Digallium trioxide single crystal substrate, method for producing digallium trioxide single crystal, and method for producing digallium trioxide single crystal substrate

Abstract

A digallium trioxide single crystal substrate having a circular main surface, wherein the diameter of the digallium trioxide single crystal substrate is 100 mm or more, the thickness of the digallium trioxide single crystal substrate is 600 μm or more, the digallium trioxide single crystal substrate comprises boron, and the concentration of boron is 4-200 mass ppm in glow discharge mass spectrometry.

Description

Gallium trioxide single crystal substrate, method for producing the same, and method for producing the same

[0001] The present disclosure relates to a digallium trioxide single crystal substrate, a method for manufacturing a digallium trioxide single crystal, and a method for manufacturing a digallium trioxide single crystal substrate.

[0002] JP 2016-079080 A (Patent Document 1), JP 2017-193466 A (Patent Document 2), JP 2020-105069 A (Patent Document 3), JP 2020-011899 A (Patent Document 4), and JP 2020-059633 A (Patent Document 5) disclose that a gallium trioxide single crystal (hereinafter also referred to as a "GaO single crystal") was grown in an air atmosphere by a vertical boat method, an EFG method (Edge-defined Film-fed Growth method), or the like, using a crucible made of a platinum-rhodium alloy (hereinafter also referred to as a "Pt-Rh alloy") or a crucible or die made of a platinum-iridium alloy (hereinafter also referred to as a "Pt-Ir alloy"). D. Sajuti et al., Mater. Trans., JIM, 34 (1993), pp. 1195-1199 (Non-Patent Document 1) discloses the feasibility of dissolving digallium trioxide (hereinafter also referred to as "GaO") in liquid boron oxide (hereinafter also referred to as "BO"), and then cooling the solution to precipitate GaO single crystals due to the difference in solubility between BO and GaO.

[0003] JP 2016-079080 A JP 2017-193466 A JP 2020-105069 A JP 2020-011899 A JP 2020-059633 A

[0004] D. Sajuti et al. Mater. Trans., JIM, 34(1993), pp.1195-1199

[0005] The digallium trioxide single crystal substrate according to the present disclosure is a digallium trioxide single crystal substrate having a circular main surface. The diameter of the digallium trioxide single crystal substrate is 100 mm or more. The thickness of the digallium trioxide single crystal substrate is 600 μm or more. The digallium trioxide single crystal substrate contains boron. The concentration of the boron is 4 ppm by mass or more and 200 ppm by mass or less, as determined by glow discharge mass spectrometry.

[0006] FIG. 1 is an explanatory diagram illustrating the main surface of a digallium trioxide single crystal substrate according to the present embodiment. FIG. 2 is an explanatory diagram illustrating five measurement points set on the main surface of the digallium trioxide single crystal substrate of FIG. 1 to determine nanoindentation hardness. FIG. 3 is an explanatory diagram illustrating a Hall measurement sample prepared using the center of the digallium trioxide single crystal substrate according to the present embodiment to measure the resistivity, carrier concentration, and electron mobility of the digallium trioxide single crystal substrate. FIG. 4 is a flowchart illustrating an example of a method for manufacturing a digallium trioxide single crystal substrate, including a method for manufacturing a digallium trioxide single crystal according to the present embodiment. FIG. 5 is a schematic diagram illustrating a manufacturing apparatus used in the method for manufacturing a digallium trioxide single crystal according to the present embodiment. FIG. 6 is a graph showing the relationship between nanoindentation hardness and crack load in a digallium trioxide single crystal substrate prepared in an example.

[0007] [Problem to be Solved by the Present Disclosure] GaO single crystals are crystals with strong cleavage properties and are prone to cracking in specific directions. Therefore, in the process of obtaining gallium trioxide single crystal substrates (hereinafter also referred to as "GaO single crystal substrates") from GaO single crystals, there is concern that many of the substrates will crack during cutting and peripheral processing of the GaO single crystals, as well as during transportation after the substrates are obtained. Therefore, there is a demand for suppressing cracking in the GaO single crystal substrates. Meanwhile, it is known that gallium arsenide single crystals doped with boron (B) as an impurity have improved strength. When GaO single crystals are obtained using the crucibles disclosed in Patent Documents 1 to 5, the possibility of B being mixed into the GaO single crystals as an impurity is extremely low. The above-mentioned Non-Patent Document 1 only mentions the feasibility of precipitating GaO single crystals due to the difference in solubility between BO and GaO, but does not suggest at all the effect of improving the strength of the GaO single crystal substrate due to the inclusion of B, or the effect of suppressing the occurrence of cracks in the GaO single crystal substrate.

[0008] In view of the above, an object of the present disclosure is to provide a gallium trioxide single crystal substrate capable of suppressing the occurrence of cracks, a method for manufacturing a gallium trioxide single crystal, and a method for manufacturing a gallium trioxide single crystal substrate.

[0009] Effect of the Present Disclosure The present disclosure can provide a digallium trioxide single crystal substrate capable of suppressing the occurrence of cracks, a method for manufacturing a digallium trioxide single crystal, and a method for manufacturing a digallium trioxide single crystal substrate.

[0010] [Summary of the Embodiments] The following describes an overview of the embodiments of the present disclosure. The present inventors have completed the present disclosure after extensive research to solve the above-mentioned problems. The present inventors have discovered that when a GaO single crystal substrate is obtained from the GaO single crystal by adding a trace amount of B to the GaO single crystal, the occurrence of cracks can be suppressed, and have discovered an appropriate concentration of B that can suppress the occurrence of cracks in the substrate. In particular, they have discovered that B, being a member of the same group as gallium (Ga), does not adversely affect the electrical properties of the substrate, and have arrived at the present disclosure.

[0011] Next, embodiments of the present disclosure will be described below. [1] A digallium trioxide single crystal substrate according to one aspect of the present disclosure is a digallium trioxide single crystal substrate having a circular main surface. The diameter of the digallium trioxide single crystal substrate is 100 mm or more. The thickness of the digallium trioxide single crystal substrate is 600 μm or more. The digallium trioxide single crystal substrate contains boron. The concentration of the boron is 4 ppm by mass or more and 200 ppm by mass or less, as determined by glow discharge mass spectrometry. A digallium trioxide single crystal substrate having these characteristics can suppress the occurrence of cracks.

[0012] [2] The boron concentration is preferably 5 ppm by mass or more and 100 ppm by mass or less, as determined by glow discharge mass spectrometry, thereby further suppressing cracking of the gallium trioxide single crystal substrate.

[0013] [3] The main surface is preferably a (001) plane of the digallium trioxide single crystal. The main surface preferably has a central portion including the center and an outer peripheral portion surrounding the central portion. The outer peripheral portion is preferably a chamfered region. In the digallium trioxide single crystal substrate, the nanoindentation hardness measured at five locations on the main surface according to a nanoindentation method using a Berkovich indenter is preferably 14.8 GPa or more and 22.0 GPa or less under the conditions of applying a maximum load of 10 mN and a load such that the crossing angle between one side of the indentation and the direction of the

[100] direction of the digallium trioxide single crystal projected onto the main surface is 0° or more and 10° or less. When the length from the center of the main surface to the boundary between the central portion and the outer periphery is defined as r, two mutually perpendicular axes on the main surface that pass through the center are defined as the X-axis and the Y-axis, and the Y-axis is defined as the b-axis of the digallium trioxide single crystal, the five coordinates (X, Y) defined by the X-axis and the Y-axis are preferably (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)). The units of r and X and Y in the coordinates (X, Y) are preferably mm. This can further suppress the occurrence of cracks in the digallium trioxide single crystal substrate.

[0014] [4] The gallium trioxide single crystal substrate may contain both or either rhodium and iridium. In this case, the rhodium concentration and the iridium concentration are preferably both 0.1 mass ppm or less as determined by glow discharge mass spectrometry. This prevents adverse effects on the electrical characteristics of the gallium trioxide single crystal substrate.

[0015] [5] The resistivity of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall method is 1.0 × 10 -3 The carrier concentration of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall measurement is preferably 4.0 × 10 17 cm-3 1.4 x 10 19 cm -3 The electron mobility of the gallium trioxide single crystal substrate measured at 25° C. by the Van der Pauw Hall method is preferably 0.2 cm or less. 2 / V・s or more 15000cm 2 / V·s or less, thereby enabling the digallium trioxide single crystal substrate to have good electrical properties.

[0016] [6] The method for producing a gallium trioxide single crystal according to one embodiment of the present disclosure is carried out in an air atmosphere. The manufacturing method includes the steps of preparing a single crystal growth apparatus including at least a cylindrical crucible and a heating device disposed so as to surround the outer periphery of the crucible, placing a seed crystal consisting of the digallium trioxide single crystal at the bottom of the crucible and placing a block or powder of digallium trioxide polycrystal, an n-type dopant, and boron oxide above the seed crystal in the crucible, heating the crucible with the heating device to melt a portion of the seed crystal and obtain a solution in which digallium trioxide derived from a portion of the seed crystal and the digallium trioxide polycrystal is dissolved at a first concentration and the n-type dopant is dissolved at a second concentration in the boron oxide, and contacting the solution with the remainder of the seed crystal, and growing a crystal from the solution on the remainder of the seed crystal to obtain a digallium trioxide single crystal. The digallium trioxide single crystal has a boron concentration of 4 ppm by mass or more and 200 ppm by mass or less, as determined by glow discharge mass spectrometry. By using the method for producing a digallium trioxide single crystal having these characteristics, it is possible to obtain a digallium trioxide single crystal for producing a digallium trioxide single crystal substrate that is capable of suppressing cracking.

[0017] [7] The method for producing a gallium trioxide single crystal according to one embodiment of the present disclosure is carried out under a nitrogen atmosphere. The manufacturing method includes the steps of: preparing a single crystal growth apparatus including at least a cylindrical crucible and a heating device disposed so as to surround the outer periphery of the crucible; accommodating a seed crystal consisting of the digallium trioxide single crystal at the bottom of the crucible, and accommodating block or powdered digallium trioxide polycrystal, an n-type dopant, and boron oxide above the seed crystal in the crucible; heating the crucible with the heating device to melt a portion of the seed crystal and obtain a solution in which digallium trioxide derived from a portion of the seed crystal and the digallium trioxide polycrystal is dissolved at a first concentration and the n-type dopant is dissolved at a second concentration in the boron oxide, and bringing the solution into contact with the remainder of the seed crystal; and growing a crystal from the solution on the remainder of the seed crystal to obtain a digallium trioxide single crystal. The crucible is made of pyrolytic boron nitride. The boron concentration in the digallium trioxide single crystal is 4 ppm by mass or more and 200 ppm by mass or less, as determined by glow discharge mass spectrometry. By using this method for producing a digallium trioxide single crystal having these characteristics, it is possible to obtain a digallium trioxide single crystal for producing a digallium trioxide single crystal substrate that is capable of suppressing cracking.

