using an ultrasonic oscillator 26 . After that, the obtained mist M or droplets are transported to the film forming chamber 30 using the carrier gas G. FIG. The carrier gas G is not particularly limited, but one or more of oxygen, ozone, inert gas such as nitrogen, and reducing gas such as hydrogen can be used.

A substrate 36 is provided in the deposition chamber 30 . The mist M or droplets transported to the film forming chamber 30 are thermally decomposed and chemically reacted there to form a semiconductor film 38 on the substrate 36 . Although the reaction temperature varies depending on the type of raw material solution L, it is preferably 300 to 800°C, more preferably 400 to 700°C. In addition, the atmosphere in the film forming chamber 30 is not particularly limited as long as a desired semiconductor film can be obtained. is selected from either

The semiconductor film thus obtained can be used as it is or divided into semiconductor elements. Alternatively, the semiconductor film may be peeled off from the composite underlying substrate to form a single film. In this case, in order to facilitate separation from the composite base substrate, a release layer may be provided in advance on the orientation layer surface (film formation surface) of the composite base substrate. Examples of such a peeling layer include those in which a C-implanted layer or an H-implanted layer is provided on the surface of the composite base substrate. Alternatively, C or H may be injected into the film at the initial stage of film formation of the semiconductor film, and a peeling layer may be provided on the semiconductor film side. Furthermore, a supporting substrate (mounting substrate) different from the composite underlying substrate is adhered and bonded to the surface of the semiconductor film formed on the composite underlying substrate (that is, the surface opposite to the composite underlying substrate), and then the semiconductor film is It is also possible to peel off the composite base substrate from. As such a support substrate (mounting substrate), a substrate having a coefficient of thermal expansion of 6 to 13 ppm/K at 25 to 400° C., for example, a substrate composed of a Cu—Mo composite metal can be used. Examples of methods for bonding and bonding the semiconductor film and the support substrate (mounting substrate) include known methods such as brazing, soldering, and solid phase bonding. Furthermore, an ohmic electrode, an electrode such as a Schottky electrode, or another layer such as an adhesive layer may be provided between the semiconductor film and the support substrate.

Manufacturing Method of Composite Undersubstrate The above-described composite undersubstrate is produced by (a) preparing a sapphire substrate, (b) producing a predetermined alignment precursor layer, and (c) heat-treating the alignment precursor layer on the sapphire substrate. It can be preferably manufactured by converting at least the portion near the sapphire substrate into an orientation layer, and optionally (d) processing such as grinding or polishing to expose the surface of the orientation layer. This orientation precursor layer becomes an orientation layer by heat treatment, and is made of a material having a corundum-type crystal structure with an a-axis length and/or c-axis length larger than sapphire, or a Contains materials that have a corundum-type crystal structure with a length greater than that of sapphire. In addition, the orientation precursor layer may contain trace components in addition to the material having a corundum type crystal structure. According to such a manufacturing method, the sapphire substrate can be used as a seed crystal to promote the growth of the orientation layer. That is, the orientation layer inherits the high crystallinity and crystal orientation peculiar to the single crystal of the sapphire substrate.

(a) Preparation of Sapphire Substrate To prepare the base substrate, first, a sapphire substrate is prepared. The sapphire substrate used may have any orientation plane. That is, it may have an a-plane, a c-plane, an r-plane, and an m-plane, and may have a predetermined off angle with respect to these planes. For example, when c-plane sapphire is used, since it is c-axis oriented with respect to the surface, it is possible to easily heteroepitaxially grow a c-axis oriented layer thereon. It is also possible to use a sapphire substrate to which a dopant is added in order to adjust the electrical properties. A known dopant can be used as such a dopant.

(b) Preparation of Oriented Precursor Layer A material having a corundum-type crystal structure with an a-axis length and/or a c-axis length larger than sapphire, or a corundum-type crystal structure with an a-axis length and/or c-axis length larger than sapphire by heat treatment. An alignment precursor layer containing a material is produced. A method for forming the alignment precursor layer is not particularly limited, and a known method can be employed. Examples of methods for forming the alignment precursor layer include AD (aerosol deposition) method, sol-gel method, hydrothermal method, sputtering method, vapor deposition method, various CVD (chemical vapor deposition) methods, PLD method, CVT (chemical vapor deposition) method, gas phase transportation) method, sublimation method, and the like. Examples of CVD methods include thermal CVD, plasma CVD, mist CVD, and MO (metal organic) CVD. Alternatively, a method may be used in which a molded body of the alignment precursor is prepared in advance and this molded body is placed on the sapphire substrate. Such a molded body can be produced by molding an alignment precursor material by a technique such as tape molding or press molding. Also, a method of using a polycrystalline body prepared in advance by various CVD methods, sintering, or the like as the orientation precursor layer and placing it on a sapphire substrate can also be used.

