GaN single crystal

Abstract

Provision of new GaN single crystals [Solution] A GaN single crystal having a gallium polarity plane as one main surface and a nitrogen polarity plane as the opposite main surface, wherein at least one square region is found on the gallium polarity plane, and each of the four sides constituting the periphery of the at least one square region has a length of 2 mm or more, and when the at least one square region is divided into a plurality of subregions, each of which is a square of 100 μm x 100 μm, 80% or more of the subregions are pit-free regions.

Description

Technical Field

[0001] The present invention mainly relates to a GaN single crystal and a method for manufacturing a GaN single crystal.

Background Art

[0002] GaN (gallium nitride) is a type of III-V compound semiconductor and has a wurtzite crystal structure belonging to the hexagonal system. In recent years, single crystal GaN wafers have attracted attention as semiconductor wafers for nitride semiconductor devices. Nitride semiconductors are also called nitride-based III-V compound semiconductors, group III nitride-based compound semiconductors, GaN-based semiconductors, etc. In addition to GaN, they include compounds in which part or all of the gallium in GaN is replaced with other group 13 elements (B, Al, In, etc.) of the periodic table. One of the highly useful single crystal GaN wafers is a C-plane GaN wafer. A C-plane GaN wafer is a single crystal GaN wafer having a main surface parallel to the C-plane or slightly inclined from the C-plane. The C-plane GaN wafer has a gallium-polar surface which is the main surface on the

[0001] side and a nitrogen-polar surface which is the main surface on the [000-1] side. Currently, mainly the gallium-polar surface is used for forming nitride semiconductor devices.

[0003] A preferred method for growing a GaN single crystal used for a C-plane GaN wafer is the ammonothermal method. In the ammonothermal method, GaN dissolved in supercritical or subcritical ammonia is precipitated as a single crystal on a seed. Non-Patent Document 1 reports that a C-plane GaN wafer was fabricated from a GaN single crystal grown by the ammonothermal method, and a dislocation-free region with an area of 1 mm 2 was observed on the surface of the C-plane GaN wafer. Non-Patent Document 2 reports that a 2-inch diameter C-plane GaN wafer was fabricated from a GaN single crystal grown by the ammonothermal method.

[0004] Patent Document 1 describes that a pattern mask having a linear opening is formed on the main surface of a C-plane GaN wafer used as a seed, and a GaN layer is grown by the ammonothermal method through the linear opening. The extending direction of the linear opening was the m-axis direction <10-10> or the a-axis direction <11-20>. It is said that the GaN crystals grown from the inside of the linear opening of the pattern mask grew laterally on the pattern mask and coalesced into one layer. Patent Document 2 describes that a pattern mask having a linear opening is formed on the nitrogen-polar surface of a C-plane GaN wafer used as a seed, and a GaN single crystal is grown by the ammonothermal method through the linear opening. It is said that the GaN crystals grown through each of the linear openings grew 10 mm in the [000-1] direction without coalescing.

[0005] Non-Patent Document 3 reports the growth rate of GaN crystals when various ammonium halide mineralizers are used in the ammonothermal method.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007]

Non-Patent Document 1

[0008] The main object of the present invention is to provide a novel GaN single crystal having improved quality, and to provide a novel method for manufacturing a GaN single crystal for manufacturing a GaN single crystal having improved quality. [Means for Solving the Problems]

[0009] According to the present invention, a GaN single crystal described below is provided. [1] In a GaN single crystal having a gallium-polar surface which is a main surface on one side and a nitrogen-polar surface which is a main surface on the opposite side, at least one square region is found on the gallium-polar surface, and the length of each of the four sides constituting the outer periphery of the at least one square region is 2 mm or more. When the at least one square region is divided into a plurality of sub-regions each being a square of 100 μm × 100 μm, 80% or more of the plurality of sub-regions are pit-free regions. A GaN single crystal characterized by this. [2] The GaN single crystal according to [1], wherein the ratio of the pit-free regions among the plurality of sub-regions is 85% or more. [3] The GaN single crystal according to [1], wherein the ratio of the pit-free regions among the plurality of sub-regions is 90% or more. [4] In the sub-region having the highest EPD among the plurality of sub-regions, the EPD is 1 × 10 6 cm -2 less than. The GaN single crystal according to any one of [1] to [3]. [5] The average value of the EPD among the plurality of sub-regions is 1 × 10 4 cm -2 less than. The GaN single crystal according to any one of [1] to [4]. [6] In the sub-region having the highest EPD among the plurality of sub-regions, the EPD is 2 × 10 5 cm -2 less than. The GaN single crystal according to [3]. [7] The average value of the EPD among the plurality of sub-regions is 3 × 10 3 cm -2 less than. The GaN single crystal according to [3] or [6]. [8] The GaN single crystal according to [3], [6] or [7], wherein each of the four sides constituting the outer periphery of the at least one square region has a length of 3.5 mm or less. [9] The GaN single crystal according to any one of [1] to [8], wherein at least one square pit-free region of 1.3 mm × 1.3 mm is found on the gallium polar surface.

[10] The GaN single crystal according to any one of [1] to [9], wherein each of the gallium polar surface and the nitrogen polar surface has a size that encloses a 10 mm × 10 mm square, and an anomalous transmission image of a 10 mm × 10 mm square region is obtained in X-ray topography.

[0010]

[11] In a GaN single crystal having a gallium polar surface as one main surface and a nitrogen polar surface as the main surface on the opposite side, at least one square pit-free region of 1.3 mm × 1.3 mm is found on the gallium polar surface. A GaN single crystal characterized in that.

[12] In a GaN single crystal having a gallium polar surface as one main surface and a nitrogen polar surface as the main surface on the opposite side, each of the gallium polar surface and the nitrogen polar surface has a size that encloses a 10 mm × 10 mm square, and an anomalous transmission image is obtained in X-ray topography. A GaN single crystal characterized by that.

[13] In a GaN single crystal having a gallium polar surface as one main surface and a nitrogen polar surface as the main surface on the opposite side, each of the gallium polar surface and the nitrogen polar surface has a size that encloses a 10 mm × 10 mm square, and an anomalous transmission image of a 10 mm × 10 mm square region is obtained in X-ray topography. A GaN single crystal characterized by that.

[14] In a GaN single crystal having a gallium polar surface as one main surface and a nitrogen polar surface as the main surface on the opposite side, at least one first line segment, which is a virtual line segment defined in the following (A), can be drawn on at least one of the gallium polar surface and the nitrogen polar surface. A GaN single crystal characterized by that; (A) The first line segment is a line segment having a length L1, and the first line segment On the above, when the X-ray incident plane during each ω scan is made parallel to the first line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec at 90% or more of all the measurement points (however, the length L1 is 20 mm or more, preferably 30 mm or more, more preferably 40 mm or more, more preferably 50 mm or more, more preferably 60 mm or more).

[15] The GaN single crystal according to

[14] , wherein the first line segment further has one or more characteristics selected from the following (A1) to (A3); (A1) On the first line segment, when the X-ray incident plane in each ω scan is made parallel to the first line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec at 95% or more, preferably 98% or more, more preferably 99% or more, more preferably 100% of all the measurement points; (A2) On the first line segment, when the X-ray incident plane in each ω scan is made parallel to the first line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 40 arcsec at 90% or more, preferably 95% or more, more preferably 98% or more of all the measurement points; (A3) On the first line segment, when the X-ray incident plane in each ω scan is made parallel to the first line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 30 arcsec at 90% or more, preferably 95% or more, more preferably 98% or more of all the measurement points.

[16] On the gallium-polar plane or the nitrogen-polar plane from which the first line segment can be drawn, at least one second line segment, which is a virtual line segment defined in the following (B), can be drawn on the GaN single crystal according to

[14] or

[15] ; (B) The second line segment is a line segment having a length L2, and is perpendicular to at least one of the above-mentioned first line segments. On the second line segment, when the X-ray incident plane in each ω scan is made parallel to the second line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec at 90% or more of all the measurement points (however, the length L2 is 20 mm or more, preferably 30 mm or more, more preferably ). is 40 mm or more, more preferably 50 mm or more, still more preferably 60 mm or more).

[17] The second line segment further has one or more characteristics selected from the following (B1) to (B3), the GaN single crystal according to

[16] ; (B1) On the second line segment, when the X-ray incident plane in each ω scan is made parallel to the second line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec at 95% or more, preferably 98% or more, still more preferably 99% or more, still more preferably 100% of all measurement points; (B2) On the second line segment, when the X-ray incident plane in each ω scan is made parallel to the second line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 40 arcsec at 90% or more, preferably 95% or more, still more preferably 98% or more of all measurement points; (B3) On the second line segment, when the X-ray incident plane in each ω scan is made parallel to the second line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 30 arcsec at 90% or more, preferably 95% or more, still more preferably 98% or more of all measurement points.

[18] In a GaN single crystal having a gallium-polar surface which is one main surface and a nitrogen-polar surface which is the main surface on the opposite side, at least one third line segment which is a virtual line segment defined in the following (C) can be drawn on at least one of the gallium-polar surface and the nitrogen-polar surface; (C) The third line segment is a line segment having a length L3, and on the third line segment, when the X-ray incident plane in each ω scan is made parallel to the third line segment and the XRC-FWHM of the (004) reflection is measured at intervals of 1 mm, the average between all measurement points is less than 20 arcsec (however, the length L3 is 20 mm or more, preferably 30 mm or more, still more preferably 40 mm or more, still more preferably 50 mm or more, still more preferably 60 mm or more).

[19] The GaN single crystal according to

[18] , wherein the third line segment further has one or more characteristics selected from the following (C1) and (C2): (C1) On the third line segment, when the X-ray incident plane in each ω scan is parallel to the third line segment and the XRC-FWHM of the (004) reflection is measured at 1 mm intervals, the average between all measurement points is less than 15 arcsec; (C2) On the third line segment, when the X-ray incident plane in each ω scan is parallel to the third line segment and the XRC-FWHM of the (004) reflection is measured at 1 mm intervals, the standard deviation between all measurement points is 5 arcsec or less.

