Crucible, method for producing beta-type gallium trioxide single crystal substrate using same, and beta-type gallium trioxide single crystal substrate

Abstract

Provided is a crucible for growth of a beta-type gallium trioxide single crystal, the crucible having a thickness of 1-10 mm inclusive, the maximum inner diameter of the crucible being 100 mm or more, the composition of the crucible being stabilized zirconia containing both or either yttrium oxide and calcium oxide, and the thickness of the crucible being 1-10 mm inclusive, the thickness of the crucible being 1-10 mm inclusive, the maximum inner diameter of the crucible being 100 mm or more, and the thickness of the crucible being 1-10 mm inclusive. The surface on the inner peripheral surface side of the crucible is coated with a thermal spray coating film containing rhodium and / or platinum, the thickness of the thermal spray coating film is 100 [mu] m to 500 [mu] m, and the stabilized zirconia contains at least 12.0 mass% to 15.5 mass% of the yttrium oxide or 10.2 mass% to 11.4 mass% of the calcium oxide.

Description

Technical Field

[0001] The present invention relates to a crucible, a method for manufacturing a β-type gallium sesquioxide single crystal substrate using the crucible, and the β-type gallium sesquioxide single crystal substrate. Background Art

[0002] Japanese Patent Application Publication No. 2016-079080 (Patent Document 1), Japanese Patent Application Publication No. 2017-193466 (Patent Document 2), Japanese Patent Application Publication No. 2021-031367 (Patent Document 3), Japanese Patent Application Publication No. 2021-031379 (Patent Document 4), Japanese Patent Application Publication No. 2020-059633 (Patent Document 5), and Inikawa et al., Journal of the Japanese Society of Crystal Growth, Vol. 44, No. 4 (2017), 44-4-03 (Non-Patent Document 1) disclose the following method: a vertical boat method using a crucible made of a platinum-rhodium alloy (hereinafter also referred to as "Pt-Rh alloy") or a crucible or die made of a platinum-iridium alloy (hereinafter also referred to as "Pt-Ir alloy"), or an edge-defined film growth (EFG) method. A method for growing a β-type gallium trioxide single crystal (hereinafter also referred to as a "β-type Ga2O3 single crystal") using a film-fed growth method, etc. Japanese Patent Application Laid-Open No. 2000-129465 (Patent Document 6) discloses a method in which platinum or a platinum-based alloy is coated on the surface of a refractory substrate such as ceramic by thermal spraying.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-079080;

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2017-193466;

[0007] Patent Document 3: Japanese Patent Application Publication No. 2021-031367;

[0008] Patent Document 4: Japanese Patent Application Publication No. 2021-031379;

[0009] Patent Document 5: Japanese Patent Application Publication No. 2020-059633;

[0010] Patent Document 6: Japanese Patent Application Laid-Open No. 2000-129465.

[0011] Non-patent literature

[0012] Non-patent document 1: Kanikawa et al., Journal of the Japanese Society of Crystal Growth, Vol. 44, No. 4 (2017), 44-4-03. Summary of the Invention

[0013] The crucible of the present invention is a crucible for growing a β-type gallium trioxide single crystal. The crucible has a thickness of at least 1 mm and at most 10 mm. The maximum inner diameter of the crucible is at least 100 mm. The crucible is composed of stabilized zirconia containing either or both of yttrium oxide and calcium oxide. The surface of the inner peripheral surface of the crucible is coated with a thermal sprayed film containing either or both of rhodium and platinum. The thickness of the thermal sprayed film is at least 100 μm and at most 500 μm. The stabilized zirconia contains at least 12.0 mass % and at most 15.5 mass % of yttrium oxide, or contains at least 10.2 mass % and at most 11.4 mass % of calcium oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram illustrating the main parts of a single crystal growth apparatus used in the method for manufacturing a β-type Ga2O3 single crystal substrate of this embodiment, and a first type of crucible used in the above-mentioned single crystal growth apparatus.

[0015] Figure 2 It is an explanation Figure 1 An enlarged cross-sectional view of a main portion of a crucible of a second embodiment used in a single crystal growth apparatus.

[0016] Figure 3 It is an explanation Figure 1 This is an enlarged cross-sectional view of the main portion of a crucible of a third type used in a single crystal growth apparatus.

[0017] Figure 4 It is an explanation Figure 1 An enlarged cross-sectional view of a main portion of a crucible of a fourth embodiment used in a single crystal growth apparatus.

[0018] Figure 5 It is an explanation Figure 1 An enlarged cross-sectional view of a main portion of a crucible of a fifth embodiment used in a single crystal growth apparatus.

[0019] Figure 6 This is a flowchart showing an example of a method for manufacturing a β-type Ga2O3 single crystal substrate according to this embodiment.

[0020] Figure 7 It is a schematic diagram illustrating a β-type Ga2O3 single crystal substrate according to this embodiment.

[0021] Figure 8This is an explanatory diagram for explaining a sample for Hall measurement produced using the central portion of the β-type Ga2O3 single crystal substrate in order to measure the carrier concentration in the substrate of this embodiment. DETAILED DESCRIPTION

[0022] [Problems to be Solved by the Invention]

[0023] As disclosed in Patent Documents 1 to 5 and Non-Patent Document 1, it is known to use crucibles made of Pt-Rh alloys or Pt-Ir alloys to grow and obtain β-Ga2O3 single crystals. These crucibles made of Pt-Rh alloys, Pt-Ir alloys, etc. are expensive, and reducing their thickness is a possible cost-effective method. However, crucibles made of Pt-Rh alloys, Pt-Ir alloys, etc. are easily deformed by thermal contraction and other factors. Therefore, during crystal growth and cooling after crystal growth, they may be cracked or damaged by the β-Ga2O3 single crystals present in the crucible. Therefore, it has been pointed out that the desired β-Ga2O3 single crystals cannot be obtained with a good yield. In particular, the cracking of the crucible during crystal growth is fatal to the production of β-Ga2O3 single crystals. The method disclosed in Patent Document 6, which covers the crucible with platinum or a platinum alloy by thermal spraying, is not intended to prevent the cracking or damage of the crucible, etc., and therefore does not provide any suggestion regarding the function or effect of preventing the cracking of the crucible during crystal growth. Therefore, a crucible using thin films of Pt-Rh alloy, Pt-Ir alloy, etc., which can obtain β-type Ga2O3 single crystals with good yield by at least suppressing the occurrence of cracks, defects, etc. during crystal growth, has not yet been obtained, and its development is eagerly awaited.

[0024] In view of the above, an object of the present invention is to provide a crucible capable of suppressing cracks, defects, etc. during crystal growth, a method for manufacturing a β-type gallium sesquioxide single crystal substrate using the crucible, and a β-type gallium sesquioxide single crystal substrate.

[0025] [Effects of the Invention]

[0026] According to the present invention, a crucible capable of suppressing the occurrence of cracks, defects, etc. during crystal growth, a method for manufacturing a β-type gallium trioxide single crystal substrate using the crucible, and a β-type gallium trioxide single crystal substrate can be provided.

[0027] [Overview of Embodiments]

[0028] Hereinafter, an outline of the embodiments of the present invention will be described. The present inventors have conducted in-depth research to solve the above-mentioned problems, thereby completing the present invention. First, as a material for a crucible for applying the vertical boat method, the present inventors focused on zirconium oxide, which is a material with low thermal conductivity, stable to temperature changes, and not easily deformed. In particular, the surface of the inner circumference of the crucible composed of the above-mentioned zirconium oxide is coated with a thin film containing both or either rhodium and platinum, for example, a thin film composed of a Pt-Rh alloy containing Rh. The above-mentioned thin film can withstand the temperature required for the growth of β-type Ga2O3 single crystals (about 1800°C). As a result, a crucible that can at least suppress the occurrence of cracks, defects, etc. during crystal growth was conceived. In addition, in order to obtain the above-mentioned single crystals with a good yield, the appropriate thickness of the above-mentioned crucible and the thickness of the above-mentioned thin film were also discovered, thereby realizing the present invention.

[0029] Next, embodiments of the present invention are listed for explanation.

[0030] [1] One embodiment of the present invention is a crucible for growing a β-type gallium trioxide single crystal. The crucible has a thickness of 1 mm or more and 10 mm or less. The maximum inner diameter of the crucible is 100 mm or more. The crucible is composed of stabilized zirconium oxide containing either or both of yttrium oxide and calcium oxide. The surface of the inner peripheral surface of the crucible is coated with a thermal spray film containing either or both of rhodium and platinum. The thickness of the thermal spray film is 100 μm or more and 500 μm or less. The stabilized zirconium oxide contains at least 12.0 mass % or more and 15.5 mass % of the yttrium oxide, or contains at least 10.2 mass % or more and 11.4 mass % of the calcium oxide. A crucible having such characteristics can suppress the occurrence of cracks, defects, etc. during crystal growth.

[0031] [2] In the crucible of [1], the thermal spray coating is preferably composed of a platinum-rhodium alloy containing 10% to 30% by mass of rhodium. This can further suppress the occurrence of cracks, defects, etc. during crystal growth.

[0032] [3] In the crucible of [2], the thermal spray coating preferably has pores. The volume ratio of the pores in the thermal spray coating, i.e., the porosity, is preferably 30% by volume or more and 50% by volume or less. This can further suppress cracking, defects, and the like during crystal growth.

[0033] [4] In the crucible of [2], the surface roughness Rz of the surface is preferably not less than 300 μm and not more than 500 μm. The thermal spray coating preferably has pores. The volume ratio of the pores in the thermal spray coating, i.e., the porosity, is preferably not less than 10% by volume and less than 30% by volume. This can further suppress the occurrence of cracks, defects, etc. during crystal growth.

[0034] [5] In the crucible of [3] above, the surface roughness Rz of the surface is preferably not less than 300 μm and not more than 500 μm. This can further suppress the occurrence of cracks, defects, etc. during crystal growth.

[0035] [6] In the crucible of [1], the thermal sprayed film preferably consists of a first film and a second film. The first film preferably covers the surface. The first film preferably consists of rhodium or a platinum-rhodium alloy containing rhodium as a main component. The second film preferably covers the first film. The second film preferably consists of platinum or a platinum-rhodium alloy containing platinum as a main component. The thickness of the thermal sprayed film is preferably not less than 100 μm and not more than 500 μm, calculated as the total thickness of the first film and the second film. This can suppress the incorporation of rhodium into the β-type gallium trioxide single crystal.

[0036] [7] In the crucible of [6], preferably, both the first film and the second film have pores. Preferably, the volume ratio of the pores in the first film, i.e., the first film porosity, and the volume ratio of the pores in the second film, i.e., the second film porosity, are both 30% by volume or more and 50% by volume or less. This can further suppress the occurrence of cracks, defects, etc. during crystal growth.

[0037] [8] In the crucible of [6], the surface roughness Rz of the surface is preferably not less than 300 μm and not more than 500 μm. It is preferred that both the first film and the second film have pores. It is preferred that the volume ratio of the pores in the first film, i.e., the first film porosity, and the volume ratio of the pores in the second film, i.e., the second film porosity, are both not less than 10% by volume and less than 30% by volume. This can further suppress the occurrence of cracks, defects, etc. during crystal growth.

[0038] [9] In the crucible of [7] above, the surface roughness Rz of the surface is preferably 300 μm or more and 500 μm or less. This can further suppress the occurrence of cracks, defects, etc. during crystal growth.

[0039]

[10] One embodiment of the present invention is a method for manufacturing a β-gallium trioxide single crystal substrate using the crucible described in any one of [1] to [9]. The manufacturing method includes: preparing the crucible; obtaining a β-gallium trioxide single crystal by a vertical boat method using the crucible; and processing the β-gallium trioxide single crystal to obtain a β-gallium trioxide single crystal substrate having a circular main surface. This manufacturing method can provide a β-gallium trioxide single crystal substrate with good yield and high product yield.

[0040]

[11] One embodiment of the present invention is a β-type gallium trioxide single crystal substrate having a circular main surface. The diameter of the β-type gallium trioxide single crystal substrate is 100 mm or more. The main surface is the (001) plane of the β-type gallium trioxide single crystal. Alternatively, the main surface is a plane having an angle of deviation greater than 0° and less than 10° from the (001) plane of the β-type gallium trioxide single crystal, and a deviation direction from the

[010] direction of the β-type gallium trioxide single crystal or a direction orthogonal to the

[010] direction. The β-type gallium trioxide single crystal substrate contains both or either rhodium and iridium. The concentration of the rhodium and the concentration of the iridium are both less than 3 mass ppm in glow discharge mass spectrometry analysis. The β-type gallium trioxide single crystal substrate having such characteristics can be excellent in both electrical and optical properties.

