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

Abstract

In the present invention, a digallium trioxide single crystal substrate has a circular main surface, the diameter of the digallium trioxide single crystal substrate being at least 100 mm, the main surface being the (100) plane of the digallium trioxide single crystals constituting the digallium trioxide single crystal substrate, the main surface having a central portion containing the center of the main surface and an outer peripheral portion surrounding the outer periphery of the central portion, and the outer peripheral portion being a processed part that has been chamfered. First nanoindention hardnesses measured according to a nanoindention method using a Berkovich indenter at nine locations on the main surface are all 13-20 GPa under a first condition in which the maximum load is set at 10 mN and a load is applied such that the angle of intersection of one side of the indention and the direction in which the [100] direction of the digallium trioxide single crystal projects onto the main surface is 0-10°.

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] As taught in Japanese Patent Laid-Open Publication No. 2008-303119 (Patent Document 1) and Non-Patent Document 1 listed below, etc., it is known that the digallium trioxide single crystal (hereinafter also referred to as "GaO single crystal") constituting the digallium trioxide single crystal substrate (hereinafter also referred to as "GaO single crystal substrate") has strong cleavage properties in a specific direction.

[0003] JP 2008-303119 A

[0004] Shimamura et al., "Powder and Powder Metallurgy," Vol. 52, No. 12 (2005), pp. 918-922

[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 main surface is a (001) plane of the digallium trioxide single crystal constituting the digallium trioxide single crystal substrate. The main surface has a central portion including the center and an outer peripheral portion surrounding the periphery of the central portion. The outer peripheral portion is a chamfered region. A first nanoindentation hardness measured at nine locations on the main surface according to a nanoindentation method using a Berkovich indenter under first conditions in which a maximum load of 10 mN is applied and an angle between one side of an indentation mark and a direction of the

[100] direction of the digallium trioxide single crystal projected onto the main surface is 0° or more and 10° or less is 13 GPa or more and 20 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 gallium trioxide 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), (0, -(r-5)), (r-1, 0), (0, r-1), (-(r-1), 0), and (0, -(r-1)). The units of r and X and Y in the coordinates (X, Y) are mm.

[0006] FIG. 1 is an explanatory diagram illustrating the main surface of a GaO single crystal substrate according to this embodiment. FIG. 2 is an explanatory diagram illustrating nine measurement points set on the main surface of the GaO single crystal substrate of FIG. 1 to determine the first and second nanoindentation hardnesses. FIG. 3 is a flowchart illustrating an example of a method for manufacturing a GaO single crystal substrate, including a method for manufacturing a GaO single crystal according to this embodiment. FIG. 4 is a schematic diagram illustrating a manufacturing apparatus used in the method for manufacturing a GaO single crystal according to this embodiment. FIG. 5 is an explanatory diagram illustrating one embodiment of a crucible (first crucible) included in the manufacturing apparatus used in the method for manufacturing a GaO single crystal according to this embodiment. FIG. 6 is an explanatory diagram illustrating another embodiment of a crucible (second crucible) included in the manufacturing apparatus used in the method for manufacturing a GaO single crystal according to this embodiment. FIG. 7 is an explanatory diagram illustrating, in plan view, one embodiment of a plate-shaped body included in the manufacturing apparatus used in the method for manufacturing a GaO single crystal according to this embodiment.

[0007] [Problem to be Solved by the Present Disclosure] It has been pointed out that GaO single crystal substrates are prone to cracking due to the strong cleavage of GaO single crystals. However, a GaO single crystal substrate with improved cracking properties has not yet been obtained, and its development is eagerly awaited.

[0008] In view of the above, an object of the present disclosure is to provide a crack-resistant digallium trioxide single crystal substrate, a method for manufacturing digallium trioxide single crystal, and a method for manufacturing a digallium trioxide single crystal substrate.

[0009] Effect of the Present Disclosure The present disclosure can provide a crack-resistant digallium trioxide single crystal substrate, a method for manufacturing 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. First, the present inventors focused on providing a GaO single crystal substrate with a uniform hardness throughout the crystal, thereby imparting a property that makes it difficult for cracks to form on the main surface. Specifically, they conceived the idea of ​​stabilizing the crystal growth rate to obtain a GaO single crystal with a uniform density of crystal defects. From the GaO single crystal, a GaO single crystal substrate was obtained having a main surface with a predetermined hardness that is uniform throughout the surface. Based on the hardness characteristics described above, the GaO single crystal substrate is difficult for cracks to form on the main surface. This resulted in the creation of a crack-resistant GaO single crystal substrate, and the present disclosure was completed.

[0011] Next, embodiments of the present disclosure will be described in detail. [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 main surface is a (001) plane of the digallium trioxide single crystal constituting the digallium trioxide single crystal substrate. The main surface has a central portion including the center and an outer peripheral portion surrounding the periphery of the central portion. The outer peripheral portion is a chamfered region. A first nanoindentation hardness measured at nine locations on the main surface according to a nanoindentation method using a Berkovich indenter under first conditions in which a maximum load of 10 mN is applied and 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 between 0° and 10°. All of the first nanoindentation hardnesses are between 13 GPa and 20 GPa. 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 Y-axis, and the Y-axis is defined as the b-axis of the digallium trioxide 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), (0, -(r-5)), (r-1, 0), (0, r-1), (-(r-1), 0), and (0, -(r-1)). The units of r and X and Y in the coordinates (X, Y) are mm. A digallium trioxide single crystal substrate having such characteristics can have crack-resistant properties.

[0012] [2] According to the nanoindentation method, the second nanoindentation hardness measured at the nine locations under second conditions, in which a maximum load of 1 mN is applied and 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, is preferably 15 GPa or more and 20 GPa or less. This makes it possible to provide a gallium trioxide single crystal substrate that is more resistant to cracking.

[0013] [3] The dislocation density at the center is 100 cm -2This makes it possible to provide a high-quality gallium trioxide single crystal substrate with a low defect density within the single crystal.

[0014] [4] The gallium trioxide single crystal substrate preferably contains a dopant. The dopant is preferably tin or silicon. The atomic concentration of the dopant is preferably 2×10 19 cm －3 It is preferable that the dopant-containing gallium trioxide single crystal substrate has crack-resistant properties.

[0015] [5] A method for producing a digallium trioxide single crystal according to one embodiment of the present disclosure includes the following steps: 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 at the bottom of the crucible and placing a massive digallium trioxide bulk body, a plate-like body made of pyrolytic boron nitride, and solid boron oxide in this order above the seed crystal in the crucible, heating the crucible with the heating device to melt the digallium trioxide bulk body and a portion of the seed crystal to obtain a digallium trioxide melt and bringing the digallium trioxide melt into contact with the remainder of the seed crystal, and growing a crystal from the digallium trioxide melt on the remainder of the seed crystal to obtain the digallium trioxide single crystal. The step of contacting the digallium trioxide melt with the remainder of the seed crystal includes placing the plate-shaped body on the digallium trioxide melt and liquefying the boron oxide. The atmosphere in which the step of obtaining the digallium trioxide single crystal is performed is an inert gas atmosphere. The crucible includes a cylindrical seed crystal accommodation portion, an increasing diameter portion connected to the seed crystal accommodation portion, and a straight body portion connected to the increasing diameter portion. The seed crystal accommodation portion has a hollow portion that opens on the side connected to the increasing diameter portion and has a bottom wall formed on the opposite side. The increasing diameter portion has a shape in which the area S of a cross section perpendicular to the axial direction of the crucible expands upward in the axial direction of the crucible, and is connected to the seed crystal accommodation portion on the small diameter side of the increasing diameter portion. The increasing diameter portion has three or four locations where the ratio S / Z, which is the ratio of the area S to the distance Z in the axial direction of the crucible from the connection point with the seed crystal accommodation portion, is 157.1 mm. The body portion has a hollow cylindrical shape and is connected to the larger diameter side of the increased diameter portion. The plate-like body has a plurality of through holes penetrating in a direction parallel to the axial direction when placed on the gallium trioxide melt. The area ratio of the plurality of through holes to a cross section of the plate-like body perpendicular to the axial direction is 0.12 to 0.28. The unit of the distance Z is mm, and the unit of the area S is mm 2The unit of S / Z is mm. 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 less likely to crack.