[20] The GaN single crystal according to

[18] or

[19] , wherein at least one fourth line segment, which is a virtual line segment defined by the following (D), can be drawn on the gallium-polarity plane or the nitrogen-polarity plane from which the third line segment can be drawn; (D) The fourth line segment is a line segment having a length L4, is orthogonal to at least one of the third line segments, and on the fourth line segment, when the X-ray incident plane in each ω scan is parallel to the fourth line segment and the XRC-FWHM of the (004) reflection is measured at 1 mm intervals, the average between all measurement points is less than 20 arcsec (however, the length L4 is 20 mm or more, preferably 30 mm or more, more preferably 40 mm or more, and even more preferably 50 mm or more).

[21] The GaN single crystal according to

[20] , wherein the fourth line segment further has one or more characteristics selected from the following (D1) and (D2): (D1) On the fourth line segment, when the X-ray incident plane in each ω scan is parallel to the fourth line segment and the XRC-FWHM of the (004) reflection is measured at 1 mm intervals, the average between all measurement points is less than 15 arcsec; (D2) On the fourth line segment, when the X-ray incident plane in each ω scan is parallel to the fourth line segment and the XRC-FWHM of the (004) reflection is measured at 1 mm intervals, the standard deviation between all measurement points is 5 arcsec or less.

[22] The GaN single crystal according to any one of [1] to

[21] , which has a linear dislocation array on the gallium-polarity plane.

[23] The GaN single crystal according to

[22] , wherein the extending direction of the linear dislocation array forms an angle within a range of 12° ± 5° with one of the intersection lines between the gallium-polarity plane and the M plane.

[0011]

[24] In a GaN single crystal having a gallium-polarity surface which is one main surface and a nitrogen-polarity surface which is the main surface on the opposite side, it has a linear dislocation array on the gallium-polarity surface, and the extending direction of the linear dislocation array forms an angle within a range of ±5° with respect to one of the intersection lines between the gallium-polarity surface and the M plane. A GaN single crystal is characterized by this.

[25] In the gallium-polarity surface, the number of dislocations existing within a 100 μm × 100 μm square region that entirely overlaps with the linear dislocation array is less than 100 (preferably less than 50, more preferably less than 30). The GaN single crystal according to any one of

[22] to

[24] .

[26] In a GaN single crystal having a gallium-polarity surface which is one main surface and a nitrogen-polarity surface which is the main surface on the opposite side, at least one fifth line segment which is a virtual line segment defined in the following (E) and at least one sixth line segment which is a virtual line segment defined in the following (F) can be drawn on at least one of the gallium-polarity surface and the nitrogen-polarity surface, respectively; (E) The fifth line segment is a line segment having a length L5 (where L5 is 40 mm or more), and on the fifth line segment, the X-ray incident plane during each ω scan is parallel to the fifth line segment Then, the XRC of the (002) reflection was measured at intervals of 5 mm (preferably 3 mm, more preferably 1 mm, even more preferably 0.6 mm), and then two points 10 mm apart from each other were arbitrarily selected from all the measurement points, and when the radius of curvature of the C-plane in the direction parallel to the fifth line segment was calculated from the difference Δω in the peak top angle of the XRC between the two points using the formula R = ΔL / Δω [where R: radius of curvature, ΔL: distance between the two points], the absolute value R5 was 40 m or more; (F) The sixth line segment is a line segment having a length L6 (where L6 is 40 mm or more), is orthogonal to the fifth line segment, and on the sixth line segment, the X-ray incident plane at the time of each ω scan was made parallel to the sixth line segment, and the XRC of the (002) reflection was measured at intervals of 5 mm (preferably 3 mm, more preferably 1 mm, even more preferably 0.6 mm), and then two points 10 mm apart from each other were arbitrarily selected from all the measurement points, and when the radius of curvature of the C-plane in the direction parallel to the sixth line segment was calculated from the difference Δω in the peak top angle of the XRC between the two points using the formula R = ΔL / Δω [where R: radius of curvature, ΔL: distance between the two points], the absolute value R6 was 40 m or more.

[27] For any of the alkali metals and alkaline earth metals, the concentration is 1×10 16 atoms / cm 3 less than that of the GaN single crystal according to any one of [1] to

[26] .

[28] For any of the halogens, the concentration is 1×10 16 atoms / cm 3 less than that of the GaN single crystal according to any one of [1] to

[27] .

[29] 10 17 atoms / cm 3 or a higher concentration of hydrogen (H) of the GaN single crystal according to any one of [1] to

[28] .

[30] In the infrared absorption spectrum, a peak attributable to a gallium vacancy-hydrogen complex is observed at 3100 to 3500 cm -1 of the GaN single crystal according to any one of [1] to

[29] .

[31] The GaN single crystal according to any one of [1] to

[30] , which is a C-plane GaN wafer.

[0012] According to the present invention, there is provided a method for manufacturing a GaN single crystal described below.

[32] A method for manufacturing a GaN single crystal, comprising: (S1) preparing a seed having a nitrogen polar plane of GaN; (S2) forming a pattern mask having a plurality of linear openings arranged in parallel to each other at a constant pitch on the nitrogen polar plane of the prepared seed; and (S3) growing a GaN crystal on the nitrogen polar plane through the linear openings of the pattern mask by an ammonothermal method. In step (S3), the GaN crystal grows from the inside of the opening of the pattern mask, then spreads laterally above the pattern mask, and coalesces while forming voids between the pattern mask.

[33] In the pattern mask formed in step (S2), the extending direction of the linear opening forms an angle within a range of 12° ± 5° with one of the intersection lines of the nitrogen polar plane and the M plane of the seed, according to the manufacturing method described in

[32] .

[34] The manufacturing method according to

[32] or

[33] , wherein the pattern mask is a stripe type.

[35] The manufacturing method according to

[32] or

[33] , wherein the pattern mask is a rhombic lattice type.

[36] The manufacturing method according to

[32] or

[33] , wherein the pattern mask is a hexagonal lattice type.

[37] The manufacturing method according to any one of

[32] to

[36] , wherein the constant pitch is 4 mm or more and 20 mm or less. [Advantages of the Invention]

[0013] According to the present invention, a novel GaN single crystal having improved quality is provided. In addition, according to the present invention, a novel method for manufacturing a GaN single crystal for manufacturing a GaN crystal having improved quality is provided. [Brief Description of the Drawings]

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Embodiments for Carrying Out the Invention

[0015] In a GaN crystal, the crystal axis parallel to

[0001] is called the c-axis, the crystal axis parallel to <10-10> is called the m-axis, and the crystal axis parallel to <11-20> is called the a-axis. The crystal plane orthogonal to the c-axis is called the C-plane, the crystal plane orthogonal to the m-axis is called the M-plane, and the crystal plane orthogonal to the a-axis is called the A-plane. Hereinafter, when referring to crystal axes, crystal planes, crystal orientations, etc., unless otherwise specified, they shall mean the crystal axes, crystal planes, crystal orientations, etc. of the GaN crystal. Hereinafter, embodiments of the present invention will be described with appropriate reference to the drawings.

[0016] 1. First Embodiment The first embodiment of the present invention relates to a GaN single crystal. 1.1. Outer Shape and Size of GaN Single Crystal The GaN single crystal according to the first embodiment has a plate shape having one main surface on one side and the main surface on the opposite side, and its thickness direction is parallel or substantially parallel to the c-axis. One of the two main surfaces is a gallium polar plane, and the other is a nitrogen polar plane. There is no particular limitation on the shape of the main surface. FIG. 1 is a drawing illustrating a shape that the GaN single crystal according to the first embodiment may have. FIG. 1(a) is a perspective view, and FIG. 1(b) is a side view. Referring to FIG. 1, the GaN single crystal 10 is a disk, and the shapes of the gallium polar plane 11 which is the main surface on the

[0001] side and the nitrogen polar plane 12 which is the main surface on the [000-1] side are circular. The gallium polar plane 11 and the nitrogen polar plane 12 are connected via a side surface 13.

[0017] FIGS. 2(a) to (c) are perspective views respectively illustrating other shapes that the GaN single crystal according to the first embodiment may have. In FIG. 2, the same reference numerals as those in FIG. 1 are assigned to the configurations corresponding to the configurations shown in FIG. 1 (the same applies to FIGS. 3 and 6 described later). In FIGS. 2(a) to 2(c), the shapes of the gallium polar plane 11 and the nitrogen polar plane 12 of the GaN single crystal 10 are a quadrilateral, a hexagon, and an octagon, respectively. The main surface of the GaN single crystal according to the first embodiment has a size that encloses a 10 mm × 10 mm square, preferably 4 cm 2 or more, more preferably 5 cm 2 or more, more preferably 15 cm 2 or more of an area. The area of the main surface is 18 cm 2 or more, 38 cm 2 or more, 71 cm 2 or more, 165 cm 2 or more, 299 cm 2 or more, or 683 cm 2 or more and may be.

[0018] In the GaN single crystal of the first embodiment, the gallium polar plane may be parallel to (0001), or may be slightly inclined from (0001). The inclination of the gallium polar plane from (0001) is usually 10° or less, preferably 5° or less, more preferably 2° or less, and may be 1° or less. In the GaN single crystal of the first embodiment, the nitrogen polar plane may be parallel to (000-1), or may be slightly inclined from (000-1). The inclination of the nitrogen polar plane from (000-1) is usually 10° or less, preferably 5° or less, more preferably 2° or less, and may be 1° or less. Although not limiting, preferably, the gallium polar plane and the nitrogen polar plane are parallel to each other.

[0019] The GaN single crystal of the first embodiment can be an ingot or a wafer (C-plane GaN wafer). When the GaN single crystal of the first embodiment is a disk-shaped ingot or wafer, its diameter is usually 20 mm or more and 305 mm or less. The diameter is typically 25 mm (about 1 inch), 45 - 55 mm (about 2 inches), 95 - 105 mm (about 4 inches), 145 - 155 mm (about 6 inches), 195 - 205 mm (about 8 inches), 295 - 305 mm (about 12 inches), etc. When the GaN single crystal of the first embodiment is an ingot or wafer having a rectangular main surface, the length of each side of the rectangle is usually 2 cm or more, preferably 3 cm or more, and usually 15 cm or less. When the GaN single crystal of the first embodiment is a C-plane GaN wafer, since a strength that does not cause inconvenience in handling is required, its thickness is preferably 250 μm or more, more preferably 300 μm or more. Depending on the size of the main surface, it can be made even thicker.

