Bulk GaN crystals, c-plane GaN wafers, and methods for producing bulk GaN crystals

Abstract

In order to provide a bulk GaN crystal in which the degree of curvature of the c-plane is reduced, the present invention provides a bulk GaN crystal having a principal surface selected from a surface that is inclined 0 degrees to 10 degrees from the (0001) crystal plane and a surface that is inclined 0 degrees to 10 degrees from the (000-1) crystal plane, the principal surface being a specific principal surface A that satisfies conditions (i) and (ii) below. (i): A first line as a virtual line segment having a length of 80 mm that extends in a first direction on the specific principal surface A can be drawn, and the difference between the maximum value and the minimum value of the peak angle of (002) XRD rocking curves of the GaN crystal, measured between 17 measurement points arranged at a 5-mm pitch on the first line and with the omega axis perpendicular to the first direction, is 0.05 degrees or less. (ii): A second line as a virtual line segment having a length of 80 mm that extends in a second direction perpendicular to the first direction on the specific principal surface A can be drawn, and the difference between the maximum value and the minimum value of the peak angle of (002) XRD rocking curves of the GaN crystal, measured between 17 measurement points arranged at a 5-mm pitch on the second line and with the omega axis perpendicular to the second direction, is 0.05 degrees or less.

Description

[Technical field]

[0001] The present invention primarily relates to bulk GaN crystals, c-plane GaN wafers, and methods for producing bulk GaN crystals. [Background technology]

[0002] GaN (gallium nitride) has a wurtzite crystal structure that belongs to the hexagonal crystal system. In recent years, GaN wafers, which are free-standing wafers made of GaN crystals, have been attracting attention as substrates for nitride semiconductor devices. Nitride semiconductor devices are semiconductor devices that use nitride semiconductors in the main part of the device structure. Nitride semiconductors are also called nitride III-V group compound semiconductors, group III nitride compound semiconductors, GaN-based semiconductors, etc., and include GaN and compounds in which part or all of the gallium in GaN is replaced with other group 13 elements of the periodic table (B, Al, In, etc.).

[0003] GaN wafers with various crystal orientations have been reported, but among them, the GaN wafers that have been the subject of vigorous research and development for application to high-output laser diodes and power semiconductor devices are those with a primary surface (large-area surface) roughly parallel to the (000±1) crystal plane, i.e., c-plane GaN wafers.

[0004] The manufacturing process of c-plane GaN wafers may include a step of slicing a bulk GaN crystal grown in the c-axis direction approximately parallel to the c-plane. The variation in the offcut angle within the primary surface of the sliced ​​c-plane GaN wafer is related to the curvature of the c-plane of the bulk GaN crystal before slicing (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2008 / 0029783 Summary of the Invention [Problem to be solved by the invention]

[0006] To manufacture c-plane GaN wafers with a narrow variation range of the offcut angle within the primary surface, it is necessary to grow bulk GaN crystals with improved c-plane curvature. In this case, reducing the degree of curvature is called curvature improvement. Objectives of the present invention include at least providing bulk GaN crystals with improved c-plane curvature, providing c-plane GaN wafers with reduced variation in offcut angle within the primary surface, and providing a novel method for producing bulk GaN crystals. [Means for solving the problem]

[0007] Embodiments of the present invention include, but are not limited to, the following. [1] A bulk GaN crystal having a primary surface selected from a plane inclined from 0 to 10 degrees from the (0001) crystal plane and a plane inclined from 0 to 10 degrees from the (000-1) crystal plane, the primary surface being a specific primary surface A that satisfies the following conditions (i) and (ii): (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the specific main surface A, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) A second line, which is an imaginary line segment having a length of 80 mm extending in a second direction perpendicular to the first direction, can be drawn on the specific main surface A, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less. [2] A bulk GaN crystal having a first principal surface and a second principal surface facing in opposite directions, one of the first principal surface and the second principal surface being inclined at an angle of 0 to 10 degrees from the (0001) crystal plane and the other surface being inclined at an angle of 0 to 10 degrees from the (000-1) crystal plane, and which satisfies the following conditions (i) and (ii): (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the first main surface, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) A second line, which is an imaginary line segment having a length of 80 mm extending on the first main surface in a second direction perpendicular to the first direction, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less. [3] A bulk GaN crystal according to [1] or [2], wherein the difference between the maximum and minimum values ​​of the peak angle under condition (i) and the difference between the maximum and minimum values ​​of the peak angle under condition (ii) are both 0.02 degrees or less. [4] A bulk GaN crystal according to any one of [1] to [3], wherein the 17 measurement points under condition (i) and the 17 measurement points under condition (ii) do not include any measurement points whose peak angle differs from adjacent measurement points by 0.01 degree or more. [5] A bulk GaN crystal according to any one of [1] to [4], wherein the radius of curvature of a plane along the first direction, calculated from the rate of change of the peak angle under condition (i), and the radius of curvature of a plane along the second direction, calculated from the rate of change of the peak angle under condition (ii), are both 300 mm or more. [6] In the specific main surface A, in all imaginary regions of 100 μm × 100 μm that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density is 1 × 10 6cm -2 The bulk GaN crystal according to any one of [1] and [3] to [5], wherein [7] In the specific main surface A, in all imaginary regions of 2 mm × 2 mm that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density is 1 × 10 5 cm -2 The bulk GaN crystal according to any one of [1] and [3] to [6], wherein [8] In any imaginary 100 μm × 100 μm region that can be arbitrarily provided in the first main surface, excluding any portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density calculated from the number of dislocations present in the region and the area of ​​the region is 1 × 10 6 cm -2 The bulk GaN crystal according to any one of [2] to [5], wherein [9] In any imaginary region of 2 mm × 2 mm that can be arbitrarily provided in the first main surface except for a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density calculated from the number of dislocations present in the region and the area of ​​the region is 1 × 10 5 cm -2 The bulk GaN crystal according to any one of [2] to [5] and [8], wherein the bulk GaN crystal has a diameter of less than 100 nm.

[10] A bulk GaN crystal according to any one of [1] to [9], which satisfies one or more conditions selected from the following (a) to (g): (a) H concentration is 1×10 17 atoms / cm 3 That's all. (b) O concentration is 1×10 17 atoms / cm 3 That's all. (c) The concentration of at least one of Li, Na, and K is 1×10 15 atoms / cm 3 is less than. (d) F concentration is 1×10 15 atoms / cm 3 That's all. (e) The concentration of at least one of Cl, Br, and I is 1×10 15atoms / cm 3 That's all. (f) I concentration is 1×10 15 atoms / cm 3 That's all. (g) Si concentration is 2×10 15 atoms / cm 3 is less than.

[11] Infrared absorption spectrum from 3140 to 3200 cm -1 [9] A bulk GaN crystal according to [9], having a peak attributable to a gallium vacancy-hydrogen complex at

[12] A method for producing a c-plane GaN wafer, comprising at least the steps of preparing a bulk GaN crystal according to any one of [1] to

[11] , and slicing the GaN crystal.

[13] The method according to

[12] , wherein the c-plane GaN wafer has a disk shape, and a diameter of a circle constituting the disk shape is 50 mm or more.

[14] A c-plane GaN wafer having a primary surface selected from a surface inclined from the (0001) crystal plane by 0 degrees or more and 10 degrees or less, and a surface inclined from the (000-1) crystal plane by 0 degrees or more and 10 degrees or less, the primary surface being a specific primary surface B that satisfies the following condition (iii): (iii) The specific main surface B has a virtual line segment of 50 mm or more that can be drawn, and the range of variation of the m-axis component and the a-axis component of the offcut angle are both 0.05 degrees or less, except for a portion that is less than 5 mm away from the outer periphery when viewed in a plan view.

[15] A c-plane GaN wafer having a third principal surface and a fourth principal surface facing in opposite directions, one of the third principal surface and the fourth principal surface being inclined at an angle of 0 to 10 degrees from a (0001) crystal plane, and the other of the third principal surface being inclined at an angle of 0 to 10 degrees from a (000-1) crystal plane; A c-plane GaN wafer, wherein the third main surface has a virtual line segment of 50 mm or more along it, and the variation ranges of the m-axis component and the a-axis component of the offcut angle are both within 0.05 degrees, except for a portion that is less than 5 mm away from the outer periphery when viewed in a plan view.

[16] The c-plane GaN wafer according to

[14] or

[15] , wherein the variation range of the offcut angle in the m-axis direction and the variation range of the offcut angle in the a-axis direction are both within 0.02 degrees.

[17] The c-plane GaN wafer according to any one of

[14] to

[16] , having a diameter selected from 50 mm or more and 55 mm or less, 75 mm or more and 80 mm or less, 100 mm or more and 105 mm or less, and 150 mm or more and 155 mm or less.

[18] In the specific main surface B, in all imaginary regions of 100 μm×100 μm that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density is 1×10 6 cm -2 The c-plane GaN wafer of any one of

[14] ,

[16] , and

[17] , wherein

[19] In the specific main surface B, in all 2 mm x 2 mm imaginary areas that can be arbitrarily provided in the part except the part that is less than 5 mm away from the outer periphery when viewed in a plane, 5 cm -2 The c-plane GaN wafer of any one of

[14] ,

[16] ,

[17] and

[18] , wherein

[20] In the third main surface, in all 100 μm × 100 μm imaginary regions that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, a dislocation density is 1 × 10 6 cm -2 The c-plane GaN wafer according to any one of

[15] to

[17] , wherein the c-plane GaN wafer has a thickness of less than 100 nm.