[0016] [6] 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 method for producing a digallium trioxide single crystal substrate having such characteristics, a digallium trioxide single crystal substrate that is less likely to crack can be obtained.

[0017] [7] In the gallium trioxide single crystal substrate according to [2] above, the dislocation density in the central portion is 100 cm -2 The gallium trioxide single crystal substrate preferably contains a dopant. The dopant is preferably tin. The atomic concentration of the dopant is preferably 2×10 19 cm －3 This makes it possible to provide a high quality gallium trioxide single crystal substrate containing tin as a dopant that is less likely to crack and has a low defect density within the single crystal.

[0018] [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.

[0019] 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.

[0020] 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.

[0021] 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).

[0022] In this specification, "dislocation" and "dislocation density" refer to "threading dislocations" identified by applying a treatment method to the main surface, which will be described later, and "threading dislocations within 1 cm of the main surface of the threading dislocations." 2 The "threading dislocation" is known as one type of crystal defect.

[0023] 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.

[0024] [Digallium Trioxide Single Crystal Substrate] The digallium trioxide single crystal substrate (GaO single crystal substrate) according to this embodiment is a GaO single crystal substrate having a circular main surface. The diameter of the GaO single crystal substrate is 100 mm or more. The main surface is the (001) plane of the digallium trioxide single crystal (GaO single crystal) constituting the GaO single crystal substrate. The main surface has a central portion including the center and an outer peripheral portion surrounding the periphery of the central portion. The outer peripheral portion is a chamfered region. According to a nanoindentation method using a Berkovich indenter, a first nanoindentation hardness measured at nine points on the main surface under first conditions in which 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 GaO single crystal projected onto the main surface is 0° or more and 10° or less is all 13 GPa or more and 20 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 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), (0, -(r-5)), (r-1, 0), (0, r-1), (-(r-1), 0), and (0, -(r-1)). The units of r and X and Y in the coordinates (X, Y) are mm. A GaO single crystal substrate having such characteristics can be crack-resistant. Hereinafter, unless otherwise specified, the terms "Ga2O3 single crystal substrate" and "Ga2O3 single crystal" in this specification mean "beta-type Ga2O3 single crystal substrate" and "beta-type Ga2O3 single crystal", respectively.

[0025] The inventors believe that the reason why the GaO single crystal substrate has crack-resistant properties is as follows. In GaO single crystal substrates having the (001) plane of the GaO single crystal as the main surface is generally known to be prone to cracking due to external stress, since the (001) plane has strong cleavage properties. In contrast, in the GaO single crystal substrate according to this embodiment, the main surface is the (001) plane of the GaO single crystal constituting the GaO single crystal substrate. However, the GaO single crystal is manufactured according to the method described in the "Method for Manufacturing Gallium Trioxide Single Crystal" section below. In other words, the GaO single crystal is grown at a stable rate using a predetermined single crystal growth apparatus, resulting in a uniform defect density within the crystal. This allows the GaO single crystal to have uniform hardness without variation within the crystal. Furthermore, the main surfaces of the GaO single crystal substrates obtained from the GaO single crystals can also be uniform in hardness with a considerable degree of consistency across the surface. Uniform in-plane hardness across the main surfaces means that starting points for cracks and other fractures are less likely to form on the main surfaces. From the above, it is believed that the GaO single crystal substrate according to this embodiment can have crack-resistant properties because starting points for cracks and other fractures are less likely to form on the main surfaces.

[0026] <Diameter> 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 mm or less. A GaO single crystal substrate having a diameter of 99.5 mm or more and 152 mm or less 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 a large-diameter GaO single crystal substrate having a diameter of 99.5 mm or more and 152 mm or less to have the characteristic of being less susceptible to cracking. Here, 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 the orientation flat (hereinafter also referred to as "OF"), index flat (hereinafter also referred to as "IF"), etc. As described above, the diameter of the Ga2O3 single crystal substrate can be measured using a conventionally known outer diameter measuring device such as a vernier caliper.

[0027] <Major Surface> (Circular Shape) The GaO single crystal substrate according to this embodiment has a circular major surface as described above. 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. 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.

[0028] (The (001) plane of the GaO single crystal) The main surface is the (001) plane of the GaO single crystal constituting the GaO single crystal substrate. As taught in Patent Document 1 and elsewhere, the (001) plane of the GaO single crystal is the second strongest cleavage plane after the (100) plane, and is generally considered to be prone to cracks and other defects caused by external stress, making it susceptible to fracture. However, since the GaO single crystal substrate has uniform in-plane hardness across the main surface as described above, starting points for cracks and other defects are unlikely to form on the main surface.

[0029] 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).

[0030] (Center and Outer Periphery) FIG. 1 is an explanatory diagram illustrating the main surface of a GaO single crystal substrate according to this embodiment. As shown in FIG. 1, the main surface 10 of the GaO single crystal substrate 1 has a center portion 11 including the center and an outer periphery portion 12 surrounding the periphery of the center portion 11. The center portion 11 is a region in the GaO single crystal substrate 1 where epitaxial layers for forming an electronic device are stacked. The outer periphery portion 12 is a region that has been chamfered. By chamfering the outer periphery portion 12, the GaO single crystal substrate 1 can be reduced in cracking and chipping at the outer edge of the outer periphery portion 12 during handling. A conventionally known method can be used to chamfer the outer periphery portion 12.

[0031] The central portion 11 preferably has a circular shape. This allows 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 to be expressed by a fixed numerical value "r" of 1. 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, a hexagon, or the like.

[0032] 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 1 having the width of the outer periphery 12 may have residual processing strain during chamfering, and is known to have large variations in the number of dislocations between substrates and poor flatness, and is therefore not normally used as a material for semiconductor devices.

[0033] The central portion 11 and the peripheral portion 12 are distinguished by the difference in thickness of the GaO single crystal substrate 1 at those locations. The thickness of the GaO single crystal substrate 1 at the peripheral portion 12 is less than 99% of the thickness of the GaO single crystal substrate 1 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 a non-contact thickness measuring device (product name (model): "TAP-2H-200XY", manufactured by COMS Co., Ltd.). The positioning accuracy of this measuring device is 25 μm. The display resolution of this measuring device is 0.01 μm. The repeatability of this measuring device is 0.01 μm. The measuring device used to measure the thickness of the central portion 11 and the peripheral portion 12 is not limited to the above-mentioned 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 1 at the central portion 11" refers to the thickness at the center O of the main surface 10 of the GaO single crystal substrate 1. 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 peripheral portion 12 to be determined as a specific numerical value (unit: mm).

[0034] (Nanoindentation Hardness) The first nanoindentation hardness of the GaO single crystal substrate measured at nine locations on the main surface under first conditions in which a maximum load of 10 mN is applied according to a nanoindentation method using a Berkovich indenter such that the crossing angle between one side of the indentation and the direction of the

[100] direction of the GaO single crystal projected onto the main surface is 0° or more and 10° or less is all 13 GPa or more and 20 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 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), (0, -(r-5)), (r-1, 0), (0, r-1), (-(r-1), 0), and (0, -(r-1)). The units of r and X and Y in the coordinates (X, Y) are mm. It is preferable that the first nanoindentation hardness measured at each of the nine locations on the main surface is greater than 13 GPa and not greater than 14 GPa. The difference between the maximum and minimum values ​​of the first nanoindentation hardness measured at nine locations on the main surface is preferably less than 0.7 GPa, more preferably 0.5 GPa or less, and most preferably 0 (zero).