[0020] In the C-plane GaN wafer, chamfering for smoothing the boundary between the gallium-polar surface and the side surface can be appropriately performed as necessary. The same applies to the boundary between the nitrogen-polar surface and the side surface. On the side surface of the GaN single crystal of the first embodiment, an orientation flat, which is a flat portion indicating the crystal orientation, can be provided, and an index flat, which is a flat portion for facilitating the identification of the gallium-polar surface and the nitrogen-polar surface, can also be provided. In addition, various markings can be applied to the GaN single crystal of the first embodiment as necessary.

[0021] 1.2. Concentrations of Alkali Metals, Alkaline Earth Metals, and Halogens The concentrations of alkali metals, alkaline earth metals, and halogens contained as impurities in the GaN crystal are generally measured by SIMS (Secondary Ion Mass Spectrometry). The concentrations of alkali metals, alkaline earth metals, and halogens mentioned below are the values in the portion with a depth of 1 μm or more from the surface measured by SIMS. In the GaN single crystal of the first embodiment, for any alkali metal containing lithium (Li), sodium (Na), and potassium (K), its concentration is preferably 1×1 0 16 atoms / cm 3 less than, more preferably 1×10 15 atoms / cm 3 less than. In the GaN single crystal of the first embodiment, for any alkaline earth metal containing magnesium (Mg) and calcium (Ca), its concentration is preferably 1×10 16 atoms / cm 3 less than, more preferably 1×10 15 atoms / cm 3 less than. The GaN single crystal of the first embodiment may include a GaN crystal grown by the ammonothermal method. In the GaN crystal grown by the ammonothermal method using ammonium halides such as ammonium chloride (NH4Cl), ammonium iodide (NH4I), ammonium bromide (NH4Br), and ammonium fluoride (NH4F) as mineralizers, the concentrations of alkali metals and alkaline earth metals are usually 1×10 15 atoms / cm 3 less than.

[0022] In the GaN single crystal of the first embodiment, even when it includes a GaN crystal grown by the ammonothermal method using ammonium halide as a mineralizer, for any halogen containing fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), its concentration is 1×10 16 atoms / cm 3 less than, and further may be less than 5×10 15 atoms / cm 3 less than. The detection limit concentration of halogen in the GaN crystal in SIMS depends on the halogen species but is generally on the order of 10 14 to 10 15 orders of magnitude (atms / cm 3 ). Therefore, this means that the concentration of any halogen can be less than the detection limit in SIMS. The concentration of halogen in GaN crystals grown by the ammonothermal method is usually less than 5×10 15 atoms / cm 3 (less than the detection limit) excluding the halogen species contained in the mineralizer. However, in the GaN single crystal of the first embodiment, the concentration of the halogen species contained in the mineralizer can also be such a value.

[0023] The GaN single crystal of the first embodiment usually contains hydrogen (H) at a concentration of 10 17 atoms / cm 3 or higher. The hydrogen concentration in the GaN single crystal of the first embodiment is typically 5×10 17 atoms / cm 3 or more, and further can be 1×10 18 atoms / cm 3 or more. The hydrogen concentration in the GaN single crystal of the first embodiment is usually 10 21 atoms / cm 3 or less, 5×10 20 atoms / cm 3 or less, 1×10 20 atoms / cm 3 or less, 5×10 19 atoms / cm 3 or less, etc. When measuring the infrared absorption spectrum of the GaN single crystal of the first embodiment, a peak attributed to a gallium vacancy-hydrogen complex appears at 3100-3500 cm -1 . Conventionally, it is known that the same kind of infrared absorption peak is observed in GaN crystals grown ammonothermally, but such an infrared absorption peak is not observed in GaN crystals grown by the HVPE method or the Na flux method.

[0024] 1.3. Dislocation density The GaN single crystal according to the first embodiment may have a linear dislocation array extending in a predetermined direction on its gallium polar surface. The angle formed by the extending direction of the linear dislocation array and one of the intersection lines between the gallium polar surface and the M plane is preferably within the range of 12° ± 5°. This angle may be within the range of 12° ± 3°, 12° ± 2° or 12° ± 1°. FIG. 3 is a plan view showing an example of a GaN single crystal having a linear dislocation array on its gallium polar surface. Referring to FIG. 3, the GaN single crystal 10 is a disk-shaped C-plane GaN wafer, and a plurality of linear dislocation arrays 14 extending in the same direction are arranged at equal intervals on its gallium polar surface 11. Therefore, the pitch P between the dislocation arrays 14 d is equal to the period of the stripe pattern formed by the plurality of dislocation arrays 14. The pitch P between the dislocation arrays 14 d is usually 3 mm or more, preferably 3.5 mm or more, more preferably 4 mm or more, and is usually 20 mm or less. The pitch P between the dislocation arrays 14 d may be 10.5 mm or less, 7.5 mm or less, or 5.5 mm or less. The width W of each dislocation array 14 is usually less than 300 μm. d

[0025] In FIG. 3, the dashed line B-B represents one of the intersection lines between the gallium polar surface 11 and the M plane. Since the gallium polar surface 11 is parallel or substantially parallel to (0001), the dashed line B-B is parallel or substantially parallel to one of the a axes. The angle θ formed by the extending direction of the linear dislocation array 14 and the dashed line B-B is preferably within the range of 12° ± 5°. The angle θ may be within the range of 12° ± 3°, 12° ± 2° or 12° ± 1°. In the example of FIG. 3, the GaN single crystal 10 is provided with an orientation flat 15. This orientation flat 15 is disposed at the end of the straight dislocation array 14 in the extending direction and is orthogonal to the extending direction. In another example, the orientation flat can be provided parallel to the extending direction of the straight dislocation array. In still another example, the orientation flat can be provided at the end of the GaN single crystal in the a-axis direction or the m-axis direction.

[0026] The dislocations that the GaN single crystal has on the gallium polar surface can be visualized by etching the GaN single crystal. This is because by etching under appropriate conditions, etch pits observable with an optical microscope, a scanning electron microscope (SEM), etc. are formed at the locations where dislocations exist. As confirmed by the present inventors, when etching is performed for 1 hour or more using 89% sulfuric acid heated to 270°C as an etchant, etch pits corresponding to all types of dislocations (edge dislocations, screw dislocations, and mixed dislocations) present on the gallium polar surface of the GaN crystal are surely formed. FIG. 4 shows an optical microscope image of the gallium polar surface of a GaN single crystal on which etch pits are formed under this etching condition. The density of etch pits on the surface of a GaN crystal etched under the condition that etch pits are formed at the locations where dislocations exist is also called "EPD" and is accepted among those skilled in the art as a value equal to or equivalent to the dislocation density.

[0027] Referring to FIG. 3 again, on the gallium polar surface 11 of the GaN single crystal 10, the number of dislocations existing within a 100 μm × 100 μm square region is less than 100, and further less than 50, even when the entire square region overlaps with the straight dislocation array 14. On the gallium polar surface of the GaN single crystal according to the preferred example, when the entire 100 μm × 100 μm square region overlaps with the straight dislocation array 14, the number of dislocations existing within the square region is usually less than 30 (EPD < 3×10 5 cm -2 ), typically 1 to 20 (1× 10 4 cm -2 ≦EPD≦2×10 5 cm -2 ) is satisfied. In the portion other than the linear dislocation array 14, the EPD of the gallium polar plane 11 is even lower. In a preferred example, in the portion sandwiched between the two linear dislocation arrays 14, a first square region can be found where the lengths of all four sides constituting the outer periphery are each 2 mm or more and (P d -0.5) mm or less. can be found. Here, the first square region is defined as a square region where, when divided into a plurality of sub-regions each being a square of 100 μm × 100 μm (a square with a side length of 100 μm), 90% or more of the plurality of sub-regions are pit-free regions. The pit-free region is a region where EPD is 0 (zero) cm -2 , that is, a region where no etch pits are observed after etching under the condition that etch pits are formed at the locations where dislocations exist.

[0028] In the sub-region with the highest EPD among the 100 μm × 100 μm sub-regions constituting the first square region, the EPD is preferably less than 2×10 5 cm -2 , more preferably less than 1.5× 10 5 cm -2 . Since the area of the sub-region is 10 -4 cm 2 , the fact that the EPD in a certain sub-region is less than 2×10 5 cm -2 means that the number of dislocations existing in that sub-region is less than 20. is satisfied. The average value of the EPD among the 100 μm × 100 μm sub-regions constituting the first square region is preferably less than 3×10 3 cm -2 , more preferably less than 2.5×10 3 cm -2 , even more preferably less than 2×10 3 cm -2 ​is less than. In a preferred example, the first square region may enclose a square pit-free region of 1.3 mm × 1.3 mm. The direction of the first square region is not limited. For example, like the square region A shown in FIG. 3, two of the four sides forming the outer periphery may be parallel to the linear dislocation array 14, or, like the square region B shown in FIG. 3, the diagonal may be perpendicular to the linear dislocation array 14. The length of each of the four sides forming the outer periphery of the first square region may be 10 mm or less, 7 mm or less, 5 mm or less, 3.5 mm or less, etc.