However, aerosol deposition (AD) methods, various CVD methods, or sputtering methods are preferred. By using these methods, it becomes possible to form a densely oriented precursor layer in a relatively short period of time, which facilitates heteroepitaxial growth using a sapphire substrate as a seed crystal. In particular, since the AD method does not require a high-vacuum process and the deposition rate is relatively high, it is preferable in terms of manufacturing cost. When the sputtering method is used, the film can be formed using a target of the same material as the alignment precursor layer, but a reactive sputtering method can also be used in which a metal target is used and the film is formed in an oxygen atmosphere. can. A method of placing a prefabricated compact on sapphire is also preferable as a simple method. However, since the orientation precursor layer is not dense, a process of densification is required in the heat treatment step described later. The method of using a prefabricated polycrystal as an orientation precursor layer requires two steps: a step of preparing the polycrystal and a step of heat-treating it on the sapphire substrate. Also, in order to improve the adhesion between the polycrystal and the sapphire substrate, it is necessary to make the surface of the polycrystal sufficiently smooth. Although known conditions can be used for any of the methods, a method of directly forming an alignment precursor layer using the AD method and a method of placing a prefabricated compact on a sapphire substrate will be described below. .

The AD method is a technology in which fine particles and fine particle raw materials are mixed with gas to form an aerosol, and this aerosol is sprayed at high speed from a nozzle to collide with the substrate to form a coating. It has characteristics. FIG. 3 shows an example of a film forming apparatus (aerosol deposition (AD) apparatus) used in such an AD method. A film forming apparatus 50 shown in FIG. 3 is configured as an apparatus used for the AD method in which raw material powder is sprayed onto a substrate under an atmosphere of pressure lower than the atmospheric pressure. The film forming apparatus 50 includes an aerosol generating section 52 for generating an aerosol of raw material powder containing raw material components, and a film forming section 60 for injecting the raw material powder onto a sapphire substrate 51 to form a film containing raw material components. there is The aerosol generation unit 52 includes an aerosol generation chamber 53 that contains raw material powder and receives carrier gas supplied from a gas cylinder (not shown) to generate an aerosol, a raw material supply pipe 54 that supplies the generated aerosol to the film formation unit 60, It has an aerosol generation chamber 53 and a vibrator 55 for applying vibrations to the aerosol therein at a frequency of 10 to 100 Hz. The film forming unit 60 includes a film forming chamber 62 for injecting an aerosol onto the sapphire substrate 51, a substrate holder 64 disposed inside the film forming chamber 62 for fixing the sapphire substrate 51, and the substrate holder 64 on the X axis-Y axis. and an XY stage 63 that moves in the directions. The film formation unit 60 also includes an injection nozzle 66 having a slit 67 formed at its tip for injecting an aerosol onto the sapphire substrate 51 and a vacuum pump 68 for reducing the pressure in the film formation chamber 62 .

It is known that the AD method can control the film thickness, film quality, etc. by changing the film forming conditions. For example, the morphology of the AD film is susceptible to the collision speed of the raw material powder against the substrate, the particle size of the raw material powder, the aggregation state of the raw material powder in the aerosol, the injection amount per unit time, and the like. The collision speed of the raw material powder against the substrate is affected by the differential pressure between the film forming chamber 62 and the injection nozzle 66, the opening area of the injection nozzle, and the like. If suitable conditions are not used, the coating may become compacted or have pores, so it is necessary to appropriately control these factors.