[0035] Furthermore, according to the nanoindentation method, the second nanoindentation hardness measured at the nine locations under second conditions, in which a maximum load of 1 mN is applied and the crossing angle between one side of the indentation and the direction of the

[100] direction of the GaO single crystal projected onto the main surface is 0° or more and 10° or less, is preferably 15 GPa or more and 20 GPa or less. This makes it possible to provide a GaO single crystal substrate that is more resistant to cracking. The second nanoindentation hardness measured at the nine locations on the main surface is preferably more than 15 GPa and 16 GPa or less. The difference between the maximum and minimum second nanoindentation hardness values ​​measured at the nine locations on the main surface is preferably less than 0.7 GPa, more preferably 0.5 GPa or less. Most preferably, the difference between the maximum and minimum second nanoindentation hardness values ​​measured at the nine locations on the main surface is 0 (zero).

[0036] FIG. 2 is an explanatory diagram illustrating nine measurement points set on the main surface of the GaO single crystal substrate of FIG. 1 to determine the first and second nanoindentation hardnesses. Hereinafter, with reference to FIG. 2, a method for measuring the first nanoindentation hardness and the second nanoindentation hardness at nine points on the main surface 10 according to the nanoindentation method using a Berkovich indenter will be described. In the following explanation, a specific example of the measurement method for determining the first nanoindentation hardness will be provided. The measurement method can be performed, for example, using a nanoindenter (product name: "Bruker Hysitron TI980 Triboindenter," manufactured by Bruker Japan Co., Ltd.).

[0037] 1) Preliminary Measurement First, a preliminary measurement is performed on the GaO single crystal substrate 1 to ensure that a load can be applied so that the intersection angle between one side of the Berkovich indenter's 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 1 is fixed to the sample stage of the nanoindenter. Next, the GaO single crystal substrate 1 on the sample stage is observed using an optical system provided in the nanoindenter, and an arbitrary position in the center 11 on the main surface 10, for example, is designated as the measurement point. In order to facilitate the main measurement described below, it is preferable that the measurement location be specified as a location other than the nine locations mentioned above on main surface 10 (i.e., other than the nine locations with coordinates (X, Y) of (0,0), (r-5,0), (0,r-5), (-(r-5),0), (0,-(r-5)), (r-1,0), (0,r-1), (-(r-1),0), and (0,-(r-1)) . Furthermore, a Berkovich indenter is moved to the measurement location, and an indentation test is performed with a maximum load of 10 mN. Thereafter, GaO single crystal substrate 1 is removed from the sample stage. At this time, an indentation of the Berkovich indenter is formed at the measurement location, making it possible to determine the intersection angle between one side of the indentation and the

[100] direction of the GaO single crystal constituting GaO single crystal substrate 1. Here, the intersection angle can be determined by a conventionally known method.

[0038] 2) Main Measurement: Next, a main measurement is performed to determine the first nanoindentation hardness. If the crossing angle determined in the preliminary measurement is between 0° and 10°, the GaO single crystal substrate 1 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 1 is adjusted so that the crossing angle is between 0° and 10°, and the GaO single crystal substrate 1 is then fixed to the sample stage. Furthermore, the GaO single crystal substrate 1 on the sample stage is observed using an optical system provided in the nanoindenter, and one of the nine coordinates (X, Y) on the main surface 10 (e.g., (0, 0)) is designated as the measurement point. Next, a Berkovich indenter is moved to the measurement point (e.g., (0, 0)), and an indentation test is performed with a maximum load of 10 mN. After that, the GaO single crystal substrate 1 is removed from the sample stage. At this time, an indentation of the Berkovich indenter is formed at the measurement point. Therefore, based on the indentation, the area (mm 2 ) can be calculated, and the area (mm 2 The first 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.

[0039] Next, the remaining nine coordinates (X, Y) on main surface 10 (for example, (r-5, 0), (0, r-5), (-(r-5), 0), (0, -(r-5)), (r-1, 0), (0, r-1), (-(r-1), 0), and (0, -(r-1)) are specified as measurement points. Thereafter, an indentation test is performed in the same manner as when (0, 0) is specified as the measurement point, and a predetermined calculation is performed, thereby determining the first nanoindentation hardness at the remaining nine coordinates (X, Y) on main surface 10.

[0040] Furthermore, the second nanoindentation hardness can be determined in the same manner as the first nanoindentation hardness, except that the maximum load of the indentation test described above is 1 mN. In the GaO single crystal substrate according to this embodiment, the first nanoindentation hardness measured at nine locations on the main surface by the above-described measurement method is 13 GPa or more and 20 GPa or less. Therefore, the GaO single crystal substrate has a substantial degree of hardness and uniformity within the main surface. Furthermore, it is preferable that the second nanoindentation hardness measured at nine locations on the main surface is 15 GPa or more and 20 GPa or less. In this case, the GaO single crystal substrate can have a substantial degree of hardness and uniformity within the main surface.

[0041] Here, the first nanoindentation hardness is the indentation hardness obtained by conducting an indentation test with a maximum load of 10 mN. The second nanoindentation hardness is the indentation hardness obtained by conducting an indentation test with a maximum load of 1 mN. When conducting an indentation test with a maximum load of 10 mN, the Berkovich indenter is thought to be pressed deeper into the GaO single crystal substrate to form an indentation mark than when conducting an indentation test with a maximum load of 1 mN. Therefore, the first nanoindentation hardness can be considered to reflect the indentation hardness of the interior of the GaO single crystal substrate compared to the second nanoindentation hardness. The second nanoindentation hardness can be considered to reflect the indentation hardness closer to the main surface of the GaO single crystal substrate compared to the first nanoindentation hardness.

[0042] <Dislocation Density> In the GaO single crystal substrate according to this embodiment, the dislocation density in the center is 100 cm -2 The dislocation density in the central portion is preferably 50 cm -2 It is more preferable that the dislocation density in the central portion is 0 cm or less. This makes it possible to provide a high-quality gallium trioxide single crystal substrate with a low defect density in the GaO single crystal. The lower limit of the dislocation density in the central portion is 0 cm as an ideal value. -2A practical lower limit of the dislocation density in the central portion is, for example, 10 cm -2 is.

[0043] Specifically, the dislocation density in the central portion is determined by counting the number of corrosion pits (hereinafter also referred to as "etch pits") that appear in the central portion of the main surface after etching the main surface with an 85% by mass phosphoric acid solution. That is, the GaO single crystal substrate according to this embodiment has an etch pit density of 100 cm -2 It is preferable that the following holds: Although etch pits are not technically synonymous with dislocations, they can be considered equivalent to dislocations in this technical field.

[0044] (Method for calculating the number of etch pits) First, the main surface of a GaO single crystal substrate is immersed in an 85% by mass phosphoric acid solution at 190°C for 30 minutes. Then, the GaO single crystal substrate is removed from the phosphoric acid solution. Any conventionally known method can be used as a method for immersing the GaO single crystal substrate. This results in a GaO single crystal substrate in which dislocations present on the main surface, particularly in the central part, appear as etch pits.

[0045] Next, a virtual lattice is formed by arranging as many squares, each 1 mm on a side, parallel to each other without overlapping each other in the center of the GaO single crystal substrate. Each square constituting the virtual lattice is then observed with a known optical microscope (e.g., trade name: ECLIPSE (registered trademark) LV150N, manufactured by Nikon Corporation), and the number of etch pits appearing in one field of view of the optical microscope is counted. In this case, the observation with the optical microscope is performed at a magnification of 100x. As a result, one field of view of the optical microscope is 1 mm x 1 mm in size, corresponding to the size of the squares. Therefore, the number of etch pits per field of view is calculated as the number of dislocations per square constituting the virtual lattice. The number of etch pits is calculated based on ... in an area of ​​100 μm. 2 Only etch pits that are confirmed to be equal to or greater than this shall be counted.

[0046] Finally, the etch pits counted for each square constituting the virtual lattice were 1 cm 2 The dislocation density per square is then calculated. The sum of the dislocation densities is then divided by the number of squares to determine the dislocation density in the central region. In this specification, "placing the squares in the central region so as to maximize the number of parallel squares without overlapping each other" means that when the squares are plastered in the central region so as to overlap each other without overlapping each other, if the squares overlap the peripheral region and its outer edge, the squares are excluded from the virtual lattice. This is because, as mentioned above, the number of dislocations in the region near the periphery, including the peripheral region, of a GaO single crystal substrate varies greatly from substrate to substrate, and is generally not used as a material for semiconductor devices.