[0029] In a preferred example, on the gallium polar plane 11, a second square region with the length of each of the four sides forming the outer periphery being greater than (P d -0.5) mm can be found (here, the unit of P d is mm). Here, when the second square region is divided into a plurality of sub-regions each being a square of 100 μm × 100 μm, it is defined as a square region where 80% or more of the plurality of sub-regions are pit-free regions. Increasing the pitch P d between the linear dislocation arrays 14 is effective in increasing the ratio of the pit-free regions among the plurality of sub-regions constituting the second square region. For example, when P is 4 mm or more, the ratio can reach 85% or more. d When P is 4 mm or more, the ratio can reach 85% or more. 6 cm -2 is less than, usually less than 5 × 10 5 cm -2 preferably less than 3 × 10 cm 5 preferably less than 3 × 10 -2 cm 5 less than, more preferably less than 2.5 × 10 -2 cm The average value of the EPD among the 100 μm × 100 μm sub-regions constituting the second square region is usually less than 1 × 10 4 cm -2 is less than. The lengths of all four sides forming the outer periphery of the second square region can each be 10 mm or less, 7 mm or less, or 5 mm or less.

[0030] On the gallium polar surface of the GaN single crystal according to the first embodiment, at least one square pit-free region, preferably 1.3 mm × 1.3 mm, more preferably 1.5 mm × 1.5 mm, is found.

[0031] 1.4. Anomalous Transmission of X-Rays The GaN single crystal according to the first embodiment may be one in which an anomalous transmission image can be obtained in X-ray topography. FIG. 5 is a drawing showing the arrangement of an X-ray source, a test piece, and a detector in X-ray topography by the Lang method. The X-ray source is arranged on one main surface side of a plate-shaped test piece having a thickness t, and the X-ray detector is arranged on the other main surface side.

[0032] Anomalous transmission of X-rays is also called the Borrmann effect, and it is a phenomenon in which X-rays penetrate a crystal having a thickness that cannot normally penetrate due to an absorption phenomenon. For example, in X-ray topography using MoKα (wavelength 0.71073 Å) as the X-ray source, when a transmission image is obtained from a C-plane GaN substrate with a thickness of 344 μm, it is an anomalous transmission image. This is because the absorption coefficient μ of GaN is 290.40 cm -1 when the X-ray source is MoKα, so when the thickness t of the C-plane GaN substrate is 344 μm, μ·t = 10.0, and a transmission image cannot be obtained under the condition of μt≧10 without anomalous transmission.

[0033] Since abnormal transmission images are not observed when the crystallinity is low, the fact that abnormal transmission images can be obtained in X-ray topography serves as evidence that the quality of the crystal as a whole is good. For single crystals of Si and GaAs, X-ray topography analysis using abnormal transmission has already been performed [for example, see J. R. Patel, Journal of Applied Physics, Vol. 44, pp. 3903-3906 (1973) and P. Mock, Journal of Crystal Growth, Vol. 224, pp. 11- 20 (2001)], but as far as the inventors know, no cases where abnormal transmission of X-rays has been observed have been reported for plate-like GaN single crystals with a C-plane as the main surface, such as C-plane GaN wafers.

[0034] In the production of GaN single crystal products from which abnormal transmission images can be obtained in X-ray topography, it is preferable to provide an inspection process that includes X-ray topography using abnormal transmission as a test item. If products with unacceptable defects are found to be non-conforming products in such an inspection process, only products with good crystal quality can be shipped.

[0035] The GaN single crystal according to the first embodiment may have a size in which each main surface includes a 10 mm × 10 mm square, and an abnormal transmission image of a 10 mm × 10 mm square region can be obtained in X-ray topography. In other words, it may have a 10 mm × 10 mm square region on at least one location of the main surface where X-rays are transmitted due to the Borrmann effect.

[0036] XRC-FWHM of 1.5.(002) reflection In the GaN single crystal according to the first embodiment, it is desirable that at least one first line segment, which is a virtual line segment defined in the following (A), can be drawn on at least one of its main surfaces; (A) The first line segment is a line segment having a length L1, and on the first line segment, each ω scan When the X-ray incident surface at that time is made parallel to the first line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec at 90% or more of all the measurement points. However, the length L1 is 20 mm or more, preferably 30 mm or more, more preferably 40 mm or more, more preferably 50 mm or more, still more preferably 60 mm or more. "Incident surface" is a common optical term, and what it means is "a plane perpendicular to the reflecting surface and containing the incident ray and the reflected ray" (the same applies when referred to in other parts of this specification). XRC refers to the X-ray rocking curve (or X-ray diffraction rocking curve), and its full width at half maximum is an index generally used for evaluating the quality of crystals. In this specification, the full width at half maximum of XRC may be abbreviated as XRC-FWHM. Since the measurement interval is 0.2 mm, when the length L1 of the first line segment is 20 mm, on the first line segment the number of measurement points of XRC-FWHM is 100.

[0037] Hereinafter, the main surface from which the above-mentioned first line segment can be drawn that the GaN single crystal according to the first embodiment may have shall be referred to as the "first main surface". The first main surface can be either a gallium-polar surface or a nitrogen-polar surface. In a GaN single crystal according to an example, both the gallium-polar surface and the nitrogen-polar surface can correspond to the first main surface. There is no limitation on the direction of the first line segment on the first main surface. The length of the first line segment can be 90% or more of the size of the first main surface measured along the direction parallel to the first line segment, but is not limited thereto. The first line segment may not include a portion where the distance from the outer edge of the first main surface is less than 2 mm, but is not limited thereto. The first line segment may pass through the center (centroid) of the first main surface, but is not limited thereto.

[0038] The first line segment preferably has one or more features selected from the following (A1) to (A3) in addition to the features included in the above-mentioned definition (A). (A1) On the first line segment, when the X-ray incident plane in each ω scan is parallel to the first line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec at 95% or more, preferably 98% or more, more preferably 99% or more, and even more preferably 100 % of all the measurement points. (A2) On the first line segment, when the X-ray incident plane in each ω scan is parallel to the first line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 40 arcsec at 90% or more, preferably 95% or more, and more preferably 98% or more of all the measurement points. (A3) On the first line segment, when the X-ray incident plane in each ω scan is parallel to the first line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 30 arcsec at 90% or more, preferably 95% or more, and more preferably 98% or more of all the measurement points.

[0039] It is desirable that at least one second line segment, which is a virtual line segment defined in the following (B), can be drawn on the first main surface; (B) The second line segment is a line segment having a length L2, is orthogonal to at least one of the first line segments and, on the second line segment, when the X-ray incident plane in each ω scan is parallel to the second line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec at 90% or more of all the measurement points. However, the length L2 is 20 mm or more and preferably 30 mm or more, more preferably 40 mm or more, even more preferably 50 mm or more, and even more preferably 60 mm or more. Since the measurement interval is 0.2 mm, when the length of the second line segment is 20 mm, the number of measurement points of the XRC-FWHM on the second line segment is 100. The length of the second line segment can be 90% or more of the size of the first main surface measured along the direction parallel to the second line segment, but is not limited thereto. The second line segment may not include a portion where the distance from the outer edge of the first main surface is less than 2 mm, but is not limited thereto. The second line segment may pass through the center (centroid) of the first main surface, but is not limited thereto.

[0040] In addition to the features included in the above-mentioned definition (B), it is desirable that the second line segment has one or more features selected from the following (B1) to (B3). (B1) On the second line segment, when the X-ray incident plane in each ω scan is made parallel to the second line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec at 95% or more, preferably 98% or more, more preferably 99% or more, and even more preferably 100% of all the measurement points. (B2) On the second line segment, when the X-ray incident plane in each ω scan is made parallel to the second line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 40 arcsec at 90% or more, preferably 95% or more, and more preferably 98% or more of all the measurement points. (B3) On the second line segment, when the X-ray incident plane in each ω scan is made parallel to the second line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 30 arcsec at 90% or more, preferably 95% or more, and more preferably 98% or more of all the measurement points.

[0041] An example of a GaN single crystal on which a virtual line segment corresponding to the first line segment and a virtual line segment corresponding to the second line segment can be drawn on the main surface is shown in FIG. 6. The GaN single crystal 10 shown in FIG. 6 is a GaN wafer or GaN ingot having a gallium-polar surface 11 parallel to the (0001) plane, and a virtual line segment LS1 corresponding to the first line segment and a virtual line segment LS2 corresponding to the second line segment can be drawn on the gallium-polar surface 11. The line segment LS1 is parallel to the m-axis, and the line segment LS2 orthogonal to the line segment LS1 is parallel to the a-axis. The length of the line segment LS1 is 20 mm or more and can be 90% or more of the size D of the gallium polar plane 11 measured along the m-axis direction. m The length of the line segment LS2 is 20 mm or more and can be 90% or more of the size D of the gallium polar plane 11 measured along the a-axis direction. a The dashed line drawn on the gallium polar plane 11 is a boundary line that demarcates a region where the distance from the outer edge of the gallium polar plane 11 is less than 2 mm and a region where it is 2 mm or more. Neither the line segment LS1 nor the line segment LS2 has a portion protruding outside the region surrounded by the dashed line. When the X-ray incident plane in each ω scan is made parallel to the line segment LS1 on the line segment LS1 and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec for 90% or more of all the measurement points. When the X-ray incident plane in each ω scan is made parallel to the line segment LS2 on the line segment LS2 and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec for 90% or more of all the measurement points.

[0042] 1.6. XRC-FWHM of (004) reflection In the GaN single crystal according to the first embodiment, it is desirable that at least one virtual line segment defined in the following (C), i.e., a third line segment, can be drawn on at least one of its main surfaces; (C) The third line segment is a line segment having a length L3. When the X-ray incident plane in each ω scan is made parallel to the third line segment on the third line segment and the XRC-FWHM of the (004) reflection is measured at intervals of 1 mm, the average between all the measurement points is less than 20 arcsec. However, the length L3 is 20 mm or more, preferably 30 mm or more, more preferably 40 mm or more, still more preferably 50 mm or more, and even more preferably 60 mm or more. Since the measurement interval is 1 mm, when the length L3 of the third line segment is 20 mm, the number of measurement points of the XRC-FWHM on the third line segment is 20.

[0043] Hereinafter, the main surface from which the aforementioned third line segment can be drawn and that a GaN single crystal according to the first embodiment may have shall be referred to as the "third main surface". The third main surface can be either a gallium polar plane or a nitrogen polar plane. In a GaN single crystal according to an example, both the gallium polar plane and the nitrogen polar plane can correspond to the third main surface. There is no limitation on the direction of the third line segment on the third main surface. The length of the third line segment can be 90% or more of the size of the third main surface measured along the direction parallel to the third line segment, but is not limited thereto. The third line segment may not include a portion where the distance from the outer edge of the third main surface is less than 2 mm, but is not limited thereto. The third line segment may pass through the center (centroid) of the third main surface, but is not limited thereto.