[0041]

[12] In the β-type gallium trioxide single crystal substrate of

[11] , it is preferred that the transmittance of the β-type gallium trioxide single crystal substrate to light with a wavelength of 400 nm or more and 430 nm or less is 70% or more. It is preferred that the carrier concentration measured at 25°C in the Hall effect measurement using the van der Pauw method is 1×10 17 cm -3 Above and 1.0×10 19 cm -3 As a result, both electrical and optical properties can be further improved.

[0042] [Details of Implementation Methods]

[0043] Hereinafter, an embodiment of the present invention (hereinafter also referred to as "this embodiment") will be described in further detail, but the present invention is not limited thereto. Figure 1 While explaining, the same or corresponding elements in this specification and the drawings are marked with the same reference numerals, and the same description thereof will not be repeated. Furthermore, in the drawings, the scales of the components are appropriately adjusted to facilitate understanding, and the scales of the components shown in the drawings are not necessarily the same as the scales of the actual components.

[0044] In this specification, expressions such as "A to B" refer to the upper and lower limits of a range (i.e., greater than or equal to A and less than or equal to B). When units are not specified for A and only units are specified for B, the units for A are the same as those for B. Furthermore, when compounds are expressed as chemical formulas in this specification, unless the atomic ratio is particularly limited, all conventionally known atomic ratios are encompassed and are not necessarily limited to the stoichiometric range.

[0045] In this specification, "yield rate" refers to the proportion of β-gallium trioxide single crystals grown to the desired thickness within a crucible without cracking or defecting. In this specification, "product yield" refers to the proportion of the mass of a β-gallium trioxide single crystal ingot grown within a crucible, excluding areas where the desired diameter cannot be achieved when processed into a β-gallium trioxide single crystal substrate due to cracking or defecting of the crucible or cracking or defecting of the crystal during cooling, and then, based on the evaluation method described below, the mass of the substrate that can be evaluated as a good quality product. The higher the "product yield" value for the single crystal, the less likely it is to crack or defect the crucible used to grow the single crystal. Furthermore, in this specification, "main component" refers to a component present in a composition such as an alloy, comprising more than 95% by mass.

[0046] In this specification, the "maximum inner diameter" of a crucible refers to the inner diameter of the crucible at the position where the inner diameter of a ring, which is a cross-section perpendicular to the axial direction of the cylindrical crucible, reaches its maximum when compared along the axial direction of the crucible. In the present invention, the crucible preferably has a structure including, for example, a cylindrical seed crystal receiving portion, an increased diameter portion connected to the seed crystal receiving portion, and a straight portion connected to the increased diameter portion, as described below. In such a crucible, the "maximum inner diameter" refers to the inner diameter of the straight portion.

[0047] In this specification, the "main surface" of a β-type gallium trioxide single crystal substrate refers to both of the two circular surfaces of the above-mentioned β-type gallium trioxide single crystal substrate. In the above-mentioned β-type gallium trioxide single crystal substrate, if at least one of the two surfaces meets the scope of the claims of the present invention, it belongs to the technical scope of the present invention. In addition, in this specification, the "surface" used in the term "in-plane" refers to the "main surface". Furthermore, when the diameter of the β-type gallium trioxide single crystal substrate is recorded as "100 mm", it means that the above-mentioned diameter is around 100 mm (about 95 to 105 mm), or it means 4 inches. When the above-mentioned diameter is recorded as "150 mm", it means that the above-mentioned diameter is around 150 mm (about 145 to 155 mm), or it means 6 inches. In addition, the above-mentioned diameter can be measured by using a conventionally known outer diameter measuring instrument such as a vernier caliper.

[0048] In the crystallographic descriptions in this specification, individual crystal directions are indicated by [], families of crystal directions are indicated by <>, individual crystal planes are indicated by (), and families of crystal planes are indicated by {}. Furthermore, negative crystallographic indices are usually indicated by adding a "- (bar)" above the number; in this specification, a minus sign is placed before the number.

[0049] [Crucible]

[0050] The crucible of the present embodiment is a crucible for growing a β-type gallium trioxide single crystal (β-type Ga2O3 single crystal). The crucible has a thickness of at least 1 mm and at most 10 mm. The maximum inner diameter of the crucible is at least 100 mm. The crucible is composed of a stabilized zirconia containing both or either yttrium oxide and calcium oxide. The surface of the inner peripheral surface of the crucible is coated with a thermal sprayed film containing both or either rhodium (Rh) and platinum (Pt). For example, the thermal sprayed film is preferably composed of a platinum-rhodium alloy (Pt-Rh alloy) containing 10% by mass or more and 30% by mass or less of Rh. The thickness of the thermal sprayed film is at least 100 μm and at most 500 μm. The stabilized zirconia contains at least 12.0% by mass or less and 15.5% by mass of the yttrium oxide, or contains at least 10.2% by mass or less and 11.4% by mass of the calcium oxide. A crucible having such characteristics can suppress the occurrence of cracks, defects, etc. during crystal growth.

[0051] As mentioned above, the crucible is a crucible for growing β-type Ga2O3 single crystals. The crucible is used for growing and obtaining β-type Ga2O3 single crystals, for example Figure 1 The single crystal growth device shown in FIG. Figure 1 The single crystal growth apparatus shown in FIG. 1 is now described in detail regarding the crucible of this embodiment. Figure 1 This is a schematic diagram illustrating the main parts of a single crystal growth apparatus used in the method for manufacturing a β-type Ga2O3 single crystal substrate of this embodiment, and a first type of crucible used in the above-mentioned single crystal growth apparatus.

[0052] like Figure 1 As shown, single crystal growth apparatus 100 includes the aforementioned crucible 5, a crucible holding table 6 for holding crucible 5, and a heating device 7 for heating crucible 5. Furthermore, single crystal growth apparatus 100 may also include a sealed container 9 for housing the apparatus itself. The size and material of sealed container 9 are not particularly limited as long as they can accommodate single crystal growth apparatus 100 and other components and can prevent the intrusion of impurities from the outside.

[0053] The crucible 5 includes a cylindrical seed crystal receiving portion 51, an increased diameter portion 52 connected to the seed crystal receiving portion 51, and a straight portion 53 connected to the increased diameter portion 52. The seed crystal receiving portion 51 is cylindrical, with an opening on one side connected to the increased diameter portion 52 and a hollow portion with a bottom wall formed on the side opposite to the increased diameter portion 52. The seed crystal receiving portion 51 is capable of receiving and holding the seed crystal 8a in the hollow portion. The increased diameter portion 52 has a truncated cone shape with a diameter that increases upward along the axial direction of the crucible 5, and is connected to the seed crystal receiving portion 51 on the small diameter side of the increased diameter portion 52. The straight portion 53 has a hollow cylindrical shape and is connected to the large diameter side of the increased diameter portion 52. The increased diameter portion 52 and the straight portion 53 have the function of holding a block of gallium trioxide (specifically, polycrystalline Ga2O3. Hereinafter, also referred to as "Ga2O3 block") therein. The enlarged diameter portion 52 and the straight cylindrical portion 53 have a function of growing a β-type Ga 2 O 3 single crystal as a crystal by solidifying a gallium trioxide melt as described later.

[0054] <Thickness and Maximum Inner Diameter>

[0055] The crucible 5 has a thickness of at least 1 mm and at most 10 mm. More specifically, the sidewalls 5a of the seed crystal receiving portion 51, the increased diameter portion 52, and the straight portion 53 of the crucible 5 each have a thickness of at least 1 mm and at most 10 mm. The sidewalls 5a of the seed crystal receiving portion 51, the increased diameter portion 52, and the straight portion 53 of the crucible 5 each preferably have a thickness of at least 5 mm and at most 10 mm. Furthermore, the maximum inner diameter of the crucible 5 is at least 100 mm. More specifically, the inner diameter of the straight portion 53 of the crucible 5 is preferably at least 100 mm. The inner diameter of the straight portion 53 of the crucible 5 is also preferably at least 150 mm. The upper limit of the maximum inner diameter of the crucible 5 is not particularly limited and is, for example, 165 mm.

[0056] If the crucible 5 is less than 1 mm thick, cracking and chipping of the crucible 5 during crystal growth may not be adequately suppressed. The crucible 5 may also deform during crystal growth. If the crucible 5 is thicker than 10 mm, the negative impact of increased crucible 5 costs may outweigh the cost reduction benefits achieved by suppressing cracking and chipping of the crucible 5 during crystal growth. By setting the maximum inner diameter of the crucible 5 to 100 mm or greater, cracking and chipping of the crucible 5 can be suppressed when manufacturing large-diameter β-Ga2O3 single crystal substrates with a diameter of 4 inches or 6 inches.

[0057] <Crucible Composition: Stabilized Zirconia>

[0058] Crucible 5 is composed of stabilized zirconium oxide (hereinafter also referred to as "stable ZrO2") containing either or both yttrium oxide (Y2O3) and calcium oxide (CaO). Crucible 5 is preferably composed of stabilized ZrO2 containing either Y2O3 or CaO. Specifically, the stabilized ZrO2 contains at least 12.0% by mass and no more than 15.5% by mass of Y2O3, or at least 10.2% by mass and no more than 11.4% by mass of CaO. By using the stabilized ZrO2 with low thermal conductivity described above as the composition of crucible 5, crystal defects generated during crystal growth can be easily repelled to the outer periphery of the crystal, thereby preventing polycrystallization of the β-type Ga2O3 single crystal during crystal growth. "Stabilized ZrO2" refers to ZrO2 that is stabilized at room temperature by adding Y2O3, CaO, magnesium oxide (MgO), aluminum oxide (alumina: Al2O3), etc. to the ZrO2, thereby allowing the high-temperature phase (typically a cubic or tetragonal solid solution) to exist stably. The oxides dissolved in stable ZrO2 are not limited to Y2O3, CaO, MgO, and Al2O3.

[0059] <Thermal spray coating>

[0060] (composition)

[0061] The inner surface of the crucible is coated with a thermal spray film containing either or both of Rh and Pt. For example, the thermal spray film is preferably composed of a Pt-Rh alloy containing 10% by mass or more and 30% by mass or less of Rh. Figure 1 The crucible 5 of the first embodiment shown is coated with a thermal sprayed film 5b composed of a platinum-rhodium alloy (Pt-Rh alloy) containing 10% to 30% by mass of Rh. The thickness of the thermal sprayed film 5b is 100 μm to 500 μm. The thermal sprayed film 5b preferably covers the entire inner peripheral surface of the crucible 5. However, even if a portion of the surface is not coated with the thermal sprayed film 5b, or the composition of the thermal sprayed film 5b is partially different, it does not depart from the scope of the present invention.

[0062] The thermal spraying can be performed using conventionally known methods, such as plasma spraying. For example, the thermal spraying can be performed by heating the Pt-Rh alloy to form molten particles or particles similar thereto (e.g., particle size: 45-300 μm). This material is then supplied to the inner circumference of the sidewall portion 5a using a thermal spray nozzle at an angle of 30-45° relative to the axial direction of the crucible 5. In this case, the distance from the tip of the thermal spray nozzle to the inner circumference of the crucible 5 is preferably 20-120 mm, for example, along the direction in which the tip of the thermal spray nozzle is pointed. Furthermore, the thickness of the thermal sprayed film 5b can be determined by controlling the supply rate of the thermal spray material. For example, the supply rate of the thermal spray material can be 50-75 g / min. The porosity (described below) can be determined by controlling the angle of the thermal spray nozzle and the supply rate of the thermal spray material. Increasing the particle size of the thermal spray material can increase the surface roughness Rz (described below).

[0063] By setting the Rh content of the Pt-Rh alloy constituting the thermal sprayed film 5b to 10% by mass or more, cracking and chipping of the crucible 5 during crystal growth can be more effectively suppressed. By setting the Rh content of the Pt-Rh alloy constituting the thermal sprayed film 5b to 30% by mass or less, cracking and chipping of the crucible 5 during crystal growth can be effectively suppressed without increasing the cost of the crucible 5. The thermal sprayed film 5b is more preferably composed of a Pt-Rh alloy containing 20% ​​by mass or more and 30% by mass or less of Rh.

[0064] If the thickness of the thermal sprayed film 5b is less than 100 μm, the thermal sprayed film 5b may peel off from the sidewall portion 5a, and cracking and chipping of the crucible 5 during crystal growth may not be sufficiently suppressed. If the thickness of the thermal sprayed film 5b exceeds 500 μm, the negative impact of increased crucible cost may outweigh the cost reduction benefits achieved by suppressing cracking and chipping of the crucible 5 during crystal growth. The thickness of the thermal sprayed film 5b is preferably not less than 200 μm and preferably not more than 500 μm.

[0065] The thickness of the thermal sprayed film is measured in accordance with JIS H 8401:1999 (Test method for thickness of thermally sprayed products). Specifically, it can be measured by directly determining the difference between the crucible thickness before and after thermal spraying using a micrometer (e.g., product name (product number): "U-shaped micrometer PMU100-25", manufactured by Mitutoyo Corporation, or product name (product number): "Laser digital micrometer LSM-501S", manufactured by Mitutoyo Corporation). The Rh concentration in the Pt-Rh alloy can be determined during the preparation of the thermal spray material.