[0047] <Dopant> The GaO single crystal substrate according to this embodiment preferably contains a dopant. The dopant is preferably tin (Sn) or silicon (Si). The atomic concentration of the dopant is preferably 2×10 19 cm －3 This makes it possible to impart n-type (electron-donating) conductivity to the Ga2O3 single crystal substrate, and also makes it possible for the Ga2O3 single crystal substrate containing the dopant to have crack-resistant properties.

[0048] The atomic concentrations of Sn or Si in the GaO single crystal substrate are measured by glow discharge mass spectrometry (GDMS). When a GaO single crystal substrate is obtained from a GaO single crystal obtained by a GaO single crystal manufacturing method described below, the GaO single crystal substrate containing the dopant can be obtained by adding a predetermined amount of the dopant to a crucible together with a raw material such as gallium trioxide bulk (hereinafter also referred to as "GaO bulk"). The dopant is more preferably tin (Sn). The atomic concentration of the dopant is 1×10 17 cm －3 2 x 10 or more 19 cm－3 More preferably, it is:

[0049] [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. The method for manufacturing the GaO single crystal may 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; and placing a seed crystal in the bottom of the crucible and a block of digallium trioxide bulk (GaO bulk), a plate-like body made of pyrolytic boron nitride (pBN), and solid boron oxide above the seed crystal in the crucible. (BO) in this order, heating the crucible with the heating device to melt the GaO bulk and a portion of the seed crystal to obtain a digallium trioxide melt (GaO melt), bringing the GaO melt into contact with the remainder of the seed crystal, and growing a crystal from the GaO melt onto the remainder of the seed crystal to obtain a GaO single crystal. The step of bringing the GaO melt into contact with the remainder of the seed crystal includes the steps of placing the plate-shaped body on the GaO melt and liquefying the BO. The step of obtaining the GaO single crystal is performed in an inert gas atmosphere.

[0050] The crucible further includes a cylindrical seed crystal accommodating portion, an increasing diameter portion connected to the seed crystal accommodating portion, and a straight body portion connected to the increasing diameter portion. The seed crystal accommodating portion has a hollow portion that opens to the side connected to the increasing diameter portion and has a bottom wall formed on the opposite side. The increasing diameter portion has a shape in which the area S of a cross section perpendicular to the axial direction expands upward in the axial direction of the crucible, and is connected to the seed crystal accommodating portion at the small diameter side of the increasing diameter portion. The increasing diameter portion has three or four locations where the ratio S / Z, which is the ratio of the area S to the distance Z in the axial direction of the crucible from the connection point with the seed crystal accommodating portion, is 157.1 mm. The straight body portion has a hollow cylindrical shape and is connected to the large diameter side of the increasing diameter portion. When placed on the GaO melt, the plate-shaped body has multiple through holes that penetrate in a direction parallel to the axial direction. The area ratio of the plurality of through holes to the cross section of the plate-like body perpendicular to the axial direction is 0.12 to 0.28. The unit of the distance Z is mm, and the unit of the area S is mm 2 The unit of S / Z is mm. By using the method for producing a Ga2O3 single crystal having such characteristics, it is possible to obtain a Ga2O3 single crystal that can be used to form a Ga2O3 single crystal substrate that is less likely to crack.

[0051] Fig. 3 is a flowchart showing an example of a method for manufacturing a GaO single crystal substrate, including the method for manufacturing a GaO 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. 3. As shown in Fig. 3, 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. 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, a seed crystal, a massive GaO bulk, a plate-like body made of pBN, and solid BO are preferably also prepared. 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 bulk, the plate-like body, and the BO in this order above the seed crystal in the crucible (second step: raw material charging step S120). The GaO single crystal production step S100 also includes a step of heating the crucible with the heating device to melt the GaO bulk and part of the seed crystal to obtain a GaO melt, and a step of bringing the GaO melt into contact with the remainder of the seed crystal (third step: raw material melting step S130). The raw material melting step S130 preferably includes a step of placing the plate-like body on the GaO melt and liquefying the BO. The GaO single crystal manufacturing step S100 further includes a step of growing a crystal from the GaO melt on the remaining portion of the seed crystal to obtain a GaO single crystal (fourth step: GaO single crystal growing step S140). The GaO single crystal growing step S140 is preferably performed in an inert gas atmosphere.

[0052] The inventors focused on the structure of the increasing diameter section of the crucible constituting a GaO single crystal growth apparatus for growing GaO single crystals that form GaO single crystal substrates having the above-mentioned characteristics. Specifically, the increasing diameter section has a cross-sectional area S perpendicular to the axial direction of the crucible that increases from the bottom to the top of the crucible, and the side surface of the increasing diameter section has a shape that approximates a polygon when viewed in cross section parallel to the axial direction. More specifically, the increasing diameter section has a structure having three or four locations where the ratio S / Z, which is the ratio of the area S to the distance Z in the axial direction of the crucible from the connection point with the seed crystal container, is 157.1 mm. As a result, when performing the GaO single crystal growth step S140, the shape of the interface between the GaO melt and the crystal (GaO single crystal) in the diameter-increasing section is circular, perpendicular to the axial direction of the crucible, and substantially smooth along the axial direction (hereinafter simply referred to as a "flat shape"). As a result, the growth rate of the GaO single crystal grown in the diameter-increasing section is stabilized, resulting in a GaO single crystal with a uniform, even density of crystal defects. The GaO single crystal can be used to produce a GaO single crystal substrate having a main surface with a predetermined, uniform hardness within the surface. Therefore, the GaO single crystal can be used to produce a GaO single crystal substrate that is less likely to develop cracks or other breakages on the main surface, thereby reducing the risk of breakage. Based on the above, the inventors have conceived a GaO single crystal manufacturing method according to this embodiment.

[0053] Hereinafter, an overview of the GaO single crystal growth apparatus and the GaO single crystal production step S100 will be described with reference to FIGS. 3 and 4 to 7. FIG. 4 is a schematic diagram illustrating the production apparatus used in the GaO single crystal production method according to this embodiment. FIG. 5 is an explanatory diagram illustrating one embodiment of a crucible (first crucible) included in the production apparatus used in the GaO single crystal production method according to this embodiment. FIG. 6 is an explanatory diagram illustrating another embodiment of a crucible (second crucible) included in the production apparatus used in the GaO single crystal production method according to this embodiment. FIG. 7 is an explanatory diagram illustrating, in plan view, one embodiment of a plate-shaped body included in the production apparatus used in the GaO single crystal production method according to this embodiment. In the GaO single crystal production method according to this embodiment (GaO single crystal production step S100), for example, the GaO single crystal growth apparatus 100 shown in FIG. 4 is used. The GaO single crystal growth apparatus 100 can grow a single crystal by the vertical boat method using a crucible 5. Hereinafter, the vertical boat method will be abbreviated as the VB method. The VB method includes the vertical Bridgman method and the vertical temperature gradient freeze method.

[0054] 4, the GaO single crystal growth apparatus 100 includes the crucible 5 described above, a crucible-holding stage 6 for holding the crucible 5, a lower shaft 7 for supporting the crucible 5 and the crucible-holding stage 6, and a heater 9 for heating the crucible 5. The GaO single crystal growth apparatus 100 also includes a plate-like body 3 that is placed on the GaO melt 82, which is the molten GaO bulk body, in the GaO single crystal growth step S140. BO, which is liquefied in the GaO single crystal growth step S140 and used to seal the GaO melt 82 in the crucible 5, is placed on the plate-like body 3. In the GaO single crystal manufacturing method according to this embodiment, in addition to the GaO single crystal growth apparatus 100, a chamber 2 is preferably used to accommodate the contents, such as the GaO bulk contained in the crucible 5, the crucible-holding stage 6, the lower shaft 7, and the heating device 9, in order to perform the GaO single crystal growth step S140 in an inert gas atmosphere. The dimensions and materials of the chamber 2 are not particularly limited as long as they are large enough to accommodate the GaO single crystal growth apparatus 100 and the like and are capable of maintaining an inert gas atmosphere inside. Furthermore, if the sidewall of the chamber has good thermal transmittance, the heating device of the GaO single crystal growth apparatus can be located outside the chamber.