[0044] In addition to the features included in the aforementioned definition (C), the third line segment preferably has one or more features selected from the following (C1) and (C2). (C1) On the third line segment, when the X-ray incident plane in each ω scan is made parallel to the third line segment and the XRC-FWHM of the (004) reflection is measured at 1 mm intervals, the average between all measurement points is less than 15 arcsec. (C2) On the third line segment, when the X-ray incident plane in each ω scan is made parallel to the third line segment and the XRC-FWHM of the (004) reflection is measured at 1 mm intervals, the standard deviation between all measurement points is 5 arcsec or less.

[0045] On the third main surface, it is desirable to draw at least one fourth line segment, which is a virtual line segment defined by the following (D); (D) The fourth line segment is a line segment having a length L4, is orthogonal to at least one of the third line segments, and on the fourth line segment, the X-ray incident plane in each ω scan is the fourth line segment When measured at 1-mm intervals parallel to it, the average among all measurement points of the XRC-FWHM of the (004) reflection is less than 20 arcsec. However, the length L4 is 20 mm or more, preferably 30 mm or more, more preferably 40 mm or more, and even more preferably 50 mm or more. Since the measurement interval is 1 mm, when the length of the fourth line segment is 20 mm, the number of measurement points of the XRC-FWHM on the fourth line segment is 20. The length of the fourth line segment can be 90% or more of the size of the third major surface measured along the direction parallel to the fourth line segment, but is not limited thereto. The fourth line segment may not include a portion less than 2 mm from the outer edge of the third major surface, but is not limited thereto. The fourth line segment may pass through the center (centroid) of the third major surface, but is not limited thereto.

[0046] In addition to the features included in the above-mentioned definition (D), the fourth line segment preferably has one or more features selected from the following (D1) and (D2). (D1) When measured at 1-mm intervals parallel to the fourth line segment with the X-ray incident plane in each ω scan parallel to the fourth line segment, the average among all measurement points of the XRC-FWHM of the (004) reflection is less than 15 arcsec. (D2) When measured at 1-mm intervals parallel to the fourth line segment with the X-ray incident plane in each ω scan parallel to the fourth line segment, the standard deviation among all measurement points of the XRC-FWHM of the (004) reflection is 5 arcsec or less.

[0047] 1.7. Radius of curvature of the C plane In the GaN single crystal according to the first embodiment, it is desirable that at least one virtual line segment defined in the following (E), i.e., the fifth line segment, and at least one virtual line segment defined in the following (F), i.e., the sixth line segment, can be drawn on at least one of its major surfaces, respectively. (E) The fifth line segment is a line segment having a length L5 (where L5 is 40 mm or more), and on the fifth line segment, the X-ray incident surface during each ω scan is made parallel to the fifth line segment. After measuring the XRC of the (002) reflection at intervals of 5 mm (preferably 3 mm, more preferably 1 mm, even more preferably 0.6 mm), two points separated from each other by 10 mm are arbitrarily selected from all the measurement points, and when the radius of curvature of the C-plane in the direction parallel to the fifth line segment is calculated using the following formula 1 from the difference Δω in the peak top angles of the XRC between the two points, the absolute value R5 thereof is 40 m or more. R = ΔL / Δω ···(Formula 1) In the above formula 1, R is the radius of curvature, and ΔL is the distance between the two points (in this case, 10 mm). (F) The sixth line segment is a line segment having a length L6 (where L6 is 40 mm or more), and is orthogonal to the fifth line segment. On the sixth line segment, the X-ray incident surface during each ω scan is made parallel to the sixth line segment. After measuring the XRC of the (002) reflection at intervals of 5 mm (preferably 3 mm, more preferably 1 mm, even more preferably 0.6 mm), two points separated from each other by 10 mm are arbitrarily selected from all the measurement points, and when the radius of curvature of the C-plane in the direction parallel to the sixth line segment is calculated using the above formula 1 from the difference Δω in the peak top angles of the XRC between the two points, the absolute value R6 thereof is 40 m or more.

[0048] In order to draw the fifth and sixth line segments on the main surface of the GaN single crystal, the size of the main surface must be not less than 40 mm in the direction of the fifth line segment and in the direction of the sixth line segment, respectively. In the above definition (E), the length L5 of the fifth line segment may be 40 mm, preferably 45 mm, more preferably 50 mm, and may also be more than 50 mm. The absolute value R5 of the radius of curvature of the C-plane referred to in the above definition (E) is preferably 50 m or more, more preferably 60 m or more, even more preferably 70 m or more. In the above definition (F), the length L6 of the sixth line segment may be 40 mm, preferably 45 mm, and may also be more than 45 mm. The absolute value R6 of the radius of curvature of the C plane referred to in the above definition (F) is preferably 50 m or more.

[0049] 1.8. Uses of GaN single crystals (1) Seed The GaN single crystal according to the first embodiment can be used as a seed when growing nitride semiconductor crystals by various methods including the vapor phase method, the liquid phase method, and the ammonothermal method. For example, GaN can be epitaxially grown on the C-plane GaN wafer according to the first embodiment by any method to obtain a bulk GaN single crystal. In another example, the GaN single crystal according to the first embodiment is used as a seed to grow a first bulk GaN single crystal, and then a part or all of the first GaN single crystal is used as a seed to grow a second bulk GaN single crystal.

[0050] (2) Nitride semiconductor device When the GaN single crystal according to the first embodiment is a C-plane GaN wafer, a nitride semiconductor device can be manufactured using the C-plane GaN wafer. Normally, one or more nitride semiconductors are epitaxially grown on the C-plane GaN wafer to form an epitaxial wafer having a nitride semiconductor device structure. As the epitaxial growth method, the MOCVD method, the MBE method, the pulse deposition method, etc. suitable for forming thin films can be preferably used. The nitride semiconductor device structure can be formed on either the gallium-polarity surface or the nitrogen-polarity surface of the C-plane GaN wafer. After necessary structures such as electrodes and protective films are provided, the epitaxial wafer is divided into nitride semiconductor device chips.

[0051] Specific examples of nitride semiconductor devices include light-emitting devices such as light-emitting diodes and laser diodes, rectifiers, bipolar transistors, field-effect transistors, and electronic devices such as HEMT (High Electron Mobility Transistor), temperature sensors, pressure sensors, radiation Examples include wire sensors, semiconductor sensors such as visible-ultraviolet detectors, and solar cells. In addition, the C-plane GaN wafer according to the first embodiment is used for SAW (Surface Acoustic Wave) devices, oscillators, resonators, oscillators, MEMS (Micro Electro Mechanical System) parts products, voltage actuators, electrodes for artificial photosynthesis devices, etc.

[0052] 2. Second Embodiment The second embodiment of the present invention relates to a nitride semiconductor device chip. The nitride semiconductor device chip according to the second embodiment is manufactured using the C-plane GaN wafer according to the first embodiment. After epitaxially growing one or more nitride semiconductors on the C-plane GaN wafer of the first embodiment to form an epitaxial wafer having a nitride semiconductor device structure, the epitaxial wafer is divided into chips for each element using a dicing saw, scriber, laser processing machine, etc. This is the nitride semiconductor device chip of the second embodiment. Usually, before dividing the epitaxial wafer into chips, structures such as necessary electrodes and protective films are provided for each element on the wafer according to the type of device.

[0053] The structure of the nitride semiconductor device chip according to the second embodiment is exemplified below. (Chip Structure 1) In a nitride semiconductor device chip comprising a C-plane GaN substrate having a gallium-polarity plane and a nitrogen-polarity plane, and one or more nitride semiconductor layers disposed on the gallium-polarity plane or the nitrogen-polarity plane, the C-plane GaN substrate has at least one square region on the gallium-polarity plane, and the length of each of the four sides constituting the outer periphery of the at least one square region is 2 mm or more. When the at least one square region is divided into a plurality of sub-regions each being a 100 μm × 100 μm square, 80% or more of the plurality of sub-regions have a dislocation density of 0 (zero) cm -2A nitride semiconductor device chip, characterized in that it is a dislocation-free region. (Chip structure 2) A nitride semiconductor device chip of chip structure 1, wherein 85% or more of the plurality of sub-regions are dislocation-free regions. (Chip structure 3) A nitride semiconductor device chip of chip structure 2, wherein 90% or more of the plurality of sub-regions are dislocation-free regions. (Chip structure 4) In the sub-region having the highest dislocation density among the plurality of sub-regions, the dislocation density is 3×10 5 cm -2 Less than that, a nitride semiconductor device chip of any one of chip structures 1 to 3.

[0054] (Chip structure 5) The average value of the dislocation density among the plurality of sub-regions is 1×10 4 cm -2 Less than that, a chip A nitride semiconductor device chip of any one of chip structures 1 to 4. (Chip structure 6) In the sub-region having the highest dislocation density among the plurality of sub-regions, the dislocation density is 2×10 5 cm -2 Less than that, a nitride semiconductor device chip of chip structure 3. (Chip structure 7) The average value of the dislocation density among the plurality of sub-regions is 3×10 3 cm -2 Less than that, a chip A nitride semiconductor device chip of chip structure 3 or 6. (Chip structure 8) For the nitride semiconductor device chip of chip structure 3, 6 or 7, each of the four sides constituting the outer periphery of the at least one square region has a length of 3.5 mm or less. (Chip structure 9) The planar shape of the C-plane GaN substrate is rectangular, and among the four sides of the rectangle, two sides form an angle within the range of 12° ± 5° with one of the intersection lines between the one main surface and the M-plane. A nitride semiconductor device chip of chip structures 3, 6, 7, or 8.

