Oxide crystals, crystalline oxide films, and methods

Abstract

The present invention provides oxide crystals with good orientation and a rutile-type structure mainly composed of germanium, crystalline oxide films, and methods for forming germanium-containing films. [Solution] By depositing germanium oxide on a rutile-type titanium oxide substrate using a mist CVD method under specific conditions, an oxide crystal containing a rutile-type oxide is obtained, which is oriented in a crystal axis direction perpendicular or parallel to the c-axis, and in which the atomic ratio of germanium among the metal elements in the oxide crystal is greater than 0.5.

Description

[Technical Field]

[0001] The present invention relates to oxide crystals, crystalline oxide films, crystalline multilayer structures, and semiconductor devices using the oxide crystals, all of which are useful for semiconductor devices. [Background technology]

[0002] Germanium oxide is attracting attention as a wide-bandgap semiconductor useful for power devices and other applications. Germanium oxide is said to have a bandgap of 4.44 eV to 4.68 eV (Non-Patent Literature 1), and according to first-principles calculations, its Hall mobility is 27 cm⁻¹. 2 / Vs (perpendicular to the c-axis) or 29cm 2 It is estimated to be / Vs (Non-Patent Document 2), and the realization of pn homojunctions is also expected.

[0003] Rather than relying on estimations based on calculations as described above, the actual fabrication of germanium oxide has also been considered. Non-Patent Literature 3 discloses the deposition of germanium oxide via a (Sn,Ge)O2 buffer layer on an R-face sapphire substrate using the MBE method. Non-Patent Literature 4 discloses the formation of a rutile-type (Sn,Ge)O2 film on a (001)TiO2 substrate using the hybrid MBE method. Thus, rutile-type germanium oxide can be combined with Sn, Si, etc., to form a mixed crystal and can be considered as a single material system. However, the method described in Non-Patent Literature 4 had the problem that if the atomic ratio of germanium in the metal in the film exceeded 0.5, the crystallinity was lost and it became amorphous. Therefore, an oxide crystal (crystalline oxide film) containing germanium oxide with crystalline quality applicable to semiconductor devices has been eagerly awaited. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] STAPELBROEK, M.; EVANS, BD Exciton structure in the uv-absorption edge of tetragonal GeO2. Solid State Communications, 1978, 25.11: 959-962. [Non-Patent Document 2] BUSHICK, Kyle, et al. Electron and hole mobility of rutile GeO2 from first principles: An ultrawide-bandgap semiconductor for power electronics. Applied Physics Letters, 2020, 117.18: 182104. [Non-Patent Document 3] CHAE, Sieun, et al. Epitaxial stabilization of rutile germanium oxide thin film by molecular beam epitaxy. Applied Physics Letters, 2020, 117.7: 072105. [Non-Patent Document 4] LIU, Fengdeng, et al. Hybrid Molecular Beam Epitaxy of Ge-based Oxides. Bulletin of the American Physical Society, 2021. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] One objective of the present invention is to provide an oxide crystal having good orientation and a rutile-type structure mainly composed of germanium. Another objective of the present invention is to provide a crystalline laminated structure comprising a tetragonal crystal substrate and a crystalline oxide film mainly composed of germanium oxide having good crystallinity, which is laminated on the crystal substrate. Another objective of the present invention is to provide a crystalline oxide film containing germanium oxide having good surface smoothness.

[0006] The inventors, through diligent research to achieve the above objectives, have succeeded for the first time in the world in creating an oxide crystal containing a rutile structure, oriented perpendicular or parallel to the c-axis, and having an atomic ratio of germanium among the metal elements in the oxide crystal greater than 0.5, by producing germanium oxide under specific conditions using the mist CVD method. Furthermore, the inventors have succeeded for the first time in the world in creating a crystalline laminated structure comprising at least a crystalline substrate and a crystalline oxide film laminated on the crystalline substrate, wherein the crystalline substrate has a tetragonal crystal structure and the atomic ratio of germanium among the metal elements in the crystalline oxide film greater than 0.5, by producing germanium oxide on a tetragonal crystal substrate under specific conditions using the mist CVD method. They have also found that such oxide crystals can solve the above-mentioned conventional problems. Furthermore, after obtaining the above findings, the inventors conducted further studies and completed the present invention.

[0007] In other words, the present invention relates to the following invention. [1] An oxide crystal containing an oxide with a rutile-type structure, which is oriented in a crystal axis direction perpendicular or parallel to the c axis, and characterized in that the atomic ratio of germanium among the metal elements in the oxide crystal is greater than 0.5. [2] The oxide crystal described in [1], which is oriented in a crystal axis direction parallel to the c axis. [3] The oxide crystal according to [1] or [2] above, wherein the rocking curve half-value width of the X-ray diffraction measurement in the direction of the oriented crystal axis is 1000 arcsec or less. [4] The oxide crystal according to any one of [1] to [3] above, which is in the form of a film. [5] The oxide crystal according to [4] above, wherein the film thickness is 100 nm or more. [6] The oxide crystal according to [4] or [5] above, wherein the surface roughness (RMS) is 10 nm or less. [7] The oxide crystal according to any one of [1] to [5] above, wherein the band gap is 4.0 eV or more. [8] A semiconductor device comprising at least an oxide semiconductor layer and an electrode, wherein the oxide conductor layer contains an oxide crystal according to any one of [1] to [7] above as a main component. [9] A crystalline oxide film containing an oxide of germanium, having a film thickness of 100 nm or more and a surface roughness (RMS) of 10 nm or less.

[10] The crystalline oxide film according to [9] above, wherein the film thickness is 200 nm or more.

[11] The crystalline oxide film according to [9] or

[10] above, having a cubic crystal structure.

[12] The crystalline oxide film according to any one of [9] to

[11] above, which is a uniaxially oriented film.

[13] The crystalline oxide film according to any one of [9] to

[12] above, wherein the half-value width of the X-ray diffraction measurement is 1000 arcsec or less.

[14] The crystalline oxide film according to any one of [9] to

[13] above, wherein the atomic ratio of germanium among the metal elements in the crystalline oxide film is greater than 0.5.

[15] The crystalline oxide film according to any one of [9] to

[14] above, wherein the band gap is 4.0 eV or more.

[16] A semiconductor device comprising at least a crystalline oxide film and an electrode, wherein the crystalline oxide film is a crystalline oxide film according to any one of [9] to

[15] above.

[17] A crystalline laminated structure comprising at least a crystalline substrate and a crystalline oxide film laminated on the crystalline substrate, wherein the crystalline substrate has a cubic crystal structure, and the atomic ratio of germanium among the metal elements in the crystalline oxide film is greater than 0.5.

[18] The crystalline laminated structure according to

[17] , wherein the crystalline oxide film has a cubic crystal structure.

[19] The crystalline laminated structure according to

[17] or

[18] , wherein the film thickness of the crystalline oxide film is 100 nm or more.

[20] The crystalline laminated structure according to any one of

[17] to

[19] , wherein the surface roughness (RMS) of the crystalline oxide film is 10 nm or less.

[21] The crystalline laminated structure according to any one of

[17] to

[20] , wherein the crystalline oxide film is a uniaxially oriented film.

[22] The crystalline laminated structure according to any one of

[17] to

[21] , wherein the rocking curve half-width of the X-ray diffraction measurement method of the crystalline oxide film is 1000 arcsec or less.

[23] The crystalline laminated structure according to any one of

[17] to

[22] , wherein the crystalline substrate is a conductive substrate.

[24] A power conversion device using the semiconductor device according to any one of [8],

[16] , and

[23] .

[25] A control system using the semiconductor device according to any one of [8],

[16] , and

[23] .

[26] A method for manufacturing a crystalline laminated structure, comprising atomizing or droplet-forming a raw material solution containing germanium, supplying a carrier gas to the obtained atomized droplets, transporting the atomized droplets to a crystalline substrate having a cubic crystal structure with the carrier gas, and then thermally reacting the atomized droplets on the crystalline substrate.