In the case of using a molded body having an orientation precursor layer formed in advance, the raw material powder of the orientation precursor can be molded to produce the molded body. For example, when press molding is used, the orientation precursor layer is a press molding. The press-formed body can be produced by press-molding the raw material powder of the orientation precursor based on a ^known technique. It may be produced by pressing with a pressure of up to 300 kgf/cm ² . Further, the molding method is not particularly limited, and in addition to press molding, tape molding, cast molding, extrusion molding, doctor blade method, and any combination thereof can be used. For example, when tape molding is used, additives such as a binder, a plasticizer, a dispersant, and a dispersion medium are appropriately added to the raw material powder to form a slurry, and the slurry is passed through a thin slit-shaped discharge port to form a sheet. Dispensing and molding are preferred. Although the thickness of the sheet-shaped molding is not limited, it is preferably 5 to 500 μm from the viewpoint of handling. Further, when a thick orientation precursor layer is required, a large number of such sheet moldings may be stacked to obtain a desired thickness.

These compacts are heat-treated on the sapphire substrate to form an orientation layer in the vicinity of the sapphire substrate. As described above, in such a method, it is necessary to sinter and densify the compact in the heat treatment step described below. For this reason, the compact may contain minor ingredients such as sintering aids in addition to materials having or providing a corundum-type crystal structure.

(c) Heat Treatment of Alignment Precursor Layer on Sapphire Substrate The sapphire substrate on which the alignment precursor layer is formed is heat treated at a temperature of 1000° C. or higher. This heat treatment makes it possible to convert at least a portion of the alignment precursor layer near the sapphire substrate into a dense alignment layer. This heat treatment also enables the orientation layer to grow heteroepitaxially. That is, by forming the orientation layer with a material having a corundum-type crystal structure, heteroepitaxial growth occurs in which the material having the corundum-type crystal structure grows during heat treatment using the sapphire substrate as a seed crystal. At that time, rearrangement of crystals occurs, and the crystals are arranged following the crystal plane of the sapphire substrate. As a result, the crystal axes of the sapphire substrate and the orientation layer can be aligned. For example, when a c-plane sapphire substrate is used, both the sapphire substrate and the orientation layer can be c-axis oriented with respect to the surface of the underlying substrate. Moreover, this heat treatment allows the formation of graded composition regions in a portion of the orientation layer. That is, during the heat treatment, a reaction occurs at the interface between the sapphire substrate and the alignment precursor layer, and the Al component in the sapphire substrate diffuses into the alignment precursor layer and/or the components in the alignment precursor layer diffuse into the sapphire substrate. to form a graded composition region composed of a solid solution containing α-Al ₂ O ₃ .

It is known that various methods such as CVD, sputtering, PLD, CVT, and sublimation may cause heteroepitaxial growth on a sapphire substrate without heat treatment at 1000° C. or higher. However, the oriented precursor layer is in a non-oriented state, that is, amorphous or non-oriented polycrystal at the time of fabrication, and it is preferable to cause crystal rearrangement using sapphire as a seed crystal during the heat treatment step. By doing so, it is possible to effectively reduce crystal defects reaching the surface of the orientation layer. Although the reason for this is not clear, it is thought that it is because the crystal defects generated in the lower portion of the orientation layer tend to annihilate.

The heat treatment is not particularly limited as long as a corundum type crystal structure is obtained and heteroepitaxial growth occurs with the sapphire substrate as a seed, and it can be performed in a known heat treatment furnace such as a tubular furnace and a hot plate. In addition to these normal pressure (pressless) heat treatments, pressure heat treatments such as hot pressing and HIP, and combinations of normal pressure heat treatments and pressure heat treatments can also be used. The heat treatment conditions can be appropriately selected depending on the material used for the orientation layer. For example, the heat treatment atmosphere can be selected from air, vacuum, nitrogen and inert gas atmospheres. The preferred heat treatment temperature also varies depending on the material used for the alignment layer, but is preferably 1000 to 2000°C, more preferably 1200 to 2000°C. The heat treatment temperature and holding time are related to the thickness of the oriented layer generated by heteroepitaxial growth and the thickness of the graded composition region formed by diffusion with the sapphire substrate. It can be adjusted appropriately depending on the thickness and the like. However, when a prefabricated compact is used as the orientation precursor layer, it must be sintered and densified during heat treatment, and normal pressure firing at high temperature, hot pressing, HIP, or a combination thereof is suitable. . For example, when hot pressing is used, the surface pressure is preferably 50 kgf/cm ² or more, more preferably 100 kgf/cm ² or more, particularly preferably 200 kgf/cm ² or more, and the upper limit is not particularly limited. Also, the firing temperature is not particularly limited as long as sintering, densification and heteroepitaxial growth occur, but is preferably 1000° C. or higher, more preferably 1200° C. or higher, further preferably 1400° C. or higher, and particularly preferably 1600° C. or higher. The firing atmosphere can also be selected from air, vacuum, nitrogen and inert gas atmospheres. Firing jigs such as molds made of graphite or alumina can be used.