[0055] (Chip structure 10) In a nitride semiconductor device chip including a C-plane GaN substrate having a gallium-polarity plane and a nitrogen-polarity plane, and one or more nitride semiconductor layers disposed on the gallium-polarity plane or the nitrogen-polarity plane, the planar shape of the C-plane GaN substrate is rectangular, and among the four sides of the rectangle, two sides form an angle within the range of 12° ± 5° with one of the intersection lines between the one main surface and the M-plane. A nitride semiconductor device chip characterized by this. (Chip structure 11) A nitride semiconductor device chip of any one of chip structures 1 to 10 having a linear dislocation array on the gallium-polarity plane. (Chip structure 12) A nitride semiconductor device chip of chip structure 11, wherein the extending direction of the linear dislocation array forms an angle within the range of 12° ± 5° with one of the intersection lines between the gallium-polarity plane and the M-plane. (Chip structure 13) In a nitride semiconductor device chip including a C-plane GaN substrate having a gallium-polarity plane and a nitrogen-polarity plane, and one or more nitride semiconductor layers disposed on the gallium-polarity plane or the nitrogen-polarity plane, the gallium-polarity plane of the C-plane GaN substrate has a linear dislocation array, and the extending direction of the linear dislocation array forms an angle within the range of 12° ± 5° with one of the intersection lines between the gallium-polarity plane and the M-plane. A nitride semiconductor device chip characterized by this.

[0056] (Chip structure 14) On the gallium-polarity plane, the number of dislocations existing within a 100 μm × 100 μm square region that entirely overlaps with the linear dislocation array is less than 100 (preferably less than 50, more preferably less than 30). A nitride semiconductor device chip of any one of chip structures 11 to 13. (Chip structure 15) In the C-plane GaN substrate, for any alkali metal and alkaline earth metal, the concentration is 1×10 16 atoms / cm 3 less than, any of the chip structures 1 to 14 nitride semiconductor device chip. (Chip structure 16) In the C-plane GaN substrate, for any halogen, the concentration is 1×10 16 atoms / cm 3 less than, any nitride semiconductor device chip of chip structures 1 to 15 chip. (Chip structure 17) The C-plane GaN substrate contains hydrogen (H 17 atoms / cm 3 ) at a concentration of 10 or higher, the nitride semiconductor device chip according to any of chip structures 1 to 16. (Chip structure 18) In the C-plane GaN substrate, a peak attributed to a gallium vacancy-hydrogen complex is observed at 3100 to 3500 cm -1 in the infrared absorption spectrum, the nitride semiconductor device chip according to any of chip structures 1 to 17.

[0057] 3. Third Embodiment The third embodiment of the present invention relates to a GaN layer-bonded substrate. A GaN layer-bonded substrate is a composite substrate in which a GaN layer is bonded to a hetero-composition substrate having a chemical composition different from that of GaN, and can be used for manufacturing light-emitting devices and other semiconductor devices. For details such as the structure, manufacturing method, and uses of the GaN layer-bonded substrate, reference can be made to Japanese Patent Application Laid-Open No. 2006-210660, Japanese Patent Application Laid-Open No. 2011-44665, etc. The GaN layer-bonded substrate according to the third embodiment is manufactured using the GaN single crystal according to the first embodiment as a material.

[0058] The GaN layer-bonded substrate is typically manufactured by performing, in this order, a step of implanting ions near the main surface of a plate-shaped GaN single crystal, a step of bonding the main surface side of the plate-shaped GaN single crystal to a hetero-composition substrate, and a step of forming a GaN layer bonded to the hetero-composition substrate by separating the plate-shaped GaN single crystal with the ion-implanted region as a boundary. As a method without performing ion implantation, there is also a method for manufacturing a GaN layer-bonded substrate in which a plate-shaped GaN single crystal is bonded to a hetero-composition substrate and then the plate-shaped GaN single crystal is mechanically cut to form a GaN layer bonded to the hetero-composition substrate. Regardless of the method used, when the GaN single crystal according to the first embodiment is used as the material, a GaN layer-bonded substrate having a structure in which a GaN layer separated from the GaN single crystal of the first embodiment is bonded to a hetero-composition substrate can be obtained.

[0059] When used as the material of the GaN layer-bonded substrate, the initial thickness of the GaN single crystal of the first embodiment can be 1 mm or more, further 2 mm or more, and further 4 mm or more. Examples of the hetero-composition substrate that can be used in the manufacture of the GaN layer-bonded substrate include a sapphire substrate, an AlN substrate, a SiC substrate, a ZnSe substrate, a Si substrate, a ZnO substrate, a ZnS substrate, a quartz substrate, a spinel substrate, a carbon substrate, a diamond substrate, a Ga2O3 substrate, a ZrB2 substrate, a Mo substrate, a W substrate, a ceramic substrate, and the like.

[0060] The structure of the GaN layer-bonded substrate according to the third embodiment is exemplified below. (Bonded substrate structure 1) A GaN layer having one main surface as a gallium polar surface and the other as a nitrogen polar surface, and the gallium In a GaN layer-bonded substrate including a hetero-composition substrate bonded to the um-polarity surface side or the nitrogen-polarity surface side, the GaN layer has at least one square region on the gallium-polarity surface, and each of the four sides constituting the outer periphery of the at least one square region has a length of 2 mm or more. When the at least one square region is divided into a plurality of sub-regions each being a 100 μm × 100 μm square, 80% or more of the plurality of sub-regions are dislocation-free regions with a dislocation density of 0 (zero) cm -2 of the GaN layer-bonded substrate, characterized in that. (Bonded substrate structure 2) In the GaN layer-bonded substrate of the bonded substrate structure 1, 85% or more of the plurality of sub-regions are dislocation-free regions. (Bonded substrate structure 3) In the GaN layer-bonded substrate of the bonded substrate structure 2, 90% or more of the plurality of sub-regions are dislocation-free regions. (Bonded substrate structure 4) In the sub-region having the highest dislocation density among the plurality of sub-regions, the dislocation density is 3 × 10 5 cm -2 less than that of the GaN layer-bonded substrate of any one of the bonded substrate structures 1 to 3. (Bonded substrate structure 5) The average value of the dislocation density among the plurality of sub-regions is 1 × 10 4 cm -2 less than that of the GaN layer-bonded substrate of any one of the bonded substrate structures 1 to 4. (Bonded substrate structure 6) In the sub-region having the highest dislocation density among the plurality of sub-regions, the dislocation density is 2 × 10 5 cm -2 less than that of the GaN layer-bonded substrate of the bonded substrate structure 3. (Bonded substrate structure 7) The average value of the dislocation density among the plurality of sub-regions is 3 × 10 3 cm -2 less than that of the GaN layer-bonded substrate of the bonded substrate structure 3 or 6. (Bonded substrate structure 8) The at least one square region has a length of each of the four sides constituting its outer periphery of 3.5 mm or less, and is a GaN layer bonding substrate of bonding substrate structures 3, 6, or 7.

[0061] (Bonding substrate structure 9) In a GaN layer bonding substrate including a GaN layer having one main surface as a gallium polar plane and the other as a nitrogen polar plane, and a different composition substrate bonded to the gallium polar plane side or the nitrogen polar plane side of the GaN layer, at least one first line segment, which is a virtual line segment defined in the following (A), can be drawn on at least one of the gallium polar plane and the nitrogen polar plane; a GaN layer bonding substrate characterized by this. (A) The first line segment is a line segment having a length of 20 mm or more. On the first line segment, when the X-ray incident plane at each ω scan is parallel to the first line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm, the measured value is less than 50 arcsec at 90% or more of all measurement points. (Bonding substrate structure 10) On the gallium polar plane or the nitrogen polar plane on which the first line segment can be drawn, at least one second line segment, which is a virtual line segment defined in the following (B), can be drawn; a GaN layer bonding substrate of bonding substrate structure 9. (B) The second line segment is a line segment having a length of 20 mm or more, is orthogonal to at least one of the first line segments, and when the X-ray incident plane in each ω scan is parallel to the second line segment and the XRC-FWHM of the (002) reflection is measured at intervals of 0.2 mm on the second line segment, the measured value is less than 50 arcsec at 90% or more of all measurement points. (Bonding substrate structure 11) A GaN layer bonding substrate of any one of bonding substrate structures 1 to 10, which has a linear dislocation array on the gallium polar plane. (Bonding substrate structure 12) A GaN layer bonding substrate of bonding substrate structure 11, in which the extending direction of the linear dislocation array forms an angle within a range of 12° ± 5° with one of the intersection lines of the gallium polar plane and the M plane. (Bonding substrate structure 13) A GaN layer-bonded substrate comprising a GaN layer having one main surface as a gallium polar plane and the other as a nitrogen polar plane, and a hetero-composition substrate bonded to either the gallium polar plane side or the nitrogen polar plane side of the GaN layer, wherein the GaN layer has a linear dislocation array on the gallium polar plane, and the extending direction of the linear dislocation array forms an angle within a range of 12° ± 5° with one of the intersection lines of the gallium polar plane and the M plane. (Bonded substrate structure 14) In the gallium polar plane, the number of dislocations existing within a 100 μm × 100 μm square region that entirely overlaps with the linear dislocation array is less than 100 (preferably less than 50, more preferably less than 30) in any of the GaN layer-bonded substrates of Bonded substrate structures 11 to 13. (Bonded substrate structure 15) A GaN layer-bonded substrate having a disk shape, having a flat portion provided on a part of the side surface, and the flat portion being orthogonal to the extending direction of the linear dislocation array in any of the GaN layer-bonded substrates of Bonded substrate structures 11 to 14. (Bonded substrate structure 16) A GaN layer-bonded substrate having a disk shape, having a flat portion provided on a part of the side surface, and the flat portion being parallel to the extending direction of the linear dislocation array in any of the GaN layer-bonded substrates of Bonded substrate structures 11 to 14. (Bonded substrate structure 17) In the GaN layer, for any alkali metal and alkaline earth metal, its concentration is 1 × 10 16 atoms / cm 3 less than in any of the GaN layer-bonded substrates of Bonded substrate structures 1 to 16 GaN layer-bonded substrate. (Bonded substrate structure 18) In the GaN layer, for any halogen, its concentration is 1 × 10 16 atoms / cm 3 less than in any of the GaN layer-bonded substrates of Bonded substrate structures 1 to 17. (Bonded substrate structure 19) The GaN layer is 10 17 atoms / cm 3containing hydrogen (H) at a concentration equal to or higher than the terrace level The GaN layer bonded substrate according to any one of the bonded substrate structures 1 to 18, having the above composition. (Bonded substrate structure 20) In the GaN layer, a peak attributed to a gallium vacancy-hydrogen complex is observed in the infrared absorption spectrum at 3100 to 3500 cm -1 The GaN layer bonded substrate according to any one of the bonded substrate structures 1 to 19, in which a peak attributed to a gallium vacancy-hydrogen complex is observed in the infrared absorption spectrum at 3100 to 3500 cm