[0055] (Crucible) As shown in FIG. 4 , in the GaO single crystal growth apparatus 100, the crucible 5 includes a cylindrical seed crystal accommodation portion 51, an increasing diameter portion 52 connected to the seed crystal accommodation portion 51, and a straight body portion 53 connected to the increasing diameter portion 52. The seed crystal accommodation portion 51 is cylindrical and has a hollow portion that opens on the side connected to the increasing diameter portion 52 and has a bottom wall formed on the side opposite the increasing diameter portion 52. The seed crystal accommodation portion 51 can accommodate and hold a seed crystal 81 in the hollow portion. The increasing diameter portion 52 has a shape in which the area S of a cross section perpendicular to the axial direction of the crucible 5 expands upward in the axial direction. The increasing diameter portion 52 is connected to the seed crystal accommodation portion 51 at its small diameter side. The straight body portion 53 has a hollow cylindrical shape and is connected to the large diameter side of the increasing diameter portion 52. In particular, the increased diameter portion 52 has three or four locations where the ratio S / Z, which is the ratio of the distance Z in the axial direction of the crucible 5 from the connection point with the seed crystal accommodation portion 51 as the starting point, to the area S, is 157.1 mm. The unit of the distance Z is mm, and the unit of the area S is mm. 2 where the unit of S / Z is mm. Details of the shape of the side surface of the diameter increasing portion 52 will be described later. The diameter increasing portion 52 and the straight body portion 53 have the function of holding a massive GaO bulk body (specifically, polycrystalline GaO) therein. The diameter increasing portion 52 and the straight body portion 53 have the function of growing a GaO single crystal by solidifying the GaO melt 82, as will be described later.

[0056] Various materials that can withstand the temperature of the GaO melt 82 can be used for the crucible 5. For example, platinum, platinum alloys containing rhodium, etc. can be used as the material for the crucible 5. Furthermore, since the GaO single crystal growth step S140 is performed in an inert gas atmosphere, pBN can also be used as the material for the crucible 5. In this case, the manufacturing cost of the GaO single crystal growth apparatus 100 can be reduced. The inner diameter of the straight body portion 53 depends on the diameter of the GaO single crystal to be produced, but is, for example, 90 mm or more and 165 mm or less. The shape of the side surface of the diameter-increasing portion 52 of the crucible 5 will be described in detail below.

[0057] 1) First Crucible In the GaO single crystal manufacturing method, a first crucible 5A as shown in FIG. 5 may be used as one embodiment of the crucible 5 constituting the GaO single crystal growth apparatus 100. The first crucible 5A has an increasing diameter portion 52 extending upward in the axial direction of the first crucible 5A, the cross-sectional area S of which is perpendicular to the axial direction. In particular, the first crucible 5A has three side portions. The three side portions are a lower portion 52a, which has the largest angle with respect to the axis of the first crucible 5A among the three side portions; a middle portion 52b, which has the second largest angle with respect to the axis of the first crucible 5A among the three side portions; and an upper portion 52c, which has the smallest angle with respect to the axis of the first crucible 5A among the three side portions.

[0058] The increasing diameter section 52 of the first crucible 5A has the three side sections described above, and thus can have three locations where the ratio S / Z, which is the ratio of the area S to the axial distance Z of the first crucible 5A from the connection point with the seed crystal accommodation section 51, is 157.1 mm. Specifically, the lower section 52a, the middle section 52b, and the upper section 52c constituting the three side sections each have one location where the S / Z is 157.1 mm. As a result, in the increasing diameter section 52 of the first crucible 5A, the interface between the GaO melt 82 and the GaO single crystal has a flatter shape than in a conventional increasing diameter section having a truncated cone shape that expands axially upward in the crucible, and this stabilizes the crystal growth rate. Therefore, in the above-mentioned method for producing GaO single crystals, the growth rate of the crystal growing in the body portion 53 can be stabilized by adjusting the output of the heating device 9 as described below, and GaO single crystals with a uniform density of crystal defects can be produced.

[0059] 2) Second Crucible In the GaO single crystal manufacturing method described above, a second crucible 5B as shown in FIG. 6 may be used as another embodiment of the crucible 5 constituting the GaO single crystal growth apparatus 100. The second crucible 5B has an increasing diameter portion 52 facing upward in the axial direction of the second crucible 5B, the portion having a shape in which the area S of a cross section perpendicular to the axial direction increases. In particular, in the second crucible 5B, the side surface of the increasing diameter portion 52 has four side surfaces. The four side portions are the lowest portion 52d, which of the four side portions has the largest angle with respect to the axis of the second crucible 5B; the first middle portion 52e, which of the four side portions has the second largest angle with respect to the axis of the second crucible 5B after the lowest portion 52d; the second middle portion 52f, which of the four side portions has the second largest angle with respect to the axis of the second crucible 5B after the lowest portion 52d and the first middle portion 52e; and the top portion 52g, which of the four side portions has the smallest angle with respect to the axis of the second crucible 5B.

[0060] The increasing diameter section 52 of the second crucible 5B has the four side sections described above, and thus can have four locations where the ratio S / Z, which is the ratio of the area S to the distance Z in the axial direction of the second crucible 5B from the connection point with the seed crystal accommodation section 51, is 157.1 mm. Specifically, the four side sections, namely the lowest section 52d, the first middle section 52e, the second middle section 52f, and the highest section 52g, each have one location where the S / Z is 157.1 mm. As a result, in the increasing diameter section 52 of the second crucible 5B, the interface between the GaO melt 82 and the GaO single crystal has a flatter shape than in a conventional increasing diameter section having a truncated cone shape that expands axially upward. This stabilizes the crystal growth rate. Therefore, in the above-mentioned method for producing GaO single crystals, the growth rate of the crystal growing in the body portion 53 can be stabilized by adjusting the output of the heating device 9 as described below, and GaO single crystals with a uniform density of crystal defects can be produced.

[0061] (Crucible-holding stage) The GaO single crystal growth apparatus 100 includes a crucible-holding stage 6 that holds the crucible 5. The crucible-holding stage 6 contacts the bottom of the crucible 5 to hold the crucible 5. The crucible-holding stage 6 may have a cylindrical appearance. The material of the crucible-holding stage 6 is not particularly limited, but may be, for example, quartz, alumina, or silicon carbide. The outer diameter of the crucible-holding stage 6 depends on the diameter of the crucible 5 to be supported, but is, for example, 75 mm or more and 200 mm or less.

[0062] (Lower Shaft) The lower shaft 7 supports the crucible-holding stage 6 from below, thereby supporting the crucible 5 and the crucible-holding stage 6. The lower shaft 7 may be, for example, rod-shaped and circular or rectangular in horizontal cross section. The lower shaft 7 may be made of, for example, molybdenum, carbon, or silicon carbide.

[0063] (Heating Device) The heating device 9 is installed for the purpose of heating the crucible 5. The heating device 9 may be, for example, a conventionally known electric heater (hereinafter also simply referred to as "heater"). For example, two heaters may be provided, and these two heaters may be arranged to surround the outer periphery of the crucible 5. The heater output may be controlled independently for each heater. In particular, the heater may be divided into multiple sections perpendicular to the axis of the crucible 5, resulting in a multi-stage configuration. In this case, it is preferable to independently control the heater output for each of the multi-stage sections. This allows the temperature of the contents in the crucible 5 to be precisely adjusted along the axial direction of the crucible 5. For example, by independently controlling the heater output for each of the multi-stage sections to heat the body portion 53, the growth rate of the crystal growing in the body portion 53 can be stabilized.

[0064] Although not shown, the GaO single crystal growth apparatus 100 may be provided with a thermocouple capable of measuring the temperature of the crucible 5 heated by the heater. A plurality of thermocouples may be arranged outside the crucible 5 along the axial direction. For example, a known temperature monitor may be used as the thermocouple.