(d) Exposure of alignment layer surface An alignment precursor layer or a poorly oriented or non-oriented surface layer may exist or remain on the alignment layer formed near the sapphire substrate by heat treatment. In this case, it is preferable to expose the surface of the alignment layer by performing processing such as grinding or polishing on the side derived from the alignment precursor layer. By doing so, the material having excellent orientation is exposed on the surface of the orientation layer, so that the semiconductor layer can be effectively epitaxially grown thereon. A technique for removing the orientation precursor layer and the surface layer is not particularly limited, but examples thereof include a technique of grinding and polishing and a technique of ion beam milling. Polishing of the surface of the alignment layer is preferably performed by lapping using abrasive grains or chemical mechanical polishing (CMP).

The invention is further illustrated by the following examples.

Example 1
(1) Preparation of α-Ga ₂ O ₃ -based semiconductor film by mist CVD method (1a) Preparation of raw material solution A 0.05 mol/L aqueous solution of gallium acetylacetonate was prepared, and 12N concentrated hydrochloric acid was added by volume. Tin (II) chloride was added to the obtained mixed solution so as to have a concentration of 0.001 mol/L to obtain a raw material solution.

(1b) Film formation preparation A mist CVD apparatus 20 having the configuration shown in FIG. 2 was prepared. The configuration of the mist CVD apparatus 20 is as described above. In the mist CVD apparatus 20 , the raw material solution L obtained in (1a) above was accommodated in the mist generation chamber 22 . A c-plane sapphire substrate having a diameter of 5.08 cm (2 inches) was set on a rotating stage 34 as the substrate 36, and the distance between the tip of the nozzle 32 and the substrate 36 was set to 120 mm. The temperature of the rotary stage 34 was raised to 480° C. by the heater 42 and held for 30 minutes for temperature stabilization. A flow control valve (not shown) was opened to supply nitrogen gas as the carrier gas G into the film forming chamber 30 through the mist generating chamber 22, and the atmosphere in the film forming chamber 30 was sufficiently replaced with the carrier gas G. After that, the flow rate of carrier gas G was adjusted to 2.0 L/min.

(1c) Film formation The raw material solution L is atomized by vibrating the ultrasonic oscillator 26 at 2.4 MHz while rotating the rotary stage 34 at a rotational speed of 60 rpm, and the generated mist M is used as a carrier gas G to form a film. It was introduced into the chamber 30 . A semiconductor film 38 was formed on the substrate 36 for one hour by reacting the mist M on the surface of the substrate 36 (specifically, the sapphire substrate) in the film forming chamber 30 . Thus, a composite material 40 composed of the substrate 36 and the semiconductor film 38 formed thereon was obtained.

(2) Evaluation of semiconductor film (2a) Surface EDX
As a result of subjecting the surface of the obtained semiconductor film 38 to composition analysis by energy dispersive X-ray spectroscopy (EDX), only Ga and O were detected. From this, it was found that the semiconductor film 38 was composed of Ga oxide.

(2b) XRD
Using an X-ray diffraction (XRD) device (Bruker-AXS Co., Ltd., D8-DISCOVER), the center point X on the surface of the semiconductor film shown in FIG. A φ scan was performed on the (104) plane of the Ga oxide film under the following conditions. That is, the XRD measurement at each of the above points was carried out by adjusting 2θ, ω, χ and φ and setting the axis so that the peak of the (104) plane of α-Ga ₂ O ₃ appeared. A current of 40 mA, a collimator diameter of 0.5 mm, an anti-scattering slit of 3 mm, a range of ω=0 to 360°, an ω step width of 0.005°, and a counting time of 0.5 seconds were used. The peak top values of the three detected main peaks were averaged to obtain the peak intensity of the main peak. Also, the peak top values of the three sub-peaks caused by the rotational domain detected at ω shifted by 60° from the main peak were averaged to obtain the peak intensity of the sub-peak caused by the rotational domain.