[0066] (pore)

[0067] The thermal sprayed film preferably has pores. The volume ratio of the pores in the thermal sprayed film, i.e., the porosity, is preferably 30% by volume or more and 50% by volume or less. This can further suppress the occurrence of cracks and defects during crystal growth. Figure 2 It is an explanation Figure 1 This is an enlarged cross-sectional view of the main part of the crucible of the second embodiment used in the single crystal growth apparatus. Figure 2 In the crucible of the second embodiment shown, the thermal sprayed film 5b present on the inner peripheral surface of the side wall portion 5a has pores 5c. The volume ratio of the pores 5c in the thermal sprayed film 5b, i.e., the porosity, is preferably 30% by volume or more and 50% by volume or less.

[0068] The porosity was measured according to JIS K 7112:1999A (water displacement method). Specifically, the density of the crucible was measured before and after thermal spraying, and the measured density of the thermal sprayed film was calculated. Furthermore, the composition of the thermal sprayed film was determined using an energy dispersive X-ray spectrometer (SEM-EDX) attached to a transmission electron microscope, and the ideal density was calculated based on this composition. The porosity can be calculated by dividing the measured density by the ideal density × 100.

[0069] Because the crucible of the second embodiment is formed from the aforementioned stabilized ZrO2, it is inherently less susceptible to deformation due to thermal contraction during crystal growth and subsequent cooling. However, even if the crucible, particularly during cooling after crystal growth, experiences some thermal contraction, causing the β-Ga2O3 single crystal present within the crucible to press against the sidewall 5a, the pores 5c contained in the thermal sprayed film 5b are crushed, thereby suppressing cracks and defects in the crucible. If the porosity is less than 30% by volume, the effect of suppressing cracks and defects in the crucible simply by crushing the pores 5c may be insufficient. If the porosity exceeds 50% by volume, it may become difficult to thermally spray such a thermal sprayed film 5b onto the sidewall 5a.

[0070] (Surface roughness)

[0071] The surface roughness Rz of the inner circumferential surface of the crucible is preferably 300 μm or more and 500 μm or less. In this case, the thermal sprayed film preferably has pores. The volume ratio of pores in the thermal sprayed film, i.e., the porosity, is preferably 10% by volume or more and less than 30% by volume. This further reduces the occurrence of cracks and defects during crystal growth. Figure 3 It is an explanation Figure 1This is an enlarged cross-sectional view of the main part of the crucible of the third type used in the single crystal growth apparatus. Figure 3 In the crucible of the third embodiment shown, the surface roughness Rz of the inner circumferential surface of the sidewall portion 5a is 300 μm or more and 500 μm or less. The thermal sprayed film 5b on the inner circumferential surface of the sidewall portion 5a has pores 5c. The volume ratio of the pores 5c in the thermal sprayed film 5b, i.e., the porosity, is 10% by volume or more and less than 30% by volume. The surface roughness Rz of the inner circumferential surface of the sidewall portion 5a is preferably 300 μm or more and 400 μm or less.

[0072] The method for measuring the surface roughness Rz of the inner peripheral surface of the side wall portion 5a is as follows. Specifically, the surface roughness Rz can be measured by determining the maximum height (Rz) specified in JIS B0601:2001 on the inner peripheral surface of the side wall portion 5a. For example, a surface roughness measuring instrument (product name (product number): "Surface Roughness Measuring Instrument SV-2100M4", manufactured by Mitutoyo Co., Ltd., or product name (product number): "Surface Roughness Measuring Instrument SURFCOM TOUCH550", manufactured by Tokyo Seimitsu Co., Ltd.) is used. A measuring unit is provided on the inner side of the crucible, and roughness measurement is performed using a display / control unit, thereby measuring the surface roughness Rz. The porosity can be measured in the same manner as the porosity measuring method for the thermal sprayed film of the crucible of the second embodiment.

[0073] Because the crucible of the third embodiment is formed from the aforementioned stable ZrO2, it is inherently less susceptible to deformation due to thermal contraction during crystal growth and cooling after crystal growth. However, even if the crucible, particularly during cooling after crystal growth, experiences some thermal contraction, causing the β-Ga2O3 single crystal present within the crucible to press against the sidewall 5a, the protrusions present on the inner circumferential surface of the sidewall 5a due to its surface roughness are compressed and damaged, thereby suppressing cracks and defects in the crucible. Furthermore, the pores 5c contained in the thermal sprayed film 5b are compressed and damaged, thereby also suppressing cracks and defects in the crucible. If the surface roughness Rz is less than 300μm, the effect of suppressing cracks and defects in the crucible by compressing the protrusions may be insufficient. If the surface roughness Rz exceeds 500μm, the crucible's inherent strength may decrease, causing the protrusions to break during crystal growth, leading to cracks and defects in the crucible. Furthermore, when the porosity is less than 10% by volume, the effect of suppressing cracking and chipping of the crucible by compressive destruction of the pores 5 c may be insufficient.

[0074] Here, in the crucible of the second embodiment, the surface roughness Rz of the above-mentioned surface is also preferably not less than 300 μm and not more than 500 μm. Thus, based on the presence of the protrusions and pores 5c on the above-mentioned surface, the occurrence of cracks, defects, etc. during crystal growth can be further suppressed. By having the above-mentioned surface roughness Rz be not less than 300 μm, the effect of suppressing the cracks and defects of the crucible due to the crushing of the protrusions can be fully obtained. By having the above-mentioned surface roughness Rz be not more than 500 μm, the effect of suppressing the cracks and defects of the crucible during crystal growth can be fully obtained without reducing the strength of the crucible itself. In addition, the embodiment in which the surface roughness Rz of the above-mentioned surface in the crucible of the second embodiment is not less than 300 μm and not more than 500 μm can have the same structure as the embodiment in which the porosity in the above-mentioned third embodiment is not less than 30 volume % and not more than 50 volume %.

[0075] (First film and second film)

[0076] The thermal sprayed film is preferably composed of a first film and a second film. The first film preferably covers the surface. The first film is preferably composed of Rh or a Pt-Rh alloy with Rh as the main component. The second film preferably covers the first film. The second film is preferably composed of Pt or a Pt-Rh alloy with Pt as the main component. The thickness of the thermal sprayed film, calculated as the total of the first and second films, is preferably not less than 100 μm and not more than 500 μm. This not only has the effect of suppressing the occurrence of cracks, defects, etc. during crystal growth, but also can prevent Rh from mixing into the β-type Ga2O3 single crystal.

[0077] Figure 4 It is an explanation Figure 1 This is an enlarged cross-sectional view of the main part of the crucible of the fourth embodiment used in the single crystal growth apparatus. Figure 4In the crucible of the fourth embodiment shown, the thermal sprayed film is composed of a first film 5b1 and a second film 5b2. The first film 5b1 covers the surface on the inner peripheral side of the side wall portion 5a. The first film 5b1 is composed of Rh or a Pt-Rh alloy with Rh as the main component, preferably composed of Rh. The second film 5b2 covers the first film 5b1. The second film 5b2 is composed of Pt or a Pt-Rh alloy with Pt as the main component, preferably composed of Pt. The thickness of the thermal sprayed film is 100 μm or more and 500 μm or less, based on the total of the first film 5b1 and the second film 5b2. The thickness of the thermal sprayed film is more preferably 100 μm or more and 300 μm or less, based on the total of the first film 5b1 and the second film 5b2. If the combined thickness of the first and second films 5b1, 5b2 is less than 100 μm, the first and second films 5b1, 5b2 may peel from the sidewall portion 5a, and the effect of suppressing cracking and damage to the crucible 5 during crystal growth due to the first and second films 5b1, 5b2 forming a thermal spray coating may be insufficient. If the combined thickness of the first and second films 5b1, 5b2 exceeds 500 μm, the negative impact of increased crucible cost may outweigh the cost reduction benefits of suppressing cracking and damage to the crucible 5 during crystal growth. The method for measuring the thickness of the first and second films can be the same as the method for measuring the thickness of the thermal spray coating of the crucible in the first embodiment.

[0078] like Figure 4 As shown, both the first film 5b1 and the second film 5b2 preferably have pores 5c. The volume ratio of pores 5c in the first film 5b1, i.e., the first film porosity, and the volume ratio of pores 5c in the second film 5b2, i.e., the second film porosity, are preferably both 30% to 50% by volume. This effect of the pores 5c can further suppress cracking, defects, and the like during crystal growth. The porosity of the first and second films can be measured using the same method as the porosity measurement method for the thermal sprayed film of the crucible in the second embodiment.

[0079] In the crucible of the fourth embodiment, the thermally sprayed film is composed of the first film 5b1 and the second film 5b2. The first film 5b1 is composed of Rh or a Pt-Rh alloy primarily composed of Rh, and the second film 5b2 is composed of Pt or a Pt-Rh alloy primarily composed of Pt. The first film 5b1 covers the inner circumferential surface of the sidewall portion 5a, and the second film 5b2 covers the first film 5b1. Therefore, the Rh in the thermally sprayed film does not directly contact the β-Ga2O3 single crystal within the crucible, or even if it does, the contact is very slight, thereby preventing Rh from incorporating into the β-Ga2O3 single crystal during crystal growth.

[0080] In the crucible of the fourth embodiment, the thermal sprayed film is composed of a first film 5b1 and a second film 5b2. Therefore, by considering the first film 5b1 and the second film 5b2 together, the thermal sprayed film can be a thermal sprayed film composed of a Pt-Rh alloy containing 10% to 30% by mass of Rh. For example, in the crucible of the fourth embodiment, the thermal sprayed film can be composed of a first film 5b1 and a second film 5b2, wherein the first film 5b1 is composed of Rh and the second film 5b2 is composed of Pt, and the thickness of the first film 5b1 is one-third the thickness of the second film 5b2. Thus, the crucible of the fourth embodiment can include a thermal sprayed film composed of a Pt-Rh alloy containing 10% to 30% by mass of Rh. Furthermore, as described above, the thickness of the thermal sprayed film, calculated as the total thickness of the first film 5b1 and the second film 5b2, is 100 μm to 500 μm.

[0081] Furthermore, in a crucible where the thermal spray coating consists of a first film and a second film, the surface roughness Rz of the inner circumferential surface is preferably 300 μm or greater and 500 μm or less. In this case, it is also preferable that both the first film and the second film have pores. The volume ratio of pores in the first film, i.e., the first film porosity, and the volume ratio of pores in the second film, i.e., the second film porosity, are preferably both 10% by volume or greater and less than 30% by volume. This further suppresses cracking and defects during crystal growth. Figure 5 It is an explanation Figure 1 This is an enlarged cross-sectional view of the main part of the crucible of the fifth embodiment used in the single crystal growth apparatus. Figure 5 In the crucible of the fifth embodiment shown, the surface roughness Rz of the inner circumferential surface of the sidewall portion 5a is 300 μm or more and 500 μm or less. The first film 5b1 and the second film 5b2 on the inner circumferential surface of the sidewall portion 5a each have pores 5c. The volume ratio of the pores 5c in the first film 5b1 and the second film 5b2, i.e., the first film porosity and the second film porosity, are each 10% by volume or more and less than 30% by volume. The surface roughness Rz of the inner circumferential surface of the sidewall portion 5a is preferably 300 μm or more and 400 μm or less.

[0082] According to the crucible of the fifth embodiment, similarly to the crucible of the third embodiment, the presence of the convex portions and pores 5 c on the inner peripheral surface further suppresses the occurrence of cracks, defects, etc. during crystal growth. Furthermore, similarly to the crucible of the fourth embodiment, the Rh in the thermal sprayed film does not directly contact the β-Ga2O3 single crystal in the crucible, or even if it does, the contact is very slight. Therefore, it is possible to suppress the incorporation of Rh into the β-Ga2O3 single crystal during crystal growth.

[0083] Here, in the crucible of the fourth embodiment, the surface roughness Rz of the above-mentioned surface is also preferably 300 μm or more and 500 μm or less. Thus, the presence of the protrusions and pores 5c on the above-mentioned surface can further suppress the occurrence of cracks, defects, etc. during crystal growth. Furthermore, the fourth embodiment of the crucible in which the surface roughness Rz of the above-mentioned surface is 300 μm or more and 500 μm or less has the same structure as the fifth embodiment of the crucible in which the first film porosity and the second film porosity are each 30% by volume or more and 50% by volume or less.

[0084] <Crucible Holding Stand>

[0085] like Figure 1 As shown, the single crystal growth apparatus 100 includes a crucible holding table 6 for holding the crucible 5. The crucible holding table 6 contacts the bottom of the crucible 5 and holds the crucible 5. The crucible holding table 6 may have a cylindrical appearance. The material of the crucible holding table 6 is not particularly limited, and examples thereof include quartz, alumina, zirconia, and silicon carbide. The outer diameter of the crucible holding table 6 also depends on the diameter of the crucible 5 it supports, and is, for example, 75 mm to 200 mm.