[0065] (Plate) The plate 3 is made of pBN. In the GaO single crystal growth apparatus 100, the plate 3 is placed above the GaO melt 82 to prevent the GaO melt 82 from coming into contact with the liquid sealant, BO 4, and dissolving (so-called dissolution loss). As shown in FIG. 7 , the plate 3 has a plurality of through-holes 3 a that penetrate the crucible 5 in a direction parallel to the axial direction when placed above the GaO melt 82. The area ratio of the through-holes 3 a to the cross section of the plate 3 perpendicular to the axial direction is 0.12 to 0.28. This allows the plate 3 to discharge bubbles generated in the GaO melt 82 through the through-holes 3 a to the outside of the crucible 5, or at least to the outside of the GaO melt 82 used for crystal growth. That is, the plurality of through holes 3a can prevent the plate-like body 3 from floating up due to bubbles generated in the GaO melt 82, which would prevent the above-mentioned purpose from being lost. Furthermore, the plurality of through holes 3a can also prevent bubbles generated in the GaO melt 82 from remaining in the GaO single crystal.

[0066] When the plate-shaped body 3 is placed above the GaO melt 82, the area ratio of the multiple through holes 3a to the cross section of the plate-shaped body 3 perpendicular to the axial direction of the crucible 5 is 0.12 to 0.28 as described above. The area ratio is preferably 0.122 to 0.275. When the area ratio is within the above range, bubbles generated in the GaO melt 82 can be efficiently discharged to the outside of the crystal growth system through the multiple through holes 3a.

[0067] <GaO Single Crystal Production Process S100> (First Step: Preparation Step S110) As shown in FIG. 3, the GaO single crystal production process S100 begins with a 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 crucible. In preparation step S110, in addition to the GaO single crystal growth apparatus 100 described above for producing the GaO single crystal, a seed crystal 81, a massive GaO bulk, a pBN plate, and solid BO are preferably also prepared. The seed crystal 81 is made of a GaO single crystal. The GaO bulk may be made of polycrystalline GaO. The seed crystal 81, massive GaO bulk, plate-like body 3, and solid BO may be prepared by conventional methods or by commercially available products. The crucible 5 constituting the GaO single crystal growth apparatus 100 is selected from the first crucible 5A and the second crucible 5B having the structure described above. The GaO single crystal growth apparatus 100 is preferably installed in a chamber 2 so that the GaO single crystal growth step S140 (described later) is performed under an inert gas atmosphere. Examples of the inert gas include nitrogen and argon. Subsequently, in the GaO single crystal production step S100, each step for obtaining a GaO single crystal is performed by growing the crystal using the GaO single crystal growth apparatus.

[0068] (Second Step: Raw Material Charging Step S120) The raw material charging step S120 is a step of placing the seed crystal at the bottom of the crucible, and placing the GaO bulk, the plate-like body, and the BO in this order above the seed crystal in the crucible. The purpose of the raw material charging step S120 is to seal various raw materials for crystal growth using the GaO single crystal growth apparatus 100 into the crucible. In the raw material charging step S120, first, a seed crystal 81 made of a GaO single crystal is charged into the hollow portion of the seed crystal accommodating portion 51 of the crucible 5. Next, multiple block-shaped GaO bulk bodies made of polycrystalline GaO are charged and stacked into the increasing diameter portion 52 and the straight body portion 53 of the crucible 5. Next, a plate-like body 3 is placed on the GaO bulk body, and solid BO is placed on the plate-like body 3. In the raw material charging step S120, it is preferable to add a predetermined amount of Sn or Si when charging a plurality of massive GaO bulk bodies into the crucible 5. This allows a GaO single crystal substrate containing the Sn or Si as a dopant to be obtained from the GaO single crystal obtained in the GaO single crystal manufacturing step S100. When adding Sn or Si, the concentration of the dopant in the GaO single crystal substrate is adjusted to 2×10 19 cm －3 or less (for example, 1.0 × 10 17 cm -3 2 x 10 or more 19 cm -3 It is preferable to adjust the amount of addition so that the following is satisfied:

[0069] (Third Step: Raw Material Melting Step S130) The raw material melting step S130 is a step of heating the crucible with the heating device to melt the GaO bulk body and a portion of the seed crystal to obtain a GaO melt, and bringing the GaO melt into contact with the remainder of the seed crystal. The purpose of the raw material melting step S130 is to melt the GaO bulk body and a portion of the seed crystal 81 to bring the remainder of the seed crystal 81 into contact with the GaO melt 82 when performing crystal growth using the GaO single crystal growth apparatus 100. This allows a GaO single crystal to be grown on the remainder of the seed crystal 81 in the next step, the GaO single crystal growth step S140. Specifically, in the raw material melting step S130, a crucible 5 containing a seed crystal 81, a GaO bulk, a plate-like body 3, and solid BO is supported on a crucible-holding stage 6 installed in the chamber 2. Thereafter, an electric current is supplied to the heating device 9 to heat the crucible 5. As a result, the solid BO melts into liquid BO4, and the GaO bulk melts into a GaO melt 82. Next, a portion of the seed crystal 81 also melts, and the remainder of the seed crystal 81 and the GaO melt 82 come into contact at the interface.

[0070] (Fourth Step: GaO Single Crystal Growth Step S140) The GaO single crystal growth step S140 is a step of growing a crystal from the GaO melt onto the remaining portion of the seed crystal to obtain the GaO single crystal. In the GaO single crystal growth step S140, for example, the crucible 5 is gradually lowered along its axis (toward the seed crystal accommodation portion 51) relative to the heating device 9, thereby forming a temperature gradient in the crucible 5 such that the temperature on the seed crystal 81 side is low and the temperature on the GaO melt 82 side is high. This solidifies the GaO melt 82 in contact with the seed crystal 81, allowing continuous crystal growth of the GaO single crystal from the GaO melt 82 on the remaining portion of the seed crystal 81. The speed at which the crucible 5 is pulled downward along its axis is not particularly limited, but may be, for example, 0.2 to 3 mm / hour.

[0071] The GaO single crystal growth step S140 is performed using a GaO single crystal growth apparatus 100 including the first crucible 5A or second crucible 5B having the above-described structure. This allows the shape of the interface between the GaO melt and the GaO single crystal to be flat, particularly when the GaO single crystal is growing in the diameter-increasing section 52, thereby stabilizing the growth rate of the GaO single crystal. Furthermore, in the GaO single crystal growth step S140, the growth rate of the GaO single crystal can be stabilized by adjusting the output of the heating device 9 when the GaO single crystal is growing in the straight body section 53. As described above, the GaO single crystal production step S100 allows the production of a GaO single crystal with a uniform, even density of crystal defects.

[0072] In the GaO single crystal growth step S140, the crucible 5 (first crucible 5A or second crucible 5B) is pulled downward along its axis relative to the heating device 9, so that the interface between the GaO single crystal and the GaO melt 82 rises toward the liquid BO side, and the GaO melt 82 is solidified as a GaO single crystal. This allows the growth of the GaO single crystal to continue until the solidification of the GaO melt 82 remaining in the straight body portion 53 of the crucible 5 (first crucible 5A or second crucible 5B) is completed. In this manner, a GaO single crystal ingot can be obtained.

[0073] [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. 3, 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 cutting steps, outer periphery grinding steps, and polishing steps, which are performed in this order to obtain a GaO single crystal substrate.

[0074] The cutting step is a step of slicing the ingot made of GaO single crystal removed from the crucible 5 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 main surfaces having the chamfered region as the outer periphery can be obtained by the periphery grinding step. 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.

[0075] [Effects] By carrying out the above steps, a 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, a GaO single crystal with a uniform, even density of crystal defects can be grown. This allows a GaO single crystal substrate having a main surface with a predetermined, uniform hardness within the surface to be obtained from the GaO single crystal. As described above, based on the hardness characteristics described above, the present disclosure allows for the production of a GaO single crystal substrate that is less likely to form starting points for cracks or other fractures on the main surface and is therefore less likely to break.