Note that the outer peripheral points A, B, C and D are i) a straight line connecting the outer peripheral points A and C and a straight line connecting the outer peripheral points B and D intersect at right angles at the center point X, and ii) Each of the shortest distances from the outer edge of the semiconductor film to the perimeter points A, B, C and D was determined to be ⅕ of the radius of the semiconductor film. The ratios Ix, IA, IB, IC and ID of the peak intensity of the minor peaks due to the rotating domain to the peak intensity of the major peak at the central point _X and the peripheral points _A , _B , _C and _D are calculated respectively. Also, the arithmetic mean values I _M and |I _X −I _M | of I _A , I _B , I _C and I _D were calculated. The results were as shown in Table 1.

(2c) Film thickness The film thickness was evaluated by cross-sectional TEM observation. The test piece used for TEM observation is the composite material 40 separately prepared by the same method as in (1) above, from the vicinity of the five points of the center point X and the outer peripheral points A, B, C and D shown in FIG. , FIB, and sliced by ion milling. Using a transmission electron microscope H-90001UHR-I manufactured by Hitachi, cross-sectional observation was performed at an acceleration voltage of 300 kV, and the film thickness of each sample was measured. The results were as shown in Table 1.

(2d) Volume resistivity The volume resistivity of the semiconductor film 38 was measured by the four-probe method using a resistivity meter (Mitsubishi Chemical, Loresta GP, MCP-T610 type). Specifically, the volume resistivities R _x , R A , R _B , R C and R D of the semiconductor film 38 at the central point X and the outer peripheral points A, _B , _C and _D shown in FIG. 1 are measured, respectively. bottom. In addition, the maximum value of R _x , R _A , R _B , R _C and R _D was defined as R _max and the minimum value as R _min , and the value of (R _max −R _min )/R _max was calculated. The results were as shown in Table 1.

(2e) Device homogeneity (device fabrication)
The composite material 40 obtained in (1c) above is cut into 10 mm squares so that the center point X and the positions of the outer peripheral points A, B, C and D are approximately at the center, and five composite material pieces 40 ' got. As shown in FIG. 4, the composite piece 40' is composed of a substrate 36 and a semiconductor film 38, and the substrate 36 serves as the underlying substrate 72 and the semiconductor film 38 serves as the n ⁺ layer 74 in fabricating the device. use. After masking a region of 2 mm×10 mm from the end of the surface of the composite material piece 40 ′ on the side of the semiconductor film 38 (n ⁺ layer 74 ) with a sapphire substrate (not shown), an n ⁻ layer 76 was formed. The n ⁻ layer 76 was formed by not adding a dopant (specifically, tin (II) chloride) in the preparation of the raw material solution in (1a) above, and by not rotating the rotating stage 34 in (1c) above. The same procedure as in (1) above was carried out, except that the film formation was carried out for 30 minutes. After forming the n ⁻ layer 76 , the sapphire substrate (not shown) as a mask was removed to expose the n ⁺ layer 74 . A Ti electrode 78 (ohmic electrode) was formed on the exposed region of the n ⁺ layer 74, while a Pt electrode 80 (Schottky electrode) was formed on the n ⁻ layer. A Pt electrode 80 was formed on the Ti electrode 78 and the n ^- layer. Thus, a lateral Schottky barrier diode 70 as shown in FIG. 4 was produced.

(device evaluation)
For the Schottky barrier diode 70, the current (ON current) ION that flows when a voltage of 10 V is applied in the forward direction and the current (OFF current) I _OFF that flows when a voltage of 10 V is applied in the reverse direction _were measured. , and the ratio of the OFF current I _OFF to the ON current I _ON (that is, _ION /I _OFF ) was taken as the P-value. At this time, the P values are measured for each of the Schottky barrier diodes 70 corresponding to the central point X and the peripheral points A, B, C and D, and P _X , P _A , P _B , P _C and P _D. Further, when the arithmetic mean value of the common logarithms logP _X , logP _A , logP _B , logP _C and logP _D is M _P , |M _P -logP _X |, |M _P -logP _A |, | Among the five values of M _P -logP _B |, |M _P -logP _C | and |M _P -logP _D |, the number of values that are 0.5 or less is S, and (S / 5) × 100 [% ] was used as an index representing the homogeneity of the device. The results were as shown in Table 1.