[0018] [8] The single crystal growth apparatus preferably has a nozzle for introducing the digallium trioxide polycrystal and the n-type dopant into the crucible, and a lid for sealing the crucible. The lid preferably has a hole through which the nozzle is inserted. The step of obtaining the digallium trioxide single crystal preferably includes the steps of: sampling the solution in the crucible sealed by the lid through the nozzle to analyze the concentrations of digallium trioxide derived from a portion of the seed crystal and the digallium trioxide polycrystal, and the n-type dopant in the solution; introducing the digallium trioxide polycrystal into the solution in the crucible through the nozzle so that the concentration is within ±5% of the first concentration, based on the analysis result of the digallium trioxide concentration; and introducing the n-type dopant into the solution in the crucible through the nozzle so that the concentration is within ±5% of the second concentration, based on the analysis result of the n-type dopant concentration. This makes it possible to obtain, with a high yield, digallium trioxide single crystals for producing digallium trioxide single crystal substrates that are capable of suppressing the occurrence of cracks.

[0019] [9] A method for producing a digallium trioxide single crystal substrate according to one embodiment of the present disclosure includes a step of processing the digallium trioxide single crystal obtained by the above-described method for producing a digallium trioxide single crystal to obtain a digallium trioxide single crystal substrate having a circular main surface. By using this characteristic production method, a digallium trioxide single crystal substrate capable of suppressing the occurrence of cracks can be obtained.

[0020]

[10] In the digallium trioxide single crystal substrate described in [2] above, the main surface is preferably a (001) plane of the digallium trioxide single crystal. The main surface preferably has a central portion including the center and an outer periphery surrounding the central portion. The outer periphery is preferably a chamfered region. In the digallium trioxide single crystal substrate, the nanoindentation hardness measured at five locations on the main surface according to a nanoindentation method using a Berkovich indenter is preferably 14.8 GPa or more and 22.0 GPa or less under the conditions of applying a maximum load of 10 mN and a load such that the crossing angle between one side of the indentation and the direction of the

[100] direction of the digallium trioxide single crystal projected onto the main surface is 0° or more and 10° or less. When the length from the center of the main surface to the boundary between the central portion and the outer periphery is defined as r, two mutually orthogonal axes on the main surface that pass through the center are defined as the X-axis and the Y-axis, and the Y-axis is defined as the b-axis of the digallium trioxide single crystal, the five coordinates (X, Y) defined by the X-axis and the Y-axis are preferably (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)). The units of r and X and Y in the coordinates (X, Y) are preferably mm. The digallium trioxide single crystal substrate preferably contains both or either rhodium and iridium. The rhodium concentration and the iridium concentration are preferably both 0.1 ppm by mass or less by glow discharge mass spectrometry. The resistivity of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall method was 1.0 x 10 -3 The carrier concentration of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall measurement is preferably 4.0 × 10 17 cm -3 1.4 x 10 19 cm -3 The electron mobility of the gallium trioxide single crystal substrate measured at 25° C. by the Van der Pauw Hall measurement is preferably 0.2 cm or less.2 / V・s or more 15000cm 2 This makes it possible to further suppress the occurrence of cracks in the gallium trioxide single crystal substrate, and also provides it with good electrical properties.

[0021] [Details of the embodiment] One embodiment according to the present disclosure (hereinafter also referred to as "the present embodiment") will be described in further detail below, but the present disclosure is not limited thereto. The following description may be made with reference to the drawings, and the same or corresponding elements in this specification and the drawings will be denoted by the same reference numerals, and the same description will not be repeated. Furthermore, the scale of the drawings has been adjusted appropriately to facilitate understanding of each component, and the scale of each component shown in the drawings does not necessarily coincide with the scale of the actual component.

[0022] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and only a unit is specified for B, the units of A and B are the same. Furthermore, when a compound or the like is expressed in this specification by a chemical formula, unless the atomic ratio is particularly limited, it is understood to include any conventionally known atomic ratio, and should not necessarily be limited to only those within a stoichiometric range.

[0023] As used herein, the "main surface" of a gallium trioxide single crystal substrate refers to both of the two circular faces of the gallium trioxide single crystal substrate. When at least one of the two faces of the gallium trioxide single crystal substrate satisfies the scope of the claims of the present disclosure, the substrate falls within the technical scope of the present disclosure. Furthermore, the term "surface" used in the term "in-plane" in the present specification refers to the "main surface." Furthermore, when the diameter of a gallium trioxide single crystal substrate is described as "100 mm," this means that the diameter is approximately 100 mm (approximately 95 to 105 mm), or 4 inches. When the diameter is described as "150 mm," this means that the diameter is approximately 150 mm (approximately 145 to 155 mm), or 6 inches. The diameter can be measured using a conventionally known outer diameter measuring instrument, such as a vernier caliper.

[0024] As used herein, "nanoindentation hardness" refers to the indentation hardness determined by performing an instrumented indentation test in accordance with ISO 14577, an international standard that includes the nanoindentation method (Ryo Nikentani, "Mechanical Property Evaluation Method Using a Nanoindenter," Bunseki, 561 (2021), pp. 457-461). Specifically, the term refers to the hardness determined by performing an indentation test using a Berkovich indenter at a predetermined position on the main surface of a gallium trioxide single crystal substrate according to the nanoindentation method, obtaining a load-displacement curve, and analyzing this load-displacement curve. The "nanoindentation hardness" refers to the maximum load (mN) applied to the gallium trioxide single crystal substrate by the Berkovich indenter, multiplied by the area (mm 2 The unit of the "nanoindentation hardness" is pascal (Pa).

[0025] In the crystallographic descriptions in this specification, individual directions are represented by [ ], collective directions by < >, individual planes by ( ), and collective planes by {}. In addition, negative crystallographic indices are usually represented by placing a "- (bar)" above the number, but in this specification, a negative sign is placed before the number.

[0026] [Digallium Trioxide Single Crystal Substrate] The digallium trioxide single crystal substrate (Ga2O3 single crystal substrate) according to this embodiment is a Ga2O3 single crystal substrate having a circular main surface. The diameter of the Ga2O3 single crystal substrate is 100 mm or more. The thickness of the Ga2O3 single crystal substrate is 600 μm or more. The Ga2O3 single crystal substrate contains boron. The boron concentration is 4 ppm by mass or more and 200 ppm by mass or less, as determined by glow discharge mass spectrometry. A Ga2O3 single crystal substrate having these characteristics can suppress the occurrence of cracks.

[0027] <Diameter and Thickness> As described above, the diameter of the GaO single crystal substrate is 100 mm or more. In particular, the diameter of the GaO single crystal substrate is preferably 99.5 mm or more and 152.5 mm or less. Specifically, such a GaO single crystal substrate is preferably a GaO single crystal substrate having a diameter of 100 mm or 150 mm, in other words, a GaO single crystal substrate having a diameter of 4 inches or 6 inches. This allows the large-diameter GaO single crystal substrate to have the characteristic of being less likely to crack.

[0028] As described above, the thickness of the GaO single crystal substrate is 600 μm or more. In particular, the thickness of the GaO single crystal substrate is preferably 650 μm or more and 700 μm or less. This allows a GaO single crystal substrate having a commonly used thickness to have the characteristic of being less susceptible to cracking. The diameter of the GaO single crystal substrate is determined based on the circular shape before the formation of the orientation flat (hereinafter also referred to as "OF"), index flat (hereinafter also referred to as "IF"), etc., even if the main surface does not have a geometrically circular shape due to the influence of such factors as orientation flats (hereinafter also referred to as "OF") and index flats (hereinafter also referred to as "IF"). Furthermore, as described above, the diameter of the GaO single crystal substrate can be measured using a conventionally known outer diameter measuring instrument such as a vernier caliper. The thickness of the GaO single crystal substrate can be measured using a non-contact thickness measuring instrument (product name (model): "TAP-2H-200XY", manufactured by COMS Co., Ltd.). The positioning accuracy of this measuring instrument is 25 μm. The display resolution of this measuring instrument is 0.01 μm. The repeatability of this measuring instrument is 0.01 μm. The measuring instrument used to measure the thickness of the GaO single crystal substrate is not limited to the above measuring instrument, and other measuring instruments can also be used as long as they have equivalent or higher positioning accuracy, display resolution, and repeatability. In this specification, the "thickness of the GaO single crystal substrate" means the thickness at the center of the main surface of the GaO single crystal substrate.

[0029] <Major Surface> (Circular Shape) As described above, the GaO single crystal substrate has a circular major surface. In this specification, the term "circular shape" used to describe the shape of the major surface includes not only a geometrically circular shape but also a shape in which the major surface does not form a geometrically circular shape due to the formation of at least one of a notch, OF, or IF on the periphery of the major surface, as described above. Here, "a shape in which the major surface does not form a geometrically circular shape" refers to a shape in which, among line segments extending from any point on the periphery of the major surface to the center of the main surface, the lengths of line segments extending from any point on the notch, OF, or IF to the center of the main surface are shorter. Furthermore, "a shape in which the main surface does not form a geometrically circular shape" also includes a shape in which the lengths of all line segments extending from any point on the periphery of the main surface to the center of the main surface are not necessarily the same due to the shape of the GaO single crystal used as the raw material for the GaO single crystal substrate. In this case, the center of the main surface refers to the position of the center of gravity, and the diameter of the GaO single crystal substrate refers to the length of the longest line segment that extends from any point on the outer periphery of the GaO single crystal substrate, passing through the center of the main surface, to another point on the outer periphery.

[0030] (The (001) plane of the GaO single crystal) The main surface is preferably the (001) plane of the GaO single crystal. GaO single crystal substrates having the (001) plane of the GaO single crystal as the main surface are known to be susceptible to cracks and other defects caused by external stress, as the (001) plane generally has strong cleavage properties. In other words, this embodiment can suppress the occurrence of cracks in GaO single crystal substrates having the (001) plane of the GaO single crystal as the main surface.

[0031] In this disclosure, the crystal plane of the main surface has an accuracy error of ±0.5°. For example, when the main surface is referred to as the "(001) plane" of a GaO single crystal, this means that the main surface may be a (001) just plane, or may be a plane having an off-angle of -0.5 to +0.5° from the (001) plane. The off-angle from the (001) plane of the main surface of a GaO single crystal substrate can be measured using a conventionally known crystal orientation measurement device (for example, the product name (product number) "2991G2" manufactured by Rigaku Corporation).