Advantages of the Invention

[0008] The rutile-type oxide crystals of the present invention exhibit excellent orientation. Furthermore, the crystalline laminated structure of the present invention has a crystalline oxide film mainly composed of germanium oxide with excellent crystallinity on a tetragonal crystalline substrate. In addition, the crystalline oxide film containing germanium oxide of the present invention has good surface smoothness. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of a film deposition apparatus preferably used in embodiments of the present invention. [Figure 2] This figure shows the measurement results of XRD (X-ray diffraction) in the example. [Figure 3] This figure shows the measurement results of XRD (X-ray diffraction) in the example. [Figure 4] This figure shows the surface observation results using AFM (atomic force microscope) in the example. [Figure 5] This figure shows the surface observation results using AFM (atomic force microscope) in the example. [Figure 6] This diagram schematically shows a preferred example of a Schottky barrier diode (SBD). [Figure 7] This diagram schematically shows a preferred example of a junction barrier Schottky diode (JBS). [Figure 8] This diagram schematically shows a preferred example of a metal-oxide-semiconductor field-effect transistor (MOSFET). [Figure 9] This diagram schematically shows a preferred example of a metal-oxide-semiconductor field-effect transistor (MOSFET). [Figure 10] This diagram schematically shows a suitable example of an insulated-gate bipolar transistor (IGBT). [Figure 11] This diagram schematically shows a suitable example of a light-emitting element (LED). [Figure 12] This is a block diagram showing an example of a control system employing a semiconductor device according to an embodiment of the present invention. [Figure 13]This is a circuit diagram showing an example of a control system employing a semiconductor device according to an embodiment of the present invention. [Figure 14] This is a block diagram showing an example of a control system employing a semiconductor device according to an embodiment of the present invention. [Figure 15] This is a circuit diagram showing an example of a control system employing a semiconductor device according to an embodiment of the present invention. [Figure 16] This diagram schematically shows a suitable example of a high electron mobility transistor (HEMT). [Figure 17] This diagram schematically shows a suitable example of a gas sensor. [Figure 18] This diagram schematically shows a suitable example of a photoelectric conversion element. [Figure 19] This diagram schematically shows a suitable example of a photodetector. [Figure 20] This diagram schematically shows a suitable example of a photoelectrode. [Figure 21] This figure shows the XRD measurement results in the example. [Figure 22] This figure schematically shows a crystalline laminated structure according to an embodiment of the present invention. [Modes for carrying out the invention]

[0010] An oxide crystal in one aspect of the present invention is an oxide crystal containing a rutile-type oxide, oriented in a crystal axis direction perpendicular or parallel to the c-axis, and characterized in that the atomic ratio of germanium among the metal elements in the oxide crystal is greater than 0.5. The oxide crystal may be a single crystal or a polycrystalline crystal. In the embodiment of the present invention, the oxide crystal is preferably a single crystal. Here, "c-axis" refers to the axis perpendicular to the (001) plane in tetragonal representation. "Crystal axis direction perpendicular to the c-axis" also includes crystal axes that are approximately perpendicular to the c-axis (within ±10% of the direction perpendicular to the c-axis). "Crystal axis direction parallel to the c-axis" also includes crystal axis directions that are approximately parallel to the c-axis (within ±10% of the direction parallel to the c-axis). In the present invention, it is preferable that the oxide crystal is oriented in a crystal axis direction parallel to the c-axis, and more preferably oriented in the c-axis direction. Note that "oriented" means a state in which crystal planes, for example, represented by the (001) plane, are aligned in a specific direction. The orientation state can be confirmed by X-ray diffraction. More specifically, for example, if the oxide crystal is oriented to the (001) plane, it can be determined that it is oriented to the (001) plane if the integrated intensity ratio of the peak originating from the (001) plane and the peak originating from other crystal planes is larger than the integrated intensity ratio of the peak originating from the (001) plane and the peak originating from other crystal planes of the same crystal randomly oriented. Furthermore, in the embodiment of the present invention, the full width at half maximum of the rocking curve measured in the direction of the oriented crystal axis is preferably 1000 arcsec or less, and more preferably 600 arcsec or less.

[0011] Furthermore, the shape of the oxide crystal is not particularly limited as long as it does not hinder the objective of the present invention. The oxide crystal may be in the form of a film, a plate, or a sheet. In the embodiments of the present invention, it is preferable that the oxide crystal is in the form of a film, as this makes it more suitably applicable to semiconductor devices. When the oxide crystal is in the form of a film, the film thickness is not particularly limited. In the embodiments of the present invention, it is preferable that the film thickness is 100 nm or more, and more preferably 200 nm or more. Also, when the oxide crystal is in the form of a film, it is preferable that the surface roughness (RMS) of the oxide crystal is 10 nm or less, and more preferably 1 nm or less. By achieving such preferred film thickness or surface roughness, when the oxide crystal is applied to a semiconductor device, it is possible to impart superior electrical properties such as voltage resistance to the semiconductor device. Note that surface roughness (RMS) refers to a value obtained by calculating based on JIS B0601 using the surface shape measurement results for a 10 μm square region by atomic force microscopy (AFM).

[0012] In embodiments of the present invention, it is preferable that the oxide crystal contains a germanium oxide with a rutile structure. In embodiments of the present invention, it is more preferable that the germanium oxide is the main component. Here, "main component" means that the germanium oxide content in the oxide crystal is 50% or more in terms of the composition ratio of the oxide crystal. In embodiments of the present invention, it is preferable that the germanium oxide content in the oxide crystal is 70% or more in terms of the composition ratio of the oxide crystal, and more preferably 90% or more. The germanium oxide is not particularly limited as long as it is a compound of oxygen and germanium. Furthermore, the oxide crystal may contain other metals other than germanium. Examples of other metals include other Group 14 metals of the periodic table (such as tin or silicon). The atomic ratio of germanium among the metal elements in the oxide crystal is not particularly limited as long as it is greater than 0.5. In embodiments of the present invention, the atomic ratio of germanium in the metal elements of the oxide semiconductor is preferably 0.7 or higher, and more preferably 0.9 or higher. If the oxide crystal contains germanium and other Group 14 metals of the periodic table (such as tin or silicon), the oxide crystal is r-(Ge x Sn 1-x It is preferable that it be O2. By forming a mixed crystal in this way, the semiconductor properties of the oxide crystal can be improved, for example, the carrier density can be 1.0 × 10⁻⁶. 18 / cm 3 The above oxide crystals can be obtained. In this case, the ratio (x) of germanium in the oxide crystal is not particularly limited as long as it is greater than 0.5. In the embodiments of the present invention, it is preferable that the ratio (x) of Ge is 0.52 or more, and also preferable that it is 0.87 or more. By setting the atomic ratio of germanium to such a preferred range, an oxide crystal having a higher band gap (for example, 4.0 eV or more, preferably 4.4 eV or more) can be realized.

[0013] The oxide crystal preferably contains a dopant. The dopant is not particularly limited as long as it does not inhibit the object of the present invention. The dopant may be an n-type dopant or a p-type dopant. Examples of the n-type dopant include antimony (Sb), arsenic (As), bismuth (Bi), fluorine (F), etc. In an embodiment of the present invention, the n-type dopant is preferably antimony (Sb). Examples of the p-type dopant include aluminum (Al), gallium (Ga), indium (In), etc. The content of the dopant in the oxide semiconductor is not particularly limited as long as it does not inhibit the object of the present invention. Specifically, the content of the dopant in the oxide semiconductor is, for example, about 1×10 16 / cm 3 ~1×10 22 / cm 3 and may be so, and according to the present invention, the dopant may be contained at a high concentration of about 1×10 20 / cm 3 or more.

[0014] As shown in FIG. 22, a crystalline laminated structure in one aspect of the present invention is a crystalline laminated structure 60 including at least a crystal substrate 61 and a crystalline oxide film 62 laminated on the crystal substrate, wherein the crystal substrate 61 has a cubic crystal structure, and the atomic ratio of germanium among the metal elements in the crystalline oxide film 62 is greater than 0.5. The crystalline oxide film is not particularly limited as long as the atomic ratio of germanium among the metal elements in the film is greater than 0.5. The crystal structure of the crystalline oxide film is also not particularly limited. Examples of the crystal structure of the crystalline oxide film include a hexagonal crystal structure or a cubic crystal structure. In an embodiment of the present invention, the crystal structure of the crystalline oxide film is preferably a cubic crystal structure, and more preferably a rutile-type structure. The crystalline oxide film may be composed of a single crystal or a polycrystal. In an embodiment of the present invention, the crystalline oxide film is preferably a single crystal.

[0015] Furthermore, in the embodiments of the present invention, it is preferable that the crystalline oxide film is a uniaxially oriented film, and more preferably oriented in a crystal axis direction perpendicular or parallel to the c-axis. Here, "c-axis" refers to the axis perpendicular to the (001) plane in tetragonal representation. Also, "crystal axis direction perpendicular to the c-axis" includes crystal axes that are approximately perpendicular to the c-axis (within ±10% of the direction perpendicular to the c-axis). "Crystal axis direction parallel to the c-axis" also includes crystal axis directions that are approximately parallel to the c-axis (within ±10% of the direction parallel to the c-axis). In the present invention, it is preferable that the crystalline oxide film is oriented in a crystal axis direction parallel to the c-axis, and more preferably oriented in the c-axis direction. Note that "oriented" means a state in which crystal planes, for example, represented by the (001) plane, are aligned in a specific direction. The orientation state can be confirmed by X-ray diffraction. More specifically, for example, if the oxide crystal is oriented to the (001) plane, it can be determined that it is oriented to the (001) plane if the integrated intensity ratio of the peak originating from the (001) plane to the peaks originating from other crystal planes is larger than the integrated intensity ratio of the peak originating from the (001) plane to the peaks originating from other crystal planes of the same crystal randomly oriented. Furthermore, in the embodiment of the present invention, the full width at half maximum of the rocking curve of the X-ray diffraction measurement in the direction of the oriented crystal axis is preferably 1000 arcsec or less, and more preferably 600 arcsec or less.

[0016] The thickness of the crystalline oxide film is not particularly limited. In the embodiments of the present invention, the thickness is preferably 100 nm or more, and more preferably 200 nm or more. In the embodiments of the present invention, the surface roughness (RMS) of the crystalline oxide film is preferably 10 nm or less, and more preferably 1 nm or less. By achieving such preferred thickness or surface roughness, when the crystalline oxide film is applied to a semiconductor device, it is possible to impart superior electrical properties such as voltage resistance to the semiconductor device. The surface roughness (RMS) refers to the value obtained by calculating it in accordance with JIS B0601 using the surface shape measurement results for a 10 μm square area by atomic force microscopy (AFM).

[0017] In embodiments of the present invention, it is preferable that the crystalline oxide film contains a germanium oxide with a rutile structure. In embodiments of the present invention, it is more preferable that the germanium oxide is the main component. Here, "main component" means that the content of germanium oxide (germanium oxide) in the crystalline oxide film is 50% or more in terms of composition ratio in the crystalline oxide film. In embodiments of the present invention, it is preferable that the content of germanium oxide in the crystalline oxide film is 70% or more in terms of composition ratio in the crystalline oxide film, and more preferably 90% or more. The germanium oxide is not particularly limited as long as it is a compound of oxygen and germanium. Furthermore, the crystalline oxide film may contain other metals besides germanium. Examples of other metals include other Group 14 metals of the periodic table (such as tin or silicon). The atomic ratio of germanium among the metal elements in the crystalline oxide film is not particularly limited as long as it is greater than 0.5. In embodiments of the present invention, the atomic ratio of germanium in the metal elements in the crystalline oxide film is preferably 0.7 or higher, and more preferably 0.9 or higher. If the crystalline oxide film contains germanium and other Group 14 metals of the periodic table (such as tin or silicon), the crystalline oxide film is r-(Ge x Sn 1-x It is preferable that it be an O2 film. By forming a mixed crystal in this way, the semiconductor properties of the crystalline oxide film can be improved, for example, the carrier density can be 1.0 × 10⁻⁶. 18 / cm 3 The above-mentioned crystalline oxide film can be obtained. In this case, the ratio (x) of germanium in the film is not particularly limited as long as it is greater than 0.5. In this embodiment of the present invention, r-(Ge x Sn 1-x The ratio (x) of Ge in the O2 film is preferably 0.52 or higher, and also preferably 0.87 or higher. By setting the atomic ratio of germanium within this preferred range, a crystalline oxide film with a higher band gap (e.g., 4.0 eV or higher, preferably 4.4 eV or higher) can be realized.

[0018] The crystalline oxide film may also preferably contain a dopant. The dopant is not particularly limited as long as it does not hinder the objectives of the present invention. The dopant may be an n-type dopant or a p-type dopant. Examples of the n-type dopant include antimony (Sb), arsenic (As), bismuth (Bi), or fluorine (F). In this embodiment of the present invention, the n-type dopant is preferably antimony (Sb). Examples of the p-type dopant include aluminum (Al), gallium (Ga), or indium (In). The dopant content in the oxide semiconductor is not particularly limited as long as it does not hinder the objectives of the present invention. Specifically, the dopant content in the oxide semiconductor is, for example, about 1 × 10⁻⁶ 16 / cm 3 ~1 × 10 22 / cm 3 Alternatively, according to the present invention, the dopant may be approximately 1 × 10 20 / cm 3 It may be included at the above high concentrations.

[0019] (Crystal substrate) The crystalline substrate is not particularly limited as long as it does not hinder the objectives of the present invention, and may be a known substrate. It may be an insulating substrate, a conductive substrate, or a semiconductor substrate. It may be a single-crystal substrate or a polycrystalline substrate. The crystalline substrate may be a substrate having a metal film on its surface. If the crystalline substrate is a conductive substrate, a vertical device can be fabricated without removing the substrate. The crystal structure of the crystalline substrate is also not particularly limited as long as it does not hinder the objectives of the present invention. Examples of the crystal structure of the crystalline substrate include a hexagonal structure and a tetragonal structure. Examples of crystalline substrates having a corundum structure include a sapphire substrate (such as an R-plane sapphire substrate). Examples of crystalline substrates having a tetragonal structure include a SrTiO3 substrate, a TiO2 substrate, and a MgF2 substrate. In the embodiments of the present invention, it is preferable that the crystalline substrate has a tetragonal structure, and more preferably a rutile-type structure. Examples of crystalline substrates having a rutile-type structure include a rutile-type titanium oxide (r-TiO2) substrate. The r-TiO2 substrate is preferably a conductive substrate containing a dopant such as Nb. The crystalline substrate may also have an off-angle. Furthermore, in the embodiments of the present invention, it is also preferable to use a Ge substrate as the crystalline substrate.

[0020] A crystalline oxide film in one embodiment of the present invention is a crystalline oxide film containing germanium oxide, characterized by having a film thickness of 100 nm or more and a surface roughness (RMS) of 10 nm or less. The crystalline oxide film may be made of a single crystal or a polycrystalline film. In the embodiment of the present invention, the crystalline oxide film is preferably a single crystal. The crystal structure of the crystalline oxide film is not particularly limited. Examples of the crystal structure of the crystalline oxide film include a hexagonal structure or a tetragonal structure. In the embodiment of the present invention, the crystal structure of the crystalline oxide film is preferably a tetragonal structure, and more preferably a rutile structure. Furthermore, in the embodiment of the present invention, the crystalline oxide film is also preferably a uniaxially oriented film, and more preferably oriented in a crystal axis direction perpendicular or parallel to the c-axis. Here, "c-axis" refers to the axis perpendicular to the (001) plane in tetragonal representation. Furthermore, "crystal axis direction perpendicular to the c-axis" also includes crystal axes that are approximately perpendicular to the c-axis (within ±10% of the direction perpendicular to the c-axis). "Crystal axis direction parallel to the c-axis" also includes crystal axis directions that are approximately parallel to the c-axis (within ±10% of the direction parallel to the c-axis). In the present invention, it is preferable that the oxide crystal is oriented in the crystal axis direction parallel to the c-axis, and more preferably in the direction of the c-axis. Note that "oriented" means a state in which crystal planes, for example, represented by the (001) plane, are aligned in a specific direction. The orientation state can be confirmed by X-ray diffraction. More specifically, for example, if the oxide crystal is oriented to the (001) plane, it can be determined that it is oriented to the (001) plane if the integrated intensity ratio of the peak originating from the (001) plane and the peak originating from other crystal planes is larger than the integrated intensity ratio of the peak originating from the (001) plane and the peak originating from other crystal planes of the same crystal that is randomly oriented. Furthermore, in the embodiments of the present invention, the full width at half maximum of the rocking curve measured in the orientation axis direction of the crystal is preferably 1000 arcsec or less, and more preferably 600 arcsec or less.

[0021] The thickness of the crystalline oxide film is not particularly limited as long as it is 100 nm or more. In the embodiments of the present invention, it is more preferable that the thickness is 200 nm or more. Similarly, the surface roughness (RMS) of the crystalline oxide film is not particularly limited as long as it is 10 nm or less, but in the embodiments of the present invention, it is preferable that it is 1 nm or less. By using such preferred thicknesses or surface roughnesses, when the oxide crystal is applied to a semiconductor device, it is possible to impart superior electrical properties such as breakdown voltage to the semiconductor device. The surface roughness (RMS) refers to the value obtained by calculating it in accordance with JIS B0601 using the surface shape measurement results for a 10 μm square area by atomic force microscopy (AFM).

[0022] In embodiments of the present invention, it is preferable that the crystalline oxide film contains a germanium oxide with a rutile structure. In embodiments of the present invention, it is more preferable that the germanium oxide is the main component. Here, "main component" means that the content of germanium oxide (germanium oxide) in the crystalline oxide film is 50% or more in terms of composition ratio in the crystalline oxide film. In embodiments of the present invention, it is preferable that the content of germanium oxide in the crystalline oxide film is 70% or more, and more preferably 90% or more in terms of composition ratio in the crystalline oxide film. The germanium oxide is not particularly limited as long as it is a compound of oxygen and germanium. Furthermore, the oxide crystal may contain other metals other than germanium. Examples of other metals include other Group 14 metals of the periodic table (such as tin or silicon). The atomic ratio of germanium among the metal elements in the oxide crystal is not particularly limited as long as it is greater than 0.5. In embodiments of the present invention, the atomic ratio of germanium in the metal elements of the oxide semiconductor is preferably 0.7 or higher, and more preferably 0.9 or higher. By setting the atomic ratio of germanium within this preferred range, a crystalline oxide film having a higher band gap (for example, 4.0 eV or higher, more preferably 4.4 eV or higher) can be realized.

[0023] The oxide crystals, crystalline oxide films, and / or crystalline stacked structures can be obtained, for example, by the following preferred film formation methods. However, methods for producing such oxide crystals (hereinafter also referred to as "oxide semiconductors" or "crystalline oxide films") are novel and useful and are included as part of the present invention.

[0024] The present invention provides a method for producing an oxide semiconductor, characterized by atomizing or dropletizing a germanium-containing raw material solution (atomization step), supplying a carrier gas to the resulting atomized droplets, transporting the atomized droplets to a crystalline substrate having a tetragonal crystal structure using the carrier gas (transportation step), and then subjecting the atomized droplets to a thermal reaction on the crystalline substrate (film formation step).

[0025] <Base> The substrate is not particularly limited as long as it can support the oxide semiconductor. The material of the substrate is also not particularly limited as long as it does not hinder the objective of the present invention, and may be a known substrate. The substrate may be made of an organic compound or an inorganic compound. The shape of the substrate is also not particularly limited as long as it does not hinder the objective of the present invention. Examples of the shape of the substrate include plate-like shapes such as flat plates and discs, fibrous shapes, rod-like shapes, cylindrical shapes, prismatic shapes, tubular shapes, spiral shapes, spherical shapes, and ring shapes, but in the present invention, the substrate is preferably a substrate, and more preferably a crystalline substrate. The thickness of the substrate is not particularly limited.

[0026] <Crystal substrate> The crystalline substrate is not particularly limited as long as it does not hinder the objectives of the present invention, and may be a known substrate. It may be an insulating substrate, a conductive substrate, or a semiconductor substrate. It may be a single-crystal substrate or a polycrystalline substrate. The crystalline substrate may be a substrate having a metal film on its surface. If the crystalline substrate is a conductive substrate, a vertical device can be fabricated without removing the substrate. The crystal structure of the crystalline substrate is also not particularly limited as long as it does not hinder the objectives of the present invention. Examples of the crystal structure of the crystalline substrate include a hexagonal structure and a tetragonal structure. Examples of crystalline substrates having a corundum structure include a sapphire substrate (such as an R-plane sapphire substrate). Examples of crystalline substrates having a tetragonal structure include a SrTiO3 substrate, a TiO2 substrate, and a MgF2 substrate. In the embodiments of the present invention, it is preferable that the crystalline substrate has a tetragonal structure, and more preferably a rutile-type structure. Examples of crystalline substrates having a rutile-type structure include a rutile-type titanium oxide (r-TiO2) substrate. The r-TiO2 substrate is preferably a conductive substrate containing a dopant such as Nb. The crystalline substrate may also have an off-angle. Furthermore, in the embodiments of the present invention, it is also preferable to use a Ge substrate as the crystalline substrate.

[0027] (Atomization process) The atomization step atomizes the raw material solution. The atomization means is not particularly limited as long as it can atomize the raw material solution, and any known means may be used, but in the present invention, an atomization means using ultrasound is preferred. The mist obtained using ultrasound is preferred because it has zero initial velocity and floats in the air, and is very suitable because, for example, it is not sprayed like a spray, but rather a mist that can be transported as a gas while floating in space, so there is no damage due to collision energy. The size of the mist droplets is not particularly limited and may be around a few millimeters, but is preferably 50 μm or less, and more preferably 100 nm to 10 μm.

[0028] (Raw material solution) The raw material solution is not particularly limited as long as it contains a dopant element and germanium, and the germanium content is greater than the dopant element content. The raw material solution may contain inorganic materials or organic materials. In the embodiments of the present invention, it is preferable that the raw material solution contains germanium in the form of an organic germanium compound. Furthermore, in the embodiments of the present invention, it is preferable that the organic germanium compound has a carboxyl group. The blending ratio of germanium (e.g., the organic germanium compound, etc.) in the raw material solution is not particularly limited, but is preferably 0.0001 mol / L to 20 mol / L and more preferably 0.001 mol / L to 1.0 mol / L relative to the total raw material solution. The raw material solution may also contain other metals other than germanium (e.g., tin or silicon, etc.).

[0029] The raw material solution may contain a dopant element. Examples of the dopant element include antimony (Sb), arsenic (As), bismuth (Bi), fluorine (F), aluminum (Al), gallium (Ga), or indium (In). In the embodiments of the present invention, it is preferable that the dopant element is antimony (Sb). The dopant element may be contained in the raw material solution in the form of an inorganic compound or in the form of an organic compound.

[0030] The solvent of the raw material solution is not particularly limited and may be an inorganic solvent such as water, an organic solvent such as alcohol, or a mixed solution of an inorganic solvent and an organic solvent. In the present invention, it is preferable that the solvent contains water, and it is also preferable that it is a mixed solvent of water and acid. More specifically, the water may include, for example, pure water, ultrapure water, tap water, well water, mineral water, mineral water, hot spring water, spring water, fresh water, and seawater, but in the present invention, ultrapure water is preferred. More specifically, the acid may include, for example, organic acids such as acetic acid, propionic acid, and butanoic acid; boron trifluoride, boron trifluoride etherate, boron trichloride, boron tribromide, trifluoroacetic acid, trifluoromethanesulfonic acid, and p-toluenesulfonic acid.

[0031] Furthermore, additives such as hydrohalic acid and oxidizing agents may be mixed into the raw material solution. Examples of hydrohalic acid include hydrobromic acid, hydrochloric acid, and hydroiodic acid. Examples of oxidizing agents include peroxides such as hydrogen peroxide (H2O2), sodium peroxide (Na2O2), barium peroxide (BaO2), and benzoyl peroxide (C6H5CO)2O2, as well as organic peroxides such as hypochlorous acid (HClO), perchloric acid, nitric acid, ozonated water, peracetic acid, and nitrobenzene.

[0032] (Conveying process) In the transport process, a carrier gas is supplied to the atomized droplets (hereinafter also simply referred to as "mist") obtained in the atomization process, and the mist is transported to the substrate by the carrier gas. The type of carrier gas is not particularly limited as long as it does not hinder the objective of the present invention, and examples include oxygen, ozone, inert gases such as nitrogen and argon, or reducing gases such as hydrogen gas and foaming gas, but in the present invention, it is preferable to use oxygen as the carrier gas. Examples of carrier gases using oxygen include air, oxygen gas, and ozone gas, but oxygen gas and / or ozone gas are particularly preferred. Furthermore, there may be one type of carrier gas, or there may be two or more types, and a dilution gas with a changed carrier gas concentration (for example, a 10-fold dilution gas) may be used as a second carrier gas. Also, there may be two or more locations for supplying the carrier gas, not just one. In the present invention, when using an atomization chamber, a supply pipe, and a film-forming chamber, it is preferable to provide a carrier gas supply point in the atomization chamber and the supply pipe, respectively, and more preferably to provide a carrier gas supply point in the atomization chamber and a dilution gas supply point in the supply pipe. The flow rate of the carrier gas is not particularly limited, but is preferably 0.01 to 20 L / min, and more preferably 1 to 10 L / min. In the case of a dilution gas, the flow rate of the dilution gas is preferably 0.001 to 2 L / min, and more preferably 0.1 to 1 L / min.

[0033] (Film forming process) In the film-forming process, the atomized droplets are subjected to a thermal reaction on the substrate to form a film on part or all of the substrate surface. The thermal reaction is not particularly limited as long as it is a thermal reaction that forms a film from the mist; it is sufficient that the mist reacts with heat, and the reaction conditions are not particularly limited as long as they do not hinder the objective of the present invention. In this process, the thermal reaction is usually carried out at a temperature above the evaporation temperature of the solvent, but it is preferable that the temperature is not too high. In the present invention, it is preferable to carry out the thermal reaction at a temperature of 700°C to 800°C. Furthermore, the thermal reaction may be carried out under any of the following atmospheres, as long as it does not hinder the objective of the present invention: under vacuum, under a non-oxygen atmosphere, under a reducing gas atmosphere, and under an oxidizing atmosphere, and may also be carried out under any of the following conditions: under atmospheric pressure, under pressure, and under reduced pressure. However, in the present invention, it is preferable to carry out the reaction under an oxidizing atmosphere, also under atmospheric pressure, and more preferably under both an oxidizing atmosphere and atmospheric pressure. Note that the "oxidizing atmosphere" is not particularly limited as long as it is an atmosphere in which the oxide semiconductor can be formed by the thermal reaction. For example, an oxidizing atmosphere can be created by using a carrier gas containing oxygen or a mist consisting of a raw material solution containing an oxidizing agent. Furthermore, the film thickness can be set by adjusting the film formation time.

[0034] In embodiments of the present invention, the film may be formed directly on the substrate, or other layers such as a layer different from the oxide semiconductor (for example, an n-type semiconductor layer, an n+-type semiconductor layer, an n--type semiconductor layer, etc.), an insulating layer (including a semi-insulating layer), or a buffer layer may be laminated on the substrate, and then the film may be formed on the substrate via the other layers. In particular, a buffer layer can be suitably used to mitigate the difference in lattice constants between the crystal substrate and the oxide crystal. Examples of constituent materials for the buffer layer include SnO2, TiO2, VO2, MnO2, RuO2, CsO2, IrO2, GeO2, CuO2, PbO2, AgO2, CrO2, SiO2, and mixed crystals thereof.

[0035] The oxide crystal obtained as described above is useful for semiconductor devices, particularly power devices, and is suitably used as a semiconductor device comprising at least an oxide semiconductor layer and an electrode, wherein the oxide semiconductor layer contains the oxide crystal as a main component. Here, "main component" means that the content of the oxide crystal in the oxide semiconductor layer is 50% or more in terms of composition ratio. In embodiments of the present invention, the content of the oxide crystal in the oxide semiconductor layer is preferably 70% or more in terms of composition ratio, and more preferably 90% or more. Examples of semiconductor devices formed using the oxide crystal include transistors such as MIS and HEMT, TFTs, Schottky barrier diodes utilizing semiconductor-metal junctions, JBS, PN or PIN diodes combined with other P layers, and light-receiving and light-emitting elements. In addition to the above, the oxide crystal can also be suitably used in photoelectric conversion elements, gas sensors, photoelectrodes, memories, etc. In embodiments of the present invention, the oxide crystal may be used in a semiconductor device as the oxide crystal after optionally removing the crystal substrate, or it may be used in a semiconductor device as a crystalline laminated structure with the crystal substrate. In particular, when the crystalline substrate is a conductive substrate, it can be suitably applied as a crystalline laminated structure to a semiconductor device (vertical device).

[0036] Furthermore, the semiconductor device can be suitably used as either a horizontal element (horizontal device) in which electrodes are formed on one side of the semiconductor layer, or a vertical element (vertical device) in which electrodes are formed on both the front and back sides of the semiconductor layer, respectively. However, in the embodiments of the present invention, it is particularly preferable to use it as a vertical device. Suitable examples of the semiconductor device include, for example, Schottky barrier diodes (SBDs), junction barrier Schottky diodes (JBSs), metal-semiconductor field-effect transistors (MESFETs), high electron-mobility transistors (HEMTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), electrostatic induction transistors (SITs), junction field-effect transistors (JFETs), insulated-gate bipolar transistors (IGBTs), or light-emitting diodes (LEDs).

[0037] The following describes preferred examples of semiconductor devices in which the oxide crystal of the present invention is applied to an n-type semiconductor layer (such as an n+-type semiconductor or an n-- semiconductor layer), using the drawings as a reference. However, the present invention is not limited to these examples.

[0038] (SBD) Figure 6 shows an example of a Schottky barrier diode (SBD) according to an embodiment of the present invention. The SBD in Figure 6 comprises an n-type semiconductor layer 101a, an n+-type semiconductor layer 101b, a Schottky electrode 105a, and an ohmic electrode 105b.

[0039] The materials for Schottky electrodes and ohmic electrodes may be known electrode materials, and examples of such electrode materials include metals or alloys thereof such as Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, Pt, V, Mn, Ni, Cu, Hf, W, Ir, Zn, In, Pd, Nd, or Ag; metal oxide conductive films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), and zinc indium oxide (IZO); organic conductive compounds such as polyaniline, polythiophene, or polypyrrole; or mixtures thereof; and laminates.

[0040] Schottky electrodes and ohmic electrodes can be formed by known means, such as vacuum deposition or sputtering. More specifically, for example, when forming a Schottky electrode using two types of metals, a first metal and a second metal, a layer made of the first metal and a layer made of the second metal can be stacked, and the layers made of the first metal and the layers made of the second metal can be patterned using photolithography.

[0041] When a reverse bias is applied to the SBD in Figure 6, a depletion layer (not shown) spreads within the n-type semiconductor layer 101a, resulting in a high-voltage SBD. When a forward bias is applied, electrons flow from the ohmic electrode 105b to the Schottky electrode 105a. In this way, the SBD using the semiconductor structure is excellent for high-voltage and high-current applications, has a fast switching speed, and is also excellent in terms of voltage resistance and reliability.

[0042] (JBS) Figure 7 shows a junction barrier Schottky diode (JBS), which is one of the preferred embodiments of the present invention. The semiconductor device in Figure 7 includes an n+ type semiconductor layer 4, an n- type semiconductor layer 3 stacked on the n- type semiconductor layer, a Schottky electrode 2 provided on the n- type semiconductor layer and capable of forming a Schottky barrier between itself and the i-type semiconductor layer, and a p-type semiconductor layer 1 provided between the Schottky electrode 2 and the n- type semiconductor layer 3. The p-type semiconductor layer 1 is embedded in the n-type semiconductor layer 3. In the present invention, it is preferable that the p-type semiconductor layers are provided at regular intervals, and it is more preferable that the p-type semiconductor layers are provided between both ends of the Schottky electrode and the n-type semiconductor layer. In this preferred embodiment, the JBS is configured to have superior thermal stability and adhesion, reduced leakage current, and superior semiconductor characteristics such as breakdown voltage. The semiconductor device in Figure 7 includes an ohmic electrode 5 on the n+ type semiconductor layer 4.

[0043] The means for forming each layer of the semiconductor device shown in Figure 7 are not particularly limited as long as they do not hinder the objective of the present invention, and may be known means. For example, means of forming a film by vacuum deposition, CVD, sputtering, various coating techniques, etc., followed by patterning by photolithography, or means of directly patterning using printing technology, etc.

[0044] (MOSFET) Figure 8 shows an example where the semiconductor device of the present invention is a MOSFET. The MOSFET in Figure 8 is a trench-type MOSFET and comprises an n-type semiconductor layer 131a, n+-type semiconductor layers 131b and 131c, a gate insulating film 134, a gate electrode 135a, a source electrode 135b, and a drain electrode 135c.

[0045] An n+ type semiconductor layer 131b with a thickness of, for example, 100 nm to 100 μm is formed on the drain electrode 135c, and an n- type semiconductor layer 131a with a thickness of, for example, 100 nm to 100 μm is formed on the n+ type semiconductor layer 131b. Furthermore, an n+ type semiconductor layer 131c is formed on the n- type semiconductor layer 131a, and a source electrode 135b is formed on the n+ type semiconductor layer 131c.

[0046] Furthermore, within the n-type semiconductor layer 131a and the n+-type semiconductor layer 131c, a plurality of trench grooves are formed, penetrating the n+-type semiconductor layer 131c and reaching partway through the n-type semiconductor layer 131a. Within these trench grooves, gate electrodes 135a are embedded and formed via gate insulating films 134 with a thickness of, for example, 10 nm to 1 μm.

[0047] In the ON state of the MOSFET in Figure 8, when a voltage is applied between the source electrode 135b and the drain electrode 135c, and a positive voltage is applied to the gate electrode 135a relative to the source electrode 135b, a channel layer is formed on the side surface of the n-type semiconductor layer 131a, electrons are injected into the n-type semiconductor layer 131a, and the MOSFET turns on. In the OFF state, by setting the voltage of the gate electrode to 0V, the channel layer does not form, the n-type semiconductor layer 131a becomes filled with a depletion layer, and the MOSFET turns off.

[0048] (HEMT) Figure 16 shows an example of a high electron mobility transistor (HEMT) according to an embodiment of the present invention. The HEMT in Figure 16 comprises a wide-bandgap n-type semiconductor layer 121a, a narrow-bandgap n-type semiconductor layer 121b, an n+-type semiconductor layer 121c, a semi-insulating layer 124, a buffer layer 128, a gate electrode 125a, a source electrode 125b, and a drain electrode 125c. In the embodiment of the present invention, for example, it is also preferable to use the oxide crystal for the wide-bandgap n-type semiconductor layer 121a and Ge for the narrow-bandgap n-type semiconductor layer 121b.

[0049] The above examples show cases where a p-type semiconductor is not used, but the embodiments of the present invention are not limited thereto, and a p-type semiconductor may be used. Examples using a p-type semiconductor are shown in Figures 9 to 11 and Figures 17 to 20. These semiconductor devices can be manufactured in the same manner as the above examples. It is preferable that the p-type semiconductor is made of the same material as the n-type semiconductor and contains a p-type dopant.

[0050] (MOSFET) Figure 9 shows a preferred example of a metal-oxide-semiconductor field-effect transistor (MOSFET) comprising an n-type semiconductor layer 131a, a first n+-type semiconductor layer 131b, a second n+-type semiconductor layer 131c, a p-type semiconductor layer 132, a p+-type semiconductor layer 132a, a gate insulating film 134, a gate electrode 135a, a source electrode 135b, and a drain electrode 135c. Note that the p+-type semiconductor layer 132a may be a p-type semiconductor layer, or it may be the same as the p-type semiconductor layer 132.

[0051] (IGBT) Figure 10 shows a preferred example of an insulated-gate bipolar transistor (IGBT) comprising an n-type semiconductor layer 151, an n-type semiconductor layer 151a, an n+-type semiconductor layer 151b, a p-type semiconductor layer 152, a gate insulating film 154, a gate electrode 155a, an emitter electrode 155b, and a collector electrode 155c.

[0052] (LED) Figure 11 shows an example where the semiconductor device according to an embodiment of the present invention is a light-emitting diode (LED). The semiconductor light-emitting device in Figure 11 has an n-type semiconductor layer 161 on a second electrode 165b, and a light-emitting layer 163 is laminated on the n-type semiconductor layer 161. A p-type semiconductor layer 162 is laminated on the light-emitting layer 163. A translucent electrode 167 that transmits light generated by the light-emitting layer 163 is provided on the p-type semiconductor layer 162, and a first electrode 165a is laminated on the translucent electrode 167. Note that the semiconductor light-emitting device in Figure 8 may be covered with a protective layer except for the electrode portion.

[0053] Examples of materials for translucent electrodes include conductive materials such as oxides containing indium (In) or titanium (Ti). More specifically, examples include In2O3, ZnO, SnO2, Ga2O3, TiO2, CeO2, or mixed crystals of two or more of these, or doped materials thereof. Translucent electrodes can be formed by providing these materials by known means such as sputtering. Alternatively, after forming the translucent electrode, thermal annealing may be performed to make the translucent electrode transparent.

[0054] In the semiconductor light-emitting element shown in Figure 11, the first electrode 165a is the positive electrode and the second electrode 165b is the negative electrode. By passing current through the p-type semiconductor layer 162, the light-emitting layer 163, and the n-type semiconductor layer 161 via these electrodes, the light-emitting layer 163 emits light.

[0055] Examples of materials for the first electrode 165a and the second electrode 165b include metals such as Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, Pt, V, Mn, Ni, Cu, Hf, W, Ir, Zn, In, Pd, Nd, or Ag, or alloys thereof; metal oxide conductive films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and zinc indium oxide (IZO); organic conductive compounds such as polyaniline, polythiophene, or polypyrrole; or mixtures thereof. The method for forming the electrodes is not particularly limited and can be formed on the substrate according to a method appropriately selected from wet methods such as printing, spraying, and coating; physical methods such as vacuum deposition, sputtering, and ion plating; and chemical methods such as CVD and plasma CVD, taking into consideration their suitability with the materials.

[0056] (Gas sensor) Figure 17 shows an example of a gas sensor according to an embodiment of the present invention. The gas sensor in Figure 17 comprises a first layer 11, a second layer 12, a first electrode 13, and a second electrode 14. The first and second layers may be n-type semiconductor layers or p-type semiconductor layers. The work function of the second layer is smaller than the work function of the first layer. Preferably, the second layer and the first electrode form a Schottky junction. Preferably, the first layer and the second electrode form a Schottky junction. The materials of the first and second electrodes are not particularly limited. Examples of materials for the first and second electrodes include gold, silver, platinum, etc. By using the oxide crystal of the present invention for the first layer and / or the second layer, a gas sensor with higher sensitivity can be realized.

[0057] (Photoelectric conversion element) Figure 18 shows an example of a photoelectric conversion element according to an embodiment of the present invention. The photoelectric conversion element in Figure 18(a) has a structure in which a conductive film 51 functioning as a lower electrode, an electron blocking layer 56a, a photoelectric conversion layer 52, and a transparent conductive film 55 functioning as an upper electrode are stacked in this order. The photoelectric conversion element in Figure 18(b) has a configuration in which an electron blocking layer 56a, a photoelectric conversion layer 52, a hole blocking layer 56b, and an upper electrode 55 are stacked on the lower electrode 51 in this order. The stacking order of the electron blocking layer 56(a), the photoelectric conversion layer 52, and the hole blocking layer 16b in Figure 18(b) may be appropriately changed depending on the application and characteristics. The oxide crystal of the present invention may be used, for example, in the photoelectric conversion layer 52, the electron blocking layer 56a, or the hole blocking layer 56b. In the photoelectric conversion element in Figure 18, it is preferable that light is incident on the photoelectric conversion layer 52 via the upper electrode 55. Such photoelectric conversion elements can be suitably applied to optical sensor and image sensor applications.

[0058] (Photodetector) Figure 19 shows an example of a photodetector according to an embodiment of the present invention. The photodetector in Figure 19 comprises a lower electrode 40, a high-concentration n-type layer 41, a low-concentration n-type layer 42, a high-concentration p-type layer 43, a Schottky electrode 44, an upper electrode 45, and a specific region 46. The materials of the lower electrode 40, the Schottky electrode 44, and the upper electrode 45 may be known electrode materials (for example, Au, Ni, Pb, Rh, Co, Re, Te, Ir, Pt, Se, etc.). The specific region 46 is, for example, a high-concentration n-type region. In the embodiment of the present invention, the oxide crystal can be suitably used for the high-concentration n-type layer 41, the low-concentration n-type layer 42, the high-concentration p-type layer 43, and the specific region 46, etc. According to the photodetector in Figure 19, when eye-safe light is incident through the window of the upper electrode 45 and the light is free-electron-absorbed by the Schottky electrode 44, electrons are emitted towards the low-concentration n-type layer 42, and these emitted electrons can be accelerated in the high-electric-field region near the tip of the specific region 46.

[0059] (Photoelectrode) Figure 20 shows an example of a photoelectrode according to an embodiment of the present invention. The photoelectrode in Figure 20 comprises a substrate 31, a conductive layer (electron conduction layer) 32 provided on the substrate 31, and a photocatalytic layer (light absorption layer) 33 provided on the conductive layer 32. For example, a glass substrate or a sapphire substrate can be used as the substrate 31. In the embodiment of the present invention, the above-mentioned crystalline substrate may be used as the substrate 31. The thickness of the conductive layer 32 is not particularly limited, but is preferably 10 nm to 150 nm. The thickness of the photocatalytic layer 33 is not particularly limited, but is preferably 100 nm or more. Furthermore, if the photocatalytic layer 33 is made of an n-type semiconductor, it is preferable to determine the combination of materials for the photocatalytic layer 33 and the conductive layer 32 such that the energy difference between the vacuum level and the Fermi level of the conductive layer 32 is smaller than the energy difference between the vacuum level and the Fermi level of the photocatalytic layer 33. Furthermore, when the photocatalytic layer 33 is made of a p-type semiconductor, it is preferable to determine the combination of materials for the photocatalytic layer 33 and the conductive layer 32 such that the energy difference between the vacuum level and the Fermi level of the conductive layer 32 is greater than the energy difference between the vacuum level and the Fermi level of the photocatalytic layer 33. In this embodiment of the present invention, the oxide crystal can be suitably used in the conductive layer 32 and / or the photocatalytic layer 33. The photoelectrode in Figure 20 is suitably used, for example, in a photoelectrochemical cell.

[0060] The crystalline oxide film, crystalline oxide film, and / or crystalline multilayer structure or semiconductor device of the present invention described above can be applied to power conversion devices such as inverters and converters in order to perform the functions described above. More specifically, they can be applied as diodes built into inverters and converters, or as switching elements such as thyristors, power transistors, IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors), etc. Figure 12 is a block diagram showing an example of a control system using a semiconductor device according to an embodiment of the present invention, and Figure 13 is a circuit diagram of the same control system, which is a control system particularly suitable for installation in electric vehicles.

[0061] As shown in Figure 12, the control system 500 includes a battery (power source) 501, a boost converter 502, a buck converter 503, an inverter 504, a motor (driven object) 505, and a drive control unit 506, all of which are mounted on an electric vehicle. The battery 501 is, for example, a storage battery such as a nickel-metal hydride battery or a lithium-ion battery, and stores power through charging at a power supply station or regenerative energy during deceleration, and can output a DC voltage necessary for the operation of the electric vehicle's drive system and electrical system. The boost converter 502 is, for example, a voltage converter equipped with a chopper circuit, and can boost a DC voltage of, for example, 200V supplied from the battery 501 to, for example, 650V by the switching operation of the chopper circuit, and output it to the drive system such as a motor. Similarly, the step-down converter 503 is a voltage conversion device equipped with a chopper circuit, but it can step down a DC voltage of, for example, 200V supplied from the battery 501 to, for example, about 12V, and output it to the electrical system, including power windows, power steering, or on-board electrical equipment.

[0062] The inverter 504 converts the DC voltage supplied from the boost converter 502 into a three-phase AC voltage by switching operation and outputs it to the motor 505. The motor 505 is a three-phase AC motor that constitutes the traction system of the electric vehicle, and is rotationally driven by the three-phase AC voltage output from the inverter 504. This rotational driving force is transmitted to the wheels of the electric vehicle via a transmission (not shown) and the like.

[0063] Meanwhile, various sensors (not shown) are used to measure actual values ​​such as wheel rotation speed, torque, and accelerator pedal depression (accelerator amount) from the electric vehicle while it is in motion, and these measurement signals are input to the drive control unit 506. At the same time, the output voltage value of the inverter 504 is also input to the drive control unit 506. The drive control unit 506 functions as a controller equipped with a calculation unit such as a CPU (Central Processing Unit) and a data storage unit such as memory. It generates control signals using the input measurement signals and outputs them as feedback signals to the inverter 504, thereby controlling the switching operation of the switching elements. As a result, the AC voltage supplied by the inverter 504 to the motor 505 is corrected instantaneously, enabling accurate operation control of the electric vehicle and realizing safe and comfortable operation of the electric vehicle. It is also possible to control the output voltage to the inverter 504 by supplying the feedback signal from the drive control unit 506 to the boost converter 502.

[0064] Figure 13 shows the circuit configuration excluding the step-down converter 503 in Figure 12, i.e., the configuration for driving the motor 505. As shown in the figure, the semiconductor device of the present invention is used for switching control by being employed, for example, as a Schottky barrier diode in the step-up converter 502 and the inverter 504. In the step-up converter 502, it is incorporated into a chopper circuit to perform chopper control, and in the inverter 504, it is incorporated into a switching circuit including an IGBT to perform switching control. In addition, current stabilization is achieved by interposing an inductor (such as a coil) at the output of the battery 501, and voltage stabilization is achieved by interposing capacitors (such as electrolytic capacitors) between the battery 501, the step-up converter 502, and the inverter 504.

[0065] Furthermore, as shown by the dotted line in Figure 13, the drive control unit 506 is equipped with a calculation unit 507 consisting of a CPU (Central Processing Unit) and a storage unit 508 consisting of non-volatile memory. Signals input to the drive control unit 506 are provided to the calculation unit 507, which performs the necessary calculations to generate feedback signals for each semiconductor element. The storage unit 508 temporarily holds the calculation results from the calculation unit 507 and stores physical constants and functions necessary for drive control in the form of a table, outputting them to the calculation unit 507 as appropriate. The calculation unit 507 and the storage unit 508 can employ known configurations, and their processing capabilities can be arbitrarily selected.

[0066] As shown in Figures 12 and 13, in the control system 500, diodes and switching elements such as thyristors, power transistors, IGBTs, and MOSFETs are used for the switching operation of the boost converter 502, the buck converter 503, and the inverter 504. Furthermore, by applying the semiconductor device etc. according to the present invention, extremely good switching characteristics can be expected, and further miniaturization and cost reduction of the control system 500 can be achieved. In other words, the effects of the present invention can be expected for each of the boost converter 502, the buck converter 503, and the inverter 504, and the effects of the present invention can be expected for any one of them, any combination of two or more of them, or in any configuration including the drive control unit 506. Furthermore, the control system 500 described above can be applied not only to the control system of an electric vehicle using the semiconductor device of the present invention, but also to control systems for a wide range of applications, such as boosting or stepping down power from a DC power source, or converting DC to AC power. It is also possible to use a power source such as a solar cell as the battery.

[0067] Figure 14 is a block diagram showing another example of a control system employing a semiconductor device according to an embodiment of the present invention, and Figure 15 is a circuit diagram of the same control system. This control system is suitable for installation in infrastructure equipment and home appliances that operate on power from an AC power source.

[0068] As shown in Figure 14, the control system 600 receives power supplied from an external source, such as a three-phase AC power supply (power source) 601, and includes an AC / DC converter 602, an inverter 604, a motor (to be driven) 605, and a drive control unit 606, which can be mounted on various devices (described later). The three-phase AC power supply 601 is, for example, a power generation facility of a power company (thermal power plant, hydroelectric power plant, geothermal power plant, nuclear power plant, etc.), and its output is supplied as AC voltage after being stepped down via a substation. Alternatively, it may be installed in a building or nearby facility in the form of a private generator, for example, and supplied via power cables. The AC / DC converter 602 is a voltage converter that converts AC voltage to DC voltage, converting the 100V or 200V AC voltage supplied from the three-phase AC power supply 601 into a predetermined DC voltage. Specifically, the voltage conversion converts it to a commonly used desired DC voltage such as 3.3V, 5V, or 12V. If the to be driven is a motor, the conversion to 12V is performed. It is also possible to use a single-phase AC power supply instead of a three-phase AC power supply, and in that case, a similar system configuration can be achieved by using an AC / DC converter with a single-phase input.

[0069] The inverter 604 converts the DC voltage supplied from the AC / DC converter 602 into a three-phase AC voltage by switching operation and outputs it to the motor 605. The form of the motor 604 varies depending on the controlled object, but if the controlled object is a train, it drives the wheels; if it is factory equipment, it drives pumps and various power sources; and if it is home appliances, it drives compressors, etc. It is a three-phase AC motor that is rotationally driven by the three-phase AC voltage output from the inverter 604 and transmits that rotational driving force to the driven object (not shown).

[0070] In addition, many home appliances, for example, can be driven directly by the DC voltage output from the AC / DC converter 302 (e.g., personal computers, LED lighting equipment, video equipment, audio equipment, etc.). In such cases, the inverter 604 is not required for the control system 600, and the DC voltage is supplied to the driven object from the AC / DC converter 602, as shown in Figure 14. In this case, for example, a 3.3V DC voltage is supplied to personal computers, and a 5V DC voltage is supplied to LED lighting equipment, etc.

[0071] Meanwhile, various sensors (not shown) are used to measure actual values ​​such as the rotational speed and torque of the driven object, as well as the temperature and flow rate of the surrounding environment of the driven object. These measurement signals are input to the drive control unit 606. At the same time, the output voltage value of the inverter 604 is also input to the drive control unit 606. Based on these measurement signals, the drive control unit 606 provides a feedback signal to the inverter 604, controlling the switching operation of the switching element. This instantly corrects the AC voltage supplied by the inverter 604 to the motor 605, enabling accurate operation control of the driven object and achieving stable operation of the driven object. Furthermore, as described above, if the driven object can be driven with a DC voltage, it is also possible to use feedback control of the AC / DC converter 602 instead of feedback to the inverter.

[0072] Figure 15 shows the circuit configuration of Figure 14. As shown in the figure, the semiconductor device of the present invention is used for switching control by being employed, for example, as a Schottky barrier diode in the AC / DC converter 602 and inverter 604. The AC / DC converter 602 uses, for example, a Schottky barrier diode configured in a bridge circuit, and performs DC conversion by converting the negative voltage component of the input voltage to a positive voltage and rectifying it. The inverter 604 is incorporated into the switching circuit of the IGBT to perform switching control. In addition, current stabilization is achieved by interposing an inductor (such as a coil) between the three-phase AC power supply 601 and the AC / DC converter 602, and voltage stabilization is achieved by interposing a capacitor (such as an electrolytic capacitor) between the AC / DC converter 602 and the inverter 604.

[0073] Furthermore, as shown by the dotted line in Figure 15, the drive control unit 606 is equipped with a calculation unit 607 consisting of a CPU and a storage unit 608 consisting of non-volatile memory. Signals input to the drive control unit 606 are provided to the calculation unit 607, which performs the necessary calculations to generate feedback signals for each semiconductor element. The storage unit 608 temporarily holds the calculation results from the calculation unit 607 and stores physical constants and functions necessary for drive control in the form of a table, outputting them to the calculation unit 607 as appropriate. The calculation unit 607 and the storage unit 608 can employ known configurations, and their processing capabilities can be arbitrarily selected.

[0074] In such a control system 600, as with the control system 500 shown in Figures 14 and 15, diodes and switching elements such as thyristors, power transistors, IGBTs, and MOSFETs are used for the rectification and switching operations of the AC / DC converter 602 and inverter 604. Furthermore, by applying the semiconductor film and semiconductor device according to the present invention, extremely good switching characteristics can be expected, and further miniaturization and cost reduction of the control system 600 can be achieved. In other words, the effects of the present invention can be expected in each of the AC / DC converter 602 and inverter 604, and the effects of the present invention can be expected in any one of them, a combination thereof, or in a configuration including the drive control unit 606.

[0075] Although Figures 14 and 15 illustrate the motor 605 as the target to be driven, the target to be driven is not necessarily limited to mechanically operating devices, and can be many devices that require AC voltage. The control system 600 is applicable as long as it drives the target to be driven by inputting power from an AC power source, and can be installed for drive control of infrastructure equipment (e.g., power equipment in buildings and factories, communication equipment, traffic control equipment, water and wastewater treatment equipment, system equipment, labor-saving equipment, trains, etc.) and home appliances (e.g., refrigerators, washing machines, personal computers, LED lighting equipment, video equipment, audio equipment, etc.).

[0076] (Example 1) 1. Film deposition equipment The mist CVD apparatus used in this embodiment will be explained with reference to Figure 1. The mist CVD apparatus 19 comprises a susceptor 21 on which a substrate 20 is placed, a carrier gas supply means 22a for supplying carrier gas, a flow control valve 23a for adjusting the flow rate of carrier gas discharged from the carrier gas supply means 22a, a carrier gas (dilution) supply means 22b for supplying carrier gas (dilution), a flow control valve 23b for adjusting the flow rate of carrier gas discharged from the carrier gas (dilution) supply means 22b, a mist source 24 containing a raw material solution 24a, a container 25 for holding water 25a, an ultrasonic transducer 26 attached to the bottom surface of the container 25, a supply pipe 27 made of a quartz tube with an inner diameter of 40 mm, and a heater 28 installed around the periphery of the supply pipe 27. The susceptor 21 is made of quartz, and the surface on which the substrate 20 is placed is inclined from the horizontal plane. By fabricating both the supply tube 27, which serves as the film deposition chamber, and the susceptor 21 from quartz, the contamination of the film formed on the substrate 20 with impurities originating from the apparatus is suppressed.