In this example, the Schottky barrier diode 70 is in the form of a horizontal device in order to easily evaluate the homogeneity of the device. shows the same trend as the horizontal device of

Example 2
Except that the concentration of tin (II) chloride was set to 0.01 mol/L in the preparation of the raw material solution in (1a) above, and that the film formation conditions in (1c) above were changed as shown in Table 1. A semiconductor film was prepared and various evaluations were performed in the same manner as in Example 1. The results were as shown in Table 1.

Example 3
A semiconductor film was produced and various evaluations were performed in the same manner as in Example 2, except that the apparatus and film formation conditions in (1b) and (1c) were changed as shown in Table 1. The results were as shown in Table 1.

Example 4
Same as Example 2 except that the raw material solution of (1a) was prepared as follows, and the apparatus and film formation conditions of (1c) and (1d) were changed as shown in Table 1. Then, semiconductor films were produced and various evaluations were performed. The results were as shown in Table 1.

(Preparation of raw material solution)
A raw material aqueous solution containing gallium bromide and germanium oxide at a substance amount ratio of 100:5 was prepared. This aqueous solution contained 10% by volume of a 48% hydrobromic acid solution. The concentration of germanium (IV) oxide was set to 5.0×10 ⁻³ mol/L.

example 5
The apparatus and film formation conditions of (1b) and (1c) above were changed as shown in Table 1, and a composite base substrate prepared as follows was used as the substrate 36 in the film formation of (1c) above. A semiconductor film was produced and various evaluations were carried out in the same manner as in Example 2 except that it was used. The results were as shown in Table 1.

(Preparation of composite base substrate)
(a) Preparation of Orientation Precursor Layer 2.4 parts by weight of TiO ₂ powder was added to 100 parts by weight of commercial Cr ₂ O ₃ powder and wet-mixed, and the obtained mixed powder was pulverized in a pot mill to form grains. A Cr ₂ O ₃ /TiO ₂ mixed powder having a diameter D50 of 0.4 μm was obtained as a raw material powder. Using this raw material powder and sapphire (diameter 5.08 cm (2 inches), thickness 0.43 mm, c-plane, off-angle 0.2°) as a seed substrate, the aerosol deposition (AD ) An AD film was formed on the seed substrate (sapphire substrate) by the apparatus 50 . The configuration of the aerosol deposition (AD) device 50 is as described above.

AD film forming conditions were as follows. That is, _N2 was used as the carrier gas, and a ceramic nozzle having a slit with a long side of 5 mm and a short side of 0.3 mm was used. The nozzle scanning conditions were as follows: 1 mm/s scanning speed, 55 mm movement in the forward direction perpendicular to the long side of the slit, 5 mm movement in the long side direction of the slit, and perpendicular to the long side of the slit in the returning direction. Scanning of moving 55 mm, moving 5 mm in the long side direction of the slit and in the direction opposite to the initial position is repeated, and when the slit is moved 55 mm from the initial position in the long side direction of the slit, scanning is performed in the opposite direction. , the cycle of returning to the initial position was defined as one cycle, and this was repeated 300 cycles. In one cycle of film formation at room temperature, the set pressure of the carrier gas was adjusted to 0.06 MPa, the flow rate was adjusted to 6 L/min, and the pressure in the chamber was adjusted to 100 Pa or less. The thickness of the AD film (orientation precursor layer) thus formed was about 60 μm.

(b) Heat Treatment of Alignment Precursor Layer The sapphire substrate on which the AD film (orientation precursor layer) was formed was removed from the AD apparatus and annealed at 1600° C. for 4 hours in a nitrogen atmosphere.

(c) Measurement of crystal growth thickness Prepare an AD film (orientation precursor layer) separately prepared by the same method as (a) and (b) above, and pass through the center of the substrate in a direction perpendicular to the plate surface. cut like this. The cross section of the cut sample was smoothed by lapping using diamond abrasive grains, and mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. The resulting cross section was photographed with a scanning electron microscope (SU-5000, manufactured by Hitachi High-Technologies Corporation). Observing the backscattered electron image of the cross section after polishing, it is possible to identify the orientation precursor layer remaining polycrystalline (hereinafter referred to as the polycrystalline portion) and the orientation layer, respectively, due to the channeling contrast due to the difference in crystal orientation. was made. As a result of estimating the thickness of each layer in this manner, the thickness of the orientation layer was about 50 μm, and the thickness of the polycrystalline portion was about 10 μm.