[0032] (Center and Outer Periphery) The main surface preferably has a center portion including the center and an outer periphery surrounding the center portion. The outer periphery is preferably a chamfered region. FIG. 1 is an explanatory diagram illustrating the main surface of a gallium trioxide single crystal substrate according to this embodiment. For example, in the GaO single crystal substrate 100 shown in FIG. 1, the main surface 10 has a center portion 11 including the center and an outer periphery 12 surrounding the periphery of the center portion 11. The center portion 11 is a region of the GaO single crystal substrate 100 where epitaxial layers are deposited to form, for example, an electronic device. The outer periphery 12 is a chamfered region. By chamfering the outer periphery 12, the GaO single crystal substrate 100 can reduce cracking and chipping at the outer edge of the outer periphery 12 during handling. A conventionally known method can be used to chamfer the outer periphery 12.

[0033] The central portion 11 preferably has a circular shape. This makes it possible to express the length from the center O of the main surface 10 to the boundary 13 between the central portion 11 and the outer peripheral portion 12 by a fixed numerical value "r" of 1, as described below. Here, the "circular shape" representing the shape of the central portion 11 includes not only a geometric circular shape but also a shape in which a geometric circular shape is not formed, such as an approximately circular shape, due to chamfering or the like of the outer peripheral portion 12. In this case, the length r from the center O of the main surface 10 to the boundary 13 between the central portion 11 and the outer peripheral portion 12 refers to the length of the shortest line segment among the line segments extending from the center O of the main surface 10 to the boundary 13 between the central portion 11 and the outer peripheral portion 12. The shape of the central portion 11 may be a polygonal shape, such as a triangle, a rectangle, or a hexagon.

[0034] The width of the outer periphery 12, that is, the length from the outer edge of the outer periphery 12 to the boundary 13 between the central portion 11 and the outer periphery 12, is preferably 2 to 5 mm. This is because the region of the GaO single crystal substrate 100 having the width of the outer periphery 12 described above is known to have residual processing strain during chamfering, large variations in the number of dislocations between substrates, and poor flatness, and is therefore not normally used as a material for semiconductor devices.

[0035] The central portion 11 and the peripheral portion 12 are distinguished by the difference in thickness of the GaO single crystal substrate 100 at those portions. The thickness of the GaO single crystal substrate 100 at the peripheral portion 12 is less than 99% of the thickness of the GaO single crystal substrate 100 at the central portion 11. In other words, the peripheral portion 12 refers to the region that has been chamfered as described above, and the thickness at this region is less than 99% of the thickness at the central portion 11. For example, if the thickness at the central portion 11 is 675 μm, the thickness at the peripheral portion 12 will be 668 μm or less. The thicknesses at the central portion 11 and the peripheral portion 12 can be measured using the non-contact thickness measuring device described above. The measuring device used to measure the thicknesses of the central portion 11 and the peripheral portion 12 is not limited to the above measuring device, and other measuring devices can also be used as long as they have equivalent or higher positioning accuracy, display resolution, and repeatability. In this specification, the "thickness of the GaO single crystal substrate 100 at the central portion 11" refers to the thickness at the center O of the main surface 10 of the GaO single crystal substrate 100. This allows the length "r" from the center O of the main surface 10 to the boundary 13 between the central portion 11 and the outer peripheral portion 12 to be determined as a specific numerical value (unit: mm).

[0036] (Nanoindentation Hardness) In the GaO single crystal substrate, the nanoindentation hardness measured at five locations on the main surface according to a nanoindentation method using a Berkovich indenter is preferably 14.8 GPa or more and 22.0 GPa or less under the conditions that a maximum load of 10 mN is applied and the load is applied so that the crossing angle between one side of the indentation and the direction of the

[100] direction of the gallium trioxide single crystal projected onto the main surface is 0° or more and 10° or less. When the length from the center of the main surface to the boundary between the central portion and the outer periphery is defined as r, two mutually perpendicular axes on the main surface that pass through the center are defined as the X-axis and the Y-axis, and the Y-axis is defined as the b-axis of the gallium trioxide single crystal, the five coordinates (X, Y) defined by the X-axis and the Y-axis are preferably (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)). The units of r and X and Y in the coordinates (X, Y) are preferably mm. It is more preferable that the nanoindentation hardness measured at five locations on the main surface is 15.0 GPa or more and 21.0 GPa or less.

[0037] Figure 2 is an explanatory diagram illustrating five measurement points set on the main surface of the digallium trioxide single crystal substrate of Figure 1 to determine the nanoindentation hardness. Hereinafter, with reference to Figure 2, a method for measuring the nanoindentation hardness measured at five points on the main surface 10 according to the nanoindentation method using a Berkovich indenter will be described. The above measurement method can be performed, for example, using a nanoindenter (product name: "Bruker Hysitron TI980 Triboindenter", manufactured by Bruker Japan Co., Ltd.).

[0038] 1) Preliminary Measurement First, a preliminary measurement is performed on the GaO single crystal substrate 100 to ensure that a load can be applied so that the intersection angle between one side of the Berkovich indentation and the direction of the

[100] direction of the GaO single crystal projected onto the main surface is between 0° and 10°. First, the GaO single crystal substrate 100 is fixed to the sample stage of the nanoindenter. Next, the GaO single crystal substrate 100 on the sample stage is observed using an optical system provided in the nanoindenter, and an arbitrary position, for example, in the center 11 on the main surface 10, is designated as the measurement point. To facilitate the main measurement described below, it is preferable to designate a measurement point other than the five points on the main surface 10 (i.e., other than the five coordinates (X, Y) of (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5))). Furthermore, a Berkovich indenter is moved to the location to be measured, and an indentation test is performed with a maximum load of 10 mN, after which the GaO single crystal substrate 100 is removed from the sample stage. At this time, an indentation of the Berkovich indenter is formed at the location to be measured, making it possible to determine the intersection angle between one side of the indentation and the

[100] direction of the GaO single crystal constituting the GaO single crystal substrate 100. Here, the intersection angle can be determined by a conventionally known method.

[0039] 2) Main Measurement Next, a main measurement is performed to determine the nanoindentation hardness. If the crossing angle determined in the preliminary measurement is between 0° and 10°, the GaO single crystal substrate 100 is fixed to the sample stage in the same orientation as in the preliminary test. If the crossing angle determined in the preliminary measurement exceeds 10°, the orientation of the GaO single crystal substrate 100 is adjusted so that the crossing angle is between 0° and 10°, and the GaO single crystal substrate 100 is then fixed to the sample stage. Furthermore, the GaO single crystal substrate 100 on the sample stage is observed using an optical system provided in the nanoindenter, and one of the five coordinates (X, Y) on the main surface 10 (for example, (0, 0)) is designated as the measurement point. Next, the Berkovich indenter is moved to the measurement point (for example, (0,0)), and after an indentation test is performed with a maximum load of 10 mN, the GaO single crystal substrate 100 is removed from the sample stage. At this time, an indentation mark of the Berkovich indenter is formed at the measurement point. Therefore, based on the indentation mark, the area (mm ) of contact between the Berkovich indenter and the GaO single crystal substrate 100 when the maximum load of 10 mN is applied can be calculated. 2 ) can be calculated, and the area (mm 2 The nanoindentation hardness at the measurement point (for example, (0,0)) can be obtained by dividing the maximum load of 10 mN by the maximum load of 10 mN.

[0040] Next, the remaining coordinates (X, Y) of the above-mentioned five locations on main surface 10 (for example, (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)) are specified as measurement locations. Thereafter, an indentation test is performed in the same manner as when (0, 0) is specified as the measurement location, and predetermined calculations are performed, thereby making it possible to determine the nanoindentation hardness at the remaining coordinates (X, Y) of the above-mentioned five locations on main surface 10.

[0041] Here, the nanoindentation hardness is the indentation hardness determined by performing an indentation test with a maximum load of 10 mN. When performing an indentation test with a maximum load of 10 mN, it is thought that the Berkovich indenter is pressed relatively deep into the GaO single crystal substrate to form an indentation mark. Therefore, the nanoindentation hardness can be considered to reflect the indentation hardness inside the GaO single crystal substrate.

[0042] <Boron (B)> As described above, the GaO single crystal substrate contains boron (B). The B concentration is 4 ppm by mass or more and 200 ppm by mass or less in glow discharge mass spectrometry (GDMS). If the B concentration is less than 4 ppm by mass in GDMS, the strength improvement effect of B may not be sufficient to resist external stresses applied during processing, transportation, etc. If the B concentration is more than 200 ppm by mass in GDMS, B may cluster in the GaO single crystal or residual strain may become too large due to thermal history during crystal growth, making the GaO single crystal substrate more susceptible to cracking. The B concentration is preferably 5 ppm by mass or more and 100 ppm by mass or less in GDMS. The concentration of B is more preferably 50 ppm by mass or more and 100 ppm by mass or less in GDMS.

[0043] The inventors of the present invention believe that the reason why the GaO single crystal substrate containing boron at the above-mentioned concentration has appropriate hardness and improved strength, thereby suppressing cracking, is as follows. Specifically, when B is contained in the GaO single crystal at the above-mentioned concentration, it is believed that B can exist in an isolated substitutional form at Ga sites in the crystal lattice constituting the GaO single crystal. In this case, the solid-solution strengthening effect of B is expected. In particular, it is believed that a B concentration of 4 ppm by mass or more can provide sufficient strength to resist external stresses applied during processing and transportation, based on the above-mentioned effect. On the other hand, it is believed that a B concentration of 200 ppm by mass or less can prevent B from clustering in the GaO single crystal or can prevent excessive strength from increasing, thereby preventing excessive residual strain caused by the thermal history during crystal growth. Therefore, it is believed that B can fully exert its effect of mitigating the fragility of the GaO single crystal substrate.

[0044] (Glow Discharge Mass Spectrometry (GDMS)) A method for measuring the B concentration in the GaO single crystal substrate using glow discharge mass spectrometry (GDMS) is described below. GDMS is a technique in which a glow discharge plasma is generated using the analytical sample as the cathode in a high-purity argon atmosphere, the surface of the analytical sample is sputtered within the plasma, and the ionized constituent elements of the analytical sample are measured using a mass spectrometer. This technique enables qualitative and quantitative analysis of impurity elements, including B, other than Ga and O contained in the GaO single crystal substrate. Either a flat cell or a pin-shaped cell is used as the ion source for the GDMS. The pin-shaped cell is applicable to analytical samples that can be formed into strips approximately 2 mm square and 20 mm long. Specifically, it is used when analyzing Si single crystals, gallium arsenide (GaAs) single crystals, indium phosphide (InP) single crystals, and other materials that can be prepared by cleavage. The flat cell can be applied to analytical samples that can be formed into a disk shape with a diameter of about 10 mm, for example, when analyzing polycrystalline bodies. In either case, it is preferable to select either a flat cell or a pin-shaped cell as the GDMS ion source from the viewpoint of avoiding contamination of the analytical sample with external impurity elements. When the GaO single crystal substrate has a (001) plane as the major surface, an analytical sample can be prepared by cleaving it in one direction. Therefore, it is preferable to prepare an analytical sample having a pin-shaped cell shape with a cleavage plane in the longitudinal direction from the GaO single crystal substrate and use this as the GDMS ion source.