[0076] 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, a GaO single crystal substrate was produced according to the flowchart shown in Fig. 3 using a GaO single crystal production apparatus as shown in Fig. 4, a crucible as shown in Figs. 5 and 6, and a plate as shown in Fig. 7. In the following description, Samples 1 and 2 are examples, and Sample a is a comparative example.

[0077] [Manufacturing GaO Single Crystal Substrate] <Sample 1> (Preparation Step S110 in GaO Single Crystal Manufacturing Step S100) First, a GaO single crystal growth apparatus 100, a seed crystal 81 made of a GaO single crystal, a GaO bulk mass made of polycrystalline GaO, a pBN plate 3, and solid BO were prepared by conventional methods or commercially available. A chamber 2 to house the GaO single crystal growth apparatus 100 was also prepared. The crucible 5 included in the GaO single crystal growth apparatus 100 was the first crucible 5A, which had the three side surfaces in the diameter-increasing section 52 as described above and was manufactured by conventional methods. Furthermore, the chamber 2 was filled with a nitrogen atmosphere for the purpose of performing the GaO single crystal growth step S140 described below under an inert gas atmosphere.

[0078] Here, the increasing diameter portion 52 of the first crucible 5A has three locations where the ratio S / Z, which is the ratio of the distance Z in the axial direction of the first crucible 5A starting from the connection point with the seed crystal accommodation portion 51 to the area S of a cross section perpendicular to the axial direction of the first crucible upward in the axial direction of the first crucible, is 157.1 mm. Specifically, the increasing diameter portion 52 of the first crucible 5A has a shape specified by the distance Z, area S, and S / Z shown in Table 1 below. That is, as shown in Table 1 below, the increasing diameter portion 52 of the first crucible 5A has a shape having three side portions: a lower portion 52a where the distance Z is from 0 mm to 11.52 mm, a middle portion 52b where the distance Z is from 11.52 mm to 28.88 mm, and an upper portion 52c where the distance Z is from 28.88 mm to 54.07 mm. Furthermore, the boundary between lower portion 52a and middle portion 52b, the boundary between middle portion 52b and upper portion 52c, and the boundary between upper portion 52c and straight body portion 53 each have a shape in which S / Z is 157.1 mm. In Table 1 below, "R" represents the radius of a cross section (circular) of increased diameter portion 52 of first crucible 5A that is perpendicular to the axial direction at the point of distance Z. The inner diameter of straight body portion 53 of first crucible 5A is 104 mm.

[0079]

[0080] (Raw Material Charging Step S120 in GaO Single Crystal Production Step S100) Next, using a conventionally known method, a seed crystal 81 was placed at the bottom of the first crucible 5A, and a GaO bulk, a plate-like body 3, and solid BO were placed in this order above the seed crystal 81 in the first crucible 5A. Specifically, the seed crystal 81 consisting of a GaO single crystal was placed in the hollow portion of the seed crystal receiving portion 51 of the first crucible 5A. Multiple GaO bulk blocks were placed and stacked in the increased diameter portion 52 and the straight body portion 53 of the first crucible 5A. Next, the plate-like body 3 was placed on the GaO bulk, and solid BO was placed on the plate-like body 3. Furthermore, when a plurality of GaO bulk bodies were placed in the first crucible 5A, a predetermined amount of Sn was added so that the atomic concentration of Sn in the GaO single crystal substrate was 3×10 18 cm －3 The amount was set to be:

[0081] (Raw material melting step S130 in GaO single crystal production process S100) Next, the first crucible 5A containing the seed crystal 81, the GaO bulk, the plate-like body 3, and the solid BO was placed in the chamber 2 and supported by the crucible-holding stage 6 installed in the chamber 2. Thereafter, an electric current was supplied to the heating device 9 to heat the first crucible 5A, thereby melting the solid BO into liquid BO4 and melting the GaO bulk into a GaO melt 82. Next, a portion of the seed crystal 81 was also melted, and the remainder of the seed crystal 81 and the GaO melt 82 were brought into contact at the interface therebetween.

[0082] (GaO Single Crystal Growth Step S140 in GaO Single Crystal Production Step S100) Next, the first crucible 5A was gradually lowered along its axis (toward the seed crystal accommodation portion 51) relative to the heating device 9, creating a temperature gradient such that the temperature on the seed crystal 81 side was lower and the temperature on the GaO melt 82 side was higher in the first crucible 5A. This solidified the GaO melt 82 in contact with the seed crystal 81, and a GaO single crystal was continuously grown from the GaO melt 82 on the remaining portion of the seed crystal 81. This operation was continued until the GaO melt 82 remaining in the straight body portion 53 of the first crucible 5A was completely solidified. The speed at which the first crucible 5A was lowered along its axis was 2 mm / hour. A GaO single crystal ingot was thus obtained.

[0083] (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 peripheral portion surrounding the periphery of the central portion. Furthermore, in the polishing process, the central portion was polished using a conventionally known polishing method to achieve a surface roughness Ra of 20 nm at the central portion, as specified in JIS B 0681-2:2018, for example. Thus, the GaO single crystal substrate of Sample 1 was manufactured.

[0084] The diameter of the GaO single crystal substrate of Sample 1 was 100 mm. The thickness of the GaO single crystal substrate of Sample 1 was 650 μm. The dislocation density at the center of the GaO single crystal substrate of Sample 1, measured by the above-mentioned method, was 100 cm -2 It was.

[0085] <Sample 2> A GaO single crystal substrate of Sample 2 was manufactured in the same manner as Sample 1, except that the second crucible 5B having the four side surfaces as described above in the diameter increasing section 52 was manufactured by a conventionally known method as the crucible 5 constituting the GaO single crystal growth apparatus 100. The diameter of the GaO single crystal substrate of Sample 2 was 100 mm. The thickness of the GaO single crystal substrate of Sample 1 was 650 μm. The dislocation density in the center of the GaO single crystal substrate of Sample 2, measured by the method described above, was 50 cm -2 It was.

[0086] Here, the increased diameter portion 52 of the second crucible 5B has four locations where the ratio S / Z, which is the ratio of the distance Z in the axial direction of the second crucible 5B from the connection point with the seed crystal accommodation portion 51 as the starting point to the area S of a cross section perpendicular to the axial direction of the second crucible 5B upward in the axial direction of the second crucible 5B, is 157.1 mm. Specifically, the increased diameter portion 52 of the second crucible 5B has a shape specified by the distance Z, area S, and S / Z shown in Table 2 below. That is, the increased diameter portion 52 of the second crucible 5B has a shape with four side portions, including a lowest portion 52d having a distance Z of 0 mm to 8.00 mm, a first middle portion 52e having a distance Z of 8.00 mm to 18.00 mm, a second middle portion 52f having a distance Z of 18.00 mm to 32.00 mm, and a highest portion 52g having a distance Z of 32.00 mm to 50.00 mm, as shown in Table 2 below. Furthermore, the shape is such that the S / Z is 157.1 mm at the boundary between the lowest portion 52d and the first middle portion 52e, the boundary between the first middle portion 52e and the second middle portion 52f, the boundary between the second middle portion 52f and the highest portion 52g, and the boundary between the highest portion 52g and the straight body portion 53. In the following Table 2, "R" represents the radius of the cross section (circular) of the increased diameter portion 52 of the second crucible 5B perpendicular to the axial direction at the point of the distance Z. The inner diameter of the straight body portion 53 of the second crucible 5B is 100 mm.

[0087]

[0088] <Sample a> A GaO single crystal substrate of sample a was manufactured in the same manner as sample 1, except that a conventionally known crucible having a truncated cone shape with a diameter expanding upward in the axial direction was manufactured and used as the crucible constituting the GaO single crystal growth apparatus. The diameter of the GaO single crystal substrate of sample a was 100 mm. The thickness of the GaO single crystal substrate of sample a was 650 μm. The dislocation density in the center of the GaO single crystal substrate of sample a, measured by the method described above, was 500 cm -2 It was.