(d) Grinding and Polishing After grinding the surface of the obtained substrate on the side derived from the AD film until the orientation layer is exposed, using a grindstone of grit up to #2000, lapping using diamond abrasive grains is performed. , further smoothed the plate surface. After that, the substrate was mirror-finished by chemical mechanical polishing (CMP) using colloidal silica to obtain a composite base substrate having an orientation layer on a sapphire substrate. The surface of the substrate on the side originating from the AD film was defined as the "surface". The amount of grinding and polishing was about 30 μm in total for the polycrystalline portion and the orientation layer, and the thickness of the orientation layer formed on the composite base substrate was about 30 μm.

Example 6
The apparatus and film formation conditions of (1b) and (1c) above were changed as shown in Table 1, a 10.0 cm composite base substrate was prepared and used, and film formation was performed by the AD method. A semiconductor film was prepared and various evaluations were performed in the same manner as in Example 5, except that the range was expanded to a 110 mm square area. The results were as shown in Table 1.

Examples 7 and 8 (comparative)
A semiconductor film was fabricated and various evaluations were performed in the same manner as in Example 1, except that the film formation conditions in (1c) above were changed as shown in Table 1 (for example, the stage rotation speed was set to 0 rpm). The results were as shown in Table 1.

Example 9 (Comparison)
The concentration of tin (II) chloride was set to 0.02 mol/L in the preparation of the raw material solution of (1a) above, and the film formation conditions of (1c) above were changed as shown in Table 1 (for example, stage rotation A semiconductor film was prepared and various evaluations were performed in the same manner as in Example 1, except that the rotation speed was set to 0 rpm. The results were as shown in Table 1.

Claims (8)

A semiconductor film whose main phase is a crystal having a corundum-type crystal structure composed of α-Ga ₂ O ₃ or an α-Ga ₂ O ₃ -based solid solution,
The semiconductor film has a circular shape with a diameter of 5.08 cm (2 inches) or more,
When X-ray diffraction (XRD) φ scan measurement is performed on the (104) plane of the crystal at each of the center point X and the four peripheral points A, B, C and D on the surface of the semiconductor film, The ratio of the peak intensity of the secondary peak due to the rotation domain to the peak intensity of the main peak is 1.00% or less,
i) a straight line connecting the outer peripheral points A and C and a straight line connecting the outer peripheral points B and D intersect at right angles at the center point X; and ii) the shortest distances of the outer perimeter points A, B, C, and D from the outer edge of the semiconductor film are determined to be ⅕ of the radius of the semiconductor film,
Let the ratio of the peak intensity of the secondary peak due to the rotation domain to the peak intensity of the main peak measured at the center point X be _IX %, and be measured at the peripheral points A, B, C and D. satisfies the relationship |I _X −I _M |≦0.20, where I _M % is the arithmetic mean value of the ratio of the peak intensity of the secondary peak due to the rotational domain to the peak intensity of the main peak. , a semiconductor film. 2. The semiconductor film according to claim 1, wherein an arithmetic mean value of thicknesses of said semiconductor film measured at said center point X and said peripheral points A, B, C and D is 2.0 [mu]m or more. 3. The semiconductor film according to claim 1, wherein the volume resistivity measured at said center point X and said peripheral points A, B, C and D is 0.10 Ω·cm or less. The maximum value R _max and the minimum value R _min of volume resistivity measured at the center point X and the peripheral points A, B, C and D are [(R _max −R _min )/R _max ]≦0.20. 4. The semiconductor film according to claim 1, which satisfies the relationship of The volume resistivities measured at the central point X and the peripheral points A, B, C and D are all 0.10 Ω·cm or less, and
Maximum value R of volume resistivity measured at the center point X and the outer peripheral points A, B, C and D _max and minimum value R _min but [(R _max -R _min )/R _max ] ≤ 0.20. 6. The semiconductor film according to claim 1, wherein said semiconductor film contains a Group 14 element as a dopant at a rate of 1.0×10 ¹⁶ to 1.0×10 ²¹ / cm ³ . 7. The semiconductor film according to claim 1, wherein said semiconductor film is formed on a circular support substrate having a diameter of 5.08 cm (φ2 inches) or more. A composite material comprising a circular support substrate having a diameter of 5.08 cm (φ2 inches) or more, and the semiconductor film according to any one of Claims 1 to 6 formed on the support substrate.

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