[0045] The GDMS can be performed, for example, as follows. First, a GaO single crystal substrate is obtained by the manufacturing method described below. The GaO single crystal substrate is then cleaved to obtain a GaO analysis sample in the form of a strip measuring 2 mm square and 20 mm long. The non-cleavage direction is cut using a known means such as a precision hand grinder. This is then placed on the sample placement section attached to the apparatus described below. It is preferable to clean the sample placement section in accordance with a conventional method to prevent and remove foreign matter, and then pre-sputter for 60 minutes.

[0046] Next, GDMS can be performed on the GaO analysis sample placed on the sample placement surface under the following conditions. Regarding B, an element other than Ga and O in the GaO analysis sample, a semi-quantitative value can be calculated by correcting the ion intensity ratio between Ga and B with the relative sensitivity factor (RSF). The relative sensitivity factor can be calculated using the value built into the software provided with the following instrument: Instrument: Glow discharge mass spectrometer (product name (product number): VG-9000, manufactured by VG Elemental); Ion source: Pin cell (cooled with liquid nitrogen during analysis); Discharge area: 10 mm diameter; Discharge gas: High-purity argon (6N grade); Discharge conditions: 2 mA, 1 kV (constant current mode); Detector: Faraday cup and multiplier; Mass resolution: 4000 m / Δm or higher (high resolution mode).

[0047] By analyzing the GaO analysis sample in the above manner, it is possible to qualitatively and quantitatively determine the B contained in the GaO single crystal substrate. The lower limit of detection of the GDMS concentration is preferably 0.01 mass ppm.

[0048] <Rhodium (Rh) and Iridium (Ir)> The GaO single crystal substrate may contain both or either of rhodium (Rh) and iridium (Ir). In this case, the Rh concentration and the Ir concentration are preferably 0.1 mass ppm or less in GDMS. It is more preferable that the Rh concentration and the Ir concentration are 0.01 mass ppm or less in GDMS. The lower limits of the Rh concentration and the Ir concentration are such that they are not detectable in GDMS. If the Rh and Ir concentrations are within the above-mentioned concentration ranges, adverse effects on electrical characteristics can be prevented.

[0049] The Rh and Ir are known as elements that may be contained in the GaO single crystal substrate. Meanwhile, when the GaO single crystal substrate is manufactured using the GaO single crystal substrate manufacturing method described below, the Rh concentration and the Ir concentration can easily be set to 0.1 mass ppm or less in GDMS by using a crucible made of platinum or pyrolytic boron nitride. The GaO single crystal substrate can suppress the occurrence of cracks and, due to the low Rh and Ir concentrations, can have good electrical properties.

[0050] (Specific Resistivity) In the GaO single crystal substrate according to this embodiment, the specific resistance of the gallium trioxide single crystal substrate measured at 25° C. by Hall measurement using the Van der Pauw method is 1.0×10 -3 Specifically, the resistivity of the GaO single crystal substrate is preferably 1.0×10 Ω·cm or more and 2.0 Ω·cm or less. Specifically, the resistivity of the GaO single crystal substrate is preferably 1.0×10 Ω·cm or more and 2.0 Ω·cm or less at 25° C. in a Hall measurement by the Van der Pauw method. -3 It is preferable that the resistivity is 1.0×10 or more and 2.0 Ω cm or less. This allows the GaO single crystal substrate to have good electrical properties as an n-type (electron-donating) GaO single crystal substrate, which can contribute to the formation of electronic devices. In the GaO single crystal substrate, the resistivity is 1.0×10 or more and 2.0 Ω cm or less. -3 If the resistivity is less than Ω cm, when a Schottky barrier diode is fabricated using the GaO single crystal substrate, the reverse current increases, the breakdown voltage deteriorates, and thermal runaway may occur. If the resistivity exceeds 2.0 Ω cm, the forward voltage may be high and the efficiency may be low. The resistivity is 5.0 × 10 -3 Ω・cm or more 1.0×10 -１ It is preferably Ω·cm or less.

[0051] The procedure for determining the resistivity will be described in detail below with reference to FIGS. 1 and 3. FIG. 3 is an explanatory diagram illustrating a Hall measurement sample prepared using the center of a gallium trioxide single crystal substrate according to this embodiment, in order to measure the resistivity, carrier concentration, and electron mobility of the substrate. First, as shown in FIG. 1, a GaO single crystal substrate 100 to be measured is obtained by applying a conventionally known processing method to a GaO single crystal obtained, for example, according to the manufacturing method described below. A rectangular slice 11a (e.g., 600 μm thick) measuring 10 mm long x 10 mm wide is prepared from the center of the GaO single crystal substrate 100, with its center (e.g., the center of the main surface 10) at its center O. Next, as shown in FIG. 3, gold electrodes 21 are formed on the four corners of the rectangular slice 11a (the surface to be measured), thereby obtaining a Hall measurement sample. The shape of the electrode 21 is not limited to the rectangular shape shown in the figure, but may be a sector or a circle. The resistivity can be determined by applying Hall measurement by the Van der Pauw method to the rectangular piece 11a provided with such electrodes 21 in an atmosphere at 25° C. In this specification, the resistivity obtained by using the rectangular piece as the measurement object is defined as the resistivity of the GaO single crystal substrate measured at 25° C. in Hall measurement by the Van der Pauw method.

[0052] (Carrier Concentration and Electron Mobility) In this embodiment, the carrier concentration of the GaO single crystal substrate measured at 25° C. by the Van der Pauw Hall measurement is 4.0×10 17 cm -3 1.4 x 10 19 cm -3 The electron mobility of the GaO single crystal substrate measured at 25° C. by the Van der Pauw Hall method is preferably 0.2 cm or less. 2 / V・s or more 15000cm 2 At the same time, the GaO single crystal substrate preferably has a carrier concentration of 4.0×10 17 cm -3If the carrier concentration is less than 1.4×10, there is a risk that loss will increase when a Schottky barrier diode is fabricated using the GaO single crystal substrate. 19 cm -3 If the value exceeds this range, when a Schottky barrier diode is fabricated from the GaO single crystal substrate, the reverse current increases, the breakdown voltage deteriorates, and thermal runaway may occur. In the GaO single crystal substrate, the carrier concentration and electron mobility can be controlled within the above-mentioned ranges to obtain a preferable resistivity within the above-mentioned range.

[0053] In particular, the carrier concentration is 4.5×10 17 cm -3 Above 4.0 x 10 18 cm -3 More preferably, the electron mobility is 10 cm or less. 2 / V・s or more 1500cm 2 / V·s or less. This allows the n-type Ga2O3 single crystal substrate to have good electrical properties that enable it to be used for various electronic devices. The carrier concentration and electron mobility can both be determined by the same method as the resistivity measurement method described above.

[0054] <Applications> The GaO single crystal substrate according to this embodiment has the above-mentioned properties and can be used as a substrate for forming optical devices and electronic devices. In particular, the GaO single crystal substrate has good electrical properties and is therefore preferably used as a substrate for forming electronic devices.

[0055] [Method for Manufacturing Digallium Trioxide Single Crystal] The method for manufacturing digallium trioxide single crystal (GaO single crystal) according to this embodiment is preferably a method for manufacturing a GaO single crystal constituting a GaO single crystal substrate having a circular main surface as described above. For example, the method for manufacturing the GaO single crystal is carried out in an air atmosphere and can include the following steps: preparing a single crystal growth apparatus (hereinafter also referred to as "GaO single crystal growth apparatus") including at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; placing a seed crystal consisting of the GaO single crystal at the bottom of the crucible and disposing a lump or powder of digallium trioxide polycrystal (GaO polycrystal), an n-type dopant, and boron oxide (BO) above the seed crystal in the crucible. the crucible is made of platinum. The gallium trioxide single crystal has a boron concentration of 4 ppm to 200 ppm by mass in GDMS. This method for producing a GaO single crystal having these characteristics can be used to produce a GaO single crystal substrate that can suppress cracking.

[0056] Furthermore, the GaO single crystal manufacturing method can also perform the above-described steps under a nitrogen atmosphere. That is, the GaO single crystal manufacturing method is performed under a nitrogen atmosphere and can include the following steps: preparing a single crystal growth apparatus (hereinafter also referred to as "GaO single crystal growth apparatus") including at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; placing a seed crystal consisting of the GaO single crystal at the bottom of the crucible and placing chunks or powders of GaO polycrystal, an n-type dopant, and BO above the seed crystal in the crucible; The method includes the steps of: heating the crucible with a heating device to melt a portion of the seed crystal and obtain a solution in which GaO derived from the portion of the seed crystal and the GaO polycrystal at a first concentration and the n-type dopant at a second concentration are dissolved in the BO; contacting the solution with the remainder of the seed crystal; and growing a crystal from the solution on the remainder of the seed crystal to obtain a GaO single crystal. In this embodiment, the crucible is made of pyrolytic boron nitride (pBN). The boron concentration in the digallium trioxide single crystal is 4 ppm by mass or more and 200 ppm by mass or less in GDMS. Even with this method for producing a GaO single crystal, a GaO single crystal capable of suppressing cracking can be obtained.

[0057] Fig. 4 is a flowchart showing an example of a method for manufacturing a gallium trioxide single crystal substrate, including a method for manufacturing a gallium trioxide single crystal according to this embodiment. The method for manufacturing a GaO single crystal according to this embodiment is preferably included in a method for manufacturing a GaO single crystal substrate, for example, as GaO single crystal manufacturing step S100 shown in the flowchart of Fig. 4. As shown in Fig. 4, the method for manufacturing a GaO single crystal substrate according to this embodiment includes a GaO single crystal manufacturing step S100 and a GaO single crystal substrate manufacturing step S200. Of these, the GaO single crystal manufacturing step S100 includes a step (first step: preparation step S110) of preparing a GaO single crystal growth apparatus including at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible. In the preparation step S110, in addition to the GaO single crystal growth apparatus, it is preferable to also prepare a seed crystal consisting of the GaO single crystal, a block or powdered GaO polycrystal, an n-type dopant, and solid BO. The GaO single crystal production step S100 includes a step of placing the seed crystal at the bottom of the crucible, and placing the GaO polycrystal, the n-type dopant, and the BO in the crucible above the seed crystal (second step: raw material placement step S120). The GaO single crystal production process S100 includes a step of melting a portion of the seed crystal by heating the crucible with the heating device, obtaining a solution in which GaO originating from the portion of the seed crystal and the GaO polycrystal is dissolved at a first concentration and the n-type dopant is dissolved at a second concentration in the BO, and contacting the solution with the remainder of the seed crystal (third step: raw material melting step S130). The GaO single crystal production process S100 further includes a step of growing a crystal from the solution on the remainder of the seed crystal to obtain a GaO single crystal (fourth step: GaO single crystal growth step S140). The atmosphere in which the GaO single crystal growth step S140 is performed is either a nitrogen atmosphere or an air atmosphere, depending on the material of the crucible.

[0058] The present inventors have focused on a method for growing GaO single crystals to form GaO single crystal substrates having the above-mentioned properties. The method involves dissolving GaO in liquid BO in a crucible, then cooling the resulting mixture to precipitate GaO single crystals due to the difference in solubility between BO and GaO. They discovered that a small amount of BO is incorporated into the precipitated GaO single crystals. Furthermore, they discovered that when GaO single crystal substrates are obtained from GaO single crystals containing a predetermined concentration of B, the occurrence of cracks in the GaO single crystal substrates is suppressed, leading to the development of a GaO single crystal manufacturing method according to this embodiment.

[0059] In this specification, the term "n-type dopant" refers to an oxide of an element that, when contained as a dopant in a GaO single crystal substrate, can impart n-type (electron-donating) conductivity to the GaO single crystal substrate. Examples of elements that can impart n-type (electron-donating) conductivity to the GaO single crystal substrate include tin (Sn), silicon (Si), and germanium (Ge).

[0060] An overview of the GaO single crystal growth apparatus and the GaO single crystal production step S100 will be described below with reference to Figures 4 and 5. Figure 5 is a schematic diagram illustrating a production apparatus used in the GaO single crystal production method according to this embodiment. In the GaO single crystal production method (GaO single crystal production step S100) according to this embodiment, for example, the GaO single crystal growth apparatus shown in Figure 5 is used.

[0061] 5, the GaO single crystal growth apparatus includes the above-described crucible 2, a crucible-holding stage 8 for holding the crucible 2, a lower shaft 9 for supporting the crucible 2 and the crucible-holding stage 8, and a heating device 1 for heating the crucible 2. The GaO single crystal growth apparatus further includes a lid 3 for sealing the crucible 2. The lid 3 has the function of preventing B2O3 from evaporating to the outside due to heating from a solution 52 (hereinafter also referred to as "B2O3-Ga2O3 solution 52") in which Ga2O3 and an n-type dopant are dissolved in B2O3 in the crucible 2 in the GaO single crystal growth step S140. The GaO single crystal growth apparatus has nozzles for introducing GaO polycrystals and an n-type dopant into the crucible 2. The nozzles consist of a first nozzle 41 and a second nozzle 42, each of which penetrates the lid 3 from the outside so that its tip is positioned inside the crucible 2. The first nozzle 41 functions as a supply path for supplying GaO polycrystals into the crucible 2 from the outside. The second nozzle 42 functions as a supply path for supplying the n-type dopant into the crucible 2 from the outside.

[0062] In the GaO single crystal manufacturing method according to this embodiment, in addition to the GaO single crystal growth apparatus described above, a chamber (not shown) may be provided to accommodate the crucible 2, lid 3, first nozzle 41, second nozzle 42, crucible-holding stage 8, lower shaft 9, and heating device 1, in order to perform the GaO single crystal growth step S140 in a nitrogen atmosphere. The dimensions and materials of the chamber are not particularly limited, as long as they are large enough to accommodate the GaO single crystal growth apparatus and the like and are capable of providing a nitrogen atmosphere inside. Furthermore, if the chamber's sidewalls have good thermal transmittance, the heating device of the GaO single crystal growth apparatus can be located outside the chamber.

[0063] (Heating Device) As shown in FIG. 5, in a GaO single crystal growth apparatus, a heating device 1 is disposed to surround the outer periphery of the crucible 2 for the purpose of heating the crucible 2. The heating device 1 may be, for example, a conventionally known electric heater (hereinafter simply referred to as "heater"). For example, two heaters are provided, and these two heaters are disposed to surround the outer periphery of the crucible 2. The heater output may be controlled independently for each heater. In particular, as shown in FIG. 5, the heater may be divided into multiple sections perpendicular to the axis of the crucible 2, resulting in a multi-stage configuration. In this case, it is preferable to independently control the heater output for each of the multiple sections. This allows the temperature of the contents in the crucible 2 to be precisely adjusted along the axial direction of the crucible 2. For example, by independently controlling the heater output for each of the multiple stages, the growth rate of the Ga2 O3 single crystal grown in the crucible 2 can be stabilized.

[0064] (Crucible) As shown in FIG. 5, the crucible 2 in the GaO single crystal growth apparatus is cylindrical. A seed crystal 51 consisting of a GaO single crystal is accommodated at the bottom of the crucible 2. Furthermore, chunks or powdered GaO polycrystals, an n-type dopant, and solid BO are accommodated on the seed crystal 51. In other words, the crucible 2 functions to hold the seed crystal 51, the GaO polycrystals, the n-type dopant, and BO. Additionally, the crucible 2 functions to grow a GaO single crystal on the seed crystal 51 by precipitating the GaO single crystal from a BO-GaO solution 52 inside the crucible 2, as described below.

[0065] Various materials that can withstand the temperature of the BO-GaO solution 52 can be used for the crucible 2. Examples of materials that can be used for the crucible 2 include platinum, platinum alloys containing rhodium or iridium, and pBN. In particular, when the GaO single crystal growth step S140 is performed in an air atmosphere, the crucible 2 is made of platinum. This allows the rhodium and iridium concentrations in the GaO single crystal obtained by the above manufacturing method to be zero or extremely low (e.g., 0.1 ppm by mass or less). Furthermore, when the GaO single crystal growth step S140 is performed in a nitrogen atmosphere, the crucible 2 is made of pBN. This reduces the manufacturing cost of the GaO single crystal growth apparatus. The rhodium and iridium concentrations in the GaO single crystal obtained by the above manufacturing method can also be zero or extremely low (e.g., 0.1 ppm by mass or less). The inner diameter of the crucible 2 depends on the diameter of the Ga2O3 single crystal to be produced, but can be set to, for example, 90 mm or more and 165 mm or less.

[0066] Although not shown, the GaO single crystal growth apparatus may be equipped with a thermocouple capable of measuring the temperature of the crucible 2 heated by the heating device 1. A plurality of thermocouples may be arranged outside the crucible 2 along the axial direction. For example, a known temperature monitor may be used as the thermocouple.

[0067] (Lid) The lid 3 is not particularly limited, but may be made of, for example, pBN or calcia (CaO) stabilized zirconia. The lid 3 is placed on top of the crucible 2 to prevent B2O3 in the B2O3-Ga2O3 solution 52 in the crucible 2 from evaporating to the outside due to heating in the Ga2O3 single crystal growth step S140. The lid 3 has holes into which nozzles (first nozzle 41 and second nozzle 42) are inserted.

[0068] (First Nozzle and Second Nozzle) The first nozzle 41 and the second nozzle 42 are not particularly limited and may be made of, for example, pBN-coated carbon or sapphire. The first nozzle 41 and the second nozzle 42 penetrate the lid 3 through the holes and have their tips positioned inside the crucible 2, thereby communicating the inside and outside of the crucible 2. This allows the first nozzle 41 to function as a supply path for supplying GaO from the outside into the crucible 2. The second nozzle 42 can function as a supply path for supplying an n-type dopant from the outside into the crucible 2. By supplying GaO polycrystals or an n-type dopant to the BO-GaO solution 52 in the crucible 2 through the first nozzle 41 and the second nozzle 42, the concentrations of GaO polycrystals and the n-type dopant in the BO-GaO solution 52 can be kept constant.

[0069] (Crucible-holding stage) The GaO single crystal growth apparatus includes a crucible-holding stage 8 that holds the crucible 2. The crucible-holding stage 8 contacts the bottom of the crucible 2 to hold the crucible 2. The crucible-holding stage 8 may have a cylindrical appearance. The material of the crucible-holding stage 8 is not particularly limited, but may be, for example, quartz, alumina, or silicon carbide. The outer diameter of the crucible-holding stage 8 depends on the diameter of the crucible 2 it supports, but is, for example, 75 mm or more and 200 mm or less.

[0070] (Lower Shaft) The lower shaft 9 supports the crucible 2 and the crucible-holding stage 8 by supporting the crucible-holding stage 8 from below. The lower shaft 9 may be, for example, rod-shaped and circular or rectangular in horizontal cross section. Materials that can be used for the lower shaft 9 include molybdenum, carbon, and silicon carbide. Each step included in the GaO single crystal manufacturing method (GaO single crystal manufacturing process S100) will be described below. First, the GaO single crystal manufacturing process S100, which is performed in an air atmosphere, will be described.

[0071] <GaO Single Crystal Production Process S100> (First Step: Preparation Step S110) As shown in FIG. 4, the GaO single crystal production process S100 begins with the preparation step S110. The preparation step S110 is a step of preparing a GaO single crystal growth apparatus including at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible. In the preparation step S110, in addition to the GaO single crystal growth apparatus described above, a seed crystal 51, bulk or powdered GaO polycrystal, an n-type dopant, and solid BO are preferably also prepared. The seed crystal 51 is made of a GaO single crystal as described above. The n-type dopant is preferably prepared as, for example, tin oxide (SnO), silicon oxide (SiO), or the like. The seed crystal 51, bulk or powdered GaO polycrystal, n-type dopant, and solid BO may be prepared by purchasing commercially available products. The crucible 2 constituting the GaO single crystal growth apparatus is made of platinum.