[21] In the third main surface, in a virtual area of ​​2 mm x 2 mm that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, 5 cm -2 The c-plane GaN wafer according to any one of

[15] to

[17] and

[20] , wherein

[22] A c-plane GaN wafer according to any one of

[14] to

[21] , which satisfies one or more conditions selected from the following (a) to (g): (a) H concentration is 1×10 17 atoms / cm 3That's all. (b) O concentration is 1×10 17 atoms / cm 3 That's all. (c) The concentration of at least one of Li, Na, and K is 1×10 15 atoms / cm 3 is less than. (d) F concentration is 1×10 15 atoms / cm 3 That's all. (e) The concentration of at least one of Cl, Br, and I is 1×10 15 atoms / cm 3 That's all. (f) I concentration is 1×10 15 atoms / cm 3 That's all. (g) Si concentration is 2×10 15 atoms / cm 3 is less than.

[23] Infrared absorption spectrum from 3140 to 3200 cm -1 The c-plane GaN wafer described in

[22] has a peak attributable to gallium vacancy-hydrogen complexes at .

[24] An epitaxial wafer comprising the c-plane GaN wafer according to any one of

[14] to

[23] and one or more nitride semiconductor layers epitaxially grown on the c-plane GaN wafer.

[25] A method for producing an epitaxial wafer, comprising the steps of: preparing a c-plane GaN wafer according to any one of

[14] to

[23] ; and epitaxially growing one or more nitride semiconductor layers on the c-plane GaN wafer.

[26] A method for manufacturing a nitride semiconductor device, comprising the steps of: preparing a c-plane GaN wafer according to any one of

[14] to

[23] ; and epitaxially growing one or more nitride semiconductor layers on the c-plane GaN wafer.

[27] A method for producing bulk GaN crystals, comprising the steps of preparing a c-plane GaN wafer as described in any one of

[14] to

[23] , and epitaxially growing GaN crystals from the vapor phase on the c-plane GaN wafer.

[28] A method for producing bulk GaN crystals, comprising the step of growing GaN crystals on a seed assembly by an ammonothermal method, the seed assembly being composed of a plurality of c-plane GaN wafers, and metal wires being used to secure the plurality of c-plane GaN wafers to each other.

[29] A method for producing bulk GaN crystals according to

[28] , wherein the orientations of the c-axis, a-axis and m-axis of all of the c-plane GaN wafers constituting the seed assembly are aligned.

[30] A method for producing bulk GaN crystals as described in

[29] , wherein, when the direction of the N-polarity side of the main surface of the c-plane GaN wafer constituting the seed assembly is defined as the front direction, the seed assembly has two or more c-plane GaN wafers, each having a rectangular or approximately rectangular main surface, arranged adjacent to each other on the front direction side of the seed assembly, and a c-plane GaN wafer is arranged on the side opposite to the front direction of the seed assembly.

[31] A method for producing bulk GaN crystals according to any one of

[28] to

[30] , wherein in the step of growing GaN crystals by the ammonothermal method, a mineralizer containing a compound containing a halogen is used, and at least one metal wire selected from a Pt wire and an Au wire is used as the metal wire. Effect of the Invention

[0008] In one aspect, bulk GaN crystals are provided that have improved c-plane curvature, in another aspect, c-plane GaN wafers are provided that have reduced variation in offcut angle within the primary surface, and in yet another aspect, a novel method for producing bulk GaN crystals is provided. If a c-plane GaN wafer has a reduced variation in the offcut angle within the main surface, semiconductor device chips manufactured from that GaN wafer can have smaller performance differences between individual device chips, making it possible to standardize the quality between lots. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 shows an example of a bulk GaN crystal according to a preferred embodiment, where FIG. 1(a) is a perspective view and FIG. 1(b) is a plan view. [Diagram 2] Figure 2(a) is a cross-sectional view of a GaN crystal in which the c-plane is curved over a long distance along the direction of the measurement line, and Figure 2(b) is a graph obtained by measuring an XRD rocking curve with the c-plane as the reflection surface along the measurement line of the GaN crystal shown in Figure 2(a) and plotting the peak angle against the position of the measurement point. [Diagram 3] Figure 3(a) is a cross-sectional view of a GaN crystal in which the c-plane is strongly curved locally along the direction of the measurement line but is not curved over a long distance, and Figure 3(b) is a graph obtained by measuring an XRD rocking curve with the c-plane as the reflection surface along the measurement line of the GaN crystal shown in Figure 3(a) and plotting the peak angle against the position of the measurement point. [Figure 4] FIG. 4 is a perspective view showing an example of a c-plane GaN wafer according to an embodiment. [Diagram 5] FIG. 5 is a diagram for explaining that the offcut angle of a c-plane GaN wafer can be decomposed into an m-axis direction component and an a-axis direction component. [Figure 6] FIG. 6 is a schematic diagram of a crystal growth apparatus that can be preferably used for growing GaN crystals by the ammonothermal method. [Figure 7] FIG. 7 is a process diagram showing the steps performed in an experiment to grow large-area bulk GaN crystals. [Figure 8] FIG. 8(a) is a plan view of a temporary seed assembly, and FIG. 8(b) is a side view of the temporary seed assembly shown in FIG. 8(a). [Figure 9] FIG. 9 is a top view of a temporary seed assembly having a plurality of through holes formed therein. [Figure 10] FIG. 10 is a cross-sectional view showing an I-shaped through-hole pair in which one end and the other end of a Pt wire are passed through one and the other of the through-holes from the front side of a permanent seed assembly and twisted together on the back side. [Figure 11] FIG. 11 is a top view of a permanent seed assembly. [Figure 12] FIG. 12 is a photograph showing the appearance of a large-area bulk GaN crystal as viewed from the N-polarity side (a photograph substituted for a drawing). [Figure 13] 13(a) and (b) are graphs showing the results of measuring the peak angles of the (002) XRD rocking curves of a large-area bulk GaN crystal every 5 mm over 80 mm along the first and second lines, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In GaN crystals, the (0001) and (000-1) crystal planes are collectively called c-planes, the {10-10} crystal planes are called m-planes, and the {11-20} crystal planes are called a-planes. The crystal axis perpendicular to the c-plane is called the c-axis, the crystal axis perpendicular to the m-plane is called the m-axis, and the crystal axis perpendicular to the a-plane is called the a-axis. In this specification, when a crystal axis, a crystal plane, a crystal orientation, etc. are mentioned, unless otherwise specified, they mean the crystal axis, crystal plane, crystal orientation, etc. of a GaN crystal. The Miller indices of hexagonal crystals (hkil) are sometimes written in three digits as (hkl) because of the relationship h+k=i. For example, (0002) is written in three digits as (002). In this specification, for convenience, the (0001) crystal plane and the (000-1) crystal plane are sometimes collectively referred to as the (000±1) crystal plane. In the drawings, the

[0001] direction is represented as the +c direction, and the [000-1] direction is represented as the -c direction. Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate. The following description is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist of the present invention. In this specification, when expressed as "X to Y" (X and Y are any numbers), unless otherwise specified, it includes the meaning of "X or more, Y or less", as well as "preferably greater than X" and "preferably smaller than Y". In addition, in this specification, the term "independently" used when describing two or more objects together means that the two or more objects may be the same or different.

[0011] 1. Bulk GaN crystal One embodiment of the present invention relates to bulk GaN crystals. A first aspect of a bulk GaN crystal that is one embodiment of the present invention is a bulk GaN crystal having a primary surface selected from a plane inclined at an angle of 0 to 10 degrees from the (0001) crystal plane and a plane inclined at an angle of 0 to 10 degrees from the (000-1) crystal plane, the primary surface being a specific primary surface A that satisfies the following conditions (i) and (ii): (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the specific main surface A, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) A second line, which is an imaginary line segment having a length of 80 mm extending in a second direction perpendicular to the first direction, can be drawn on the specific main surface A, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

[0012] Moreover, a second aspect of a bulk GaN crystal which is one embodiment of the present invention is a bulk GaN crystal having a first principal surface and a second principal surface facing in opposite directions, one of the first principal surface and the second principal surface being inclined at an angle of 0 to 10 degrees from the (0001) crystal plane and the other surface being inclined at an angle of 0 to 10 degrees from the (000-1) crystal plane, and which satisfies the following conditions (i) and (ii): (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the first main surface, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) A second line, which is an imaginary line segment having a length of 80 mm extending on the first main surface in a second direction perpendicular to the first direction, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

[0013] In the first embodiment described above, from the viewpoint of obtaining the effects of the present invention, so long as the primary surface is selected from a surface having an inclination of 0 to 10 degrees from the (0001) crystal plane and a surface having an inclination of 0 to 10 degrees from the (000-1) crystal plane, the modes of the other surfaces constituting the bulk GaN crystal are not particularly limited, and may be flat or may have irregularities. In the bulk GaN crystal of the first embodiment, if one of the faces selected from the face tilted at an angle of 0 to 10 degrees from the (0001) crystal face and the face tilted at an angle of 0 to 10 degrees from the (000-1) crystal face is the specific primary face A, and the bulk GaN crystal further has a primary face on the opposite side to the specific primary face A, which is the face not selected as the specific primary face A among the two faces, then the bulk GaN crystal will have the same embodiment as the bulk GaN crystal of the second embodiment. In this case, the specific primary face A in the first embodiment will be the first primary face in the second embodiment. A specific embodiment of the bulk GaN crystal in the second embodiment (also simply referred to as "bulk GaN crystal") will be described below, but the configuration, characteristics, uses, etc. of each requirement of the bulk GaN crystal, including the embodiments of conditions (i) and (ii), can be similarly applied to the bulk GaN crystal in the first embodiment.

[0014] FIG. 1 shows an example of a bulk GaN crystal according to a preferred embodiment, where FIG. 1(a) is a perspective view and FIG. 1(b) is a plan view. 1, bulk crystal 10 is a plate made of only GaN crystal and has two principal surfaces (large area surfaces) facing in opposite directions, i.e., a first principal surface 11 and a second principal surface 12. One of first principal surface 11 and second principal surface 12 is Ga polar, and the other is N polar. First principal surface 11 and second principal surface 12 are parallel to each other, but are not necessarily required to be strictly parallel. When the first main surface 11 has Ga polarity and the second main surface 12 has N polarity, the inclination of the first main surface with respect to the (0001) crystal plane is from 0 to 10 degrees. In other words, the inclination of the first main surface with respect to the (0001) crystal plane is the angle between the

[0001] direction of the bulk crystal 10 and the normal vector of the first main surface. When the first main surface 11 has N polarity and the second main surface 12 has Ga polarity, the inclination of the first main surface with respect to the (000-1) crystal plane is 0 degrees or more and 10 degrees or less. The first main surface 11 and the second main surface 12 may be in an as-grown state after crystal growth, or may be surfaces that have been flattened by processing.