[0086] (Heating device)

[0087] The heating device 7 is provided for heating the crucible 5. The heating device 7 can be, for example, a conventionally known electric heater (hereinafter also referred to as a "heater"). For example, two heaters can be provided, and these two heating devices can be arranged so as to surround the outer circumference of the crucible 5. The output of each heater can sometimes be controlled independently. In particular, each heater is sometimes divided into a plurality of parts in a direction perpendicular to the axis of the crucible 5, thereby forming a multi-stage structure. In this case, it is preferred to independently control the output of the heater of each part constituting the multiple stages. In this way, the temperature of the contents in the crucible 5 can be finely adjusted along the axial direction of the crucible 5. For example, by independently controlling the output of the heater of each part constituting the multiple stages to heat the enlarged diameter portion 52 and the straight cylindrical portion 53, the growth rates of the crystals grown at the enlarged diameter portion 52 and the straight cylindrical portion 53 can be stabilized respectively.

[0088] Although not shown, the single crystal growth apparatus 100 may include a thermocouple capable of measuring the temperature of the crucible 5 heated by the heater. A plurality of thermocouples may be arranged along the axial direction outside the crucible 5. For example, a known temperature monitor may be used as the thermocouple.

[0089] [Method for manufacturing a β-type gallium trioxide single crystal substrate]

[0090] The method for manufacturing a β-gallium trioxide single crystal substrate (β-Ga2O3 single crystal substrate) according to this embodiment preferably uses, for example, the aforementioned crucible. Specifically, the method preferably includes: preparing the crucible; obtaining a β-gallium trioxide single crystal (β-Ga2O3 single crystal) using a vertical boat method using the crucible; and processing the β-Ga2O3 single crystal to obtain a β-Ga2O3 single crystal substrate having a circular main surface. This method for manufacturing a β-Ga2O3 single crystal substrate reduces the risk of cracking and damage to the crucible during crystal growth, thereby enabling the production of β-Ga2O3 single crystal substrates with a high yield.

[0091] Figure 6 This is a flowchart showing an example of a method for manufacturing a β-type Ga2O3 single crystal substrate according to this embodiment. The method for manufacturing a β-type Ga2O3 single crystal substrate according to this embodiment preferably includes, for example, Figure 6 The β-type Ga2O3 single crystal manufacturing process S100 and the β-type Ga2O3 single crystal substrate manufacturing process S200 are shown in the flowchart. Figure 6 More specifically, the method for manufacturing a β-Ga2O3 single crystal substrate of this embodiment preferably includes, as the β-Ga2O3 single crystal manufacturing step S100, a step of preparing a single crystal growth apparatus (first step: preparation step S110). The single crystal growth apparatus includes at least a cylindrical crucible and a heating device disposed so as to surround the outer circumference of the crucible. In preparation step S110, in addition to the single crystal growth apparatus and the crucible constituting the crucible, a seed crystal and a bulk Ga2O3 mass are preferably also prepared.

[0092] The β-Ga2O3 single crystal manufacturing process S100 preferably includes the step of accommodating the seed crystal at the bottom of the crucible and accommodating the Ga2O3 bulk in a portion above the seed crystal in the crucible (second step: raw material loading step S120). In the raw material loading step S120, the Ga2O3 bulk is preferably accommodated in a portion above the seed crystal in the crucible. The β-Ga2O3 single crystal manufacturing process S100 preferably includes the step of heating the crucible with the heating device to melt the Ga2O3 bulk and a portion of the seed crystal to obtain a Ga2O3 melt, and bringing the Ga2O3 melt into contact with the remaining portion of the seed crystal (third step: raw material melting step S130). Furthermore, the β-type Ga2O3 single crystal manufacturing step S100 preferably includes a step of obtaining a β-type Ga2O3 single crystal by growing a crystal from the Ga2O3 melt on the remaining portion of the seed crystal (fourth step: Ga2O3 single crystal growth step S140).

[0093] The method for manufacturing a β-Ga2O3 single crystal substrate of this embodiment can include the following steps: a slicing step, a peripheral grinding step, and a polishing step as a β-Ga2O3 single crystal substrate manufacturing step S200. In the β-Ga2O3 single crystal substrate manufacturing step S200, the β-Ga2O3 single crystal substrate can be obtained by sequentially performing the above steps.

[0094] Below, by reference Figure 1 and Figure 6 The steps of the manufacturing method of the β-type Ga2O3 single crystal substrate of this embodiment are described below. Figure 1 The crucible 5 shown in the single crystal growth apparatus 100 is used to grow a β-Ga2O3 single crystal using the vertical boat method. Crucible 5 can be any of the crucibles described in the first through fifth methods. Hereinafter, the vertical boat method will be abbreviated as the VB method. The VB method includes the vertical Bridgman method and the vertical temperature gradient solidification method.

[0095] <β-Ga2O3 Single Crystal Manufacturing Process S100>

[0096] (Preparation Step S110)

[0097] like Figure 1 and Figure 6 As shown, first, in the β-Ga2O3 single crystal manufacturing process S100, a process of preparing a single crystal growth device 100 (preparation process S110) is performed. The above-mentioned single crystal growth device 100 has at least a cylindrical crucible 5 and a heating device 7 configured in a manner surrounding the outer periphery of the crucible 5. In the preparation process S110, in addition to the above-mentioned single crystal growth device 100 for manufacturing the β-Ga2O3 single crystal 81, it is preferred to also prepare a seed crystal 8a and a massive Ga2O3 block. The seed crystal 8a is composed of a β-Ga2O3 single crystal. The Ga2O3 block is sometimes composed of polycrystalline Ga2O3. The seed crystal 8a and the massive Ga2O3 block can be prepared by a conventionally known method or by obtaining a commercially available product.

[0098] In the preparation step S110, any of the first to fifth embodiments described above can be prepared as the crucible 5. The crucibles of the first to fifth embodiments can each have the aforementioned characteristics using conventionally known methods. Specifically, a crucible 5 having a sidewall 5a thickness of 1 to 10 mm and an inner diameter of the straight tube 53 of 100 mm or greater can be manufactured using conventionally known methods. In this case, the crucible 5 can be composed of, for example, stabilized ZrO containing at least 12.0% to 15.5% by mass of Y2O3 or at least 10.2% to 11.4% by mass of CaO.

[0099] Furthermore, by plasma spraying the crucible 5 using the prepared spray material under the following conditions, for example, the surface of the inner peripheral surface of the side wall portion 5a can be covered with the thermal spray film 5b.

[0100] Thermal spray material: Pt-Rh alloy containing 10-30% by mass of Rh

[0101] Particle size of thermal spraying material: 45~300μm

[0102] Thermal spray material supply speed: 50-75g / min

[0103] Direction of thermal spray nozzle: 30-45° relative to the axial direction of the crucible

[0104] The distance between the thermal spray nozzle and the inner peripheral surface of the side wall of the crucible was 20 to 120 mm.

[0105] By controlling the supply rate of the spray material, the thickness of the thermal spray film 5b can be adjusted to, for example, 100 to 500 μm. By controlling the angle of the spray nozzle and the supply rate of the spray material, the porosity of the thermal spray film 5b can be adjusted to 10 to 50% by volume. By controlling the particle size of the spray material, the surface roughness Rz of the inner circumferential surface of the sidewall portion 5a of the crucible 5 can be adjusted to 300 to 500 μm.

[0106] When preparing crucibles according to the fourth and fifth embodiments, a first spraying material composed of Rh or a Pt-Rh alloy primarily composed of Rh and having a particle size of 45 to 300 μm, and a second spraying material composed of a Pt-Rh alloy primarily composed of Pt and having a particle size of 45 to 300 μm can be used as the spraying material. In this case, by plasma spraying the first spraying material, the inner circumferential surface of the sidewall 5a of the crucible 5 can be coated with a first film. Furthermore, by plasma spraying the second spraying material, the first film can be coated with a second film. By controlling the supply rates of the first and second spraying materials, the angle of the spraying nozzle, and the particle sizes of the first and second spraying materials, the thickness of the first and second films, the porosity of the first and second films, and the surface roughness Rz of the inner circumferential surface of the sidewall 5a of the crucible 5 can be adjusted.

[0107] (Raw Material Loading Step S120)

[0108] The raw material loading step S120 is a step of storing the seed crystal at the bottom of the crucible and storing a massive Ga2O3 block in a portion above the seed crystal in the crucible. In the raw material loading step S120, it is preferred to store the massive Ga2O3 block and solid B2O3 in a portion above the seed crystal 8a in the crucible 5. The purpose of the raw material loading step S120 is to seal various raw materials used for crystal growth using the single crystal growth device 100 into the crucible. In the raw material loading step S120, first, a seed crystal 8a composed of a β-type Ga2O3 single crystal is loaded into the hollow portion of the seed crystal receiving portion 51 of the crucible 5. Next, a plurality of massive Ga2O3 blocks composed of polycrystalline Ga2O3 are loaded into the diameter-enhanced portion 52 and the straight cylindrical portion 53 of the crucible 5 and stacked. In the raw material charging step S120, a predetermined amount of Sn or Si is preferably added when a plurality of bulk Ga2O3 blocks are charged into the crucible 5. Thus, a β-Ga2O3 single crystal substrate containing the above-mentioned Sn or Si as a dopant is obtained from the β-Ga2O3 single crystal 81 obtained in the β-Ga2O3 single crystal production step S100. When the above-mentioned Sn or Si is added, it is preferred that the concentration of the above-mentioned dopant in the β-Ga2O3 single crystal substrate be, for example, 1.0×10 18 cm -3 (5.0×10 17 cm -3 Above and 4.0×10 19 cm -3 The addition amount is adjusted in the following manner.

[0109] (Raw Material Melting Step S130)

[0110] The raw material melting step S130 is a step in which the crucible is heated using the heating device to melt the Ga2O3 bulk and a portion of the seed crystal to form a Ga2O3 melt, and the Ga2O3 melt is brought into contact with the remaining portion of the seed crystal. The purpose of the raw material melting step S130 is to melt the Ga2O3 bulk and a portion of the seed crystal 8a during crystal growth using the single crystal growth apparatus 100, thereby bringing the remaining portion of the seed crystal 8a into contact with the Ga2O3 melt 82. This allows β-type Ga2O3 single crystal 81 to grow on the remaining portion of the seed crystal 8a in the subsequent Ga2O3 single crystal growth step S140. Specifically, in the raw material melting step S130, the crucible 5 containing the seed crystal 8a and the Ga2O3 bulk is supported by the crucible holding table 6. Then, current is supplied to the heating device 7 to heat the crucible 5. This causes the Ga2O3 bulk to melt and form the Ga2O3 melt 82. Next, a portion of the seed crystal 8a also melts, and the remaining portion of the seed crystal 8a comes into contact with the Ga2O3 solution 82 at the interface.

[0111] (Ga2O3 Single Crystal Growth Step S140)

[0112] The Ga2O3 single crystal growth step S140 is a step for obtaining a β-type Ga2O3 single crystal by growing a crystal from the Ga2O3 melt on the remaining portion of the seed crystal. The Ga2O3 single crystal growth step S140 is performed, for example, by slowly lowering the crucible 5 relative to the heating device 7 along the crucible 5 axis (toward the seed crystal receiving portion 51), thereby creating a temperature gradient in the crucible 5 such that the temperature is lower on the seed crystal 8a side and higher on the Ga2O3 melt 82 side. This allows the Ga2O3 melt 82 in contact with the seed crystal 8a to solidify, allowing a β-type Ga2O3 single crystal 81 to continuously grow from the Ga2O3 melt 82 on the remaining portion of the seed crystal 8a. At this time, the temperature on the Ga2O3 melt 82 side is, for example, 1800-1820°C. The temperature gradient at the interface between the Ga2O3 melt 82 and the growing β-type Ga2O3 single crystal 81 is, for example, 3-8°C / cm. The speed at which the crucible 5 descends along its axis is not particularly limited, and can be, for example, 0.1 to 2 mm / hour.

[0113] In the Ga2O3 single crystal growth step S140, the crucible 5 is slowly lowered relative to the heating device 7 along the axis of the crucible 5. This causes the interface between the β-Ga2O3 single crystal 81 and the Ga2O3 melt 82 to rise toward the Ga2O3 side of the liquid, and the Ga2O3 melt 82 to solidify as the β-Ga2O3 single crystal 81. Thus, the crystal growth of the β-Ga2O3 single crystal 81 continues until the Ga2O3 melt 82 remaining in the straight cylindrical portion 53 of the crucible 5 has completed solidification. In this manner, an ingot of the β-Ga2O3 single crystal 81 can be obtained.