[0062] 4. Fourth Embodiment The fourth embodiment of the present invention relates to a method for manufacturing a GaN single crystal. The method for manufacturing a GaN single crystal according to the fourth embodiment includes: (S1) preparing a seed having a nitrogen polar plane of GaN; (S2) forming a pattern mask having a plurality of linear openings arranged in parallel to each other at a constant pitch on the nitrogen polar plane of the prepared seed; (S3) growing a GaN crystal on the nitrogen polar plane through the linear openings of the pattern mask by an ammonothermal method; and The nitrogen polar plane of GaN included in the seed prepared in step (S1) may be parallel to (000-1) or may be slightly inclined from (000-1). In the pattern mask formed in step (S2), the extending direction of the linear opening preferably forms an angle within a range of 12°±5° with one of the intersection lines of the nitrogen polar plane of the seed and the M plane. The angle may be within a range of 12°±3°, 12°±2°, or 12°±1°. In step (S3), the GaN crystal grows from the inside of the opening of the pattern mask, then spreads laterally above the pattern mask, and coalesces while forming voids between the pattern mask.

[0063] Hereinafter, the method for manufacturing a GaN single crystal according to the fourth embodiment will be described in detail step by step. 4.1. Step of Preparing a Seed The GaN crystal constituting the seed used in the method for manufacturing a GaN single crystal according to the fourth embodiment may be grown by any method, and is not limited, but may be, for example, grown by the HVPE method, the flux method, the ammonothermal method, or the high-pressure nitrogen method. When manufacturing the GaN crystal for the seed by the HVPE method, techniques such as DEEP (epitaxial-growth with inverse-pyramidal pits) [K. Motoki et al., Journal of Crystal Growth 237-239 (2002) 912], VAS (Void-Assisted Separation) [Y. Oshima et al., Japanese Journal of Applied Physics 42 (2003) L1] can be appropriately used. When using Advanced-DEEP [K. Motoki et al., Journal of Crystal Growth 305 (2007) 377], it is preferable to align the stretching direction (in the case of a stripe core) or the array direction (in the case of a dot core) of the core (domain with inverted polarity) formed in the GaN crystal to be grown with the stretching direction of the linear opening provided in the pattern mask in a later step.

[0064] Details of techniques required for slicing the GaN crystal, flattening the cut surface, removing the damaged layer from the cut surface, etc., which are necessary for producing the seed, are well known to those skilled in the art, and thus no particular explanation is required. The nitrogen polar plane is preferably flattened and the damaged layer is removed by performing Chemical Mechanical Polishing (CMP). The nitrogen polar plane may be parallel to (000-1), or may be slightly inclined from (000-1). The inclination of the nitrogen polar plane from (000-1) is usually 10° or less, preferably 5° or less, more preferably 2° or less, and even more preferably 1° or less. In a preferred example, the seed can be a C-plane GaN wafer.

[0065] 4.2. Step of forming a pattern mask In this step, a pattern mask for restricting the region where GaN can grow is formed on the nitrogen-polar surface of GaN possessed by the seed prepared in the previous step. The material of the pattern mask may be any material that does not dissolve or decompose during the growth of GaN crystals by the ammonothermal method. Although not limited, for example, single substances or alloys of Ca, Mg, Si, Al, W, Mo, Ti, Pt, Ir, Ag, Au, Ta, Ru, Nb, or Pd, or their oxides, nitrides, or fluorides can be mentioned.

[0066] The pattern mask is provided with a plurality of linear openings parallel to each other at equal intervals. In other words, the pattern mask is provided with a plurality of linear openings parallel to each other at a certain pitch. An example will be described with reference to FIGS. 7 and 8. FIG. 7(a) is a perspective view showing an example of a seed. The seed 20 is a disk-shaped C-plane GaN wafer and has a gallium-polar surface 21, a nitrogen-polar surface 22, and a side surface 23. FIG. 7(b) is a perspective view showing a state where a stripe-shaped pattern mask 30 having a plurality of linear openings 31 extending in the same direction is formed on the nitrogen-polar surface 22 of the seed 20 in FIG. 7(a). FIG. 8 is a plan view showing only the stripe-shaped pattern mask 30 extracted.

[0067] Referring to FIG. 8, the width W of the linear opening 31 op is usually 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and is usually 500 μm or less, preferably 200 μm or less, more preferably 100 μm or less. The pitch P between the linear openings 31 op is usually 3 mm or more, preferably 3.5 mm or more, more preferably 4 mm or more, and is usually 20 mm or less. The pitch P between the linear openings 31 op can be 10.5 mm or less, 7.5 mm or less, or 5.5 mm or less. When the reference direction is the direction in which one of the intersection lines between the nitrogen polar plane and the M plane extends, the angle θ formed by the extending direction of the linear opening 31 and the reference direction op is preferably within the range of 12° ± 5°. The angle θ op can be within the range of 12° ± 3°, 12° ± 2° or 12° ± 1°. The angle θ op When it is within the above-mentioned preferred range, in the step of growing GaN crystals by the ammonothermal method (described later), the GaN crystals growing through the linear opening are likely to laterally grow above the pattern mask and become coreless.

[0068] FIG. 9 is a plan view showing another pattern mask that can be formed on the nitrogen polar plane of the seed. The pattern mask 30 shown in FIG. 9 is of a rhombic lattice type, and a plurality of first linear openings 31-1 extending along the first extending direction and second linear openings 31-2 extending along the second extending direction are provided respectively. The pitch P op -1 between the first linear openings 31-1 and the pitch P op -2 between the second linear openings 31-2 are each constant. The width W op -1 of the first linear opening 31-1 and the width W op -2 of the second linear opening are both usually 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and are usually 500 μm or less, preferably 200 μm or less, more preferably 100 μm or less.

[0069] The pitch P op -1 between the first linear openings 31-1 is usually 3 mm or more, preferably 3.5 mm or more, more preferably 4 mm or more, and is usually 20 mm or less. The pitch P op -2 between the second linear openings 31-2 is usually 3 mm or more, preferably 6 mm or more, more preferably 9 mm or more, and is usually 20 mm or less. When the reference direction is the direction in which one of the intersection lines between the nitrogen polar plane and the M plane extends, the angle θ formed by the first extending direction and the reference direction op-1 is preferably within the range of 12° ± 5°. The angle θ op -1 can be within the range of 12° ± 3°, 12° ± 2° or 12° ± 1°. The angle θ op -2 formed by the second extension direction and the reference direction is preferably within the range of 72° ± 5°. op -2 can be within the range of 72° ± 3°, 72° ± 2° or 72° ± 1°. The angle formed by the first extension direction and the second extension direction may be 60°. The angle θ op -1 and θ op When -1 and θ

[0070] FIG. 10 is a plan view showing still another pattern mask that can be formed on the nitrogen polar surface of the seed. The pattern mask 30 shown in FIG. 10 is of a hexagonal lattice type, and a plurality of first linear openings 31-1 extending along the first extension direction, second linear openings 31-2 extending along the second extension direction, and third linear openings 31-3 extending along the third extension direction are provided respectively. The pitch P op -1 between the first linear openings 31-1, the pitch P op -2 between the second linear openings 31-2, and the pitch P op -3 between the third linear openings 31-3 are each constant.

[0071] The width W op -1 of the first linear opening 31-1, the width W op -2 of the second linear opening, and the width W op -3 of the third linear opening are all usually 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and usually 500 μm or less, preferably 200 μm or less, more preferably 100 μm or less. The pitch P op -1 between the first linear openings 31-1, the pitch Pop -2 and the pitch P between the third linear opening 31-3 op -3 are all usually 4 mm or more, preferably 5 mm or more, more preferably 6 mm or more, and are usually 20 mm or less.

[0072] When the direction in which one of the intersection lines of the nitrogen polar plane and the M plane extends is taken as the reference direction, the angle θ formed by the first extension direction and the reference direction op -1 is preferably within the range of 12° ± 5°. The angle θ op -1 can be within the range of 12° ± 3°, 12° ± 2° or 12° ± 1°. The angle θ formed by the second extension direction and the reference direction op -2 is preferably within the range of 72° ± 5°. The angle θ op -2 can be within the range of 72° ± 3°, 72° ± 2° or 72° ± 1°. The angle formed by the first extension direction and the second extension direction may be 60°. The angle θ formed by the third extension direction and the reference direction op -3 is preferably within the range of 132° ± 5°. The angle θ op -3 can be within the range of 132° ± 3°, 132° ± 2° or 132° ± 1°. The angle formed by the first extension direction and the third extension direction may be 120°. The angle θ op -1, θ op -2 and θ op When -3 are within the above preferred ranges, in the step of growing GaN crystals by the ammonothermal method (described later), the GaN crystals growing through the first linear opening, the second linear opening and the third linear opening can easily laterally grow above the pattern mask and coalesce.