[0015] The first main surface 11 of the bulk crystal 10 may be substantially rectangular, with two sides of the rectangle being substantially parallel to the orthogonal projection of the m-axis on the first main surface 11 and the other two sides being substantially parallel to the orthogonal projection of the a-axis on the first main surface 11. The shape and dimensions of the second main surface 12 are substantially the same as those of the first main surface 11. In a modified embodiment, the first main surface 11 may have a shape other than a rectangle, such as a rectangle with some or all of the four corners cut off, a hexagon, a circle, or even an irregular shape. The first main surface 11 of the bulk crystal 10 has at least an area on which two imaginary lines, each of which is perpendicular to each other and has a length of 80 mm, can be drawn. When the first main surface 11 of the bulk crystal 10 is circular, it preferably has an area large enough to allow an imaginary circle with a diameter of 85 mm, more preferably 110 mm, to be drawn thereon, and may also have an area large enough to allow an imaginary circle with a diameter of 160 mm to be drawn thereon. The thickness of bulk crystal 10, that is, the dimension in the direction perpendicular to first main surface 11 and second main surface 12, is preferably 1 mm or more, more preferably 2 mm or more, and is preferably 30 mm or less, more preferably 20 mm or less.

[0016] The curvature of the c-plane in a GaN crystal having a primary surface oriented along the c-axis can be evaluated by measuring the (002) XRD rocking curve, with the c-plane as the reflection plane, at regular intervals along a measurement line extending on the primary surface and examining the change in the peak angle. In the XRD rocking curve measurement at each measurement point, the omega axis is set perpendicular to the measurement line, which allows us to determine how the tilt of the c-axis changes along the measurement line, i.e., the curvature of the c-plane along the measurement line. The omega axis is the axis of rotation of the sample when measuring the XRD rocking curve. XRD rocking curve measurement is also known as the omega scan.

[0017] For example, in a GaN crystal in which the c-plane is curved over a long distance along the measurement line as shown in Fig. 2(a), when an XRD rocking curve is measured along the measurement line with the c-plane as the reflection surface and the peak angle ω is plotted against the measurement point position, a graph like that shown in Fig. 2(b) is obtained. The stronger the degree of curvature, the greater the rate of change of ω. On the other hand, in the example shown in Figure 3(a), the c-plane is strongly curved locally along the direction of the measurement line, but the direction of the curvature alternates between up and down along the measurement line, and no curvature is observed over a long distance. When the XRD rocking curve of such a GaN crystal is similarly measured along the measurement line and the peak angle ω is plotted against the position of the measurement point, a graph like that shown in Figure 3(b) is obtained. As can be seen from Figures 2 and 3, both the long-range curvature of the c-plane and the local curvature increase the maximum and minimum values ​​of the peak angles of the XRD rocking curve measured on the measurement line.

[0018] In the bulk crystal 10, the curvature of the c-plane is improved to the extent that the following conditions (i) and (ii) are satisfied. (i) A first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the first main surface 11, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the bulk crystal 10 measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less. (ii) A second line, which is an imaginary line segment having a length of 80 mm extending in a second direction perpendicular to the first direction, can be drawn on the first main surface 11, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the bulk crystal 10 measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

[0019] In conditions (i) and (ii), the first direction may be, for example, but is not limited to, perpendicular to the a-axis. There may be multiple lines that correspond to the first line referred to in condition (i), but if at least one such line is found, that is, if the peak angle of the (002) XRD rocking curve of bulk crystal 10 is measured on a line that is at least one imaginary line segment extending in the first direction, with the omega axis perpendicular to the line over a distance of 80 mm and at a pitch of 5 mm, and the difference between the maximum and minimum values ​​is 0.05 degrees or less, then it can be evaluated that the degree of curvature of the c-plane in bulk crystal 10 is sufficiently reduced in the first direction. The same applies to condition (ii), where the peak angle of the (002) XRD rocking curve of bulk crystal 10 is measured on a line that is at least one imaginary line segment extending in the second direction, with the omega axis perpendicular to the line over a distance of 80 mm and at a pitch of 5 mm; if the difference between the maximum and minimum values ​​is 0.05 degrees or less, it can be evaluated that the degree of curvature of the c-plane in bulk crystal 10 is sufficiently reduced in the second direction. The difference between the maximum and minimum values ​​of the peak angle of the rocking curve among the 17 measurement points in condition (i) and the difference between the maximum and minimum values ​​of the peak angle of the rocking curve among the 17 measurement points in condition (ii) are independently preferably 0.04 degrees or less, more preferably 0.03 degrees or less, and even more preferably 0.02 degrees or less. This suitable range may be satisfied by only one of condition (i) and condition (ii), but it is preferable that both conditions are satisfied.

[0020] For example, in the extreme case where the curvature of the c-plane of the bulk crystal 10 in the first direction is only a long-distance curve as in the example shown in Fig. 2 and the peak angle of the rocking curve changes monotonically along the first line, the difference between the maximum and minimum values ​​of the peak angle among the 17 measurement points referred to in condition (i) is equal to the difference between the peak angle between the two measurement points at both ends separated by 80 mm. In such a case, as the difference between the maximum and minimum values ​​decreases to 0.05 degrees, 0.04 degrees, 0.03 degrees, and 0.02 degrees, the radius of curvature of the c-plane along the first direction increases to about 92 m, about 115 m, about 153 m, and about 229 m. Preferably, the 17 measurement points in condition (i) and the 17 measurement points in condition (ii) do not include any measurement points whose peak angles in the rocking curve differ from adjacent measurement points by 0.01 degrees or more. In other words, the tilt of the c-axis does not change by 0.01 degrees or more per 5 mm within an 80 mm section including each of the 17 measurement points on the first line or the second line. This means that there are no locally strongly curved portions on the c-plane of the bulk crystal 10. The above preferred range may be satisfied by only one of condition (i) and condition (ii), but it is preferable that both conditions are satisfied.

[0021] In a preferred embodiment, the radius of curvature of the c-plane along the first direction calculated from the rate of change of the peak angle of the rocking curve among the 17 measurement points in the condition (i) and the radius of curvature of the c-plane along the second direction calculated from the rate of change of the peak angle of the rocking curve among the 17 measurement points in the condition (ii) are independently 300 m or more. This preferred range may be satisfied by only one of the conditions (i) and (ii), but it is preferable that both conditions are satisfied. In calculating the radius of curvature, a value obtained by linear approximation using the least squares method is used as the rate of change of the peak angle of the rocking curve among 17 measurement points.

[0022] In the bulk crystal 10, except for a portion that is less than 5 mm away from the outer periphery in plan view, in any 100 μm×100 μm region on the first main surface 11, the dislocation density calculated from the number of dislocations present in the region and the area of ​​the region is 1×10 6 cm -2 This means that in any imaginary 100 μm×100 μm region that can be arbitrarily provided in the first main surface except for the portion that is less than 5 mm away from the outer periphery when viewed in plan, the dislocation density calculated from the number of dislocations present in the region and the area of ​​the region can be less than 1×10 6 cm -2 This alternative expression also applies in the following description. In the bulk crystal 10, except for the portion that is less than 5 mm away from the outer periphery in plan view, in any 2 mm×2 mm region on the first main surface 11, the dislocation density calculated from the number of dislocations present in the region and the area of ​​the region is 1×10 5 cm -2 It may be less than.

[0023] The dislocation density of the first principal surface 11 can be examined by observing a cathodoluminescence (CL) image or a photoluminescence (PL) image. However, since the bulk crystal 10 is grown by the ammonothermal method, dislocations do not appear as dark spots with clear contrast in the CL image or PL image due to the influence of strong yellow band emission. Therefore, in order to make the dislocations easier to see, a GaN thin film may be formed on the first principal surface 11 by a vapor phase method, and a surface CL image or surface PL image of the GaN thin film may be observed. When the first main surface 11 has Ga polarity, the etch pit density may be regarded as the dislocation density. If necessary, the surface may be planarized by CMP (chemical mechanical polishing), and then etched for one hour with 89% sulfuric acid heated to 270°C, thereby forming etch pits in one-to-one correspondence with the dislocations on the first main surface. When the first main surface 11 is N-polar, the bulk crystal 10 is cut in the thickness direction, and the etch pit density on a cut surface of Ga polarity located within a distance of several hundred μm from the first main surface is measured, and this may be regarded as the dislocation density on the first main surface 11.

[0024] Bulk crystal 10 preferably satisfies one or more conditions selected from the following (a) to (g). (a) H concentration is 1×10 17 atoms / cm 3 That's all. (b) O concentration is 1×10 17 atoms / cm 3 That's all. (c) The concentration of at least one of Li, Na, and K is 1×10 15 atoms / cm 3 is less than. (d) F concentration is 1×10 15 atoms / cm 3 That's all. (e) The concentration of at least one of Cl, Br, and I is 1×10 15 atoms / cm 3 That's all. (f) I concentration is 1×10 15 atoms / cm 3 That's all. (g) Si concentration is 2×10 15 atoms / cm 3 is less than. The conditions (a) to (g) are explained below.

[0025] The bulk crystal 10 is grown by the ammonothermal method, so H (hydrogen) is added at 1×10 17 atoms / cm 3 It may be contained in a concentration of 1 or more. The bulk crystal 10 has a mass of 1×10 O due to the raw materials used in the ammonothermal method. 17 atoms / cm 3 It may be contained in a concentration of 1 or more. The bulk crystal 10 is preferably grown by an ammonothermal method that does not use an alkali metal-containing compound as a mineralizer, so that the concentration of at least one of Li (lithium), Na (sodium) and K (potassium) is 1×10 15 atoms / cm 3 It may be less than. The bulk crystal 10 is preferably grown ammonothermally using a compound containing F (fluorine) as a mineralizer, so that F is 1×10 15 atoms / cm 3 It may be contained in a concentration of 1 or more.

[0026] Typical examples of compounds containing F that can be preferably used as a mineralizer include HF, NHF, GaF, etc. When HF is used, it may react with NH3 charged as a solvent or GaN charged as a raw material in the growth vessel to produce NHF or GaF. Since the bulk crystal 10 is preferably grown by the ammonothermal method using a compound containing halogen other than F as a mineralizer in addition to a compound containing F, in addition to F, at least one of Cl, Br and I is preferably present in an amount of 1×10 15 atoms / cm 3 It may be contained in a concentration of 1 or more. Typical examples of compounds containing halogens other than F that can be preferably used as mineralizers include HCl, NH4Cl, GaCl3, HBr, NH4Br, GaBr3, HI, NHI, IGaI3, etc. When HX (X=Cl, Br or I) is used, it may react with NH3 charged as a solvent or GaN charged as a raw material in the growth vessel to produce NH4X or GaX3.

[0027] The bulk crystal 10 is preferably grown by the ammonothermal method using a compound containing I (iodine) in addition to a compound containing F as a mineralizer, so that I is 1×10 15 atoms / cm 3 It may be contained in a concentration of 1 or more. The bulk crystal 10 is grown by the ammonothermal method, so the Si concentration is 2×10 15 atoms / cm 3 In the ammonothermal process, the use of NH4F alone or in combination with HX as a mineralizer is effective in reducing the concentration of Si. Since the bulk crystal 10 is grown by the ammonothermal method, the infrared absorption spectrum of 3140 to 3200 cm -1 may have a peak attributable to a gallium vacancy-hydrogen complex.

[0028] 2. c-plane GaN wafer Another embodiment of the present invention includes a c-plane GaN wafer obtained by a method including at least the steps of preparing the bulk GaN crystal described above and slicing the bulk GaN crystal, and a method for producing the same. In the step of slicing the bulk GaN crystal, it is preferable to slice the crystal approximately parallel to the c-plane. However, the c-plane GaN wafer according to the other embodiment is not limited to one obtained from the bulk GaN crystal described above. FIG. 4 shows a perspective view of an example of a c-plane GaN wafer (also referred to as a "c-plane wafer") according to one embodiment. Referring to the figure, a c-plane wafer 100 has a disk shape and two main surfaces facing in opposite directions, i.e., a third main surface 101 and a fourth main surface 102. One of the third main surface 101 and the fourth main surface 102 has Ga polarity, and the other has N polarity. The third main surface 101 and the fourth main surface 102 are parallel to each other, but are not necessarily required to be strictly parallel. Here, the disk shape means a cylindrical shape in which the diameter (d) of the circle is larger than the height (l), and the ratio (d / l) is usually 20 or more.

[0029] Although there is no particular limitation on the shape of the third main surface of the c-plane wafer 100, it is preferable that an imaginary line segment of 50 mm or more can be drawn on the main surface. The line segment may be 75 mm or more, 100 mm or more, or 150 mm or more. The third main surface of the c-plane wafer 100 is preferably circular, and when the shape of the c-plane wafer 100 is disc-shaped, the diameter of the circle (upper or lower surface of the disc-shaped) constituting the disc shape is not limited, but is usually 50 mm or more, and typically 50 mm or more and 55 mm or less (about 2 inches), 75 mm or more and 80 mm or less (about 3 inches), 100 mm or more and 105 mm or less (about 4 inches), 150 mm or more and 155 mm or less (about 6 inches), etc. The diameter of the c-plane wafer 100 may be outside these ranges, i.e., less than 50 mm, more than 55 mm and less than 75 mm, more than 80 mm and less than 100 mm, more than 105 mm and less than 150 mm, or more than 155 mm. The c-plane wafer 100 is required to have a strength sufficient for easy handling, so its thickness is usually 250 μm or more, and is made thicker depending on its diameter. When the diameter of the c-plane wafer 100 is about 2 inches, the thickness is preferably 250 μm or more, more preferably 300 μm or more, and is preferably 450 μm or less, more preferably 400 μm or less. When the diameter of the c-plane wafer 100 is about 4 inches, the thickness is preferably 350 μm or more, more preferably 400 μm or more, and is preferably 750 μm or less, more preferably 650 μm or less. When the diameter of the c-plane wafer 100 is about 6 inches, the thickness is preferably 400 μm or more, more preferably 450 μm or more, even more preferably 550 μm or more, and is preferably 800 μm or less, more preferably 700 μm or less. In this specification, "about" in relation to the diameter of the c-plane wafer 100 means within a range of ±20%, or within a range of ±10%, or ±0 to +20%, or ±0 to +10%.

[0030] The c-plane wafer 100 may have an offcut angle of 10 degrees or less. The offcut angle of the c-plane wafer 100 can be broken down into an m-axis component and an a-axis component. With reference to FIG. 5, when the normal vector of the third main surface 101 is vector N, the offcut angle of the c-plane wafer 100 is the inclination θ of vector N from the c-axis. This vector N is the a-axis component of vector N a and the m-axis component of vector N m The orthogonal projection of vector N on the m-plane is vector N a and the orthogonal projection of vector N on the a-plane is vector N m It is. When vector N is decomposed in this way, vector N a The inclination from the c-axis is the a-axis component θ of the offcut angle θ a and vector N m The inclination from the c-axis is the m-axis component θ of the offcut angle θ m It is.

[0031] Since the c-plane wafer 100 is sliced ​​from the bulk crystal 10 according to the embodiment, the variation in the offcut angle within the third principal surface 101 is reduced. Specifically, in the c-plane wafer 100, except for a portion that is less than 5 mm away from the outer periphery in plan view, the variation range of the m-axis component of the offcut angle and the variation range of the a-axis component of the offcut angle in the third main surface 101 are both within 0.05 degrees. The variation range of the m-axis component of the offcut angle and the variation range of the a-axis component of the offcut angle are independently preferably less than 0.05 degrees, preferably within 0.04 degrees, more preferably within 0.03 degrees, and even more preferably within 0.02 degrees. Although only one of the two variation ranges may be satisfied, it is preferable that both of the variation ranges are satisfied.

[0032] Also, in the c-plane wafer 100, except for a portion that is less than 5 mm away from the outer periphery when viewed in plan, the variation range of any first axis direction component corresponding to the diameter in the third main surface 101 and the variation range of the second axis direction component corresponding to the diameter in the direction perpendicular to the first axis can be read as being within 0.05 degrees. The variation range of the first axis direction component and the variation range of the second axis direction component of the offcut angle are preferably less than 0.05 degrees, preferably within 0.04 degrees, more preferably within 0.03 degrees, and even more preferably within 0.02 degrees. This preferred range may be satisfied by only one of the two variation ranges described above, but it is preferable that both of the variation ranges are satisfied.

[0033] The third principal surface 101 of the c-plane wafer 100 is the “front surface”, and when the c-plane wafer 100 is used to manufacture a semiconductor device, a semiconductor layer is epitaxially grown on the third principal surface 101. The processing performed to planarize the third main surface 101 may include one or more selected from grinding, polishing, and CMP. In addition to these processing, etching may be performed to remove a damaged layer. The root mean square (RMS) roughness of third main surface 101 measured by AFM is preferably less than 5 nm, more preferably less than 2 nm, and even more preferably less than 1 nm, and may be less than 0.5 nm in a measurement range of 2 μm×2 μm. The fourth major surface 102 of c-plane wafer 100 is the "backside" surface and may be mirror-finished or may be roughened or etched.

[0034] 4, the edge of the c-plane wafer 100 may be chamfered. In addition, various markings may be provided on the c-plane wafer 100 as necessary, such as an orientation flat or notch that indicates the crystal orientation, and an index flat that makes it easy to distinguish between the front and back surfaces. The c-plane wafer 100 may be preferably used in the manufacture of nitride semiconductor devices. An example of a method for manufacturing a nitride semiconductor device includes a step of preparing the above-mentioned c-plane GaN wafer and a step of epitaxially growing one or more nitride semiconductor layers on the c-plane GaN wafer. The manufacturing method can also be applied to the manufacture of an epitaxial wafer, and specifically, one or more nitride semiconductor layers are epitaxially grown on the third main surface of a c-plane wafer 100 to form an epitaxial wafer. As the epitaxial growth method, a vapor phase method such as MOVPE (Metal Organic Vapor Phase Epitaxy), MBE (Molecular Beam Epitaxy), PXD (Pulsed Excitation Deposition), sputtering, or HVPE (Hydride Vapor Phase Epitaxy) can be preferably used. Epitaxially grown nitride semiconductor layers can be doped to have n-type conductivity, p-type conductivity or semi-insulating.

[0035] Examples of nitride semiconductor devices that can be manufactured using the c-plane wafer 100 include light-emitting devices such as light-emitting diodes (LEDs) and laser diodes (LDs), electronic devices such as rectifiers, bipolar transistors, field-effect transistors, and HEMTs (High Electron Mobility Transistors), semiconductor sensors such as temperature sensors, pressure sensors, radiation sensors, and visible-ultraviolet light detectors, and solar cells. Another use of the c-plane wafer 100 is as a seed for growing bulk GaN crystals by HVPE, Tri-Halide Vapor Phase Epitaxy (THVPE), Oxide Vapor Phase Epitaxy (OVPE), ammonothermal, Na flux, and various other methods.

[0036] Another embodiment of the c-plane GaN wafer is a c-plane GaN wafer having a primary surface selected from a plane inclined at an angle of 0 to 10 degrees from the (0001) crystal plane and a plane inclined at an angle of 0 to 10 degrees from the (000-1) crystal plane, the primary surface being specific primary surface B that satisfies the following condition (iii): (iii) The specific main surface B has a virtual line segment of 50 mm or more that can be drawn, and the range of variation of the m-axis component and the a-axis component of the offcut angle are both 0.05 degrees or less, except for a portion that is less than 5 mm away from the outer periphery when viewed in a plan view. In this embodiment, from the viewpoint of obtaining the effects of the present invention, as long as the main surface is selected from a surface having an inclination of 0 degrees or more and 10 degrees or less from the (0001) crystal surface and a surface having an inclination of 0 degrees or more and 10 degrees or less from the (000-1) crystal surface, the aspect of the surface opposite the main surface is not particularly limited, and may or may not be parallel to the main surface, and may be a crystal surface other than the (0001) crystal surface and the (000-1) crystal surface. In the c-plane GaN wafer in the above embodiment (referred to as the "second embodiment of the c-plane GaN wafer"), if one of the faces selected from the face with an inclination of 0 to 10 degrees from the (0001) crystal face and the face with an inclination of 0 to 10 degrees from the (000-1) crystal face is the specific main face B, and if there is a main face on the opposite side of the specific main face B, and the opposite main face is the face not selected as the specific main face B among the above two faces, the above bulk GaN crystal will be in the same embodiment as the above embodiment having the third and fourth main faces (referred to as the "first embodiment of the c-plane GaN wafer"). In this case, the specific main face B of the c-plane GaN wafer in the second embodiment will be the third main face in the first embodiment. The configuration, characteristics, applications, and the like of each requirement of the c-plane GaN wafer in the first embodiment of the c-plane GaN wafer can be similarly applied to the c-plane GaN wafer in the second embodiment of the c-plane GaN wafer.

[0037] 3. Manufacturing method of bulk GaN crystal The above-mentioned bulk GaN crystal can be obtained by, for example, a manufacturing method including a step of preparing the above-mentioned c-plane GaN wafer and a step of epitaxially growing GaN crystal from a vapor phase on the c-plane GaN wafer, or a manufacturing method including a step of growing GaN crystal by an ammonothermal method on a seed assembly composed of a plurality of c-plane GaN wafers. The above-mentioned embodiment of the epitaxial growth can be applied to the embodiment in the description of the c-plane GaN wafer.

[0038] A method for producing bulk GaN crystals using a seed assembly will now be described in detail. The main feature of the seed assembly is that the c-plane GaN wafers that make up the assembly are fixed to each other with metal wires. Specifically, each c-plane GaN wafer has a small through hole, and each c-plane GaN wafer is bound to other c-plane GaN wafers with metal wires that are passed through the through hole. The metal wire may be any wire that can withstand the ammonothermal environment to which it is exposed during the growth of GaN crystals. When a halogen-containing compound is used as a mineralizer in the process of growing GaN crystals by the ammonothermal method, the metal wire that can be preferably used is at least one metal wire selected from Pt wire and Au wire, more preferably Pt wire, but may also be W wire, Mo wire, Ag wire, etc. In addition, the metal wire is not limited to only metal wires as long as it is made of a material that can withstand the ammonothermal environment and can fix c-plane GaN wafers to each other.

[0039] In one embodiment of the seed assembly, the seed assembly is characterized in that the orientations of the c-axis, a-axis, and m-axis of all the c-plane GaN wafers constituting the seed assembly are aligned. Therefore, in the crystal growth process, GaN crystals starting to grow from the surfaces of different c-plane GaN wafers are successfully integrated (coreless). This is presumably useful in preventing the occurrence of harmful stress. Incidentally, the orientations of the c-axis, a-axis, and m-axis of the c-plane GaN wafers being aligned means that the polarity directions of the c-plane GaN wafers are also aligned. When the front and back of the seed assembly are defined with the N-polarity main surface of the c-plane GaN wafer constituting the seed assembly facing the front side of the seed assembly, two or more c-plane GaN wafers, each having a rectangular or approximately rectangular main surface, are arranged adjacent to each other on the front side of the seed assembly. When the N-polarity side of the main surface of the c-plane GaN wafer constituting the seed assembly is defined as the front direction, the seed assembly can also be expressed as two or more c-plane GaN wafers, each having a rectangular or approximately rectangular main surface, on the front direction side of the seed assembly. Two or more adjacent c-plane GaN wafers are preferably arranged without gaps. Here, the gap means a gap that can be visually confirmed, and more preferably, the c-plane GaN wafers are arranged adjacent to each other so that there is no gap at the level of observation with an optical microscope. The two or more c-plane GaN wafers are preferably sliced ​​in parallel from the same bulk GaN crystal. Specifically, two or more c-plane GaN wafers may be cut in parallel from one slice of a bulk GaN crystal, or two or more c-plane GaN wafers may be cut in parallel from different slices. When cutting c-plane GaN wafers from different slices, it is preferable to cut two or more in a direction that was parallel in the original bulk GaN crystal. For example, it is also preferable to cut two or more wafers different in the thickness direction at the same position in the original bulk GaN crystal and combine them to form a seed assembly. In this case, it is also possible to cut and use the wafers so that they are not exactly at the same position, but at least overlap in the thickness direction. Here, when obtaining a c-plane GaN wafer by any of the above methods, it is important that the crystal orientations of the c-plane GaN wafers are aligned. Specifically, a seed assembly is made by combining wafers in which the deviations in the a-axis direction and the m-axis direction of the c-plane GaN wafer are independently usually less than 0.05°, preferably less than 0.02°, more preferably less than 0.01°, and even more preferably less than 0.005°. The crystal axis direction of the c-plane GaN wafer can be measured by XRD. A c-plane GaN wafer serving as a connecting plate is placed on the back side of the seed assembly (opposite the front side).

[0040] The method of arranging multiple wafers in parallel as a seed assembly and growing GaN crystals on its surface has been commonly used in vapor phase growth methods such as HVPE. This is because in manufacturing methods such as HVPE, it is possible to firmly fix the seed assembly to the susceptor. In contrast, in the ammonothermal method, the seed assembly is suspended by wires in ammonia or other liquid, so even if multiple wafers are arranged in parallel and integrated into a seed assembly, it is difficult to fix them to each other. Due to this problem, the tile method has not been used in the ammonothermal method in the past, but as mentioned above, this problem can be solved by fixing them with wires.

[0041] For growing GaN crystals by the ammonothermal method, a crystal growth apparatus shown in FIG. 6 can be preferably used. Referring to Fig. 6, the crystal growth apparatus includes an autoclave and a capsule placed therein. Inside the capsule, a dissolution zone and a growth zone are provided, which are separated from each other by a baffle. When growing GaN crystals, a feedstock is placed in the dissolution zone together with a mineralizer (not shown), and a seed is suspended by a wire in the growth zone. Gas lines to which a vacuum pump, an ammonia cylinder and a nitrogen cylinder are connected are connected to the autoclave and the capsule via valves.

[0042] When putting NH3 (ammonia) into the capsule, it is possible to check the amount of NH3 supplied from the ammonia cylinder using a mass flow meter. When the capsule is heated to a given temperature, the pressure inside the capsule is determined by the free volume of the capsule and the amount of NH3 placed in the capsule. When growing GaN, seeds, feedstock, mineralizers, and NH3 are placed in the capsule. The capsule is sealed and heated from the outside of the autoclave by a heater (not shown) so that the inside of the capsule is in a supercritical state. At this time, NH3 is enclosed not only in the capsule but also in the space between the autoclave and the capsule so that the pressure inside and outside the capsule are balanced. The upper and lower parts of the autoclave are heated separately using multiple heaters to provide a temperature gradient between the dissolution and growth zones.

[0043] When a halogen-containing compound such as HX, NH4X, GaX3 (where X=F, Cl, Br, or I) is used as the mineralizer, the capsule, the baffles and jigs installed in the capsule, and the wire for suspending the seeds are preferably made of Pt (platinum) or an alloy mainly composed of Pt. In particular, the capsule is preferably made of a Pt-Ir alloy.

[0044] 4. Experimental Results 4.1. Preparation of large-area bulk GaN crystals A large-area bulk GaN crystal was produced by sequentially performing steps 1 to 4 shown in Figure 7. Here, "large area" is not limited to a specific area, but specifically, it is an area large enough to draw two imaginary lines that are perpendicular to each other and each 80 mm long on the main surface. The outline of each step is as follows. In step 1, the seed assembly was prepared. In step 2, first-generation GaN crystals were grown on the seed assemblies. In step 3, c-plane GaN wafers were sliced ​​from the first-generation GaN crystal that had grown on the front side of the seed assembly. In step 4, second-generation GaN crystals were grown on the c-plane GaN wafers sliced ​​in step 3. In all of the experiments described herein, a crystal growth apparatus of the type shown in FIG. 6 was used for growing GaN crystals by the ammonothermal method. Each step will now be described in detail.

[0045] [Step 1] In step 1, the seed assembly was prepared as described below. a. Growth of seed GaN crystals A 4-inch diameter c-plane GaN wafer (hereafter referred to as "HVPE wafer") was prepared, which was made of GaN crystals grown on a sapphire substrate by the HVPE method and had an N-polar surface that was finished to a mirror flat surface. The N-polar surface refers to the primary surface on the [000-1] side. A stripe-patterned selective growth mask was formed on the N-polar surface of the HVPE wafer using the lift-off method, which consisted of a two-layer sputtered film consisting of a 100-nm-thick TiW underlayer and a 100-nm-thick Pt surface layer. The selective growth mask had a linear opening with a line width of 50 μm and a pitch of 4 mm, and the stripe direction was parallel to the a-plane of the GaN crystal constituting the HVPE wafer.

[0046] After forming a selective growth mask, GaN crystals were grown on the HVPE wafer by the ammonothermal method. The feedstock used was polycrystalline GaN, which was produced by contacting elemental Ga with HCl gas under heating to generate gaseous GaCl, which was then reacted with NH3 gas. NH4F and NHI were used as mineralizers. NHI was synthesized by reacting HI (hydrogen iodide) gas with NH3 in a capsule. The molar ratios of F and I contained in the mineralizer to NH3 used as the solvent were 0.5% and 4.0%, respectively. The growth conditions are the temperature of the melting zone TD and the growth zone temperature T G The average temperature of both zones is 600°C, and the temperature difference between the two zones is T D -T G is about 5℃ (T D >T G ), and the pressure was about 220 MPa.

[0047] On the N-polarity surface of the HVPE wafer, a GaN crystal was grown in a layer shape through the selective growth mask described above. A c-plane GaN wafer was sliced ​​from this GaN crystal, and a new GaN crystal was grown by ammonothermal method using the c-plane GaN wafer as a seed. When ammonothermally grown c-plane GaN wafers were used as seeds, no selective growth mask was used, and the molar ratios of F and I to NH3 contained in the mineralizer were 5.0% and 3.5%, respectively. When using a c-plane GaN wafer grown by the ammonothermal method as a seed, the growth conditions are the melting zone temperature T D and the growth zone temperature T G The average temperature between the two zones is 605 to 615°C, and the temperature difference between the two zones is T D -T G is about 15 to 20 degrees Celsius (T D >T G ), and the pressure was about 210-220 MPa.

[0048] b. Assembling the seed assembly From one bulk GaN crystal grown by the procedure described in the above item a., several c-plane wafers were sliced ​​in parallel using a multi-wire saw, and three of them were selected. The crystal orientation of the three selected wafers was confirmed using an X-ray diffraction device, and then the edges were partially cut off using a dicing saw so that the main surface was rectangular or approximately rectangular. In this way, wafers A to C shown in Table 1 below were prepared.

[0049] [Table 1]

[0050] In the process of producing wafer A, dicing saw processing was performed so that one of the long sides of the approximately rectangular main surface was within ±0.005 degrees from the m-axis direction. A similar dicing saw process was also performed in the preparation of wafer B.

[0051] Wafer A, Wafer B and Wafer C were then fixed together using wax as an adhesive to form a temporary seed assembly as shown in FIG. Fig. 8(a) is a plan view of the temporary seed assembly seen from the front side, and Fig. 8(b) is a side view of the temporary seed assembly seen from a direction parallel to the long side of wafer A. In this experiment, the side on which the N-polarity main surfaces of wafers A to C face is referred to as the front side of the temporary seed assembly. The directions of the c-axis, a-axis, and m-axis of the three wafers A to C, including their polarities, were aligned. Wafer A and wafer B were arranged on the front side of the temporary seed assembly with their long sides aligned to within ±0.005 degrees from the m-axis direction, with no visible gaps between them. Wafer C was placed on the back side of the temporary seed assembly, half overlapping with wafer A and half overlapping with wafer B.

[0052] A 0.7 mm diameter ultrasonic drill was then used to drill multiple through-holes in the temporary seed assembly, as shown in FIG. Each of the multiple through holes penetrated two wafers. That is, the through hole formed in the overlapping area of ​​wafer A and wafer C penetrated both wafers A and C, and the through hole formed in the overlapping area of ​​wafer B and wafer C penetrated both wafers B and C. The multiple through holes were arranged so that each was paired with another through hole, and the distance between the central axes of the two through holes in a pair was 2 mm for the I-type through hole pair and 4 mm for the II-type through hole pair. Here, a type I through hole pair refers to a through hole pair in which both of the two through holes that make up the pair penetrate wafer A and wafer C, or both of the two through holes that make up the pair penetrate wafer B and wafer C, and a type II through hole pair refers to a through hole pair in which one of the two through holes that make up the pair penetrates wafer A and wafer C, and the other penetrates wafer B and wafer C. When the temporary seed assembly was viewed in a plan view, the line connecting the central axes of the two through-holes that make up a type I through-hole pair was parallel to the <10-10> crystal axis, and the line connecting the central axes of the two through-holes that make up a type II through-hole pair was perpendicular to the boundary between wafer A and wafer B. In addition to the through-holes described above, this process also formed through-holes necessary for suspending a permanent seed assembly, which will be formed later, within the capsule, but these are not shown in FIG.

[0053] After the through-holes were formed, the temporary seed assembly was disassembled by heating and melting the wax used for bonding. Wafers A, B, and C were wiped to remove the wax and etched with 48% KOH aqueous solution heated to 100°C to remove the damaged layers. A permanent seed assembly was then constructed consisting of wafer A, wafer B and wafer C secured together in the same orientation as the temporary seed assembly. In assembling the permanent seed assembly, one end and the other end of a Pt wire with a diameter of 0.2 mm were passed through one and the other of the through holes that make up the pair from the front side, respectively, and twisted together on the back side. Here, the side on which the N-polarity main surfaces of wafers A to C face is called the front side of the permanent seed assembly. Figure 10 shows an example, a cross-sectional view of a pair of I-shaped through holes provided at the overlapping portion of wafer A and wafer C, in which one end and the other end of a Pt wire are passed through one and the other of the through holes from the front side as described above, and then brought together on the back side. Figure 11 is a plan view of the completed permanent seed assembly from the front side. Wafer C, outlined in dashed lines in Figure 11, is placed on the back side of the seed assembly and serves as a connecting plate connecting wafers A and B.

[0054] [Step 2] In step 2, first-generation GaN crystals were grown by ammonothermal method on a permanent seed assembly (hereinafter simply referred to as "seed assembly") as follows. The feedstock used was polycrystalline GaN, which was produced by exposing elemental Ga to HCl gas under heating to generate gaseous GaCl, which was then reacted with NH3 gas. The mineralizers used were NH4F and NHI. NHI was synthesized by reacting HI (hydrogen iodide) gas with NH3 in a Pt-Ir capsule. The molar ratios of F and I contained in the mineralizer to NH3 used as a solvent were 5.0% and 3.5%, respectively. The growth conditions for the first generation GaN crystal are the melting zone temperature T D and the growth zone temperature T G The average temperature between the two zones is about 605 to 615°C, and the temperature difference between the two zones is T D -T G is about 15 to 20 degrees Celsius (T D >T G ), and the pressure inside the capsule was approximately 210-220 MPa. The grown first-generation GaN crystal enveloped the entire seed assembly, but because it was entirely transparent, it was possible to visually confirm that there was no evidence of abnormal growth caused by the through-holes formed in the c-plane GaN wafer constituting the seed or the Pt wires passing through the through-holes.

[0055] [Step 3] As mentioned above, the first-generation GaN crystal grown in step 2 enveloped the entire seed assembly, and multiple c-plane wafers were sliced ​​from the portion of the first-generation GaN crystal that had grown on the front side of the seed assembly using a wire saw. [Step 4] In step 4, one of the c-plane GaN wafers sliced ​​in step 3 was used as a seed to grow second-generation GaN crystal by the ammonothermal method, thereby producing a large-area bulk GaN crystal containing the seed inside. In the growth of the second generation GaN crystals, the feedstock used and the molar ratio of F and I contained in the mineralizer to NH3 used as the solvent were the same as those used in the growth of the first generation GaN crystals, and the growth conditions used were also the same as those used in the growth of the first generation GaN crystals. The appearance of the obtained large-area bulk GaN crystal, as viewed from the N-polarity side, is shown in Figure 12. This crystal was a plate-shaped crystal with a main surface oriented along the c-axis, and had a thickness of 2.93 mm including the seed contained therein. The main surface had a shape in which the four corners were cut off from a square with two sides approximately parallel to the m-axis and the other two sides approximately parallel to the a-axis. The total width of the crystal was 8.8 cm in the direction indicated as the m-axis direction in Figure 12, and 9.1 cm in the direction indicated as the a-axis direction in Figure 12. The main surface was a circle with a diameter of 7.5 cm (area approximately 44 cm 2 ) was spacious enough to fit in with ease.

[0056] 4.2. Evaluation of large-area bulk GaN crystals In order to evaluate the degree of curvature of the c-plane in the large-area bulk GaN crystal obtained in 4.1 above, XRD rocking curve measurements were performed on the N-polarity side of the crystal, along a line that was an imaginary line segment passing through the approximate center of the main surface, over a length of 80 mm, every 5 mm, with the (002) crystal plane as the reflecting surface. Therefore, the number of measurement points on one line was 17. The X-ray diffraction device used for the measurement was a PANalytical X'Part PRO manufactured by Spectris, Inc. The CuKα radiation source included in the device was operated at 30 kV and 10 mA, and CuKα1 radiation was obtained using a Ge(220) hybrid monochromator. The measurements were performed along a first line, which is an imaginary line segment perpendicular to the a-axis and approximately parallel to the direction indicated as the m-axis direction in Figure 12, and a second line, which is an imaginary line segment perpendicular to the first line. For measurements on the first line, the omega axis was set perpendicular to the first line and the plane of incidence of the X-rays was set parallel to the first line, and for measurements on the second line, the omega axis was set perpendicular to the second line and the plane of incidence of the X-rays was set parallel to the second line.

[0057] The measurement results on the first line are shown in FIG. 13(a), and the measurement results on the second line are shown in FIG. 13(b). In each of FIG. 13(a) and FIG. 13(b), the horizontal axis represents the relative position of each measurement point when the central measurement point is set as the origin, that is, the distance from the origin, and the vertical axis represents the peak angle ω of the rocking curve at each measurement point and the average value ω of the peak angle among all 17 measurement points. AVE The difference between Δω(=ω-ω AVE ). The variation range of Δω was extremely small on both the first and second lines, and the difference between the maximum and minimum values ​​of Δω among the 17 measurement points on both lines was 0.012 degrees. As can be understood from the definition of Δω, the difference between the maximum and minimum values ​​of Δω is the same as the difference between the maximum and minimum values ​​of the peak angle ω of the rocking curve. Furthermore, there was no portion on either the first or second line where the absolute value of the peak angle difference of the rocking curve between two adjacent measurement points was 0.01 degrees or more. The maximum value (absolute value) of the peak angle difference of the rocking curve between two adjacent measurement points was 0.007 degrees on the first line and 0.004 degrees on the second line. As shown in Figures 13(a) and (b), no tendency for Δω to monotonically increase or decrease was observed on either the first or second line, and the radius of curvature of the c-plane calculated from the rate of change of Δω linearly approximated by the least squares method was 1050 m on the first line and 450 m on the second line. By slicing the large-area bulk GaN crystal produced in 4.1 above along the c-plane, a c-plane GaN wafer can be obtained that has a diameter of about 2 inches (50 to 55 mm) to about 3 inches (75 to 80 mm) and in which the variation range of the offcut angle in the m-axis direction and the a-axis direction components is both 0.012 degrees or less within the primary surface.

[0058] In addition, based on the results of measurements of GaN crystals grown by similar or equivalent methods, in any 100 μm × 100 μm region on the primary surface of the large-area bulk GaN crystal fabricated in 4.1 above, the dislocation density calculated from the number of dislocations present in that region and the area of ​​that region is estimated at 1 × 10 6 cm -2 In any 2 mm × 2 mm region, the dislocation density calculated from the number of dislocations present in the region and the area of ​​the region is estimated at 1 × 10 5 cm -2 is less than.

[0059] As the evaluation results show, the large-area bulk GaN crystal produced in the above 4.1. had a large area of ​​about 9 cm in both length and width, and the curvature of the c-plane was greatly improved. This shows that the seed assembly according to the inventors' technical idea is useful as a means of enlarging the area of ​​the GaN crystal grown thereon without imposing stress. In addition, it is noteworthy that, even though two c-plane GaN wafers were placed on the front side of the seed assembly, no clear jump in the c-axis tilt was observed in the large-area bulk GaN crystal containing the GaN crystal grown on top of them. Although the detailed mechanism by which this result was obtained is unclear, it is possible that the growing GaN crystals spontaneously aligned themselves. For example, in the ammonothermal process, the surface of the seed assembly melts before the growth zone reaches a supersaturated state, and the Pt wires may have become loose due to the widening of the through holes, which may have caused the seed assembly to spontaneously deform in a way that minimizes the stress on the growing GaN crystals.

[0060] Reasonably, it can be said that the favorable effects obtained based on the use of the seed assembly are not significantly hindered even if the area of ​​the GaN wafers constituting the seed assembly is increased or the number of GaN wafers constituting the seed assembly is increased. Therefore, by increasing the area and / or number of GaN wafers constituting the seed assembly, it is possible to produce large-area bulk GaN crystals with vertical and horizontal dimensions of about 4 inches (100-105 mm) or even about 6 inches (150-155 mm) having the same quality as those produced in the above experiment.

[0061] Although the present invention has been described above with reference to specific embodiments, each embodiment is presented as an example and does not limit the scope of the present invention. Each embodiment described in this specification can be modified in various ways without departing from the spirit of the invention, and can be combined with features described in other embodiments within the scope of feasibility. [Explanation of symbols]

[0062] 10 Bulk crystals 11 First principal surface 12 Second principal surface 100 C-plane wafer 101 Third principal surface 102 Fourth principal surface

Claims

1. The present invention has a principal surface selected from a surface having an inclination angle of 0 to 10 degrees from the (0001) crystal surface and a surface having an inclination angle of 0 to 10 degrees from the (000-1) crystal surface, the principal surface being a specific principal surface A that satisfies the following conditions (i) and (ii): A bulk GaN crystal, wherein the radius of curvature of a plane along a first direction described below, calculated from the rate of change of the peak angle under condition (i) below, and the radius of curvature of a plane along a second direction described below, calculated from the rate of change of the peak angle under condition (ii) below, are both 300 nm or greater. (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the specific main surface A, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) A second line, which is an imaginary line segment having a length of 80 mm extending in a second direction perpendicular to the first direction, can be drawn on the specific main surface A, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

2. The present invention has a principal surface selected from a surface having an inclination angle of 0 to 10 degrees from the (0001) crystal surface and a surface having an inclination angle of 0 to 10 degrees from the (000-1) crystal surface, the principal surface being a specific principal surface A that satisfies the following conditions (i) and (ii): In the specific main surface A, in all 100 μm×100 μm imaginary regions that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density is 1×10 ６ cm －２ Bulk GaN crystals. (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the specific main surface A, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) A second line, which is an imaginary line segment having a length of 80 mm extending in a second direction perpendicular to the first direction, can be drawn on the specific main surface A, and the omega axis of the GaN crystal is measured perpendicular to the second direction between 17 measurement points arranged at a pitch of 5 mm on the second line. 002) The difference between the maximum and minimum peak angles of the XRD rocking curve is 0.05 degrees or less.

3. The present invention has a principal surface selected from a surface having an inclination angle of 0 to 10 degrees from the (0001) crystal surface and a surface having an inclination angle of 0 to 10 degrees from the (000-1) crystal surface, the principal surface being a specific principal surface A that satisfies the following conditions (i) and (ii): In the specific main surface A, in all imaginary regions of 2 mm × 2 mm that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density is 1 × 10 ５ cm －２ Bulk GaN crystals. (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the specific main surface A, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) A second line, which is an imaginary line segment having a length of 80 mm extending in a second direction perpendicular to the first direction, can be drawn on the specific main surface A, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

4. The present invention has a principal surface selected from a surface having an inclination angle of 0 to 10 degrees from the (0001) crystal surface and a surface having an inclination angle of 0 to 10 degrees from the (000-1) crystal surface, the principal surface being a specific principal surface A that satisfies the following conditions (i) and (ii): A bulk GaN crystal that satisfies one or more conditions selected from the following (a) to (g): (a) H concentration is 1×10 １７ atoms / cm ３ That's all. (b) O concentration is 1×10 １７ atoms / cm ３ That's all. (c) The concentration of at least one of Li, Na, and K is 1×10 １５ atoms / cm ３ is less than. (d) F concentration is 1×10 １５ atoms / cm ３ That's all. (e) The concentration of at least one of Cl, Br, and I is 1×10 １５ atoms / cm ３ That's all. (f) I concentration is 1×10 １５ atoms / cm ３ That's all. (g) Si concentration is 2×10 １５ atoms / cm ３ is less than. (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the specific main surface A, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) A second line, which is an imaginary line segment having a length of 80 mm extending in a second direction perpendicular to the first direction, can be drawn on the specific main surface A, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

5. The present invention has a principal surface selected from a surface having an inclination angle of 0 to 10 degrees from the (0001) crystal surface and a surface having an inclination angle of 0 to 10 degrees from the (000-1) crystal surface, the principal surface being a specific principal surface A that satisfies the following conditions (i) and (ii): Infrared absorption spectrum 3140-3200 cm －１ A bulk GaN crystal having a peak at .beta. attributable to gallium vacancy-hydrogen complexes. (i) A first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the specific main surface A, can be drawn, and the (002) XRD lock of the GaN crystal measured with the omega axis perpendicular to the first direction between 17 measurement points arranged at a pitch of 5 mm on the first line can be obtained. The difference between the maximum and minimum peak angles of the curve is 0.05 degrees or less; (ii) A second line, which is an imaginary line segment having a length of 80 mm extending in a second direction perpendicular to the first direction, can be drawn on the specific main surface A, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

6. a first main surface and a second main surface facing in opposite directions, one of the first main surface and the second main surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (0001) crystal plane, and the other surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (000-1) crystal plane, and satisfying the following conditions (i) and (ii): A bulk GaN crystal, wherein the radius of curvature of a plane along a first direction described below, calculated from the rate of change of the peak angle under condition (i) below, and the radius of curvature of a plane along a second direction described below, calculated from the rate of change of the peak angle under condition (ii) below, are both 300 nm or greater. (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the first main surface, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) a second line, which is an imaginary line segment having a length of 80 mm extending on the first main surface in a second direction perpendicular to the first direction, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

7. a first main surface and a second main surface facing in opposite directions, one of the first main surface and the second main surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (0001) crystal plane, and the other surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (000-1) crystal plane, and satisfying the following conditions (i) and (ii): In the first main surface, in all 100 μm×100 μm imaginary regions that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, a dislocation density calculated from the number of dislocations present in the region and the area of ​​the region is 1×10 ６ cm －２ Bulk GaN crystals. (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the first main surface, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) a second line, which is an imaginary line segment having a length of 80 mm extending on the first main surface in a second direction perpendicular to the first direction, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

8. a first main surface and a second main surface facing in opposite directions, one of the first main surface and the second main surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (0001) crystal plane, and the other surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (000-1) crystal plane, and satisfying the following conditions (i) and (ii): In the first main surface, in all imaginary regions of 2 mm×2 mm that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, a dislocation density calculated from the number of dislocations present in the region and the area of ​​the region is 1×10 ５ cm －２ Bulk GaN crystals. (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the first main surface, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) a second line, which is an imaginary line segment having a length of 80 mm extending on the first main surface in a second direction perpendicular to the first direction, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

9. a first main surface and a second main surface facing in opposite directions, one of the first main surface and the second main surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (0001) crystal plane, and the other surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (000-1) crystal plane, and satisfying the following conditions (i) and (ii): A bulk GaN crystal that satisfies one or more conditions selected from the following (a) to (g): (a) H concentration is 1×10 １７ atoms / cm ３ That's all. (b) O concentration is 1×10 １７ atoms / cm ３ That's all. (c) The concentration of at least one of Li, Na, and K is 1×10 １５ atoms / cm ３ is less than. (d) F concentration is 1×10 １５ atoms / cm ３ That's all. (e) The concentration of at least one of Cl, Br, and I is 1×10 １５ atoms / cm ３ That's all. (f) I concentration is 1×10 １５ atoms / cm ３ That's all. (g) Si concentration is 2×10 １５ atoms / cm ３ is less than. (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the first main surface, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) a second line, which is an imaginary line segment having a length of 80 mm extending on the first main surface in a second direction perpendicular to the first direction, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

10. a first main surface and a second main surface facing in opposite directions, one of the first main surface and the second main surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (0001) crystal plane, and the other surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (000-1) crystal plane, and satisfying the following conditions (i) and (ii): Infrared absorption spectrum 3140-3200 cm －１ A bulk GaN crystal having a peak at .beta. attributable to gallium vacancy-hydrogen complexes. (i) a first line, which is an imaginary line segment having a length of 80 mm extending in a first direction on the first main surface, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the first direction among 17 measurement points arranged at a pitch of 5 mm on the first line is 0.05 degrees or less; (ii) a second line, which is an imaginary line segment having a length of 80 mm extending on the first main surface in a second direction perpendicular to the first direction, can be drawn, and the difference between the maximum and minimum peak angles of the (002) XRD rocking curve of the GaN crystal measured with the omega axis perpendicular to the second direction among 17 measurement points arranged at a pitch of 5 mm on the second line is 0.05 degrees or less.

11. 11. The bulk GaN crystal according to claim 1, wherein the difference between the maximum and minimum values ​​of the peak angle under condition (i) and the difference between the maximum and minimum values ​​of the peak angle under condition (ii) are both 0.02 degrees or less.

12. 12. The bulk GaN crystal according to claim 1, wherein neither the 17 measurement points under condition (i) nor the 17 measurement points under condition (ii) includes a measurement point whose peak angle differs from an adjacent measurement point by 0.01 degrees or more.

13. 11. The bulk GaN crystal according to claim 2, wherein the radius of curvature of the plane along the first direction, calculated from the rate of change of the peak angle under condition (i), and the radius of curvature of the plane along the second direction, calculated from the rate of change of the peak angle under condition (ii), are both 300 mm or greater.

14. In the specific main surface A, in all 100 μm×100 μm imaginary regions that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density is 1×10 ６ cm －２ The bulk GaN crystal of any one of claims 1 and 3-5, wherein the thickness of the bulk GaN crystal is less than 100 nm.

15. In the specific main surface A, in all imaginary regions of 2 mm × 2 mm that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density is 1 × 10 ５ cm －２ 6. The bulk GaN crystal of claim 1 , wherein the thickness of the bulk GaN crystal is less than 100 nm.

16. In the first main surface, in all 100 μm×100 μm imaginary regions that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, a dislocation density calculated from the number of dislocations present in the region and the area of ​​the region is 1×10 ６ cm －２ The bulk GaN crystal of any one of claims 6 and 8-10, wherein the thickness of the bulk GaN crystal is less than 100 nm.

17. In the first main surface, in all imaginary regions of 2 mm×2 mm that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, a dislocation density calculated from the number of dislocations present in the region and the area of ​​the region is 1×10 ５ cm －２ 11. The bulk GaN crystal of claim 6, 7, 9, or 10, wherein the thickness of the bulk GaN crystal is less than 100 nm.

18. A bulk GaN crystal according to any one of claims 1 to 3, 5 to 8, and 10, which satisfies one or more conditions selected from the following (a) to (g): (a) H concentration is 1×10 １７ atoms / cm ３ That's all. (b) O concentration is 1×10 １７ atoms / cm ３ That's all. (c) The concentration of at least one of Li, Na, and K is 1×10 １５ atoms / cm ３ is less than. (d) F concentration is 1×10 １５ atoms / cm ３ That's all. (e) The concentration of at least one of Cl, Br, and I is 1×10 １５ atoms / cm ３ That's all. (f) I concentration is 1×10 １５ atoms / cm ３ That's all. (g) Si concentration is 2×10 １５ atoms / cm ３ is less than.

19. Infrared absorption spectrum 3140-3200 cm －１ 10. The bulk GaN crystal according to claim 1, having a peak attributable to a gallium vacancy-hydrogen complex at .gamma.

20. Providing a bulk GaN crystal according to any one of claims 1 to 19; and slicing the aN crystal.

21. The method of claim 20, wherein the c-plane GaN wafer is disk-shaped, and the diameter of a circle constituting the disk is 50 mm or more.

22. A c-plane GaN wafer having a primary surface selected from a surface having an inclination from 0 to 10 degrees from the (0001) crystal plane and a surface having an inclination from 0 to 10 degrees from the (000-1) crystal plane, the primary surface being a specific primary surface B that satisfies the following condition (iii): (iii) A virtual line segment of 50 mm or more can be drawn on the specific main surface B, and the variation range of the m-axis component and the variation range of the a-axis component of the offcut angle are both 0.05 degrees or less, except for a portion that is less than 5 mm away from the outer periphery when viewed in a plane.

23. a c-plane GaN wafer having a third principal surface and a fourth principal surface facing in opposite directions, one of the third principal surface and the fourth principal surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (0001) crystal plane, and the other of the third principal surface and the fourth principal surface being inclined at an angle of 0 degrees or more and 10 degrees or less from a (000-1) crystal plane; A c-plane GaN wafer, wherein the third main surface has a virtual line segment of 50 mm or more along it, and the variation ranges of the m-axis component and the a-axis component of the offcut angle are both within 0.05 degrees, except for a portion that is less than 5 mm away from the outer periphery when viewed in a plan view.

24. 24. The c-plane GaN wafer according to claim 22, wherein the variation range of the offcut angle in the m-axis direction and the variation range of the offcut angle in the a-axis direction are both within 0.02 degrees.

25. 25. The c-plane GaN wafer according to claim 22, having a diameter selected from the group consisting of 50 mm to 55 mm, 75 mm to 80 mm, 100 mm to 105 mm, and 150 mm to 155 mm.

26. In the specific main surface B, in all 100 μm × 100 μm imaginary regions that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, the dislocation density is 1 × 10 ６ cm －２ 23. The c-plane GaN wafer of claim 22, wherein the n-type GaN wafer is less than 100 nm.

27. In the specific main surface B, in all 2 mm x 2 mm imaginary regions that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, ５ cm －２ 27. The c-plane GaN wafer of claim 22 or 26, wherein the n-axis angle is less than 100 nm.

28. In the third main surface, in all 100 μm×100 μm imaginary regions that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, a dislocation density is 1×10 ６ cm －２ 24. The c-plane GaN wafer of claim 23, wherein the n-type GaN wafer is less than 100 nm.

29. In the third main surface, in a virtual area of ​​2 mm x 2 mm that can be arbitrarily provided in a portion excluding a portion that is less than 5 mm away from the outer periphery when viewed in a plan view, ５ cm －２ 30. The c-plane GaN wafer of claim 23 or 28, wherein the n-axis direction of the c-plane GaN wafer is less than 100 nm.

30. 30. The c-plane GaN wafer according to claim 22, which satisfies one or more conditions selected from the following (a) to (g): (a) H concentration is 1×10 １７ atoms / cm ３ That's all. (b) O concentration is 1×10 １７ atoms / cm ３ That's all. (c) The concentration of at least one of Li, Na, and K is 1×10 １５ atoms / cm ３ is less than. (d) F concentration is 1×10 １５ atoms / cm ３ That's all. (e) The concentration of at least one of Cl, Br, and I is 1×10 １５ atoms / cm ３ That's all. (f) I concentration is 1×10 １５ atoms / cm ３ That's all. (g) Si concentration is 2×10 １５ atoms / cm ３ is less than.

31. Infrared absorption spectrum 3140-3200 cm －１ 31. The c-plane GaN wafer of claim 30, having a peak attributable to a gallium vacancy-hydrogen complex at

32. An epitaxial wafer comprising the c-plane GaN wafer according to any one of claims 22 to 31, and one or more nitride semiconductor layers epitaxially grown on the c-plane GaN wafer.

33. A method for producing an epitaxial wafer, comprising the steps of: providing a c-plane GaN wafer according to any one of claims 22 to 31; and epitaxially growing one or more nitride semiconductor layers on the c-plane GaN wafer.

34. A method for manufacturing a nitride semiconductor device, comprising the steps of: providing a c-plane GaN wafer according to any one of claims 22 to 31; and epitaxially growing one or more nitride semiconductor layers on the c-plane GaN wafer.

35. A method for producing bulk GaN crystals, comprising the steps of: preparing a c-plane GaN wafer according to any one of claims 22 to 31; and epitaxially growing a GaN crystal on the c-plane GaN wafer from a vapor phase.

36. A method for producing bulk GaN crystals, comprising a step of growing GaN crystals on a seed assembly by an ammonothermal method, the seed assembly being composed of a plurality of c-plane GaN wafers, and metal wires being used to secure the plurality of c-plane GaN wafers to each other.

37. 37. The method for producing bulk GaN crystals as recited in claim 36, wherein the c-axis, a-axis, and m-axis orientations of all of the c-plane GaN wafers constituting the seed assembly are aligned.

38. 38. The method for producing bulk GaN crystals as described in claim 37, wherein, when the direction of the N-polarity side of the main surface of the c-plane GaN wafer constituting the seed assembly is defined as the front direction, the seed assembly arranges two or more c-plane GaN wafers, each having a rectangular or approximately rectangular main surface, adjacent to each other on the front direction side of the seed assembly, and a c-plane GaN wafer is arranged on the side opposite to the front direction of the seed assembly.

39. The method for producing bulk GaN crystals according to any one of claims 36 to 38, wherein in the step of growing GaN crystals by the ammonothermal method, a mineralizer containing a compound containing a halogen is used, and at least one metal wire selected from an Ag wire, a Pt wire, and an Au wire is used as the metal wire.

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