[0089] [Measurement of nanoindentation hardness] The first nanoindentation hardness and the second nanoindentation hardness were determined at nine predetermined locations on the main surface of the GaO single crystal substrates of Samples 1, 2, and a by carrying out the above-described measurement method. The measurement apparatus and measurement conditions used to carry out the above-described measurement method are as follows:

[0090] Equipment used: Nanoindenter (product name: "Bruker Hysitron TI980 Triboindenter", manufactured by Bruker Japan Co., Ltd.) Indenter used: Berkovich indenter Maximum load: 1 mN or 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°.

[0091] The same location on the same substrate was measured three times, and the average values ​​(unit: GPa) of the three measured values ​​were used as the first nanoindentation hardness and the second nanoindentation hardness at each of the nine predetermined locations on the main surface. Furthermore, the difference (Δ(max-min)) between the maximum and minimum values ​​of the first nanoindentation hardness and the second nanoindentation hardness at each of the nine predetermined locations on the main surface was also calculated. The nine predetermined locations refer to the following positions on the main surface: That is, 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), (0, -(r-5)), (r-1, 0), (0, r-1), (-(r-1), 0), and (0, -(r-1)). The units of r and X and Y in the coordinates (X, Y) are in mm. The r in the GaO single crystal substrates of Samples 1 and 2 and Sample a was 48 mm. The results are shown in Tables 3 and 4. Table 3 shows the first nanoindentation hardness at nine predetermined locations on the main surface, and Table 4 shows the second nanoindentation hardness at nine predetermined locations on the main surface. Tables 3 and 4 also show the standard deviation (unit: GPa) of three measured values ​​obtained by measuring the same location on the same substrate three times.

[0092]

[0093]

[0094] [Discussion] According to Tables 3 and 4, the first nanoindentation hardnesses of the Ga2O3 single crystal substrates of Samples 1 and 2 measured at nine locations on the main surface were all 13 GPa or more and 20 GPa or less. This suggests that the Ga2O3 single crystal substrates of Samples 1 and 2 are less likely to form starting points for cracks or other fractures on the main surface, and are therefore less likely to break. Furthermore, the second nanoindentation hardnesses of the Ga2O3 single crystal substrates of Samples 1 and 2 measured at nine locations on the main surface were all 15 GPa or more and 20 GPa or less, suggesting that they are even more resistant to fracture. On the other hand, the first nanoindentation hardnesses of the Ga2O3 single crystal substrate of Sample a measured at nine locations on the main surface were less than 13 GPa at any of the locations.

[0095] 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.

[0096] 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.

[0097] 1 Gallium trioxide single crystal substrate (Ga2O3 single crystal substrate), 10 Main surface, 11 Center, 12 Outer periphery, 13 Boundary, 2 Chamber, 3 Plate-shaped body, 3a Through-hole, 4 Liquid boron oxide (B2O3), 5 Crucible, 5A First crucible, 5B Second crucible, 51 Seed crystal accommodating section, 52 Increasing diameter section, 52a Lower section, 52b Middle section, 52c Upper section, 52d Lowermost section, 52e First middle section, 52f Second middle section, 52g Uppermost section, 53 Straight body section 6 Crucible holding stage, 7 Lower shaft, 81 Seed crystal, 82 Gallium trioxide melt (Ga2O3 melt), 9 Heating device, 100 Single crystal growth device, O Center, r Length from the center of the main surface to the boundary between the central part and the outer periphery, S area, Z distance, S100 Ga2O3 single crystal manufacturing process, S110 preparation process, S120 raw material loading process, S130 raw material melting process, S140 Ga2O3 single crystal growth process, S200 Ga2O3 single crystal substrate manufacturing 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 main surface is a (001) plane of the digallium trioxide single crystal constituting the digallium trioxide single crystal substrate, the main surface has a central portion including the center thereof and an outer periphery surrounding the periphery of the central portion, The outer periphery is a chamfered region, a first nanoindentation hardness measured at nine points on the main surface under first conditions in which a maximum load of 10 mN is applied according to a nanoindentation method using a Berkovich indenter such that an intersection angle between one side of an indentation and a direction in which the [100] direction of the gallium trioxide single crystal is projected onto the main surface is equal to or greater than 0° and equal to or less than 10°; and a digallium trioxide single crystal substrate, wherein r is the length from the center of the main surface to the boundary between the central portion and the outer periphery, two axes passing through the center and perpendicular to each other on the main surface are the X-axis and the Y-axis, and the Y-axis is the b-axis of the digallium trioxide single crystal, the nine coordinates (X, Y) of the X-axis and the Y-axis are (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), (0, -(r-5)), (r-1, 0), (0, r-1), (-(r-1), 0), and (0, -(r-1)), and the units of r and X and Y in the coordinates (X, Y) are mm.

2. 2. The digallium trioxide single crystal substrate according to claim 1, wherein the second nanoindentation hardness measured at the nine locations under second conditions in which a maximum load of 1 mN is applied according to the nanoindentation method and a load is applied such that an intersection angle between one side of the indentation and a direction in which the [100] direction of the digallium trioxide single crystal is projected onto the main surface is 0° or more and 10° or less is 15 GPa or more and 20 GPa or less.

3. The dislocation density in the center is 100 cm -2 3. The gallium trioxide single crystal substrate according to claim 1, wherein:

4. the gallium trioxide single crystal substrate contains a dopant; the dopant is tin or silicon; The atomic concentration of the dopant is 2×10 19 cm －3 3. The gallium trioxide single crystal substrate according to claim 1, wherein:

5. A method for producing gallium trioxide single crystals, comprising: 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; a step of placing a seed crystal at the bottom of the crucible, and placing a massive gallium trioxide bulk body, a plate-like body made of pyrolytic boron nitride, and solid boron oxide in this order above the seed crystal in the crucible; heating the crucible with the heating device to melt the gallium trioxide bulk and a portion of the seed crystal to obtain a gallium trioxide melt, and bringing the gallium trioxide melt into contact with the remainder of the seed crystal; and growing a crystal from the digallium trioxide melt on the remainder of the seed crystal to obtain the digallium trioxide single crystal, the step of bringing the digallium trioxide melt into contact with the remainder of the seed crystal includes the steps of placing the plate-shaped body on the digallium trioxide melt and liquefying the boron oxide; The atmosphere in which the step of obtaining the gallium trioxide single crystal is performed is an inert gas atmosphere, The crucible includes a cylindrical seed crystal accommodating portion, an increasing diameter portion connected to the seed crystal accommodating portion, and a straight body portion connected to the increasing diameter portion, the seed crystal accommodating portion has a hollow portion that opens to a side connected to the diameter increasing portion and has a bottom wall formed on the opposite side, The increasing diameter portion has a shape in which an area S of a cross section perpendicular to the axial direction expands upward in the axial direction of the crucible, and is connected to the seed crystal accommodation portion at a small diameter side of the increasing diameter portion, The increasing diameter portion has three or four portions where S / Z, which is a ratio of a distance Z in the axial direction of the crucible from a connection point with the seed crystal accommodation portion as a starting point to the area S, is 157.1 mm; The straight body portion has a hollow cylindrical shape and is connected to the large diameter side of the increased diameter portion, the plate-like body has a plurality of through holes that penetrate in a direction parallel to the axial direction when placed on the gallium trioxide melt, an area ratio of the plurality of through holes to a cross section of the plate-like body perpendicular to the axial direction is 0.12 or more and 0.28 or less; The unit of the distance Z is mm, and the unit of the area S is mm 2 and the unit of S / Z is mm.

6. A method for producing a digallium trioxide single crystal substrate, comprising the step of processing the digallium trioxide single crystal obtained by the method for producing a digallium trioxide single crystal according to claim 5 to obtain a digallium trioxide single crystal substrate having a circular main surface.

7. The dislocation density in the center is 100 cm -2 is as follows: the gallium trioxide single crystal substrate contains a dopant; the dopant is tin; The atomic concentration of the dopant is 2×10 19 cm －3 3. The gallium trioxide single crystal substrate according to claim 2, wherein: