Oxide crystal, crystalline oxide film, crystalline laminated structure and semiconductor device

Abstract

The present invention provides an oxide crystal that has a favorable orientation, that has germanium as the main component, and that has a rutile-type structure. By using mist CVD under specific conditions to form a germanium oxide film on a titanium oxide substrate having a rutile-type structure, obtained is an oxide crystal containing an oxide having a rutile-type structure, wherein: the oxide crystal is oriented in the crystal axis direction perpendicular or parallel to the c axis; and the atomic ratio of germanium is greater than 0.5 in metal elements in the oxide crystal.

Description

[Technical Field]

[0001] The present invention relates to an oxide crystal, a crystalline oxide film, a crystalline layered structure useful for a semiconductor device, and a semiconductor device using the oxide crystal. [Background technology]

[0002] Germanium oxide has attracted attention as a wide bandgap semiconductor useful for power devices, etc. Germanium oxide is said to have a bandgap of 4.44 eV to 4.68 eV (Non-Patent Document 1), and according to first-principles calculations, the hole mobility is 27 cm 2 / Vs (direction perpendicular to the c-axis) or 29 cm 2 / Vs (Non-Patent Document 2), and the realization of a pn homojunction is also expected.

[0003] Rather than relying on calculations as described above, the actual fabrication of germanium oxide has also been investigated. Non-Patent Document 3 discloses the formation of a germanium oxide film on an R-plane sapphire substrate via a (Sn,Ge)O buffer layer using the MBE method. Non-Patent Document 4 also discloses the formation of a rutile-structured (Sn,Ge)O film on a (001) TiO substrate using a hybrid MBE method. Thus, rutile-structured germanium oxide can be combined with Sn, Si, etc. to form a mixed crystal and be considered as a single material system. However, the method described in Non-Patent Document 4 suffers from the problem of loss of crystallinity and amorphization when the atomic ratio of germanium to metal in the film exceeds 0.5. Therefore, there has been a long-awaited demand for an oxide crystal (crystalline oxide film) containing germanium oxide with crystalline quality suitable for semiconductor devices. [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. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an oxide crystal having a rutile structure that has good orientation and contains germanium as its main component. Another object of the present invention is to provide a crystalline layered structure that includes a crystal substrate having a tetragonal structure and a crystalline oxide film that is stacked on the crystal substrate and contains germanium oxide as its main component and has good crystallinity. Another object of the present invention is to provide a crystalline oxide film containing germanium oxide that has good surface smoothness.

[0006] As a result of extensive research to achieve the above-mentioned object, the inventors have succeeded, for the first time in the world, in creating oxide crystals containing rutile oxide, which are oriented perpendicular or parallel to the c-axis, and in which the atomic ratio of germanium to the metal elements in the oxide crystals is greater than 0.5, by using a mist CVD method to prepare germanium oxide under specific conditions. Furthermore, the inventors have succeeded, for the first time in the world, in creating a crystalline layered structure comprising at least a crystal substrate and a crystalline oxide film laminated on the crystal substrate, by using a mist CVD method to prepare germanium oxide under specific conditions, wherein the crystal substrate has a tetragonal crystal structure and the atomic ratio of germanium to the metal elements in the crystalline oxide film is greater than 0.5. They have also found that such oxide crystals can solve the above-mentioned problems of the prior art. Furthermore, after obtaining the above findings, the present inventors conducted further studies and have now completed the present invention.

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

[10] The crystalline oxide film according to [9] above, having a film thickness of 200 nm or more.

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

[10] above, which has a tetragonal 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, which has a half-width of 1000 arcsec or less in X-ray diffraction measurement.

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

[13] , wherein the atomic ratio of germanium to 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, which has a band gap of 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 the crystalline oxide film according to any one of [9] to

[15] above.

[17] A crystalline layered structure comprising at least a crystalline substrate and a crystalline oxide film stacked 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 is greater than 0.5.

[18] The crystalline layered structure according to

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

[19] The crystalline layered structure according to

[17] or

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

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

[17] to

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

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

[17] to

[21] , wherein the crystalline oxide film has a rocking curve half-width of 1000 arcsec or less as measured by X-ray diffraction.

[23] The crystalline layered 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 producing a crystalline laminated structure, comprising atomizing or forming droplets from a raw material solution containing germanium, supplying a carrier gas to the resulting atomized droplets, transporting the atomized droplets to a crystal substrate having a tetragonal crystal structure using the carrier gas, and then thermally reacting the atomized droplets on the crystal substrate. [Effects of the Invention]

[0008] The oxide crystals of the present invention have excellent orientation. The crystalline layered structure of the present invention has a crystalline oxide film containing germanium oxide as a main component and having excellent crystallinity on a crystal substrate having a tetragonal crystal structure. The crystalline oxide film containing germanium oxide of the present invention has good surface smoothness. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating the configuration of a film forming apparatus that is preferably used in an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing the results of measurements by XRD (X-ray diffractometer) in Examples. [Figure 3] FIG. 1 is a diagram showing the results of measurements by XRD (X-ray diffractometer) in Examples. [Figure 4] FIG. 2 is a diagram showing the results of AFM (atomic force microscope) surface observation in an example. [Figure 5] FIG. 2 is a diagram showing the results of AFM (atomic force microscope) surface observation in an example. [Figure 6] FIG. 1 is a diagram schematically illustrating a preferred example of a Schottky barrier diode (SBD). [Figure 7] FIG. 1 is a diagram schematically illustrating a preferred example of a junction barrier Schottky diode (JBS). [Figure 8] FIG. 1 is a diagram schematically illustrating a preferred example of a metal oxide semiconductor field effect transistor (MOSFET). [Figure 9] FIG. 1 is a diagram schematically illustrating a preferred example of a metal oxide semiconductor field effect transistor (MOSFET). [Figure 10] FIG. 1 is a diagram schematically illustrating a preferred example of an insulated gate bipolar transistor (IGBT). [Figure 11] 1 is a diagram schematically illustrating a preferred example of a light-emitting element (LED). [Figure 12] 1 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]1 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] 1 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] 1 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] FIG. 1 is a diagram schematically illustrating a preferred example of a high electron mobility transistor (HEMT). [Figure 17] FIG. 1 is a diagram schematically illustrating a preferred example of a gas sensor. [Figure 18] FIG. 1 is a diagram schematically illustrating a preferred example of a photoelectric conversion element. [Figure 19] FIG. 2 is a diagram schematically illustrating a preferred example of a light receiving element. [Figure 20] FIG. 1 is a diagram schematically illustrating a preferred example of a photoelectrode. [Figure 21] FIG. 1 is a diagram showing the results of XRD measurements in Examples. [Figure 22] 1 is a diagram schematically illustrating a crystalline layered structure according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The oxide crystal according to one aspect of the present invention is an oxide crystal containing an oxide having a rutile structure, characterized in that the oxide crystal is oriented in a crystal axis direction perpendicular or parallel to the c-axis, and the atomic ratio of germanium to the metal elements in the oxide crystal is greater than 0.5. The oxide crystal may be a single crystal or a polycrystal. In an embodiment of the present invention, the oxide crystal is preferably a single crystal. Here, the "c-axis" refers to the axis perpendicular to the (001) plane in tetragonal notation. The "crystal axis direction perpendicular to the c-axis" also includes a crystal axis that is approximately perpendicular to the c-axis (within ±10% of the direction perpendicular to the c-axis). The "crystal axis direction parallel to the c-axis" also includes a crystal axis that is approximately parallel to the c-axis (within ±10% of the direction parallel to the c-axis). In the present invention, the oxide crystal is preferably oriented in a crystal axis direction parallel to the c-axis, and more preferably in the c-axis direction. Note that "oriented" refers to a state in which a crystal plane, for example, represented by the (001) plane, is aligned in a specific direction. The orientation state can be confirmed by X-ray diffraction. More specifically, for example, when the oxide crystal is oriented in the (001) plane, it can be determined that the oxide crystal is oriented in the (001) plane when the integrated intensity ratio of the peak derived from the (001) plane to the peak derived from other crystal planes is larger than the integrated intensity ratio of the peak derived from the (001) plane of the same randomly oriented crystal to the peak derived from other crystal planes. In addition, in an embodiment of the present invention, the rocking curve half-width in the oriented crystal axis direction in X-ray diffraction measurement is preferably 1000 arcsec or less, more preferably 600 arcsec or less.

[0011] The shape of the oxide crystal is not particularly limited as long as it does not impede the objectives of the present invention. The oxide crystal may be film-like, plate-like, or sheet-like. In an embodiment of the present invention, the oxide crystal is preferably film-like, since it is more suitable for use in semiconductor devices. When the oxide crystal is film-like, the film thickness is not particularly limited. In an embodiment of the present invention, the film thickness is preferably 100 nm or more, more preferably 200 nm or more. Furthermore, when the oxide crystal is film-like, the surface roughness (RMS) of the oxide crystal is preferably 10 nm or less, more preferably 1 nm or less. By achieving such a preferable film thickness or surface roughness, the oxide crystal can be applied to a semiconductor device to impart superior electrical properties, such as superior voltage resistance, to the semiconductor device. The surface roughness (RMS) refers to a value calculated based on JIS B0601 using the surface shape measurement results of a 10 μm square area using an atomic force microscope (AFM).

[0012] In an embodiment of the present invention, the oxide crystal preferably contains germanium oxide having a rutile structure. In an embodiment of the present invention, it is more preferable that the oxide crystal contains the germanium oxide as a main component. Here, "main component" refers to a content of germanium oxide (germanium oxide) in the oxide crystal being 50% or more in terms of the composition ratio of the oxide crystal. In an embodiment of the present invention, the content of germanium oxide in the oxide crystal is preferably 70% or more, more preferably 90% or more, in terms of the composition ratio of the oxide crystal. The germanium oxide is not particularly limited as long as it is a compound of oxygen and germanium. The oxide crystal may also contain metals other than germanium. Examples of such metals include metals of Group 14 of the periodic table other than germanium (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 an embodiment of the present invention, the atomic ratio of germanium to metal elements in the oxide semiconductor is preferably 0.7 or more, more preferably 0.9 or more. When the oxide crystal contains germanium and a metal of Group 14 of the periodic table other than germanium (such as tin or silicon), the oxide crystal is r-(Ge x Sn 1-x By forming a mixed crystal in this way, the semiconductor properties of the oxide crystal can be improved, and for example, the carrier density can be 1.0×10 18 / cm 3 The above oxide crystal 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 an embodiment of the present invention, the ratio (x) of Ge is preferably 0.52 or more, and also preferably 0.87 or more. By setting the atomic ratio of germanium in this 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 impede 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), and fluorine (F). 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), and indium (In). The content of the dopant in the oxide semiconductor is not particularly limited as long as it does not impede 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 In accordance with the present invention, the dopant may be about 1×10 20 / cm 3 It may be contained in a concentration higher than this.

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

[0015] In an embodiment of the present invention, the crystalline oxide film is preferably a uniaxially oriented film, and more preferably oriented in a crystal axis direction perpendicular or parallel to the c axis. Here, the "c axis" refers to the axis perpendicular to the (001) plane in tetragonal notation. The "crystal axis direction perpendicular to the c axis" also includes a crystal axis approximately perpendicular to the c axis (within ±10% of the direction perpendicular to the c axis). The "crystal axis direction parallel to the c axis" also includes a crystal axis direction approximately parallel to the c axis (within ±10% of the direction parallel to the c axis). In the present invention, the crystalline oxide film is preferably oriented in a crystal axis direction parallel to the c axis, and more preferably in the c axis direction. The term "oriented" refers to a state in which the crystal plane, for example, the (001) plane, is aligned in a specific direction. The orientation can be confirmed by X-ray diffraction. More specifically, for example, when the oxide crystal is oriented in the (001) plane, it can be determined that the crystal is oriented in the (001) plane when the integrated intensity ratio of the peak derived from the (001) plane to the peak derived from other crystal planes is larger than the integrated intensity ratio of the peak derived from the (001) plane to the peak derived from other crystal planes of the same randomly oriented crystal. In addition, in an embodiment of the present invention, the rocking curve half-width in the oriented crystal axis direction in X-ray diffraction measurement is preferably 1000 arcsec or less, more preferably 600 arcsec or less.

[0016] The thickness of the crystalline oxide film is not particularly limited. In an embodiment of the present invention, the thickness is preferably 100 nm or more, more preferably 200 nm or more. Furthermore, in an embodiment of the present invention, the surface roughness (RMS) of the crystalline oxide film is preferably 10 nm or less, more preferably 1 nm or less. By achieving such a preferable thickness or surface roughness, when the crystalline oxide film is applied to a semiconductor device, the semiconductor device can be endowed with superior electrical properties such as high voltage resistance. The surface roughness (RMS) refers to a value calculated based on JIS B0601 using the results of surface profile measurement of a 10 μm square area using an atomic force microscope (AFM).

[0017] In an embodiment of the present invention, the crystalline oxide film preferably contains germanium oxide having a rutile structure. In an embodiment of the present invention, it is more preferable that the crystalline oxide film contains germanium oxide as a main component. Here, "main component" refers to a content of germanium oxide (germanium oxide) in the crystalline oxide film being 50% or more in terms of its composition ratio in the crystalline oxide film. In an embodiment of the present invention, the content of germanium oxide in the crystalline oxide film is preferably 70% or more, more preferably 90% or more, in terms of its 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. The crystalline oxide film may also contain metals other than germanium. Examples of such metals include metals of Group 14 of the periodic table other than germanium (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 an embodiment of the present invention, the atomic ratio of germanium to the metal elements in the crystalline oxide film is preferably 0.7 or more, more preferably 0.9 or more. When the crystalline oxide film contains germanium and a metal of Group 14 of the periodic table other than germanium (such as tin or silicon), the crystalline oxide film is r-(Ge x Sn 1-x By forming the mixed crystal in this way, the semiconductor properties of the crystalline oxide film can be improved, and for example, the carrier density can be 1.0×10 18 / cm 3 The crystalline oxide film described above 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 an embodiment of the present invention, r-(Ge x Sn 1-x The ratio (x) of Ge in the SiO2 film is preferably 0.52 or more, and more preferably 0.87 or more. By setting the atomic ratio of germanium in this preferred range, a crystalline oxide film with a higher band gap (for example, 4.0 eV or more, preferably 4.4 eV or more) can be realized.

[0018] The crystalline oxide film preferably contains a dopant. The dopant is not particularly limited as long as it does not impede 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), and fluorine (F). 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), and indium (In). The content of the dopant in the oxide semiconductor is not particularly limited as long as it does not impede 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 In accordance with the present invention, the dopant may be about 1×10 20 / cm 3 It may be contained in a concentration higher than this.

[0019] (crystal substrate) The crystal substrate is not particularly limited as long as it does not impede 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 crystal substrate may also be a substrate having a metal film on its surface. When the crystal substrate is a conductive substrate, a vertical device can be fabricated without removing the substrate. The crystal structure of the crystal substrate is also not particularly limited as long as it does not impede the objectives of the present invention. Examples of the crystal structure of the crystal substrate include a hexagonal crystal structure and a tetragonal crystal structure. Examples of crystal substrates having a corundum structure include a sapphire substrate (e.g., an R-plane sapphire substrate). Examples of crystal substrates having a tetragonal crystal structure include an SrTiO3 substrate, a TiO2 substrate, and an MgF2 substrate. In an embodiment of the present invention, the crystal substrate preferably has a tetragonal crystal structure, and more preferably a rutile structure. Examples of crystal substrates having a rutile structure include a rutile titanium oxide (r-TiO2) substrate. The r-TiO2 substrate is preferably a conductive substrate containing a dopant such as Nb. The crystalline substrate may have an off-axis angle. In an embodiment of the present invention, a Ge substrate is also preferably used as the crystalline substrate.

[0020] The crystalline oxide film according to one aspect of the present invention is a crystalline oxide film containing germanium oxide, characterized by a film thickness of 100 nm or more and a surface roughness (RMS) of 10 nm or less. The crystalline oxide film may be either single-crystal or polycrystalline. In an embodiment of the present invention, the crystalline oxide film is preferably single-crystal. The crystalline structure of the crystalline oxide film is not particularly limited. Examples of the crystalline structure of the crystalline oxide film include a hexagonal structure and a tetragonal structure. In an embodiment of the present invention, the crystalline structure of the crystalline oxide film is preferably a tetragonal structure, and more preferably a rutile structure. In another embodiment of the present invention, the crystalline oxide film is preferably a uniaxially oriented film, and more preferably oriented in a crystal axis direction perpendicular or parallel to the c-axis. Here, the "c-axis" refers to the axis perpendicular to the (001) plane in tetragonal crystal notation. Furthermore, the term "crystal axis direction perpendicular to the c-axis" also includes a crystal axis approximately perpendicular to the c-axis (within ±10% of the direction perpendicular to the c-axis). The term "crystal axis direction parallel to the c-axis" also includes a crystal axis direction approximately parallel to the c-axis (within ±10% of the direction parallel to the c-axis). In the present invention, the oxide crystal is preferably oriented in a crystal axis direction parallel to the c-axis, and more preferably in the c-axis direction. Note that "oriented" means that the crystal plane, for example, represented by the (001) plane, is aligned in a specific direction. The orientation state can be confirmed by X-ray diffraction. More specifically, for example, when the oxide crystal is oriented in the (001) plane, it can be determined that the oxide crystal is oriented in the (001) plane if the integrated intensity ratio of the peak derived from the (001) plane to the peak derived from other crystal planes is larger than the integrated intensity ratio of the peak derived from the (001) plane to the peak derived from other crystal planes of the same randomly oriented crystal. In an embodiment of the present invention, the half-width of the rocking curve measured by X-ray diffraction in the oriented crystal axis direction 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 an embodiment of the present invention, the thickness is more preferably 200 nm or more. The surface roughness (RMS) of the crystalline oxide film is also not particularly limited as long as it is 10 nm or less, but in an embodiment of the present invention, it is preferably 1 nm or less. By achieving such a preferable thickness or surface roughness, when the oxide crystal is applied to a semiconductor device, it is possible to impart to the semiconductor device superior electrical properties such as voltage resistance. The surface roughness (RMS) refers to a value calculated based on JIS B0601 using the surface shape measurement results of a 10 μm square area using an atomic force microscope (AFM).

[0022] In an embodiment of the present invention, the crystalline oxide film preferably contains germanium oxide having a rutile structure. In an embodiment of the present invention, it is more preferable that the crystalline oxide film contains germanium oxide as a main component. Here, "main component" refers to a content of germanium oxide (germanium oxide) in the crystalline oxide film being 50% or more in terms of its composition ratio in the crystalline oxide film. In an embodiment of the present invention, the content of germanium oxide in the crystalline oxide film is preferably 70% or more, more preferably 90% or more, in terms of its 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. The oxide crystal may also contain a metal other than germanium. Examples of the other metal include metals of Group 14 of the periodic table other than germanium (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 an embodiment of the present invention, the atomic ratio of germanium to metal elements in the oxide semiconductor is preferably 0.7 or more, more preferably 0.9 or more. By setting the atomic ratio of germanium in this preferred range, a crystalline oxide film having a higher band gap (for example, 4.0 eV or more, more preferably 4.4 eV or more) can be realized.

[0023] The oxide crystal, the crystalline acid oxide film, and / or the crystalline stacked layer structure can be obtained, for example, by the following suitable film formation method. The method for producing such an oxide crystal (hereinafter also referred to as an "oxide semiconductor" or a "crystalline oxide film") is also novel and useful, and is included in the present invention.

[0024] The method for producing an oxide semiconductor of the present invention is characterized by atomizing or forming droplets from a raw material solution containing germanium (atomization step), supplying a carrier gas to the obtained atomized droplets, transporting the atomized droplets to a crystalline substrate having a tetragonal crystal structure by the carrier gas (transportation step), and then thermally reacting the atomized droplets 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 impede the object 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 impede the object of the present invention. Examples of the shape of the substrate include a plate-like shape such as a flat plate or a disk, a fiber-like shape, a rod-like shape, a column-like shape, a prism-like shape, a cylindrical shape, a spiral shape, a spherical shape, and a ring-like shape. 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 crystal substrate is not particularly limited as long as it does not impede 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 crystal substrate may also be a substrate having a metal film on its surface. When the crystal substrate is a conductive substrate, a vertical device can be fabricated without removing the substrate. The crystal structure of the crystal substrate is also not particularly limited as long as it does not impede the objectives of the present invention. Examples of the crystal structure of the crystal substrate include a hexagonal crystal structure and a tetragonal crystal structure. Examples of crystal substrates having a corundum structure include a sapphire substrate (e.g., an R-plane sapphire substrate). Examples of crystal substrates having a tetragonal crystal structure include an SrTiO3 substrate, a TiO2 substrate, and an MgF2 substrate. In an embodiment of the present invention, the crystal substrate preferably has a tetragonal crystal structure, and more preferably a rutile structure. Examples of crystal substrates having a rutile structure include a rutile titanium oxide (r-TiO2) substrate. The r-TiO2 substrate is preferably a conductive substrate containing a dopant such as Nb. The crystalline substrate may have an off-axis angle. In an embodiment of the present invention, a Ge substrate is also preferably used as the crystalline substrate.

[0027] (Atomization process) In the atomization step, the raw solution is atomized. The atomization means is not particularly limited as long as it can atomize the raw solution, and any known means may be used, but in the present invention, an atomization means using ultrasonic waves is preferred. The mist obtained using ultrasonic waves is preferable because it has an initial velocity of zero and floats in the air. For example, rather than being sprayed like a spray, it is a mist that floats in space and can be transported as a gas, so it is very suitable because it is not damaged by collision energy. The size of the mist droplets is not particularly limited and may be on the order of several mm, 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, with the germanium content being greater than the dopant element. The raw material solution may contain an inorganic material or an organic material. In an embodiment of the present invention, the raw material solution preferably contains germanium in the form of an organogermanium compound. In another embodiment of the present invention, the organogermanium compound preferably has a carboxy group. The blending ratio of germanium (e.g., the organogermanium compound) in the raw material solution is not particularly limited, but is preferably 0.0001 mol / L to 20 mol / L, 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 metals other than germanium (e.g., tin or silicon).

[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), and indium (In). In an embodiment of the present invention, the dopant element is preferably antimony (Sb). The dopant element may be contained in the raw material solution in the form of an inorganic compound or an organic compound.

[0030] The solvent for 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, the solvent preferably contains water, and a mixed solvent of water and an acid is also preferred. More specific examples of the water include pure water, ultrapure water, tap water, well water, mineral water, hot spring water, spring water, fresh water, and seawater, with ultrapure water being preferred in the present invention. More specific examples of the acid include 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] The raw material solution may also contain additives such as hydrohalic acids and oxidizing agents. Examples of hydrohalic acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid. Examples of oxidizing agents include peroxides such as hydrogen peroxide (HO), sodium peroxide (NaO), barium peroxide (BaO), and benzoyl peroxide (CHCO)O, as well as hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, and organic peroxides such as peracetic acid and nitrobenzene.

[0032] (Transportation process) In the transport step, a carrier gas is supplied to the atomized droplets (hereinafter simply referred to as "mist") obtained in the atomization step, and the mist is transported to a substrate by the carrier gas. The type of carrier gas is not particularly limited as long as it does not impede the object of the present invention, and examples thereof include oxygen, ozone, inert gases such as nitrogen and argon, and reducing gases such as hydrogen gas and forming gas. However, in the present invention, oxygen is preferably used as the carrier gas. Examples of carrier gases using oxygen include air, oxygen gas, and ozone gas, with oxygen gas and / or ozone gas being particularly preferred. In addition, the type of carrier gas may be one type, but may also be two or more types. A dilution gas with a different carrier gas concentration (e.g., a 10-fold dilution gas) may also be used as a second carrier gas. In addition, the number of carrier gas supply locations may be one or more than one. In the present invention, when an atomization chamber, a supply pipe, and a film-forming chamber are used, it is preferable to provide a carrier gas supply point in each of the atomization chamber and the supply pipe, and it is more preferable 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, 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, more preferably 0.1 to 1 L / min.

[0033] (Film forming process) In the film-forming process, the atomized droplets are thermally reacted 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 forms a film from the mist, and the mist is reacted with heat. The reaction conditions are also not particularly limited as long as they do not impede the objectives of the present invention. In this process, the thermal reaction is typically carried out at a temperature equal to or higher than the evaporation temperature of the solvent, but preferably at a temperature not too high. In the present invention, the thermal reaction is preferably carried out at a temperature of 700°C to 800°C. Furthermore, the thermal reaction may be carried out under any of the following conditions: vacuum, oxygen-free atmosphere, reducing gas atmosphere, and oxidizing atmosphere, as long as it does not impede the objectives of the present invention. It may also be carried out under atmospheric pressure, elevated pressure, or reduced pressure. However, in the present invention, an oxidizing atmosphere is preferred, and atmospheric pressure is also preferred, with an oxidizing atmosphere and atmospheric pressure being more preferred. 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 of a raw material solution containing an oxidizing agent. The film thickness can be set by adjusting the film formation time.

[0034] In an embodiment of the present invention, a film may be formed directly on the substrate. Alternatively, other layers, such as a layer different from the oxide semiconductor (e.g., an n-type semiconductor layer, an n+-type semiconductor layer, an n-type semiconductor layer, etc.), an insulator layer (including a semi-insulator layer), or a buffer layer, may be stacked on the substrate, and then the film may be formed on the substrate via the other layers. In particular, a buffer layer is preferably used to reduce the difference in lattice constant between the crystal substrate and the oxide crystal. Examples of materials constituting 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" refers to a compositional ratio of the oxide crystal in the oxide semiconductor layer of 50% or more. In an embodiment of the present invention, the compositional ratio of the oxide crystal in the oxide semiconductor layer is preferably 70% or more, 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 using semiconductor-metal junctions, JBS, PN or PIN diodes combined with other P layers, and light-emitting / receiving elements. In addition to the above, the oxide crystal can also be suitably used in photoelectric conversion elements, gas sensors, photoelectrodes, memories, and the like. In an embodiment of the present invention, the oxide crystal may be used as the oxide crystal in a semiconductor device, after removing the crystal substrate as desired, or may be used as a crystalline layered structure with the crystal substrate in a semiconductor device. In particular, when the crystalline substrate is a conductive substrate, the crystalline laminated structure can be suitably applied to a semiconductor device (vertical device).

[0036] The semiconductor device can be suitably used as either a horizontal element (horizontal device) in which an electrode is formed on one side of a semiconductor layer, or a vertical element (vertical device) in which electrodes are formed on both the front and back sides of a semiconductor layer, but in the embodiments of the present invention, it is preferably used as a vertical device. Suitable examples of the semiconductor device include a Schottky barrier diode (SBD), a junction barrier Schottky diode (JBS), a metal semiconductor field effect transistor (MESFET), a high electron mobility transistor (HEMT), a metal oxide semiconductor field effect transistor (MOSFET), a static induction transistor (SIT), a junction field effect transistor (JFET), an insulated gate bipolar transistor (IGBT), and a light emitting diode (LED).

[0037] Hereinafter, preferred examples of the semiconductor device in which the oxide crystal of the present invention is applied to an n-type semiconductor layer (an n+ type semiconductor, an n- semiconductor layer, etc.) will be described with reference to the drawings, but the present invention is not limited to these examples.

[0038] (SBD) Fig. 6 shows an example of a Schottky barrier diode (SBD) according to an embodiment of the present invention. The SBD in Fig. 6 includes 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 the Schottky electrode and the ohmic electrode may be known electrode materials, and examples of the electrode materials 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, and Ag, or alloys thereof; conductive metal oxide films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); organic conductive compounds such as polyaniline, polythiophene, and polypyrrole; and mixtures and laminates thereof.

[0040] The Schottky electrode and the ohmic electrode can be formed by known means such as vacuum deposition or sputtering. More specifically, when forming a Schottky electrode using two types of metals, a first metal and a second metal, the Schottky electrode can be formed by stacking a layer made of the first metal and a layer made of the second metal, and then patterning the layer made of the first metal and the layer made of the second metal using a photolithography technique.

[0041] When a reverse bias is applied to the SBD shown in Figure 6, a depletion layer (not shown) expands into 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. Thus, an SBD using this semiconductor structure is excellent for high-voltage and large-current applications, has fast switching speeds, and excels in voltage resistance and reliability.

[0042] (JBS) FIG. 7 shows a junction barrier Schottky diode (JBS) according to a preferred embodiment of the present invention. The semiconductor device of FIG. 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 disposed on the n-type semiconductor layer and capable of forming a Schottky barrier between the i-type semiconductor layer and the Schottky electrode 2, and a p-type semiconductor layer 1 disposed 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, the p-type semiconductor layers are preferably disposed at regular intervals, and more preferably, the p-type semiconductor layers are disposed between both ends of the Schottky electrode and the n-type semiconductor layer. This preferred embodiment provides a JBS with superior thermal stability and adhesion, reduced leakage current, and superior semiconductor properties such as breakdown voltage. The semiconductor device of FIG. 7 also includes an ohmic electrode 5 on the n+-type semiconductor layer 4.

[0043] 7 may be formed by any known method as long as it does not impede the object of the present invention, such as forming a film by vacuum deposition, CVD, sputtering, or various coating techniques, followed by patterning by photolithography, or directly patterning by printing technology.

[0044] (MOSFET) An example of a case where the semiconductor device of the present invention is a MOSFET is shown in Fig. 8. The MOSFET in Fig. 8 is a trench MOSFET, and includes 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 having a thickness of, for example, 100 nm to 100 μm is formed on the drain electrode 135c, and an n- type semiconductor layer 131a having 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, a plurality of trenches are formed in the n-type semiconductor layer 131a and the n+ type semiconductor layer 131c, each of which penetrates the n+ semiconductor layer 131c and reaches partway through the n- type semiconductor layer 131a. A gate electrode 135a is embedded in the trench via a gate insulating film 134 having a thickness of, for example, 10 nm to 1 μm.

[0047] 8, when a voltage is applied between the source electrode 135b and the drain electrode 135c and a positive voltage with respect to the source electrode 135b is applied to the gate electrode 135a, 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 is turned on. When the voltage of the gate electrode is set to 0V, no channel layer is formed, and the n-type semiconductor layer 131a becomes filled with a depletion layer, resulting in the MOSFET being turned 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 includes an n-type semiconductor layer 121a with a wide bandgap, an n-type semiconductor layer 121b with a narrow bandgap, 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 an embodiment of the present invention, it is preferable to use the oxide crystal for the n-type semiconductor layer 121a with a wide bandgap and Ge for the n-type semiconductor layer 121b with a narrow bandgap, for example.

[0049] In the above example, an example was shown in which a p-type semiconductor was not used, but embodiments of the present invention are not limited to this and a p-type semiconductor may also be used. Examples using a p-type semiconductor are shown in Figures 9 to 11 and 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 be made of the same material as the n-type semiconductor and contain a p-type dopant.

[0050] (MOSFET) 9 shows a preferred example of a metal oxide semiconductor field effect transistor (MOSFET) including 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 may be the same as the p-type semiconductor layer 132.

[0051] (IGBT) FIG. 10 shows a preferred example of an insulated gate bipolar transistor (IGBT) including 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) FIG. 11 shows an example of a semiconductor device according to an embodiment of the present invention that is a light-emitting diode (LED). The semiconductor light-emitting device of FIG. 11 includes an n-type semiconductor layer 161 on a second electrode 165b, and a light-emitting layer 163 is stacked on the n-type semiconductor layer 161. A p-type semiconductor layer 162 is stacked 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 stacked on the translucent electrode 167. The semiconductor light-emitting device of FIG. 8 may be covered with a protective layer except for the electrode portion.

[0053] Examples of materials for the translucent electrode include conductive oxide materials 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. The translucent electrode can be formed by depositing these materials using known means such as sputtering. After the translucent electrode is formed, it may be subjected to thermal annealing to make the translucent electrode transparent.

[0054] In the semiconductor light-emitting device of FIG. 11, the first electrode 165a is a positive electrode and the second electrode 165b is a negative electrode, and current is passed through these electrodes to the p-type semiconductor layer 162, the light-emitting layer 163, and the n-type semiconductor layer 161, causing the light-emitting layer 163 to emit 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, and Ag, or alloys thereof; conductive metal oxide films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); organic conductive compounds such as polyaniline, polythiophene, and polypyrrole; and mixtures thereof. The method for forming the electrodes is not particularly limited, and they can be formed on the substrate by 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 for the materials.

[0056] (gas sensor) FIG. 17 shows an example of a gas sensor according to an embodiment of the present invention. The gas sensor of FIG. 17 includes 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 or p-type semiconductor layers. The work function of the second layer is smaller than that of the first layer. The second layer and the first electrode preferably form a Schottky junction. The first layer and the second electrode preferably 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, and platinum. 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) FIG. 18 shows an example of a photoelectric conversion element according to an embodiment of the present invention. The photoelectric conversion element of FIG. 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 of FIG. 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 in this order on a lower electrode 51. The stacking order of the electron blocking layer 56a, the photoelectric conversion layer 52, and the hole blocking layer 56b in FIG. 18(b) may be changed as appropriate 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 of FIG. 18, light is preferably incident on the photoelectric conversion layer 52 through the upper electrode 55. Such a photoelectric conversion element can be suitably used as an optical sensor and an imaging element.

[0058] (photodetector) FIG. 19 shows an example of a light-receiving element according to an embodiment of the present invention. The light-receiving element of FIG. 19 includes 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 for the lower electrode 40, the Schottky electrode 44, and the upper electrode 45 may be known electrode materials (e.g., 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 this embodiment of the present invention, the oxide crystals 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, the specific region 46, etc. In the photodetector of FIG. 19, eye-safe band light is incident through the window portion of the upper electrode 45, and when the light is absorbed by free electrons in the Schottky electrode 44, electrons are emitted toward 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) FIG. 20 shows an example of a photoelectrode according to an embodiment of the present invention. The photoelectrode of FIG. 20 includes a substrate 31, a conductive layer (electron-conducting layer) 32 provided on the substrate 31, and a photocatalytic layer (light-absorbing layer) 33 provided on the conductive layer 32. The substrate 31 may be, for example, a glass substrate or a sapphire substrate. In an embodiment of the present invention, the substrate 31 may be any of the above-mentioned crystal substrates. 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. When 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 so 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 between the photocatalytic layer 33 and the conductor layer 32 so that the energy difference between the vacuum level and the Fermi level of the conductor layer 32 is larger than the energy difference between the vacuum level and the Fermi level of the photocatalytic layer 33. In an embodiment of the present invention, the oxide crystal can be suitably used for the conductor layer 32 and / or the photocatalytic layer 31. The photoelectrode of FIG. 20 is suitably used in, for example, a photoelectrochemical cell or the like.

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

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

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

[0063] Meanwhile, various sensors (not shown) measure actual values ​​such as wheel rotation speed, torque, and accelerator pedal depression (acceleration amount) from the electric vehicle while it is running, 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 a memory. It generates a control signal using the input measurement signal and outputs it as a feedback signal to the inverter 504, thereby controlling the switching operation of the switching elements. This allows the AC voltage provided by the inverter 504 to be instantly corrected, enabling accurate operation control of the electric vehicle and realizing safe and comfortable operation of the electric vehicle. The output voltage to the inverter 504 can also be controlled by providing a feedback signal from the drive control unit 506 to the boost converter 502.

[0064] 13 shows the circuit configuration of FIG. 12 excluding the step-down converter 503, i.e., the circuit configuration showing only the configuration for driving the motor 505. As shown in the figure, the semiconductor device of the present invention is used, for example, as a Schottky barrier diode in a step-up converter 502 and an inverter 504 to provide switching control. 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. Note that current is stabilized by inserting an inductor (such as a coil) into the output of the battery 501, and voltage is stabilized by inserting capacitors (such as an electrolytic capacitor) between the battery 501, the step-up converter 502, and the inverter 504.

[0065] 13, the drive control unit 506 includes a calculation unit 507 made up of a CPU (Central Processing Unit) and a storage unit 508 made up of non-volatile memory. Signals input to the drive control unit 506 are given to the calculation unit 507, which performs the necessary calculations to generate feedback signals for each semiconductor element. The storage unit 508 also temporarily stores the results of calculations performed by the calculation unit 507, and accumulates physical constants and functions necessary for drive control in the form of a table and outputs them to the calculation unit 507 as appropriate. The calculation unit 507 and storage unit 508 can be configured as known units, and their processing capabilities, etc. can be selected as desired.

[0066] 12 and 13, in control system 500, diodes and switching elements such as thyristors, power transistors, IGBTs, and MOSFETs are used for the switching operations of boost converter 502, buck converter 503, and 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 control system 500 can be realized. That is, the effects of the present invention can be expected for each of boost converter 502, buck converter 503, and inverter 504, and the effects of the present invention can be expected for any one of these, any combination of two or more of them, or any form including drive control unit 506. The semiconductor device of the present invention can be applied to the control system 500 described above not only for electric vehicles but also for all kinds of control systems for boosting or lowering power from a DC power source, converting DC to AC, etc. Also, a power source such as a solar cell can be used as the battery.

[0067] FIG. 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 FIG. 15 is a circuit diagram of the same control system, which is suitable for installation in infrastructure equipment, home appliances, and the like that operate on power from an AC power source.

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

[0069] Inverter 604 converts the DC voltage supplied from AC / DC converter 602 into a three-phase AC voltage by switching operation and outputs it to motor 605. Motor 604 has different configurations depending on the controlled object, but is a three-phase AC motor for driving wheels if the controlled object is a train, pumps and various power sources if the controlled object is factory equipment, or compressors if the controlled object is a home appliance, and is rotationally driven by the three-phase AC voltage output from inverter 604, and transmits the rotational driving force to a driven object (not shown).

[0070] Note that, for example, among home appliances, there are many devices to be driven that can be supplied with the DC voltage output from AC / DC converter 302 as is (for example, personal computers, LED lighting equipment, video equipment, audio equipment, etc.), in which case inverter 604 is not required in control system 600, and the DC voltage is supplied to the device to be driven from AC / DC converter 602, as shown in Fig. 14. In this case, for example, a personal computer or the like is supplied with a DC voltage of 3.3 V, and an LED lighting equipment or the like is supplied with a DC voltage of 5 V.

[0071] Meanwhile, various sensors (not shown) are used to measure actual values ​​such as the rotation speed and torque of the driven object, or the temperature and flow rate of the environment surrounding the driven object, and 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 to control the switching operation of the switching element. This allows the AC voltage provided by the inverter 604 to be instantly corrected, thereby 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 by a DC voltage, it is also possible to perform feedback control of the AC / DC converter 602 instead of feedback to the inverter.

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

[0073] 15, the drive control unit 606 includes a calculation unit 607 consisting of a CPU and a storage unit 608 consisting of a non-volatile memory. Signals input to the drive control unit 606 are given to the calculation unit 607, which performs the necessary calculations to generate feedback signals for each semiconductor element. The storage unit 608 also temporarily stores the results of calculations performed by the calculation unit 607, and accumulates physical constants and functions required for drive control in the form of a table and outputs them to the calculation unit 607 as appropriate. The calculation unit 607 and storage unit 608 can be configured as known units, and their processing capabilities can be selected as desired.

[0074] 14 and 15, in this control system 600, 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 realized. That is, the effects of the present invention can be expected for each of the AC / DC converter 602 and the inverter 604, and the effects of the present invention can be expected in any one of them, or in a combination thereof, or in any form including the drive control unit 606.

[0075] 14 and 15 show motor 605 as an example of a device to be driven, but the device to be driven is not necessarily limited to mechanically operated devices, and can be many devices that require AC voltage. Control system 600 can be applied as long as it inputs power from an AC power source to drive the device to be driven, and can be installed for drive control of devices such as infrastructure equipment (for example, power equipment in buildings and factories, communication equipment, traffic control equipment, water and sewage treatment equipment, system equipment, labor-saving equipment, trains, etc.) and home appliances (for example, 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 example will be described with reference to Figure 1. The mist CVD apparatus 19 includes a susceptor 21 on which a substrate 20 is placed, a carrier gas supply means 22a for supplying a carrier gas, a flow rate control valve 23a for adjusting the flow rate of the carrier gas delivered from the carrier gas supply means 22a, a carrier gas (dilution) supply means 22b for supplying a carrier gas (dilution), a flow rate control valve 23b for adjusting the flow rate of the carrier gas delivered from the carrier gas (dilution) supply means 22b, a mist generator 24 containing a raw material solution 24a, a container 25 for containing water 25a, an ultrasonic vibrator 26 attached to the bottom 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 supply pipe 27. The susceptor 21 is made of quartz, and the surface on which the substrate 20 is placed is inclined relative to the horizontal. By fabricating both the supply pipe 27 and the susceptor 21, which form the film formation chamber, from quartz, impurities originating from the apparatus are prevented from being mixed into the film formed on the substrate 20.

[0077] 2. Preparation of the Stock Solution Bis[2-carboxyethylgermanium(IV)]sesquioxide(CH 10 A 0.025 M aqueous solution of Ge2O7) was mixed with 10% by volume of hydrochloric acid (HCl) to prepare a raw material solution.

[0078] 3. Film preparation The raw material solution 24a obtained in 2 above was contained in the mist generating source 24. Next, a (001) 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 rate control valves 23a and 23b were opened, and carrier gas was supplied from the carrier gas supply means 22a and 22b, which are the carrier gas sources, into the supply pipe 27. After the atmosphere in the supply pipe 27 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas was adjusted to 3.0 L / min and the flow rate of the carrier gas (diluted) to 0.5 L / min, respectively. Note that oxygen was used as the carrier gas.