[0114] <β-type Ga2O3 single crystal substrate manufacturing step S200>

[0115] The manufacturing method of the above-mentioned β-type Ga2O3 single crystal substrate is as follows Figure 6 As shown, the process includes processing the β-Ga2O3 single crystal obtained in the Ga2O3 single crystal growth step S140 to obtain a β-Ga2O3 single crystal substrate having a circular main surface (β-Ga2O3 single crystal substrate manufacturing step S200). The β-Ga2O3 single crystal substrate manufacturing step S200 includes the following steps: slicing, outer periphery grinding, and polishing. By sequentially performing these steps, a β-Ga2O3 single crystal substrate can be obtained.

[0116] The cutting process is a process for slicing the ingot into a wafer having a predetermined thickness in order to obtain a β-Ga2O3 single crystal substrate from the ingot composed of the β-Ga2O3 single crystal taken out of the crucible. Furthermore, the peripheral grinding process is a process for obtaining a β-Ga2O3 single crystal substrate having a circular main surface by grinding the periphery of the wafer. The peripheral grinding process may include, for example, a process of implementing chamfering. As the cutting process and the peripheral grinding process, conventionally known cutting methods and peripheral grinding methods can be used. Furthermore, the polishing process is a process for mirror-finishing the central portion of the above-mentioned main surface. As the polishing process, conventionally known polishing methods can be used. Through the polishing process, the above-mentioned central portion can have a surface roughness Ra of less than 10 nm, for example, as specified in JIS B0681-2:2018.

[0117] Effects

[0118] By performing the above steps, the β-Ga2O3 single crystal substrate of this embodiment can be produced. In the above-described method for producing a β-Ga2O3 single crystal substrate, since the β-Ga2O3 single crystal is produced using any of the crucibles described in the first through fifth methods, cracking and damage to the crucible during crystal growth can be reduced. Consequently, β-Ga2O3 single crystal substrates can be obtained with a high yield.

[0119] [β-type gallium trioxide single crystal substrate]

[0120] The β-type gallium trioxide single crystal substrate (β-type Ga2O3 single crystal substrate) of this embodiment is a β-type Ga2O3 single crystal substrate having a circular main surface. The diameter of the above-mentioned β-type Ga2O3 single crystal substrate is 100 mm or more. The above-mentioned main surface is the (001) plane of the β-type Ga2O3 single crystal. Or the above-mentioned main surface is a plane having a deviation angle greater than 0° and less than 10° from the (001) plane of the above-mentioned β-type Ga2O3 single crystal, and a deviation direction from the

[010] direction of the above-mentioned β-type Ga2O3 single crystal or a direction orthogonal to the above-mentioned

[010] direction. The above-mentioned β-type Ga2O3 single crystal substrate contains both or either rhodium (Rh) and iridium (Ir). The concentration of the above-mentioned Rh and the concentration of the above-mentioned Ir are both less than 3 mass ppm in glow discharge mass spectrometry (GDMS). The β-type Ga 2 O 3 single crystal substrate having such characteristics can be excellent in both electrical and optical properties because it contains extremely small amounts of the above-mentioned Rh and the above-mentioned Ir.

[0121] The present inventors focused on minimizing the concentrations of rhodium and iridium in the substrate. These rhodium and iridium, which may be contained in the β-Ga2O3 single crystal substrate and are not in the same group as gallium (Ga), could hinder the substrate's favorable electrical and optical properties. Specifically, when manufacturing the β-Ga2O3 single crystal used to obtain the β-Ga2O3 single crystal substrate, Rh and Ir were prevented from coming into direct contact with the β-Ga2O3 single crystal and the Ga2O3 melt serving as its raw material. More specifically, for example, a β-Ga2O3 single crystal was manufactured using the crucible of the fifth embodiment described above, and a β-Ga2O3 single crystal substrate was obtained from the β-Ga2O3 single crystal. This led to the development of a β-Ga2O3 single crystal substrate having both the Rh and Ir concentrations less than 3 mass ppm, leading to the completion of the present invention.

[0122] <diameter>

[0123] Figure 7 Schematic diagram illustrating the β-type Ga2O3 single crystal substrate of this embodiment. Figure 7 In the β-type Ga2O3 single crystal substrate 1 shown, its diameter is greater than 100 mm. In particular, the diameter of the β-type Ga2O3 single crystal substrate 1 is preferably greater than 100 mm and less than 155 mm. Specifically, the β-type Ga2O3 single crystal substrate 1 with a diameter of greater than 100 mm and less than 155 mm preferably has a diameter of 101.6 mm or 152.4 mm, in other words, it is preferably 4 inches or 6 inches in diameter. Thus, in a large-diameter β-type Ga2O3 single crystal substrate with a diameter of greater than 100 mm and less than 155 mm, it is possible to excel in both electrical and optical properties. Here, with respect to the diameter of the β-type Ga2O3 single crystal substrate, even if the main surface does not form a geometrically circular shape due to the influence of the orientation flat (hereinafter also referred to as "OF"), the index flat (hereinafter also referred to as "IF"), etc., it is obtained based on the circular shape before the above-mentioned OF, IF, etc. are formed. As described above, the diameter of the β-type Ga2O3 single crystal substrate can be measured using a conventionally known outer diameter measuring instrument such as a vernier caliper. In addition, in this specification, the definition of "circular shape" representing the shape of the main surface will be described later.

[0124] <Main Surface>

[0125] (Circular shape)

[0126] As described above, the β-Ga2O3 single crystal substrate 1 has a circular main surface 10. In this specification, the "circular shape" representing the shape of the main surface includes, in addition to a geometric circular shape, a shape in which the main surface does not form a geometric circular shape due to at least one of a notch, OF, or IF being formed on the periphery of the main surface 10. Here, the "shape in which the main surface does not form a geometric circular shape" refers to a shape in which, among the line segments extending from any point on the periphery of the main surface 10 to the center of the main surface 10, the length of the line segment extending from any point on the above-mentioned notch, OF, and IF to the center of the main surface becomes shorter. Furthermore, the "shape in which the main surface does not form a geometric circular shape" also includes a shape in which the lengths of the line segments extending from any point on the periphery of the main surface 10 to the center of the main surface 10 are not necessarily all the same due to the shape of the β-Ga2O3 single crystal that is the raw material of the β-Ga2O3 single crystal substrate 1. In this case, the center of the main surface 10 refers to the position of the center of gravity, and the diameter of the β-type Ga2O3 single crystal substrate 1 refers to the length of the longest line segment among the line segments that pass through the center of the main surface 10 from any point on the periphery of the β-type Ga2O3 single crystal substrate 1 and extend to other points on the above-mentioned periphery.

[0127] ((001) plane of β-type Ga2O3 single crystal)

[0128] The main surface 10 is the (001) plane of a β-Ga2O3 single crystal. Alternatively, the main surface 10 is a plane having an angle of deviation from the (001) plane of the β-Ga2O3 single crystal that is greater than 0° and less than 10°, and having a deviation direction from the

[010] direction of the β-Ga2O3 single crystal or a direction orthogonal to the

[010] direction. Thus, a β-Ga2O3 single crystal substrate 1 having the (001) plane of the β-Ga2O3 single crystal as the main surface 10 can be provided, which is widely used in forming optical devices, electronic devices, and the like.

[0129] Here, in this specification, the crystal plane of the main surface 10 has an accuracy error of ±0.5°. For example, in the case where the main surface 10 is the "(001) plane" of the β-type Ga2O3 single crystal, it means that the main surface 10 may be the (001) just plane, or the main surface 10 may be a plane with an offset angle of -0.5 to +0.5° from the (001) plane. The offset angle and deviation direction of the main surface 10 of the β-type Ga2O3 single crystal substrate 1 relative to the (001) plane can be measured by using a conventionally known crystal orientation measuring device (for example, trade name (product number): "FSASIII", manufactured by Rigaku Corporation).

[0130] <Rhodium (Rh) and Iridium (Ir)>

[0131] The β-type Ga2O3 single crystal substrate contains both or either rhodium (Rh) and iridium (Ir). The concentration of the Rh and the concentration of the Ir are both less than 3 mass ppm in GDMS. The concentration of the Rh and the concentration of the Ir are both preferably less than 1 mass ppm in GDMS, more preferably less than 0.1 mass ppm, and further preferably less than 0.01 mass ppm. The lower limits of the concentration of Rh and the concentration of Ir are both undetectable in GDMS. The β-type Ga2O3 single crystal substrate can excel in both electrical and optical properties by having the Rh and Ir contents less than 3 mass ppm.

[0132] Rh and Ir are known elements that can be contained in the β-Ga2O3 single crystal substrate. For example, when the β-Ga2O3 single crystal substrate is obtained using the crucible of the fifth embodiment and the method for manufacturing a β-Ga2O3 single crystal substrate, the crucible material and the structure of the thermal sprayed film composed of the first and second films can easily reduce the Rh and Ir concentrations in the GDMS to less than 3 mass ppm. This allows for the production of β-Ga2O3 single crystal substrates with excellent electrical and optical properties at a high yield.

[0133] (Glow Discharge Mass Spectrometry (GDMS))

[0134] The following describes a method for measuring the concentrations of Rh and Ir in the β-Ga2O3 single crystal substrate using glow discharge mass spectrometry (GDMS). GDMS is a method in which a glow discharge plasma is generated in a high-purity argon environment using the analysis sample as a cathode. The surface of the analysis sample is sputtered within the plasma, and the constituent elements in the ionized analysis sample are measured using a mass spectrometer. This method enables qualitative and quantitative analysis of impurity elements, including Rh and Ir, contained in the β-Ga2O3 single crystal substrate, excluding Ga and O. The GDMS ion source can be either a flat cell or a pin-shaped cell. Pin-shaped cells are suitable for analysis samples that can be formed into strips approximately 2 mm square and 20 mm long. Specifically, it can be used when analyzing Si single crystals, gallium arsenide (GaAs) single crystals, and indium phosphide (InP) single crystals, which can be sampled by cleavage. Sheet-shaped discharge cells can be used for analysis samples that can be formed into a disk shape with a diameter of approximately 10 mm, and are used, for example, in the analysis of polycrystals. To prevent contamination of the analysis sample by external impurities, either sheet-shaped discharge cells or needle-shaped discharge cells are preferred as the ion source for GDMS. Because the β-Ga2O3 single crystal substrate can be used to produce a needle-shaped analysis sample with its cleavage direction as its longitudinal direction, it is preferable to use this substrate to produce a needle-shaped analysis sample as the ion source for GDMS.

[0135] The GDMS can be performed, for example, using the following method. First, a β-Ga2O3 single crystal substrate is obtained using the manufacturing method described below. Furthermore, a 2 mm square and 20 mm long Ga2O3 strip analysis sample is prepared by aligning the cleavage direction with the longitudinal direction of the β-Ga2O3 single crystal substrate. This sample is then placed in the sample placement section included with the apparatus described below. The sample placement section is preferably cleaned and pre-sputtered for 60 minutes according to conventional methods to prevent and remove foreign matter. The analysis value during pre-sputtering serves as the background value.

[0136] Next, GDMS can be performed on the Ga2O3 analysis sample placed on the sample placement surface under the following conditions. Furthermore, for Rh and Ir, which are elements other than Ga and O in the Ga2O3 analysis sample, semi-quantitative values ​​can be calculated by correcting the ion intensity ratio of Ga to Rh or the ion intensity ratio of Ga to Ir using relative sensitivity factors (RSFs), respectively. The relative sensitivity factors can be used as values ​​built into the software included with the following device.

[0137] Apparatus: Glow discharge mass spectrometer (trade name (product number): VG-9000, manufactured by VG Elemental)

[0138] Ion source: Needle discharge cell (cooled with liquid nitrogen during analysis)

[0139] Discharge area: 10mm diameter

[0140] Discharge gas: high purity argon (6N grade)

[0141] Discharge conditions: 2mA, 1kV (constant current mode)

[0142] Detectors: Faraday cups and multipliers

[0143] Mass spectrometry resolution: more than 4000 m / Δm (high resolution mode)

[0144] As described above, by analyzing the Ga2O3 analysis sample, it is possible to qualitatively and quantitatively determine the Rh and Ir contained in the β-type Ga2O3 single crystal substrate. The detection limit concentration of this GDMS is preferably 0.01 mass ppm.

[0145] (Transmittance and carrier concentration)

[0146] In the above-mentioned β-type Ga2O3 single crystal substrate, the transmittance to light with a wavelength of 400 nm to 430 nm is preferably 70% or more. In the above-mentioned Hall measurement using the van der Pauw method, the carrier concentration measured at 25°C is preferably 1×10 17 cm -3 Above and 1.0×10 19 cm -3 As a result, both electrical and optical properties can be further improved.

[0147] As described above, in the β-type Ga2O3 single crystal substrate, the transmittance to light with a wavelength of more than 400nm and less than 430nm is preferably more than 70%. The above transmittance is more preferably more than 75%, and further preferably more than 80%. The ideal upper limit of the above transmittance is 100%. The above transmittance can be obtained by measuring the transmittance of light to the β-type Ga2O3 single crystal substrate using an ultraviolet-visible-infrared spectrophotometer or the like. Figure 7 The specific steps for obtaining the above-mentioned transmittance will be described.

[0148] First, for example, a β-Ga2O3 single crystal substrate 1 is obtained based on the above-described manufacturing method. A rectangular slice 10a (e.g., 600 μm thick) having a size of 20 mm in length and 20 mm in width, centered at the center O (e.g., the center O of the main surface 10), is prepared from this β-Ga2O3 single crystal substrate 1 to obtain a sample for transmittance measurement. Next, using an ultraviolet-visible-infrared spectrophotometer (trade name (product number): "U-4000," manufactured by Hitachi High-Technologies Corporation), light having a wavelength of 400 nm to 430 nm (e.g., a wavelength of 427 nm) is directed perpendicularly to the center of the rectangular slice 10a. This allows the transmittance of the light in the β-Ga2O3 single crystal substrate 1 to be measured.

[0149] (Carrier concentration)

[0150] In this embodiment, in the Hall measurement using the van der Pauw method, the carrier concentration measured at 25° C. is preferably 1×10 17 cm -3 Above and 1.0×10 19 cm -3 Specifically, in the Hall measurement using the van der Pauw method with the center of the β-type Ga2O3 single crystal substrate as the measurement object, the carrier concentration obtained at 25°C is preferably 1×10 17 cm -3 Above and 1.0×10 19 cm -3 Below. When the carrier concentration is less than 1.0×10 17 cm -3 In the case of the above carrier concentration exceeding 1.0×10 19 cm -3 In this case, it is suggested that the crystal contains 1.0×10 19 cm -3 The above inactive impurities may have adverse effects on the operation of the device. The above carrier concentration is more preferably 5.0×10 17 cm -3 Above and 3.8×10 18 cm -3 As a result, the n-type β-Ga2O3 single crystal substrate can have good electrical properties that can be widely used in various electronic devices and optical devices. The carrier concentration can be determined by the following measurement method.

[0151] Below, for reference Figure 7 and Figure 8 The steps for determining the above-mentioned carrier concentration will be described in detail. Figure 8 This is an explanatory diagram for explaining a sample for Hall measurement made using the central portion of the substrate in order to measure the carrier concentration in the β-type Ga2O3 single crystal substrate of this embodiment. Figure 7 As shown, first, for example, a β-type Ga2O3 single crystal substrate 1 is obtained based on the above-mentioned manufacturing method. From the center of this β-type Ga2O3 single crystal substrate 1, a rectangular slice 10a (for example, 600 μm thick) with a length of 4 mm and a width of 4 mm centered at the center O (for example, the center O of the main surface 10) is produced. Figure 8 As shown, electrodes 21 composed of an alloy containing gold and titanium are formed at the four corners of the rectangular slice 10a (the surface to be measured), thereby obtaining a sample for Hall measurement. Here, the shape of the electrode 21 is not limited to the rectangle shown in the figure, but can also be a fan-shaped or circular shape. For the rectangular slice 10a having such an electrode 21, the carrier concentration can be determined by applying the Hall measurement using the van der Pauw method under an environment of 25°C. In addition, in this specification, the carrier concentration obtained based on the above-mentioned rectangular slice as the measurement object is defined as the carrier concentration of the above-mentioned β-type Ga2O3 single crystal substrate measured at 25°C in the Hall measurement using the van der Pauw method.

[0152] <Purpose>

[0153] The β-Ga2O3 single crystal substrate of this embodiment has superior electrical and optical properties and can therefore be used as a substrate for forming optical and electronic devices. In particular, the β-Ga2O3 single crystal substrate is preferably used as a substrate for forming electronic devices due to its excellent electrical properties.

[0154] Example

[0155] Hereinafter, examples are given to illustrate the present invention in more detail, but the present invention is not limited thereto. Figure 1 The single crystal manufacturing apparatus shown in FIG. Figures 2 to 5 The main parts of the crucible are shown in the following way. Figure 6 In the following description, samples 101 to 115, 201 to 213, and 301 to 313 are examples. Samples 10A to 10C and 20A to 20C are comparative examples.

[0156] The "crystal outer diameter" of the β-type Ga2O3 single crystal in each sample below refers to the crystal outer diameter determined by the following method. Specifically, the outer diameters of the β-type Ga2O3 single crystal ingot removed from the crucible were determined at three points: a position corresponding to the boundary between the enlarged diameter portion and the straight portion (hereinafter referred to as "measurement point 1"), a position 10 mm downward from the side where crystal growth terminated (hereinafter referred to as "measurement point 2"), and a position midway between these two points (hereinafter referred to as "measurement point 3"). The average of these values ​​was defined as the "crystal outer diameter."

[0157] [Manufacturing of Ga2O3 single crystal substrate]

[0158] <Sample 10A>

[0159] According to the method disclosed in the above-mentioned patent document 1, by using the vertical Bridgman (VB: Vertical Bridgeman) method, an attempt was made to produce a β-type Ga2O3 single crystal with the growth direction being the

[001] direction. When obtaining the above-mentioned β-type Ga2O3 single crystal, a crucible composed of a Pt-Rh alloy containing 30% by mass of Rh was used. The inner diameter of the straight cylindrical part of the above-mentioned crucible was 105 mm. Furthermore, the thickness of the side wall portion of the above-mentioned crucible was 0.2 μm, and the surface roughness Rz of the surface on the inner peripheral side of the above-mentioned side wall portion was 20 μm. However, since the above-mentioned crucible broke during crystal growth, the above-mentioned β-type Ga2O3 single crystal could not be obtained, and therefore the β-type Ga2O3 single crystal substrate of sample 10A could not be obtained.

[0160] <Sample 10B>

[0161] The β-type Ga2O3 single crystal was manufactured by the same method as the method for obtaining the β-type Ga2O3 single crystal substrate of sample 10A, with the growth direction being the

[001] direction. In this experimental example, no cracking of the crucible was found. The crystal outer diameter of the above-mentioned β-type Ga2O3 single crystal was 120 mm. Furthermore, the above-mentioned cutting process, peripheral grinding process, and polishing process were sequentially performed on the above-mentioned β-type Ga2O3 single crystal. In the above manner, the β-type Ga2O3 single crystal substrate of sample 10B was obtained. The diameter of the β-type Ga2O3 single crystal substrate of sample 10B was 101.6 mm and the thickness was 650 μm. The concentration of Rh in the β-type Ga2O3 single crystal substrate of sample 10B was 25 mass ppm in the above-mentioned GDMS, and the concentration of Ir in the above-mentioned GDMS was 0.02 mass ppm.

[0162] <Sample 10C>

[0163] The thickness of the side wall of the crucible was set to 1.0 mm. In addition, the β-Ga2O3 single crystal was produced by setting the growth direction to the

[001] direction in the same manner as the method for obtaining the β-Ga2O3 single crystal substrate of sample 10A. In this experimental example, no cracking of the crucible was observed. The outer diameter of the above-mentioned β-Ga2O3 single crystal was 108 mm. Furthermore, the above-mentioned cutting process, peripheral grinding process, and polishing process were sequentially performed on the above-mentioned β-Ga2O3 single crystal. In the above manner, the β-Ga2O3 single crystal substrate of sample 10C was obtained. The diameter of the β-Ga2O3 single crystal substrate of sample 10C was 101.6 mm and the thickness was 650 μm. The concentration of Rh in the β-Ga2O3 single crystal substrate of sample 10C was 45 mass ppm in the above-mentioned GDMS, and the concentration of Ir in the above-mentioned GDMS was 0.02 mass ppm.

[0164] <Sample 101>

[0165] (Preparation Step S110)

[0166] First, a single crystal growth apparatus 100, a seed crystal 8a composed of a β-type Ga2O3 single crystal, and bulk Ga2O3 polycrystals are prepared using conventionally known methods or by obtaining commercially available products. The crucible 5 constituting the single crystal growth apparatus 100 includes a crucible having a 3 mm thick sidewall 5a composed of 89.2 mass % pure stabilized ZrO2 containing 10.8 mass % CaO, and a 500 μm thick thermal sprayed coating 5b. More specifically, the inner diameter of the straight cylindrical portion of the crucible 5 is 105 mm. Furthermore, the surface roughness Rz of the inner circumferential surface of the sidewall 5a is 20 μm. The thermal sprayed coating 5b is composed of a Pt-Rh alloy containing 30 mass % Rh, and has a porosity of 10%.

[0167] (Raw Material Charging Step S120 and Raw Material Melting Step S130)

[0168] Next, by a conventionally known method, the seed crystal 8a is stored in the seed crystal storage portion 51 of the crucible 5, and a bulk Ga2O3 polycrystal is stored in the portion above the seed crystal 8a. Specifically, a plurality of bulk Ga2O3 polycrystals are stored and stacked in the diameter-enlarged portion 52 and the straight cylindrical portion 53. Next, the crucible 5 containing the seed crystal 8a and the bulk Ga2O3 polycrystal is supported by the crucible holding table 6. Then, an electric current is supplied to the heating device 7 to heat the crucible 5, so that a portion of the Ga2O3 polycrystal and the seed crystal 8a are dissolved, respectively, to prepare a Ga2O3 melt 82. Next, the remaining portion of the seed crystal 8a is brought into contact with the Ga2O3 melt 82 at their interface.

[0169] (Ga2O3 Single Crystal Growth Step S140)

[0170] Next, the crucible 5 is slowly lowered downward (toward the bottom) along the axis of the crucible 5 relative to the heating device 7, thereby forming a temperature gradient in the crucible 5, where the temperature is low on the seed crystal 8a side and high on the Ga2O3 solution 82 side. As a result, a β-type Ga2O3 single crystal 81 grown in the

[001] direction from the Ga2O3 solution 82 is obtained on the remaining portion of the seed crystal 8a side. This operation is continued until the lowering distance reaches 100 mm. The temperature of the interface between the growing β-type Ga2O3 single crystal 81 and the Ga2O3 solution 82 is set to 1800-1820°C. The temperature gradient at the above interface is set to 5°C / cm. The speed at which the crucible 5 descends downward along its axis is set to 1 mm / hour. In the above manner, an ingot of β-type Ga2O3 single crystal is obtained. The outer diameter of the crystal of the above-mentioned β-type Ga2O3 single crystal is 105.8 mm. In addition, although no cracks were observed in the crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0171] (Ga2O3 Single Crystal Substrate Manufacturing Step S200)

[0172] Finally, the β-type Ga2O3 single crystal ingot obtained in the Ga2O3 single crystal growth step S140 is processed in each step of a cutting step, a peripheral grinding step, and a polishing step, thereby obtaining a β-type Ga2O3 single crystal substrate. First, in the cutting step, the ingot is sliced ​​into wafers having a thickness of 700 μm using a conventionally known method. In the peripheral grinding step, the periphery of the wafer is ground using a conventionally known method to perform chamfering processing on the periphery, thereby obtaining a wafer having a main surface consisting of a center portion and a peripheral portion surrounding the periphery of the center portion. Furthermore, in the polishing step, the center portion is polished using a conventionally known polishing method, and the surface roughness Ra of the center portion is made to be 8 nm, for example, as specified in JIS B 0681-2:2018.

[0173] The β-Ga2O3 single crystal substrate of Sample 101 was produced in the above manner. The diameter of the β-Ga2O3 single crystal substrate of Sample 101 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 101 was 15 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS.

[0174] <Sample 102>

[0175] In the preparation step, a crucible having a porosity of 20% in the thermal sprayed film 5b covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 101. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 102 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 102 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 102 was 20 mass ppm in the GDMS, and the Ir concentration was 0.01 mass ppm in the GDMS. Crucible 5 did not show any cracking during crystal growth, but cracking was observed during cooling after crystal growth.

[0176] <Sample 103>

[0177] In the preparation step, a crucible having a porosity of 30% in the thermal sprayed film 5b covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 101. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 103 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 103 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 103 was 18 mass ppm in the GDMS, and the Ir concentration in the GDMS was 0.01 mass ppm.

[0178] <Sample 104>

[0179] In the preparatory step, a crucible with a 200 μm thick thermal spray film 5b covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 101. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 104 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 104 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 104 was 17 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Furthermore, while no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0180] <Sample 105>

[0181] In the preparatory step, a crucible with a 200 μm thick thermal sprayed film 5b covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 102. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 105 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 105 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 105 was 25 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0182] <Sample 106>

[0183] In the preparation step, a crucible having a thermal spray coating 5b with a thickness of 200 μm covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 103. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 106 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 106 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 106 was 40 mass ppm in the GDMS, and the Ir concentration in the GDMS was less than 0.01 mass ppm.