[0072] (Second Step: Raw Material Accommodation Step S120) Next, in the GaO single crystal production process S100, the raw material accommodation step S120 is performed. The raw material accommodation step S120 is a step of accommodating the seed crystal at the bottom of the crucible, and accommodating the GaO polycrystal, the n-type dopant, and the BO above the seed crystal in the crucible. The purpose of the raw material accommodation step S120 is to accommodate various raw materials for crystal growth using a GaO single crystal growth apparatus in the crucible 2. In the raw material accommodation step S120, first, a seed crystal 51 made of a GaO single crystal is accommodated at the bottom of the crucible 2. Next, multiple chunks or powdered GaO polycrystals are accommodated and stacked on the seed crystal 51 accommodated in the crucible 2. Furthermore, an n-type dopant and solid BO are accommodated. The amount of n-type dopant contained in the crucible 2 is preferably determined in advance so that the dopant concentration in the GaO single crystal to be grown is appropriate. In this way, an n-type GaO single crystal substrate is obtained from the GaO single crystal obtained by the GaO single crystal manufacturing process S100. The amount of n-type dopant contained in the crucible 2 is, for example, such that the atomic concentration of Sn, Si, or Ge as a dopant is 2.0 × 10 in the GaO single crystal substrate. 19 cm －3 or less (for example, 1.0 × 10 17 cm -3 Above 2.0 x 10 19 cm -3 It is preferable to adjust the temperature so that the temperature satisfies the following conditions:

[0073] (Third Step: Raw Material Melting Step S130) Next, in the GaO single crystal manufacturing process S100, the raw material melting step S130 is performed. The raw material melting step S130 is a step of heating the crucible with the heating device to melt a portion of the seed crystal and obtain a solution in which GaO derived from the portion of the seed crystal and the GaO polycrystal at a first concentration and the n-type dopant at a second concentration are dissolved in the BO, and the solution is brought into contact with the remainder of the seed crystal. The purpose of the raw material melting step S130 is to perform crystal growth using a GaO single crystal growth apparatus by heating the crucible 2 with the heating device 1 to melt a portion of the seed crystal 51 and obtain a BO-GaO solution 52 in which GaO originating from the portion of the seed crystal 51 and the GaO polycrystal is dissolved at a first concentration and the n-type dopant is dissolved at a second concentration in BO. The purpose is to further bring the BO-GaO solution 52 into contact with the remainder of the seed crystal 51. This allows a GaO single crystal to grow on the remainder of the seed crystal 51 in the next step, the GaO single crystal growth step S140. Specifically, in the raw material melting step S130, the crucible 2 containing the seed crystal 51, the GaO polycrystal, the n-type dopant, and the BO is supported by the crucible-holding stage 8. Thereafter, current is supplied to the heating device 1 to heat the crucible 2. As a result, the solid B2O3 melts and becomes liquid B2O3. As the B2O3 temperature rises above a predetermined temperature (approximately 1000°C), the Ga2O3 polycrystal gradually dissolves in the B2O3. The n-type dopant also dissolves in the B2O3. Subsequently, a portion of the seed crystal 51 also melts and dissolves in the B2O3. As a result, the remainder of the seed crystal 51 comes into contact with the B2O3-Ga2O3 solution 52.

[0074] Here, the first concentration, i.e., the concentration of GaO in BO in the BO-GaO solution 52, is preferably 20 to 40 mass %. The concentration of GaO that becomes soluble in BO depends on the temperature of the BO. Therefore, in the raw material melting step S130, the BO-GaO solution 52 is preferably heated to 1200 to 1500°C. In this case, the second concentration, i.e., the concentration of the n-type dopant in BO in the BO-GaO solution 52, may be any concentration that is used in conventionally known GaO single crystal manufacturing methods, and is preferably, for example, 2 to 300 mass ppm. The first and second concentrations can be measured in the same manner as the GaO concentration and n-type dopant concentration measured in the analysis step described below.

[0075] (Fourth Step: GaO Single Crystal Growth Step S140) Next, in the GaO single crystal production step S100, the GaO single crystal growth step S140 is carried out. The GaO single crystal growth step S140 is a step of obtaining a GaO single crystal by growing a crystal from the solution on the remaining portion of the seed crystal. In the GaO single crystal growth step S140, for example, the crucible 2 is gradually lowered along its axis (toward the bottom of the crucible 2) relative to the heating device 1, thereby forming a temperature gradient in the crucible 2 such that the temperature on the seed crystal 51 side is low and the temperature on the BO-GaO solution 52 side is high. This allows continuous crystal growth by precipitating GaO single crystals due to the difference in solubility between BO and GaO in the portion of the BO-GaO solution 52 that contacts the seed crystal 51. In this case, to obtain a GaO single crystal as a single crystal ingot with a continuous crystal lattice, it is preferable to set the speed at which the crucible 2 is pulled downward along its axis to, for example, 1 to 3 mm / hour. The temperature of the portion of the BO-GaO solution 52 that contacts the seed crystal 51 (hereinafter also referred to as the "seed crystal portion") is preferably 1150 to 1430°C, more preferably 1200 to 1388°C.

[0076] In the GaO single crystal growth step S140, because GaO single crystals are precipitated from the BO-GaO solution 52 due to the difference in solubility between BO and Ga, the GaO concentration and the n-type dopant concentration in the BO-GaO solution 52 decrease as the step proceeds. For this reason, the GaO single crystal growth step S140 preferably includes a step of analyzing the concentrations of GaO and the n-type dopant originating from a portion of the seed crystal and the GaO polycrystal in the solution by sampling the solution in the crucible sealed with the lid through the nozzle (hereinafter also referred to as the "analysis step"). Furthermore, the GaO single crystal growth step S140 preferably includes a step of introducing the GaO polycrystal into the solution in the crucible through the nozzle to adjust the GaO concentration to within ±5% of the first concentration, based on the analysis results of the GaO concentration (hereinafter also referred to as the "GaO concentration adjustment step"). The GaO single crystal growth step S140 preferably includes a step of introducing the n-type dopant into the solution in the crucible through the nozzle to adjust the GaO concentration to within ±5% of the second concentration, based on the analysis results of the n-type dopant concentration (hereinafter also referred to as the "n-type dopant concentration adjustment step"). By including these steps, the manufacturing method can stabilize the concentrations of GaO and n-type dopant in the BO-GaO solution 52 from the beginning to the end of the GaO single crystal growth step S140. This makes it possible to obtain a Ga2O3 single crystal in which the concentration of B is uniform throughout the single crystal, thereby making it possible to obtain, with a good yield, Ga2O3 single crystals for manufacturing Ga2O3 single crystal substrates that can suppress the occurrence of cracks.

[0077] Specifically, in the analysis step, during the GaO single crystal growth step S140, the BO—GaO solution 52 in the crucible 2 sealed by the lid 3 is sampled by an appropriate means at predetermined time intervals (for example, every two hours) through the first nozzle 41 or the second nozzle 42. Sampling can be performed, for example, by using a pipe made of the same material as the nozzles to collect about 0.5 g of the BO—GaO solution 52 in the crucible 2 through the first nozzle 41 or the second nozzle 42. Furthermore, about 0.5 g of this B2O3-Ga2O3 solution 52 is dissolved in acid by a known method, and then the concentrations of Ga2O3 and the n-type dopant in the B2O3-Ga2O3 solution 52 can be analyzed by using high-frequency inductively coupled plasma (ICP) emission spectroscopy or ICP-mass spectroscopy.

[0078] In the GaO concentration adjusting step, GaO polycrystals are introduced into the BO-GaO solution 52 in the crucible 2 through the first nozzle 41 so that the GaO concentration is within ±5% of the first concentration, based on the analysis results of the GaO concentration obtained from the analysis step performed at predetermined time intervals. Note that in the GaO concentration adjusting step, if the analysis results of the GaO concentration are within ±5% of the first concentration, GaO polycrystals are not introduced.

[0079] Furthermore, in the GaO single crystal growth step S140, the n-type dopant concentration in the BO-GaO solution 52 also decreases as the GaO single crystal is precipitated. Therefore, in the n-type dopant concentration adjustment step, an n-type dopant is introduced into the BO-GaO solution 52 in the crucible 2 through the second nozzle 42 in accordance with the analysis results of the GaO concentration obtained from the analysis step performed at predetermined time intervals, so that the n-type dopant concentration is within ±5% of the second concentration. Note that in the n-type dopant concentration adjustment step, if the analysis results of the n-type dopant concentration are within ±5% of the second concentration, the n-type dopant is not introduced.

[0080] In the GaO single crystal growth step S140, as the GaO single crystal is precipitated as described above, the BO in the BO-GaO solution 52 may be lost due to sublimation while being incorporated into the GaO single crystal. Therefore, if the BO concentration in the BO-GaO solution 52 becomes too low, the first nozzle 41 can be used to add BO to adjust the BO concentration.

[0081] In the GaO single crystal growth step S140, the crucible 2 is pulled downward along its axis relative to the heating device 1 at the speed described above. A GaO single crystal is continuously precipitated from the BO-GaO solution 52 in the crucible 2, increasing its thickness as an ingot. The interface between the GaO single crystal and the BO-GaO solution 52 rises toward the lid 3. The crystal growth of the GaO single crystal continues until the GaO single crystal ingot reaches the desired thickness. This process allows the GaO single crystal to be obtained. The boron concentration in the GaO single crystal is 4 ppm by mass or more and 200 ppm by mass or less in GDMS. The boron concentration in the GaO single crystal is preferably 5 ppm by mass or more and 100 ppm by mass or less in GDMS. The GDMS for the Ga2O3 single crystal can be carried out in the same manner as the GDMS for the Ga2O3 single crystal substrate described above.

[0082] In the GaO single crystal manufacturing method, the above-described series of steps can also be performed under a nitrogen atmosphere. In such an embodiment, the crucible 2 constituting the GaO single crystal growth apparatus is made of pBN. Furthermore, in order to perform the above-described series of steps under a nitrogen atmosphere, the GaO single crystal growth apparatus is housed in a chamber filled with nitrogen. Even with this GaO single crystal manufacturing method, it is possible to obtain GaO single crystals for producing GaO single crystal substrates that are capable of suppressing cracking.

[0083] [Method for Manufacturing Gallium Trioxide Single Crystal Substrate] <GaO Single Crystal Substrate Manufacturing Step S200> The method for manufacturing a GaO single crystal substrate according to this embodiment includes processing a GaO single crystal obtained by the GaO single crystal manufacturing method described above to obtain a GaO single crystal substrate having a circular main surface. As shown in FIG. 4, the method for manufacturing a GaO single crystal substrate includes a GaO single crystal manufacturing step S100 and a GaO single crystal substrate manufacturing step S200. The purpose of the GaO single crystal substrate manufacturing step S200 is to obtain a GaO single crystal substrate by processing the GaO single crystal obtained by the GaO single crystal manufacturing step S100. The GaO single crystal substrate manufacturing step S200 includes the following steps: cutting, outer periphery grinding, and polishing. These steps are performed in this order to obtain a GaO single crystal substrate.

[0084] The cutting step is a step of slicing the GaO single crystal ingot removed from the crucible 2 into wafers having a predetermined thickness to obtain GaO single crystal substrates. Furthermore, the periphery grinding step is a step of grinding the periphery of the wafer to obtain wafers having main surfaces composed of a central portion and an outer periphery surrounding the periphery of the central portion. Specifically, the periphery grinding step is a step of chamfering. Therefore, the periphery grinding step can obtain main surfaces having a chamfered region as the outer periphery. Conventionally known cutting and periphery grinding methods can be used for the cutting step and the periphery grinding step. Furthermore, the polishing step is a step of mirror-finishing the central portion of the main surface. Conventionally known polishing methods can be used for the polishing step. The polishing step can achieve a surface roughness Ra of 20 nm or less for the central portion, as specified in JIS B 0681-2:2018, for example.