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

[0080] 5. Evaluation The GeO2 film obtained in step 4 above was identified using an X-ray diffractometer, and was found to be a (001)-oriented r-GeO2 film with a rutile structure. The XRD results are shown in Figure 2. The rocking curve half-width at the 002 diffraction peak was 911 arcsec. For reference, Figure 2 also shows the results for film deposition temperatures of 700°C, 725°C, and 775°C. Furthermore, when the film surface was observed using an atomic force microscope (AFM), 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 (CH 10 A GeO2 film was deposited in the same manner as in Example 1, except that the concentration of Ge2O7) was 0.001 M (mol / L) and the deposition temperature was 725°C. The thickness of the resulting GeO2 film was 200 nm. The resulting GeO2 film was identified using an X-ray diffractometer and found to be a (001)-oriented r-GeO2 film with a rutile structure. The XRD results are shown in Figure 3. The rocking curve half-width at the 002 diffraction peak was 560 arcsec. Figure 3(a) shows the results of a 2θ / ω scan, and Figure 3(b) shows the results of an ω scan. 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 was bis[2-carboxyethylgermanium(IV)] sesquioxide (CH 10 The film was formed in the same manner as in Example 2, except that a solution of 0.001M Ge2O7) and 0.0005M tin chloride dihydrate was used, to which 10% by volume of hydrochloric acid (sHCl) was added. The film was identified using an X-ray diffractometer, and it was found that the film was composed of r-(Ge 0.52 ,Sn 0.48 The film thickness was 208 nm. The results of XRD are shown in Figure 21. The rocking curve half-width at the 002 diffraction peak was 113 arcsec. Furthermore, Hall effect measurement of the obtained film revealed that the carrier type was "n" and the carrier density was 8.40 x 10 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 (CH 10 The film was formed 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. The film was identified using an X-ray diffractometer, and it was found that the film was composed of r-(Ge 0.87 ,Sn 0.13 The film thickness was 150 nm. The results of XRD 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 (CH 10The film was formed 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. The film was identified using an X-ray diffractometer, and it was found that the film was composed of r-(Ge 0.61 ,Sn 0.39 The film thickness was 365 nm. The XRD results are shown in Figure 21. [Industrial Applicability]

[0085] The oxide crystals, crystalline oxide films, and crystalline laminated 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 related devices, and industrial materials, but are particularly useful in semiconductor devices and materials therefor. [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 First Layer 12 Second Layer 13 First electrode 14 Second electrode 19 Mist CVD equipment 20 Substrate (crystal substrate) 21 Susceptor 22a Carrier gas supply means 22b Carrier gas (dilution) supply means 23a Flow control valve 23b Flow control valve 24 Mist source 24a Raw material solution 25 Container 25a water 26 Ultrasonic vibrator 27 Supply pipe 28 Heater 29 Exhaust port 31 PCB 32 Conductor layer (electron conductive layer) 33 Photocatalytic layer (light absorption layer) 40 Lower electrode 41 Highly concentrated n-type layer 42 Low concentration n-type layer 43 High concentration p-type layer 44 Schottky electrode 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 stacked structure 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 gate electrode 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 insulating film 155a Gate electrode 155b Emitter electrode 155c Collector electrode 161 n-type semiconductor layer 162 p-type semiconductor layer 163 Light-emitting layer 165a first electrode 165b second electrode 167 Translucent electrode 500 Control System 501 Battery (power supply) 502 Boost Converter 503 Buck 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 section 608 Storage section

Claims

1. An oxide crystal containing an oxide of a rutile structure, characterized in that the crystal axis direction is perpendicular or parallel to the c-axis, and the atomic ratio of germanium among the metal elements in the oxide crystal is greater than 0.

5.

2. 2. The oxide crystal according to claim 1, wherein the crystal axis is oriented parallel to the c-axis.

3. 3. The oxide crystal according to claim 1, wherein the half-width of a rocking curve measured by X-ray diffraction in the oriented crystal axis direction is 1000 arcsec or less.

4. 3. The oxide crystal according to claim 1, which is in the form of a film.

5. 5. The oxide crystal according to claim 4, having a film thickness of 100 nm or more.

6. 5. The oxide crystal according to claim 4, having a surface roughness (RMS) of 10 nm or less.

7. 3. The oxide crystal according to claim 1, 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 semiconductor layer contains the oxide crystal according to claim 1 or 2 as a main component.

9. A crystalline oxide film containing an oxide of germanium, the crystalline oxide film having a thickness of 100 nm or more and a surface roughness (RMS) of 10 nm or less.

10. 10. The crystalline oxide film according to claim 9, having a film thickness of 200 nm or more.

11. 11. The crystalline oxide film according to claim 9, which has a tetragonal crystal structure.

12. 11. The crystalline oxide film according to claim 9, which is a uniaxially oriented film.

13. 11. The crystalline oxide film according to claim 9, wherein the half-width of the film measured by X-ray diffraction is 1000 arcsec or less.

14. 11. The crystalline oxide film according to claim 9, wherein the atomic ratio of germanium to the metal elements in the crystalline oxide film is greater than 0.

5.

15. 11. The crystalline oxide film according to claim 9, 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 the crystalline oxide film according to claim 9 or 10.

17. A crystalline layered structure comprising at least a crystalline substrate and a crystalline oxide film stacked 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 is greater than 0.

5.

18. 18. The crystalline layered structure according to claim 17, wherein the crystalline oxide film has a tetragonal crystal structure.

19. 19. The crystalline layered structure according to claim 17, wherein the crystalline oxide film has a thickness of 100 nm or more.

20. 19. The crystalline layered structure according to claim 17 or 18, wherein the surface roughness (RMS) of the crystalline oxide film is 10 nm or less.

21. 19. The crystalline layered structure according to claim 17, wherein the crystalline oxide film is a uniaxially oriented film.

22. 19. The crystalline layered structure according to claim 17 or 18, wherein the rocking curve half width of the crystalline oxide film measured by X-ray diffraction is 1000 arcsec or less.

23. The crystalline layered structure according to claim 17 or 18, wherein the crystalline substrate is a conductive substrate.

24. A power conversion device using the semiconductor device according to claim 8.

25. A control system using the semiconductor device according to claim 8.

26. A method for producing a crystalline laminated structure, comprising atomizing or forming droplets from a raw material solution containing germanium, supplying a carrier gas to the resulting atomized droplets, transporting the atomized droplets to a crystal substrate having a tetragonal crystal structure by the carrier gas, and then thermally reacting the atomized droplets on the crystal substrate.

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