[0184] <Sample 107>

[0185] In the preparation step, a crucible having a surface roughness Rz of 100 μm on the inner circumferential side of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 104. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 107 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 107 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 107 was 28 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0186] <Sample 108>

[0187] In the preparation step, a crucible having a surface roughness Rz of 100 μm on the inner circumferential side of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 105. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 108 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 108 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 108 was 15 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0188] <Sample 109>

[0189] In the preparation step, a crucible having a surface roughness Rz of 300 μm on the inner peripheral surface of the side wall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 104. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 109 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 109 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 109 was 22 mass ppm in the GDMS, and the Ir concentration in the GDMS was less than 0.01 mass ppm.

[0190] <Sample 110>

[0191] In the preparation step, a crucible having a surface roughness Rz of 300 μm on the inner peripheral surface of the side wall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 105. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 110 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 110 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 110 was 25 mass ppm in the GDMS, and the Ir concentration in the GDMS was 0.02 mass ppm.

[0192] <Sample 111>

[0193] In the preparation step, a crucible having a surface roughness Rz of 300 μm on the inner peripheral surface of the side wall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 106. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 111 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 111 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 111 was 27 mass ppm in the GDMS, and the Ir concentration in the GDMS was less than 0.01 mass ppm.

[0194] <Sample 112>

[0195] An ingot of β-Ga2O3 single crystal was obtained by the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 111. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 112 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 112 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 112 was 20 mass ppm in the GDMS, and the Ir concentration in the GDMS was less than 0.01 mass ppm.

[0196] <Sample 113>

[0197] In the preparatory step, a crucible was prepared in which the inner circumferential surface of the sidewall portion 5a was coated with a thermally sprayed film composed of the following first film 5b1 and second film 5b2. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 109. Specifically, in the preparatory step of this experimental example, the inner circumferential surface of the sidewall portion 5a of the crucible 5 was coated with a first film 5b1 composed of Rh, having a porosity of 30% and a thickness of 50 μm by thermally spraying a first thermally sprayed material onto the surface. Furthermore, a second thermally sprayed material was thermally sprayed onto the first film 5b1, thereby coating the first film 5b1 with a second film 5b2 composed of Pt, having a porosity of 30% and a thickness of 150 μm.

[0198] The resulting β-Ga2O3 single crystal had an outer diameter of 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate, Sample 113, was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate, Sample 113, had a diameter of 101.6 mm and a thickness of 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate, Sample 113, was less than 0.01 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS.

[0199] <Sample 114>

[0200] An ingot of β-Ga2O3 single crystal was obtained by the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 113. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 114 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 114 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 114 was 0.08 mass ppm in the GDMS, and the Ir concentration in the GDMS was less than 0.01 mass ppm.

[0201] <Sample 115>

[0202] An ingot of β-Ga2O3 single crystal was obtained by the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 113. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 115 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 115 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 115 was 2.9 mass ppm in the GDMS, and the Ir concentration in the GDMS was 0.01 mass ppm.

[0203] <Sample 20A and Sample 20B>

[0204] The β-Ga2O3 single crystal substrates of Samples 20A and 20B were attempted to be produced, respectively, by the same methods as those used to produce the β-Ga2O3 single crystal substrates of Samples 10A and 10B, except that the inner diameter of the straight cylindrical portion of the crucible used for growing the Ga2O3 single crystal was 156 mm. However, the β-Ga2O3 single crystal substrates of Samples 20A and 20B could not be produced because the crucible cracked during crystal growth.

[0205] <Sample 20C>

[0206] The thickness of the side wall of the crucible was set to 1.0 mm. A β-Ga2O3 single crystal was produced by setting the growth direction to the

[001] direction in the same manner as the method for obtaining the β-Ga2O3 single crystal substrates of Samples 20A and 20B. In this experimental example, no cracking of the crucible was observed. The outer diameter of the β-Ga2O3 single crystal was 165 mm. Furthermore, the β-Ga2O3 single crystal was subjected to the above-mentioned cutting step, peripheral grinding step, and polishing step in sequence. In the above manner, a β-Ga2O3 single crystal substrate of Sample 20C was obtained. The diameter of the β-Ga2O3 single crystal substrate of Sample 20C was 152.4 mm and the thickness was 650 μm. The concentration of Rh in the β-Ga2O3 single crystal substrate of Sample 20C was 38 mass ppm in the above-mentioned GDMS, and the concentration of Ir in the above-mentioned GDMS was 0.01 mass ppm.

[0207] <Sample 201>

[0208] In the preparation step, a crucible having an inner diameter of 156 mm in the straight cylindrical portion was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 101. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 201 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 201 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 201 was 15 mass ppm in the GDMS, and the Ir concentration was 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in Crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0209] <Sample 202>

[0210] In the preparation step, a crucible having a porosity of 20% in the thermal sprayed film 5b covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 201. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 202 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 202 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 202 was 20 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Crucible 5 did not crack during the heated crystal growth, but cracking was observed during cooling after crystal growth.

[0211] <Sample 203>

[0212] In the preparation step, a crucible having a porosity of 30% in the thermal sprayed film 5b covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 201. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 203 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 203 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 203 was 23 mass ppm in the GDMS, and the Ir concentration was 0.01 mass ppm in the GDMS.

[0213] <Sample 204>

[0214] In the preparation step, a crucible with a 200 μm thick thermal sprayed film 5b covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 201. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 204 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 204 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 204 was 27 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0215] <Sample 205>

[0216] In the preparatory step, a crucible with a 200 μm thick thermal spray film 5b covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 202. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 205 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 205 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 205 was 15 mass ppm, and the Ir concentration in the GDMS was 0.02 mass ppm. Although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0217] <Sample 206>

[0218] In the preparation step, a crucible having a thermal spray coating 5b with a thickness of 200 μm covering the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 203. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 206 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 206 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 206 was 35 mass ppm in the GDMS, and the Ir concentration in the GDMS was less than 0.01 mass ppm.

[0219] <Sample 207>

[0220] In the preparation step, a crucible having a surface roughness Rz of 100 μm on the inner circumferential side of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 204. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 207 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 207 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 207 was 18 mass ppm in the GDMS, and the Ir concentration was 0.01 mass ppm in the GDMS. Although no cracks were observed in Crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0221] <Sample 208>

[0222] In the preparation step, a crucible having a surface roughness Rz of 100 μm on the inner circumferential surface of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 205. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 208 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 208 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 208 was 25 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in Crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0223] <Sample 209>

[0224] In the preparation step, a crucible having a surface roughness Rz of 300 μm on the inner circumferential side of the sidewall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 204. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 209 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 209 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 209 was 32 mass ppm in the GDMS, and the Ir concentration in the GDMS was less than 0.01 mass ppm.

[0225] <Sample 210>

[0226] In the preparation step, a crucible having a surface roughness Rz of 300 μm on the inner peripheral surface of the side wall portion 5a was prepared. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 205. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 210 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 210 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 210 was 26 mass ppm in the GDMS, and the Ir concentration in the GDMS was 0.02 mass ppm.

[0227] <Sample 211>

[0228] In the preparatory step, a crucible was prepared in which the inner circumferential surface of the sidewall portion 5a was coated with a thermally sprayed film composed of the following first film 5b1 and second film 5b2. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 209. Specifically, in the preparatory step of this experimental example, the inner circumferential surface of the sidewall portion 5a of the crucible 5 was coated with a first film 5b1 composed of Rh, having a porosity of 30% and a thickness of 50 μm by thermally spraying a first thermally sprayed material onto the surface. Furthermore, a second thermally sprayed material was thermally sprayed onto the first film 5b1, thereby coating the first film 5b1 with a second film 5b2 composed of Pt, having a porosity of 30% and a thickness of 150 μm.

[0229] The resulting β-Ga2O3 single crystal had an outer diameter of 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate, Sample 211, was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 211 had a diameter of 152.4 mm and a thickness of 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 211 was 0.02 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS.

[0230] <Sample 212>

[0231] An ingot of β-Ga2O3 single crystal was obtained by the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 211. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 212 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 212 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 212 was less than 0.01 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS.

[0232] <Sample 213>

[0233] An ingot of β-Ga2O3 single crystal was obtained by the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 211. The outer diameter of the β-Ga2O3 single crystal was 157.1 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 213 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 213 was 152.4 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 213 was 2.8 mass ppm in the GDMS, and the Ir concentration in the GDMS was 0.01 mass ppm.

[0234] <Sample 301>

[0235] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 11 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 101. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 301 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 301 had a diameter of 101.6 mm and a thickness of 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 301 was 14 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0236] <Sample 302>

[0237] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 11 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 102. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 302 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 302 had a diameter of 101.6 mm and a thickness of 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 302 was 21 mass ppm in the GDMS, and the Ir concentration was 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0238] <Sample 303>

[0239] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 11 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 103. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 303 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 303 had a diameter of 101.6 mm and a thickness of 650 μm. The concentration of Rh in the β-type Ga 2 O 3 single crystal substrate of sample 303 was 19 mass ppm in the above-mentioned GDMS, and the concentration of Ir in the above-mentioned GDMS was less than 0.01 mass ppm.

[0240] <Sample 304>

[0241] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 11 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 104. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 304 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 304 had a diameter of 101.6 mm and a thickness of 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 304 was 18 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0242] <Sample 305>

[0243] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 11 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 105. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 305 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 305 had a diameter of 101.6 mm and a thickness of 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 305 was 24 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0244] <Sample 306>

[0245] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 10 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 106. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 306 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 306 had a diameter of 101.6 mm and a thickness of 650 μm. The concentration of Rh in the β-type Ga 2 O 3 single crystal substrate of sample 306 was 22 mass ppm in the above-mentioned GDMS, and the concentration of Ir in the above-mentioned GDMS was less than 0.01 mass ppm.

[0246] <Sample 307>

[0247] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 10 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 107. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 307 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 307 had a diameter of 101.6 mm and a thickness of 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 307 was 25 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0248] <Sample 308>

[0249] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 10 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 108. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 308 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 308 had a diameter of 101.6 mm and a thickness of 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 308 was 17 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS. Furthermore, although no cracks were observed in crucible 5 during crystal growth, cracks were observed during cooling after crystal growth.

[0250] <Sample 309>

[0251] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 10 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 109. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 309 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 309 had a diameter of 101.6 mm and a thickness of 650 μm. The concentration of Rh in the β-type Ga2O3 single crystal substrate of sample 309 was 21 mass ppm in the above-mentioned GDMS, and the concentration of Ir in the above-mentioned GDMS was less than 0.01 mass ppm.

[0252] <Sample 310>

[0253] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 10 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 110. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 310 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 310 had a diameter of 101.6 mm and a thickness of 650 μm. The concentration of Rh in the β-type Ga 2 O 3 single crystal substrate of sample 310 was 26 mass ppm in the above-mentioned GDMS, and the concentration of Ir in the above-mentioned GDMS was 0.01 mass ppm.

[0254] <Sample 311>

[0255] In preparation step S110, a 9 mm thick sidewall 5a composed of 86.2 mass% pure stabilized ZrO containing 13.8 mass% Y2O3 was used as the crucible 5 constituting the single crystal growth apparatus 100. The composition of the thermal sprayed film 5b coating the inner circumference of the crucible's sidewall 5a was changed to a Pt-Rh alloy containing 10 mass% Rh. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 111. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 311 was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate of Sample 311 had a diameter of 101.6 mm and a thickness of 650 μm. The concentration of Rh in the β-type Ga2O3 single crystal substrate of Sample 311 was 14 mass ppm in the above-mentioned GDMS, and the concentration of Ir in the above-mentioned GDMS was less than 0.01 mass ppm.

[0256] <Sample 312>

[0257] An ingot of β-Ga2O3 single crystal was obtained by the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 311. The outer diameter of the β-Ga2O3 single crystal was 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate of Sample 312 was obtained from the β-Ga2O3 single crystal. The diameter of the β-Ga2O3 single crystal substrate of Sample 312 was 101.6 mm and the thickness was 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate of Sample 312 was 13 mass ppm in the GDMS, and the Ir concentration in the GDMS was less than 0.01 mass ppm.

[0258] <Sample 313>

[0259] In the preparatory step, a crucible was prepared in which the inner circumferential surface of the sidewall portion 5a was coated with a thermally sprayed film composed of the following first film 5b1 and second film 5b2. A β-Ga2O3 single crystal ingot was obtained using the same method as that used to obtain the β-Ga2O3 single crystal substrate of Sample 309. Specifically, in the preparatory step of this experimental example, the inner circumferential surface of the sidewall portion 5a of the crucible 5 was coated with a first film 5b1 composed of Rh, having a porosity of 30% and a thickness of 50 μm by thermally spraying a first thermally sprayed material onto the surface. Furthermore, a second thermally sprayed material was thermally sprayed onto the first film 5b1, thereby coating the first film 5b1 with a second film 5b2 composed of Pt, having a porosity of 30% and a thickness of 150 μm.