[0077] 2. Preparation of raw material solution Bis[2-carboxyethylgermanium(IV)]sesquioxide (C6H 10 To a 0.025 M aqueous solution of Ge2O7, 10% by volume of hydrochloric acid (HCl) was added, and this was used as the starting solution.

[0078] 3. Film preparation preparation The raw material solution 24a obtained in step 2 above was placed inside the mist generating source 24. Next, a (001)-plane r-TiO2 substrate was placed on the susceptor 21 as the substrate 20, and the temperature of the heater 28 was raised to 750°C. Next, the flow control valves 23a and 23b were opened, and carrier gas was supplied into the supply pipe 27 from the carrier gas supply means 22a and 22b, which are the carrier gas sources. After the atmosphere inside the supply pipe 27 was sufficiently replaced with carrier gas, the flow rate of the carrier gas was adjusted to 3.0 L / min and the flow rate of the carrier gas (dilution) was adjusted to 0.5 L / min. Oxygen was used as the carrier gas.

[0079] 4. Film formation Next, the ultrasonic transducer 26 was vibrated at 2.4 MHz, and the vibrations were propagated through water 25a to the raw material solution 24a, thereby atomizing the raw material solution 24a and generating mist (atomized droplets) 24b. This mist 24b was introduced into the deposition chamber 30 through the supply pipe 27 by a carrier gas, and under atmospheric pressure and at 750°C, the mist underwent a thermal reaction on the substrate 20 to deposit a GeO2 film on the substrate 20. The thickness of the obtained GeO2 film was 843 nm. The deposition rate was 2.5 μm / hour.

[0080] 5. Rating The GeO2 film obtained in step 4 above was identified using an X-ray diffractometer, and it was determined to be an r-GeO2 film with a rutile-type structure and (001) plane orientation. The XRD results are shown in Figure 2. The full width at half maximum of the rocking curve at the 002 diffraction peak was 911 arcsecs. For reference, Figure 2 also shows the results when the film deposition temperature was 700°C, 725°C, and 775°C. Furthermore, observation of the film surface using an atomic force microscope (AFM) revealed that the surface roughness (RMS) was 0.126 nm, as shown in Figure 4, indicating excellent surface smoothness.

[0081] (Example 2) Bis[2-carboxyethylgermanium(IV)] sesquioxide (C6H) in the raw material solution 10 A GeO2 film was fabricated in the same manner as in Example 1, except that the concentration of Ge2O7 was 0.001 M (mol / L) and the film deposition temperature was 725°C. The thickness of the obtained GeO2 film was 200 nm. When the obtained GeO2 film was identified using an X-ray diffractometer, the obtained film was found to be an r-GeO2 film with a rutile-type structure and (001) plane orientation. The XRD results are shown in Figure 3. The full width at half maximum of the rocking curve at the 002 diffraction peak was 560 arcsecs. Figure 3(a) shows the results of the 2θ / ω scan, and Figure 3(b) shows the results of the ω scan. Furthermore, when the film surface was observed using an atomic force microscope (AFM), as shown in Figure 5, the surface roughness (RMS) was 0.138 nm, indicating excellent surface smoothness.

[0082] (Example 3) In Example 3, the raw material solution used was bis[2-carboxyethylgermanium(IV)]sesquioxide (C6H 10 Film formation was carried out in the same manner as in Example 2, except that a solution was used in which 10% by volume of hydrochloric acid (sHCl) was added to an aqueous solution of Ge2O7) (0.001M) and tin chloride dihydrate (0.0005M). When the obtained film was identified using an X-ray diffractometer, the obtained film was found to be a (001) plane-oriented r-(Ge) film having a rutile-type structure. 0.52 ,Sn 0.48 The film was an O2 film. The film thickness was 208 nm. The XRD results are shown in Figure 21. The full width at half maximum of the rocking curve at the O02 diffraction peak was 113 arcsecs. Furthermore, when the Hall effect was measured on the obtained film, the carrier type was "n" and the carrier density was 8.40 × 10⁻⁶. 19 / cm 3 The band gap, determined by spectroscopic ellipsometry, was 4.02 eV.

[0083] (Example 4) In Example 4, bis[2-carboxyethylgermanium(IV)]sesquioxide (C6H) was used in the raw material solution. 10 The film was fabricated in the same manner as in Example 3, except that the concentration of Ge2O7 was 0.01 M and the concentration of tin chloride dihydrate was 0.0025 M. When the obtained film was identified using an X-ray diffractometer, the obtained film was found to be a (001) plane-oriented r-(Ge) film with a rutile-type structure. 0.87 ,Sn 0.13 The film was an O2 film. The film thickness was 150 nm. The XRD results are shown in Figure 21. The band gap determined by spectroscopic ellipsometry was 4.44 eV.

[0084] (Example 5) In Example 5, bis[2-carboxyethylgermanium(IV)]sesquioxide (C6H) was used in the raw material solution. 10The film was fabricated in the same manner as in Example 3, except that the concentration of Ge2O7 was 0.005 M and the concentration of tin chloride dihydrate was 0.0025 M. When the obtained film was identified using an X-ray diffractometer, the obtained film was found to be a (001) plane-oriented r-(Ge) film with a rutile-type structure. 0.61 ,Sn 0.39 The film was an O2 film. The film thickness was 365 nm. The XRD results are shown in Figure 21. [Industrial applicability]

[0085] The oxide crystals, crystalline oxide films, or crystalline stacked structures of the present invention can be used in a wide range of fields, including semiconductors (e.g., compound semiconductor electronic devices), electronic components, electrical equipment components, optical and electrophotographic equipment, and industrial materials, but are particularly useful for semiconductor devices and their components. [Explanation of Symbols]

[0086] 1 p-type semiconductor layer 2 Schottky electrodes 3 n-type semiconductor layer 4 n+ type semiconductor layer 5 Ohmic electrodes 11. The first layer 12. Second Layer 13 First electrode 14. Second electrode 19. Mist CVD apparatus 20 Substrates (crystal substrates) 21 Susceptor 22a Carrier gas supply means 22b Carrier gas (dilution) supply means 23a Flow control valve 23b Flow control valve 24 Mist Sources 24a Raw material solution 25 Container 25a water 26. Ultrasonic transducer 27 Supply pipe 28 Heater 29 Exhaust vent 31 circuit boards 32 Conductive layer (electron conduction layer) 33. Photocatalytic layer (light-absorbing layer) 40 Lower electrode 41 Highly concentrated n-type layer 42 Low concentration n-type layer 43 High concentration p-type layer 44 Schottky electrodes 45 Upper electrode 46 Specific area 51 Conductive film 52 Photoelectric conversion layer 55 Transparent conductive film 56a Electron blocking layer 56b Hole blocking layer 60 Crystalline layered structures 61 Crystal Substrate 62 Crystalline oxide film 101a n-type semiconductor layer 101b n+ type semiconductor layer 105b Ohmic electrode 105a Schottky electrode 131a n-type semiconductor layer 131b First n+ type semiconductor layer 131c Second n+ type semiconductor layer 132 p-type semiconductor layer 132a p+ type semiconductor layer 134 Gate insulating film 135a Token 135b Source electrode 135c drain electrode 151 n-type semiconductor layer 151a n-type semiconductor layer 151b n+ type semiconductor layer 152 p-type semiconductor layer 154 Gate Insulator 155a Terminal 155b Emitter electrode 155c collector electrode 161 n-type semiconductor layer 162 p-type semiconductor layer 163 Emitting layer 165a First electrode 165b Second electrode 167 Translucent electrode 500 Control Systems 501 Battery (Power Supply) 502 Boost Converter 503 Step-Down Converter 504 Inverter 505 Motor (Driven object) 506 Drive Control Unit 507 Arithmetic section 508 Storage section 600 Control System 601 Three-phase AC power supply (power supply) 602 AC / DC Converter 604 Inverter 605 Motor (Driven object) 606 Drive Control Unit 607 Arithmetic unit 608 Storage section

Claims

1. An oxide crystal containing an oxide with a rutile-type structure, characterized in that it is uniaxially oriented, and the atomic ratio of germanium among the metal elements in the oxide crystal is greater than 0.

5.

2. A crystalline oxide film containing germanium oxide, characterized in that its surface roughness (RMS) is 10 nm or less.

3. A crystalline oxide film containing a germanium oxide with a rutile-type structure, oriented in a crystal axis direction perpendicular or parallel to the c-axis, and having a full width at half maximum (FWHM) of 600 arcsec or less as measured by X-ray diffraction.

4. A method for forming a germanium-containing film from a raw material solution containing a germanium-containing metal complex, A method wherein the ratio of germanium to the raw material solution is 0.0001 mol / L to 20 mol / L.

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