[0085] [Effects] By carrying out the above steps, the GaO single crystal substrate according to this embodiment is manufactured. In the GaO single crystal manufacturing method, particularly in the GaO single crystal growth step S140, it is possible to grow a GaO single crystal in which a small amount of BO is incorporated into the precipitated GaO single crystal. This makes it possible to obtain a GaO single crystal substrate having an appropriate strength that can suppress cracking from occurring from the B-containing GaO single crystal.

[0086] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. In these examples, GaO single crystal substrates were manufactured using a GaO single crystal manufacturing apparatus as shown in Figure 5 and according to the flowchart shown in Figure 4. In the following description, Samples 11 to 19 are examples, and Samples a to c are comparative examples.

[0087] [Manufacturing of GaO single crystal substrate] <Sample a> A GaO single crystal was obtained using the vertical Bridgeman (VB) method in accordance with the method disclosed in Patent Document 1. When obtaining the GaO single crystal, an appropriate amount of tin oxide (SnO) was added as an n-type dopant. The GaO single crystal was then subjected to the above-described cutting, outer periphery grinding, and polishing processes in this order to obtain the GaO single crystal substrate of Sample a. The GaO single crystal substrate of Sample a had a diameter of 100 mm and a thickness of 650 μm.

[0088] <Sample b> (Preparation step S110 in GaO single crystal production process S100) First, the GaO single crystal growth apparatus, the seed crystal 51 made of a GaO single crystal, a block of GaO polycrystal, SnO as an n-type dopant, and solid BO were prepared by a conventionally known method or by purchasing commercially available products. The crucible 2 constituting the GaO single crystal growth apparatus had an inner diameter of 105 mm and was made of platinum.

[0089] (Raw material placement step S120 in GaO single crystal manufacturing step S100) Next, using a conventionally known method, a seed crystal 51 was placed at the bottom of the crucible 2, and a chunk of GaO polycrystal, SnO, and solid BO were placed above the seed crystal 51 in this order. Specifically, a plurality of chunks of GaO polycrystal were placed and stacked. Next, SnO was added to the GaO polycrystal, and solid BO was placed thereon. The amount of SnO added was determined so that the atomic concentration of Sn in the GaO single crystal substrate was 3.0 × 10. 18 cm －3 The amount was set to be:

[0090] (Raw Material Melting Step S130 in GaO Single Crystal Production Process S100) Next, a crucible 2 containing a seed crystal 51, a block of GaO polycrystals, SnO, and solid B2O3 was supported by a crucible-holding stage 8. Then, a current was supplied to the heating device 1 to heat the crucible 2, melting the solid B2O3 into liquid B2O3. The GaO polycrystals, a portion of the seed crystal 51, and SnO2 were dissolved in the B2O3 to prepare a B2O3-Ga2O3 solution 52. The first concentration, which is the concentration of GaO3 in B2O3 in the B2O3-Ga2O3 solution 52, was set to 20 mass%. The second concentration, which is the concentration of SnO2 in the B2O3, was set to 100 mass ppm. Next, the remainder of the seed crystal 51 and the B2O3--Ga2O3 solution 52 were brought into contact at their interface.

[0091] (GaO Single Crystal Growth Step S140 in GaO Single Crystal Production Step S100) Next, the crucible 2 was gradually pulled downward (toward the bottom) along its axis relative to the heating device 1, creating a temperature gradient such that the temperature on the seed crystal 51 side of the crucible 2 was lower and the temperature on the BO-GaO solution 52 side was higher. This resulted in GaO single crystals being precipitated in the seed crystal portion, which is the portion in contact with the seed crystal 51 in the BO-GaO solution 52, due to the solubility difference between BO and GaO, and continuous crystal growth was achieved. This operation was continued until the GaO single crystal reached a thickness of 30 mm. The temperature of the seed crystal portion was set to 1100°C. The speed at which the crucible 2 was pulled downward along its axis was set to 2 mm / hour. A GaO single crystal ingot was thus obtained.

[0092] In the GaO single crystal growth step S140, the above-described analysis step, GaO concentration adjustment step, and n-type dopant concentration adjustment step were carried out, thereby controlling the GaO and n-type dopant concentrations in the BO-GaO solution 52 to within ±5% from the beginning to the end of the GaO single crystal growth step S140.

[0093] (GaO single crystal substrate manufacturing process S200) Finally, the GaO single crystal ingot obtained in the GaO single crystal growth process S140 was processed in the cutting process, periphery grinding process, and polishing process to obtain a GaO single crystal substrate. First, in the cutting process, the ingot was sliced ​​into wafers with a thickness of 700 μm using a conventionally known method. In the periphery grinding process, the wafer was ground to chamfer the periphery using a conventionally known method to obtain wafers having main surfaces consisting of a central portion and an outer periphery surrounding the periphery of the central portion. Furthermore, in the polishing process, the central portion was polished using a conventionally known polishing method to obtain a surface roughness Ra of 0.2 nm at the central portion, as specified in JIS B 0681-2:2018, for example.

[0094] In this way, a GaO single crystal substrate of sample b was produced. The GaO single crystal substrate of sample b had a diameter of 100 mm and a thickness of 650 μm.

[0095] <Sample c> A GaO single crystal substrate of sample c was manufactured in the same manner as sample b, except that the first concentration in the BO-GaO solution 52 prepared in the raw material melting step S130 was set to 25 mass %, and the temperature of the seed crystal portion was set to 1500° C. in the GaO single crystal growth step S140. The GaO single crystal substrate of sample c had a diameter of 100 mm and a thickness of 650 μm.

[0096] <Sample 11> A GaO single crystal substrate of Sample 11 was manufactured in the same manner as Sample b, except that the first concentration in the BO-GaO solution 52 prepared in the raw material melting step S130 was set to 20 mass %, and the temperature of the seed crystal portion was set to 1200°C in the GaO single crystal growth step S140. The GaO single crystal substrate of Sample 11 had a diameter of 100 mm and a thickness of 650 μm.

[0097] <Sample 12> A GaO single crystal substrate of Sample 12 was produced in the same manner as Sample 11, except that the temperature of the seed crystal portion was set to 1273°C in the GaO single crystal growth step S140. The GaO single crystal substrate of Sample 12 had a diameter of 100 mm and a thickness of 650 µm.

[0098] <Sample 13> A GaO single crystal substrate of Sample 13 was manufactured in the same manner as Sample 11, except that the first concentration in the BO—GaO solution 52 prepared in the raw material melting step S130 was set to 25 mass %, and the temperature of the seed crystal portion was set to 1,323° C. in the GaO single crystal growth step S140. The GaO single crystal substrate of Sample 13 had a diameter of 100 mm and a thickness of 650 μm.

[0099] <Sample 14> A GaO single crystal substrate of Sample 14 was produced in the same manner as Sample 13, except that a chamber housing a single crystal growth apparatus and a crucible 2 made of pBN were prepared in Preparation Step S110, the raw material melting step S130 and the GaO single crystal growth step S140 were performed in a nitrogen atmosphere, and the temperature of the seed crystal portion was set to 1348°C in GaO single crystal growth step S140. The GaO single crystal substrate of Sample 14 had a diameter of 100 mm and a thickness of 650 µm.

[0100] <Sample 15> A GaO single crystal substrate of Sample 15 was produced in the same manner as Sample 13, except that the temperature of the seed crystal portion was set to 1368°C in the GaO single crystal growth step S140. The GaO single crystal substrate of Sample 15 had a diameter of 100 mm and a thickness of 650 µm.

[0101] <Sample 16> A GaO single crystal substrate of Sample 16 was produced in the same manner as Sample 13, except that the temperature of the seed crystal portion was set to 1388°C in the GaO single crystal growth step S140. The GaO single crystal substrate of Sample 16 had a diameter of 100 mm and a thickness of 650 µm.

[0102] <Sample 17> A GaO single crystal substrate of Sample 17 was produced in the same manner as Sample 13, except that a crucible 2 with an inner diameter of 160 mm was prepared in Preparation Step S110 and the temperature of the seed crystal portion was set to 1273°C in GaO single crystal growth Step S140. The GaO single crystal substrate of Sample 17 had a diameter of 150 mm and a thickness of 680 µm.

[0103] <Sample 18> A GaO single crystal substrate of Sample 18 was produced in the same manner as Sample 17, except that the temperature of the seed crystal portion was set to 1323°C in the GaO single crystal growth step S140. The GaO single crystal substrate of Sample 18 had a diameter of 150 mm and a thickness of 680 µm.

[0104] <Sample 19> A GaO single crystal substrate of Sample 19 was produced in the same manner as Sample 17, except that a chamber housing a single crystal growth apparatus and a crucible 2 made of pBN were prepared in Preparation Step S110, the raw material melting step S130 and the GaO single crystal growth step S140 were performed in a nitrogen atmosphere, and the temperature of the seed crystal portion in GaO single crystal growth step S140 was set to 1388°C. The GaO single crystal substrate of Sample 19 had a diameter of 150 mm and a thickness of 680 µm.

[0105] [Composition Analysis by GDMS] The composition analysis method using GDMS described above was performed on the GaO single crystal substrates of Samples a to c and Samples 11 to 19 to measure the concentration of boron (B) contained in the GaO single crystal substrates. The results are shown in Table 1. The unit of concentration of each element shown in Table 1 is ppm by mass. In Table 1, "<0.3" means that the concentration was less than 0.3 ppm by mass.

[0106] [Measurement of nanoindentation hardness] The nanoindentation hardness was determined at five predetermined locations on the main surface by carrying out the above-mentioned measurement method for the GaO single crystal substrates of samples a to c and samples 11 to 19. The measurement apparatus and measurement conditions used to carry out the above-mentioned measurement method are as follows:

[0107] Apparatus used: Nanoindenter (product name: "Bruker Hysitron TI980 Triboindenter", manufactured by Bruker Japan Co., Ltd.) Indenter used: Berkovich indenter Maximum load: 10 mN Measurement atmosphere: air Measurement temperature: room temperature (25°C) Intersection angle between at least one side of the indenter ridge and the direction of the

[100] direction of the Ga2O3 single crystal projected onto the main surface: 0 to 10°.