[0260] The resulting β-Ga2O3 single crystal had an outer diameter of 105.8 mm. Furthermore, a β-Ga2O3 single crystal substrate, Sample 313, was obtained from the β-Ga2O3 single crystal. The β-Ga2O3 single crystal substrate, Sample 313, had a diameter of 101.6 mm and a thickness of 650 μm. The Rh concentration in the β-Ga2O3 single crystal substrate, Sample 313, was less than 0.01 mass ppm in the GDMS, and the Ir concentration was less than 0.01 mass ppm in the GDMS.

[0261] Tables 1, 2, and 3 list the crucible configurations (including the inner diameter of the straight tube, composition, surface roughness Rz, sidewall thickness, composition, porosity, and thickness of the thermal sprayed film) used to manufacture the β-Ga2O3 single crystal substrates for Samples 10A to 10C, Samples 101 to 115, Samples 20A to 20C, Samples 201 to 213, and Samples 301 to 313. In Tables 1 and 3, the composition, porosity, and thickness of the thermal sprayed film when it is a single layer are listed in the "Thermal sprayed film (innermost layer: second film)" column.

[0262] [Table 1]

[0263] Table 1

[0264]

[0265] [Table 2]

[0266] Table 2

[0267]

[0268] [Table 3]

[0269] Table 3

[0270]

[0271] [evaluate]

[0272] <Product Yield>

[0273] The yield of the β-Ga2O3 single crystals used to obtain the β-Ga2O3 single crystal substrates for Samples 10B to 10C, Samples 101 to 115, Sample 20C, Samples 201 to 213, and Samples 301 to 313 was determined using the following method. As described above, the "yield" refers to the proportion of the mass of the β-Ga2O3 single crystal ingot after crystal growth in a crucible, excluding areas where the desired diameter cannot be achieved when processed into β-Ga2O3 single crystal substrates due to cracking or chipping of the crucible or cracking or chipping of the crystal during cooling, and the mass of the substrates that can be evaluated as good quality using the evaluation method described below. A better yield of the single crystal indicates a greater lack of cracks, chips, etc. in the crucible used to grow the single crystal.

[0274] First, an ingot of β-Ga2O3 single crystal of each sample was removed from a crucible. A disc-shaped measurement sample (thickness: 1 mm) having a (001) main surface was cut out from the ingot at measurement point 1 and measurement point 2, respectively, which served as the positions for measuring the outer diameter of the crystal. Furthermore, the main surface of each measurement sample was polished and etched using conventionally known molten potassium hydroxide.

[0275] Next, the entire surface of the above-mentioned measurement sample is observed using a differential interference microscope (trade name (product number): "LV-150", manufactured by Nikon Corporation), and the number of crystal defects appearing in one field of view of the above-mentioned differential interference microscope is counted for each field of view, and it is determined whether polycrystallization has occurred. In this case, the above-mentioned observation using the differential interference microscope is performed at a magnification of 10 times. Thus, one field of view of the above-mentioned differential interference microscope becomes 10mm×10mm in size, and the number of crystal defects in each field of view is directly expressed as density (cm -2 ) in the form of a pore. Furthermore, the crystal defects described above refer to "etch pits" that appear as etch holes on the main surface due to the etching. While these etch pits are not synonymous with dislocations in academic terms, they can be considered equivalent to dislocations in this technical field. Furthermore, the "dislocations" described above refer to "threading dislocations" that exist within a β-type Ga2O3 single crystal, and are considered a form of crystal defect.

[0276] Next, if no polycrystallization is observed in the measurement sample, the measurement sample is evaluated as a good product. On the other hand, if at least polycrystallization is observed in the measurement sample, the measurement sample is evaluated as a poor product. A new measurement sample is cut from the ingot from which the poorly evaluated measurement sample was cut, at a position 10 mm from the measurement point 1 or the measurement point 2, where the measurement sample was cut, toward the measurement point 3, and the new measurement sample is observed using the differential interference microscope. This operation is repeated until the measurement sample is judged to be a good product.

[0277] Finally, the volume of the ingot was calculated based on the length (height) encompassing the locations where the sample judged to be good was cut from the ingot, and the diameter of the β-Ga2O3 single crystal substrate of each sample (i.e., 101.6 mm or 152.4 mm). The mass of the ingot suitable for production (hereinafter referred to as "good quality") was calculated based on this volume. Next, the proportion of this good quality to the mass of the region of the ingot between measurement points 1 and 2 was calculated, and this was taken as the "product yield." The results are shown in Tables 4, 5, and 6.

[0278] [Determination of activation rate]

[0279] For the β-Ga2O3 single crystal substrates of Samples 10B to 10C, Samples 101 to 115, Sample 20C, Samples 201 to 213, and Samples 301 to 313, the carrier concentration of each sample was determined by performing the above-mentioned measurement method on Hall measurement samples made using the central portion of the above-mentioned substrates. In addition, the impurity concentration of Sn or Si in the above-mentioned β-Ga2O3 single crystal substrates was determined using glow discharge mass spectrometry (GDMS). The activation rate of each sample was calculated by dividing the carrier concentration of each sample by the impurity concentration determined by GDMS. The results are shown in Tables 4, 5, and 6.

[0280] [Measurement of transmittance]

[0281] The transmittance of light at a wavelength of 427 nm was determined for each of the β-GaO single crystal substrates (Samples 10B to 10C, Samples 101 to 115, Sample 20C, Samples 201 to 213, and Samples 301 to 313) using the aforementioned measurement method, using transmittance measurement samples fabricated using the central portion of these substrates. The results are shown in Tables 4, 5, and 6.

[0282] [Table 4]

[0283] Table 4

[0284]

[0285] Regarding "crucible cracking", NG means that cracking was observed during crystal growth, and G means that no cracking was observed.

[0286] *Indicates breakage during cooling after crystal growth.

[0287] [Table 5]

[0288] Table 5

[0289]

[0290] Regarding "crucible cracking", NG means that cracking was observed during crystal growth, and G means that no cracking was observed.

[0291] *Indicates breakage during cooling after crystal growth.

[0292] [Table 6]

[0293] Table 6

[0294]

[0295] Regarding "crucible cracking", NG means that cracking was observed during crystal growth, and G means that no cracking was observed.

[0296] *Indicates breakage during cooling after crystal growth.

[0297] [Investigation]

[0298] According to Table 4, the product yield of the β-Ga2O3 single crystal substrates of Samples 101 to 115 is better than that of the β-Ga2O3 single crystal substrates of Samples 10B to 10C. Therefore, it can be concluded that the crucibles used to manufacture the β-Ga2O3 single crystal substrates of Samples 101 to 115 are more capable of suppressing cracking and defects during crystal growth than the crucibles used to manufacture the β-Ga2O3 single crystal substrates of Samples 10B to 10C. According to Table 5, the product yield of the β-Ga2O3 single crystal substrates of Samples 201 to 213 is better than that of the β-Ga2O3 single crystal substrate of Sample 20C. Therefore, it can be concluded that the crucibles used to manufacture the β-Ga2O3 single crystal substrates of Samples 201 to 213 are more capable of suppressing cracking and defects during crystal growth than the crucibles used to manufacture the β-Ga2O3 single crystal substrate of Sample 10C. Table 6 shows that the production yields of the β-Ga2O3 single crystal substrates of Samples 301 to 313 were as good as those of the β-Ga2O3 single crystal substrates of Samples 101 to 115. Therefore, it can be concluded that the crucibles used to produce the β-Ga2O3 single crystal substrates of Samples 301 to 313 were able to suppress cracking and defects during crystal growth.

[0299] In particular, the β-Ga2O3 single crystal substrates of Samples 113 to 115, and the β-Ga2O3 single crystal substrates of Samples 211 to 213, and Sample 313 exhibited superior activation rates and transmittance compared to the other samples. Therefore, it can be concluded that the β-Ga2O3 single crystal substrates of Samples 113 to 115, Samples 211 to 213, and Sample 313 can provide compound semiconductor substrates with excellent both electrical and optical properties.

[0300] Although the embodiments and examples of the present invention have been described above, it has been planned from the outset that the above-described embodiments and examples can be appropriately combined.

[0301] The embodiments and examples disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated not by the embodiments and examples described above but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0302] Description of Reference Numerals

[0303] 100: Single crystal growth device; 5: Crucible; 51: Seed crystal receiving portion; 52: Diameter-enlarging portion; 53: Straight tube portion; 5a: Sidewall portion; 5b: Thermal spray coating; 5b1: First coating; 5b2: Second coating; 5c: Pores; 6: Crucible holding table; 7: Heating device; 8a: Seed crystal; 81: β-Ga2O3 single crystal; 82: Gallium sesquioxide melt (Ga2O3 melt); 9: Sealed container; 1: β-Ga2O3 Gallium single crystal substrate (β-type Ga2O3 single crystal substrate); 10: main surface; 10a: rectangular slice; O: center; OF: positioning edge; 21: electrode; S100: β-type Ga2O3 single crystal manufacturing process; S110: preparation process; S120: raw material storage process; S130: raw material melting process; S140: Ga2O3 single crystal growth process; S200: β-type Ga2O3 single crystal substrate manufacturing process.

Claims

1. A crucible for growing β-type gallium trioxide single crystals. The crucible has a thickness of 1 mm or more and 10 mm or less, The maximum inner diameter of the crucible is more than 100 mm, The crucible is composed of stabilized zirconium oxide containing either or both yttrium oxide and calcium oxide, The inner peripheral surface of the crucible is coated with a thermal spray film containing either or both of rhodium and platinum. The thickness of the thermal sprayed film is not less than 100 μm and not more than 500 μm. The stabilized zirconia contains at least 12.0 mass % to 15.5 mass % of the yttrium oxide, or contains at least 10.2 mass % to 11.4 mass % of the calcium oxide.

2. The crucible according to claim 1, wherein The thermal sprayed film is composed of a platinum-rhodium alloy containing 10% by mass or more and 30% by mass or less of rhodium.

3. The crucible according to claim 2, wherein The thermal spraying film has pores, The volume ratio of the pores in the thermal sprayed film, that is, the porosity, is 30 volume % or more and 50 volume % or less.

4. The crucible according to claim 2, wherein The surface roughness Rz of the surface is 300 μm or more and 500 μm or less, The thermal spraying film has pores, The volume ratio of the pores in the thermal sprayed film, that is, the porosity, is 10 volume % or more and less than 30 volume %.

5. The crucible according to claim 3, wherein The surface roughness Rz of the surface is 300 μm or more and 500 μm or less. The crucible according to claim 1 , wherein: The thermal spraying film is composed of a first film and a second film. The first film covers the surface, The first film is composed of rhodium or a platinum-rhodium alloy with rhodium as the main component. The second film covers the first film, The second film is composed of platinum or a platinum-rhodium alloy with platinum as the main component. The thermal sprayed film has a thickness of 100 μm or more and 500 μm or less as a total of the first film and the second film.

7. The crucible according to claim 6, wherein The first membrane and the second membrane both have pores, The first membrane porosity, which is a volume ratio of the pores in the first membrane, and the second membrane porosity, which is a volume ratio of the pores in the second membrane, are both 30% by volume or more and 50% by volume or less.

8. The crucible according to claim 6, wherein The surface roughness Rz of the surface is 300 μm or more and 500 μm or less, The first membrane and the second membrane both have pores, The volume ratio of the pores in the first membrane, i.e., the first membrane porosity, and the volume ratio of the pores in the second membrane, i.e., the second membrane porosity, are both 10% by volume or more and less than 30% by volume.

9. The crucible according to claim 7, wherein The surface roughness Rz of the surface is 300 μm or more and 500 μm or less.

10. A method for producing a β-type gallium sesquioxide single crystal substrate, the method comprising using the crucible according to any one of claims 1 to 9. The manufacturing method comprises: The process of preparing the crucible; a step of obtaining a β-type gallium trioxide single crystal by a vertical boat method using the crucible; The step of processing the β-type gallium sesquioxide single crystal to obtain a β-type gallium sesquioxide single crystal substrate having a circular main surface.

11. A β-type gallium trioxide single crystal substrate having a circular main surface. The diameter of the β-type gallium trioxide single crystal substrate is greater than 100 mm. The main surface is the (001) plane of the β-type gallium trioxide single crystal; or The main surface is a surface having an off angle greater than 0° and less than 10° from the (001) plane of the β-type gallium trioxide single crystal, and an off direction in the [010] direction of the β-type gallium trioxide single crystal or a direction orthogonal to the [010] direction. The β-type gallium trioxide single crystal substrate contains both or either rhodium and iridium, The concentration of the rhodium and the concentration of the iridium were both less than 3 mass ppm in glow discharge mass spectrometry analysis.

12. The β-type gallium trioxide single crystal substrate according to claim 11, wherein The transmittance of the β-type gallium trioxide single crystal substrate to light with a wavelength of 400 nm to 430 nm is 70% or more. In the Hall measurement using the van der Pauw method, the carrier concentration measured at 25°C is 1×10 17 cm -3 Above and 1.0×10 19 cm -3 the following.

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