[0108] The nanoindentation hardness was determined by averaging three measurements taken at the same location on the same substrate three times. This average value (unit: GPa) was calculated for each of the five nanoindentation hardness values ​​measured at the five locations. The difference between the maximum and minimum nanoindentation hardness values ​​at each of the five locations on the main surface (referred to as "maximum-minimum difference" in Table 1) was also calculated. The five locations refer to the following positions on the main surface. Specifically, when the length from the center of the main surface to the boundary between the central portion and the outer periphery is defined as r, two mutually orthogonal axes on the main surface that pass through the center are defined as the X-axis and the Y-axis, and the Y-axis is defined as the b-axis of the GaO single crystal, the coordinates (X, Y) of the X-axis and the Y-axis at the nine locations are (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)). The units of r and X and Y in the coordinates (X, Y) are mm. The r of samples a, b, c, and 11 to 16 is 48 mm. The r of samples 17 to 19 is 74 mm. The results are shown in Table 1.

[0109] [Crack Load Test] The load at which the Ga2O3 single crystal substrates of Samples a to c and Samples 11 to 19 would crack was examined by applying a load to the center of the main surface using a force gauge. The results are shown in Table 1. The larger the measured load, the less likely the substrate is to crack. The force gauge and attachment used to carry out the above-mentioned crack load test are as follows: Force gauge: "PS-200N (model)", manufactured by Imada Co., Ltd., maximum load 200N Attachment: conical (S-3).

[0110] [Resistivity, Carrier Concentration, and Electron Mobility] For each of the GaO single crystal substrates of Samples a to c and Samples 11 to 19, Hall measurement samples were prepared using the central portions of the substrates, and the above-described measurement method was carried out on each Hall measurement sample to determine the resistivity, carrier concentration, and electron mobility of each sample. The results are shown in Table 2.

[0111]

[0112]

[0113] [Discussion] According to Tables 1 and 2, the Ga2O3 single crystal substrates of Samples 11 to 19 all had a B concentration in GDMS of 4 ppm to 200 ppm by mass. In these cases, the average nanoindentation hardness was 14.8 GPa to 22.0 GPa, and the crack load was 90 N or more. In contrast, the Ga2O3 single crystal substrates of Samples a to c all had a B concentration in GDMS of less than 4 ppm by mass or more than 200 ppm by mass. In these cases, the average nanoindentation hardness was less than 14.8 GPa or more than 22.0 GPa, and the crack load was less than 90 N. This suggests that the Ga2O3 single crystal substrates of Samples 11 to 19 are less likely to crack.

[0114] 6 is a graph showing the relationship between nanoindentation hardness and crack load for the gallium trioxide single crystal substrates prepared in the examples. In particular, Fig. 6 shows that the GaO single crystal substrates exhibit a crack load of 90 N or more when the nanoindentation hardness is in the range of 14.8 GPa or more and 22.0 GPa or less.

[0115] Although the embodiments and examples of the present disclosure have been described above, it is also planned from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined.

[0116] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0117] 100 gallium trioxide single crystal substrate (Ga2O3 single crystal substrate), O center, r length from the center of the main surface to the boundary between the center and the outer periphery, 10 main surface, 11 center, 12 outer periphery, 13 boundary, 21 electrode, 1 heating device, 2 crucible, 3 lid, 41 first nozzle, 42 second nozzle, 51 seed crystal, 52 B2O3-Ga2O3 solution, 8 crucible holding stage, 9 lower shaft, O center, r length from the center of the main surface to the boundary between the center and the outer periphery, S100 Ga2O3 single crystal production process, S110 preparation process, S120 raw material accommodation process, S130 raw material melting process, S140 Ga2O3 single crystal growth process, S200 Ga2O3 single crystal substrate production process.

Claims

1. A gallium trioxide single crystal substrate having a circular main surface, The diameter of the gallium trioxide single crystal substrate is 100 mm or more, The thickness of the gallium trioxide single crystal substrate is 600 μm or more, the gallium trioxide single crystal substrate contains boron; The gallium trioxide single crystal substrate has a boron concentration of 4 ppm by mass or more and 200 ppm by mass or less, as measured by glow discharge mass spectrometry.

2. 2. The gallium trioxide single crystal substrate according to claim 1, wherein the concentration of boron is 5 ppm by mass or more and 100 ppm by mass or less, as determined by glow discharge mass spectrometry.

3. the main surface is a (001) plane of a gallium trioxide single crystal; the main surface has a central portion including a center thereof and an outer periphery surrounding the central portion, The outer periphery is a chamfered region, nanoindentation hardness measured at five points on the main surface according to a nanoindentation method using a Berkovich indenter under conditions of a maximum load of 10 mN and a crossing angle between one side of an indentation and a direction of the [100] direction of the gallium trioxide single crystal projected onto the main surface being 0° or more and 10° or less, is 14.8 GPa or more and 22.0 GPa or less, When the length from the center of the main surface to the boundary between the central portion and the outer periphery is defined as r, two mutually perpendicular axes on the main surface that pass through the center are defined as the X-axis and the Y-axis, and the Y-axis is defined as the b-axis of the digallium trioxide single crystal, the five coordinates (X, Y) defined by the X-axis and the Y-axis are (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)), and the units of r and X and Y in the coordinates (X, Y) are mm. The digallium trioxide single crystal substrate according to claim 1 or 2.

4. the gallium trioxide single crystal substrate contains both or either one of rhodium and iridium; 3. The gallium trioxide single crystal substrate according to claim 1, wherein the rhodium concentration and the iridium concentration are both 0.1 ppm by mass or less by glow discharge mass spectrometry.

5. The resistivity of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall method is 1.0 x 10 -3 Ω cm or more and 2.0 Ω cm or less, The carrier concentration of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall method was 4.0 × 10 17 cm -3 1.4 x 10 19 cm -3 is as follows: The electron mobility of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall method is 0.2 cm 2 / V・s or more 15000cm 2 The digallium trioxide single crystal substrate according to claim 1 or claim 2, wherein the SiO 2 film thickness is 1 / V·s or less.

6. A method for producing gallium trioxide single crystals, comprising: The manufacturing method is carried out under an atmospheric atmosphere; and A step of preparing a single crystal growth apparatus including at least a cylindrical crucible and a heating device disposed so as to surround the outer periphery of the crucible; placing a seed crystal made of the digallium trioxide single crystal at the bottom of the crucible, and placing a block or powder of digallium trioxide polycrystal, an n-type dopant, and boron oxide above the seed crystal in the crucible; heating the crucible with the heating device to melt a portion of the seed crystal and obtain a solution in which digallium trioxide derived from the portion of the seed crystal and the digallium trioxide polycrystal is dissolved in the boron oxide at a first concentration and the n-type dopant is dissolved in a second concentration, and contacting the solution with the remainder of the seed crystal; and growing a crystal from the solution onto the remainder of the seed crystal to obtain a digallium trioxide single crystal; The crucible is made of platinum, The method for producing a digallium trioxide single crystal, wherein the concentration of boron in the digallium trioxide single crystal is 4 ppm by mass or more and 200 ppm by mass or less, as measured by glow discharge mass spectrometry.

7. A method for producing gallium trioxide single crystals, comprising: The method is carried out under a nitrogen atmosphere; and A step of preparing a single crystal growth apparatus including at least a cylindrical crucible and a heating device disposed so as to surround the outer periphery of the crucible; placing a seed crystal made of the digallium trioxide single crystal at the bottom of the crucible, and placing a block or powder of digallium trioxide polycrystal, an n-type dopant, and boron oxide above the seed crystal in the crucible; heating the crucible with the heating device to melt a portion of the seed crystal and obtain a solution in which digallium trioxide derived from the portion of the seed crystal and the digallium trioxide polycrystal is dissolved in the boron oxide at a first concentration and the n-type dopant is dissolved in a second concentration, and contacting the solution with the remainder of the seed crystal; and growing a crystal from the solution onto the remainder of the seed crystal to obtain a digallium trioxide single crystal; the crucible is made of pyrolytic boron nitride; The method for producing a digallium trioxide single crystal, wherein the concentration of boron in the digallium trioxide single crystal is 4 ppm by mass or more and 200 ppm by mass or less, as measured by glow discharge mass spectrometry.

8. the single crystal growth apparatus has a nozzle for introducing the gallium trioxide polycrystal and the n-type dopant into the crucible, and a lid for sealing the crucible; the lid has a hole into which the nozzle is inserted, The step of obtaining the digallium trioxide single crystal comprises: a step of analyzing the concentrations of digallium trioxide derived from a portion of the seed crystals and the digallium trioxide polycrystals, and the n-type dopant in the solution by sampling the solution in the crucible sealed by the lid through the nozzle; According to the analysis result of the concentration of the digallium trioxide, adding the digallium trioxide polycrystals to the solution in the crucible through the nozzle so that the concentration is within ±5% of the first concentration; and adding the n-type dopant to the solution in the crucible through the nozzle so that the n-type dopant concentration is within ±5% of the second concentration according to the analysis result of the concentration of the n-type dopant. The method for producing a gallium trioxide single crystal according to claim 6 or 7, comprising the steps of:

9. A method for manufacturing a digallium trioxide single crystal substrate, comprising a step of processing a digallium trioxide single crystal obtained by the method for manufacturing a digallium trioxide single crystal described in claim 6 or claim 7 to obtain a digallium trioxide single crystal substrate having a circular main surface.

10. the main surface is a (001) plane of a gallium trioxide single crystal; the main surface has a central portion including a center thereof and an outer periphery surrounding the central portion, The outer periphery is a chamfered region, nanoindentation hardness measured at five points on the main surface according to a nanoindentation method using a Berkovich indenter under conditions of a maximum load of 10 mN and a crossing angle between one side of an indentation and a direction of the [100] direction of the gallium trioxide single crystal projected onto the main surface being 0° or more and 10° or less, is 14.8 GPa or more and 22.0 GPa or less, where r is the length from the center of the main surface to the boundary between the central portion and the outer periphery, two axes on the main surface that pass through the center and are perpendicular to each other are the X-axis and Y-axis, and the Y-axis is the b-axis of the gallium trioxide single crystal, the five coordinates (X, Y) defined by the X-axis and the Y-axis are (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)), and the units of r and X and Y in the coordinates (X, Y) are mm, the gallium trioxide single crystal substrate contains both or either one of rhodium and iridium; the rhodium concentration and the iridium concentration are each 0.1 ppm by mass or less as measured by glow discharge mass spectrometry; The resistivity of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall method is 1.0 x 10 -3 Ω cm or more and 2.0 Ω cm or less, The carrier concentration of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall method was 4.0 × 10 17 cm -3 1.4 x 10 19 cm -3 is as follows: The electron mobility of the gallium trioxide single crystal substrate measured at 25°C by the Van der Pauw Hall method is 0.2 cm 2 / V・s or more 15000cm 2 The digallium trioxide single crystal substrate according to claim 2, wherein the resistivity is 0.1 / V·s or less.