[0073] 4.3. Step of growing GaN crystals by the ammonothermal method In this step, GaN crystals are grown by the ammonothermal method on the nitrogen polar plane of the seed on which the pattern mask was formed in the previous step. FIG. 11 is a cross-sectional view showing how GaN crystals grow. Figure 11(a) shows a state before the growth of GaN crystals begins. On the nitrogen-polarity surface 22 of the seed 20, a pattern mask 30 with a linear opening 31 extending in a direction perpendicular to the plane of the paper is formed. Figure 11(b) shows where GaN crystals 40 have started to grow inside the linear opening 31 of the pattern mask 30. When passing through the linear opening 31 of the pattern mask 30, as shown in Figure 11(c), the GaN crystals 40 grow not only in the [000-1] direction but also in the lateral direction (the direction parallel to the nitrogen-polarity surface 22). Eventually, as shown in Figure 11(d), the GaN crystals 40 coalesce above the pattern mask 30, and the growth front becomes a single plane. Each GaN crystal growing through a linear opening grows in the [000-1] direction by usually 1 mm or more before contacting and starting to coalesce with the GaN crystal growing through an adjacent linear opening. Therefore, voids 50 are formed between the pattern mask 30 and the GaN crystals 40. The size of the voids 50 in the c-axis direction, that is, the distance from the surface (nitrogen-polarity surface) of the seed 20 to the coalesced part of the GaN crystals 40, is 1 mm or more. In such a growth mode, the contact between the GaN crystals and the pattern mask is reduced, so the influence of the pattern mask on the crystallinity of the GaN crystals is reduced. Since the pitch of the linear openings 31 is usually 3 mm or more, the total area of the interface between the GaN crystals 40 and the seed 20 is small, and the propagation of dislocation defects from the seed to the GaN crystals is suppressed. After coalescence, as shown in Figure 11(e), the GaN crystals 40 are further grown in the [000-1] direction. It should be noted that GaN crystals also grow on the gallium-polarity surface of the seed, but the illustration is omitted in Figure 11.

[0074] The growth of GaN crystals by the ammonothermal method can be carried out using the crystal growth apparatus 100 shown in Figure 12. The crystal growth apparatus 100 includes a cylindrical autoclave 101 and a cylindrical growth container 102 installed therein. The growth container 102 is divided into a raw material dissolution zone 102a partitioned from each other by baffles 103 and It has a crystal growth zone 102b inside. A feedstock F is placed in the raw material dissolution zone 102a. A seed (C-plane GaN wafer) S suspended by a platinum wire 104 is placed in the crystal growth zone 102b. A gas line to which a vacuum pump 105, an ammonia cylinder 106, and a nitrogen cylinder 107 are connected is connected to the autoclave 101 and the growth vessel 102 via a valve 108. When ammonia is introduced into the growth vessel 102, the amount of ammonia supplied from the ammonia cylinder 106 can be confirmed by a mass flow meter 109.

[0075] The feedstock is powder, granules, or chunks of single crystal or polycrystalline GaN. The amount of impurities such as water and oxygen contained in the ammonia used as the solvent is preferably 0.1 ppm or less. A mineralizer is used to facilitate dissolution of the feedstock. The mineralizer is preferably a combination of ammonium fluoride (NH4F) and ammonium iodide (NH4I). Ammonium fluoride may be obtained by reacting ammonia with hydrogen fluoride (HF) in the growth vessel. Similarly, ammonium iodide may be obtained by reacting ammonia with hydrogen iodide (HI) in the growth vessel. Within a certain temperature range, including 550-650°C, in the growth chamber, if ammonium fluoride is the only mineralizer, the temperature dependence of the solubility of GaN becomes negative and difficult to control. This problem can be solved by using ammonium iodide in combination. Ammonium chloride and ammonium bromide have similar effects. When the temperature in the growth vessel is within the above-mentioned specific range, it is not recommended to use only ammonium halides selected from ammonium chloride, ammonium bromide, and ammonium iodide as mineralizers.When these mineralizers are used without ammonium fluoride, GaN crystals grow substantially only in the [000-1] direction within the above-mentioned temperature range, and almost no lateral growth occurs. When ammonium fluoride is used alone as the mineralizer, lateral growth is strongly promoted, making it difficult to form voids between the GaN crystal and the pattern mask. This tendency becomes prominent when the growth rate in the [000-1] direction is reduced to less than 100 μm / day.

[0076] When growing a GaN crystal on the seed S, ammonia is also introduced into the space between the autoclave 101 and the growth vessel 102, and then heated from the outside of the autoclave 101 with a heater (not shown) to bring the inside of the growth vessel 102 to a supercritical state or a subcritical state. Above the pattern mask, to successfully coreless the GaN crystal, for example, the amounts of ammonium fluoride and ammonium iodide are set to 0.5% and 4.0% respectively in terms of the molar ratio to ammonia used as the solvent, and the pressure inside the growth vessel is about 220 MPa, the average value of the temperature Ts of the raw material dissolution zone and the temperature Tg of the crystal growth zone is about 600 °C, and the temperature difference Ts - Tg between these two zones is about 5 °C (Ts > Tg). After coreless, the GaN crystal is further grown under the same conditions or under conditions where the growth rate of GaN in the [000-1] direction is changed to be higher than that before coreless. In the step of growing a GaN crystal by the ammonothermal method, the growth vessel can be replaced each time the feedstock is exhausted, and regrowth can be repeated.

[0077] Through the above procedure, a plate-like GaN single crystal with the thickness direction parallel or substantially parallel to the c-axis can be obtained. This GaN single crystal can be sliced in various directions to obtain GaN wafers. For example, slicing parallel to the C-plane can obtain C-plane GaN wafers. The obtained GaN wafers can be preferably used in the manufacture of semiconductor devices and the like, and can also be used as seeds for growing bulk GaN crystals.

[0078] 4.4. Others In the stripe-type pattern mask 30 shown in FIG. 8, the angle θ formed between the extending direction of the linear opening 31 and the reference direction (the direction in which one of the intersection lines of the nitrogen polar plane and the M plane extends) op affects the ratio of the growth rates in the [000-1] direction and the lateral direction of the GaN crystal growing through the linear opening. To put it simply, when the angle θ op is close to 0°, the growth in the [000-1] direction becomes dominant. On the contrary, when the angle θ op is close to 30°, the growth in the lateral direction tends to be dominant. Therefore, in order to grow the GaN crystal by 1 mm or more in the [000-1] direction until coreless start, it is desirable not to make the angle θ op too large. Specifically, the angle θ op is preferably less than 25°, more preferably less than 20°. The angle θ op may be less than 7°, but as it approaches 0°, it tends to be difficult for coreless to occur between GaN crystals growing through each of two adjacent linear openings arranged in parallel. The same applies to the angle θ op in the rhombic lattice-type pattern mask 30 shown in FIG. 9, and the same also applies to the angles θ op -1 and θ op -2, and the same also applies to the angles θ op -1, θ op -2 and θ op -3 in the hexagonal lattice-type pattern mask shown in FIG. 10.

[0079] Arranging the linear openings in the pattern mask at a long pitch of 3 mm or more makes it difficult for coreless to occur between GaN crystals growing through each of two adjacent linear openings arranged in parallel. To overcome such a tendency and increase the probability of coreless occurrence, it is effective to lower the growth rate of the GaN crystal. One means of lowering the growth rate of the GaN crystal is to reduce the temperature difference between the raw material melting zone and the crystal growth zone in the growth vessel. In addition, making the pattern of the pattern mask into a rhombic lattice type or a hexagonal lattice type is also effective in facilitating the occurrence of coreless of GaN crystals.

[0080] 5. Experimental Results 5.1. Experiment 1 (1) Preparation of Seeds As seeds, C-plane GaN wafers (hereinafter referred to as "HVPE seeds") fabricated from GaN crystals grown by the HVPE method were prepared. Both the nitrogen-polarity surface and the gallium-polarity surface of the HVPE seeds were polished by CMP. The nitrogen-polarity surface was inclined from (000-1), and the inclination angle was less than 1°.

[0081] (2) Formation of Pattern Mask On the nitrogen-polarity surface of the HVPE seed, a stripe-type pattern mask having a 100-nm-thick Pt layer on a 100-nm-thick TiW layer and having a linear opening with a width of 50 μm and a pitch of 4 mm was formed by the lift-off method. The stretching direction of the linear opening was inclined by 12° from one of the intersection lines of the M-plane and the nitrogen-polarity surface in the HVPE seed.

[0082] (3) Growth of GaN Crystals by the Amonothermal Method GaN crystals were grown by the amonothermal method on the HVPE seed on which the above pattern mask was formed. As the feedstock, polycrystalline GaN (oxygen concentration: about 5×10 17 cm -3 ) produced by reacting ammonia and gallium chloride (GaCl) in a gas-phase reaction was used, and ammonium fluoride and ammonium iodide were used as mineralizers. The amounts of ammonium fluoride and ammonium iodide were 0.5% and 4.0% respectively in terms of the molar ratio to ammonia put into the growth vessel. Ammonium iodide was generated by introducing hydrogen iodide (HI) into the growth vessel after putting ammonia. .

[0083] The growth conditions were as follows: the average value of the temperature Tg in the crystal growth zone and the temperature Ts in the raw material melting zone was 598 °C, the temperature difference between the crystal growth zone and the raw material melting zone was 5 °C (Ts > Tg), and the pressure in the growth vessel was 220 MPa. When 35 days had elapsed since the start of growth, the growth vessel was opened, and the grown GaN crystal was taken out and observed. On the nitrogen-polar surface side of the HVPE seed, GaN had grown 1.1 mm in the [000-1] direction. Therefore, the growth rate was 31 μm / day. The growth front of the GaN crystal had passed through a linear opening and reached above the pattern mask. However, the lateral growth rate was not uniform in the plane, and coreless growth had already started in some parts, but most parts were before coreless growth.

[0084] After observation, the GaN crystal was transferred to a newly prepared growth vessel, and regrowth was performed again under the same ammonothermal growth conditions. When 35 days had elapsed since the start of regrowth, the growth vessel was opened, and the GaN crystal was taken out. During regrowth, the GaN crystal became completely coreless, and the growth front was flattened. The growth amount of GaN in the [000-1] direction during regrowth was 3.6 mm. Therefore, the growth rate was 103 μm / day. In total, the GaN crystal grew approximately 4.7 mm in the [000-1] direction in 70 days. V-grooves were observed on the

[0001] side of the ammonothermally grown GaN crystal. More specifically, when the grown GaN crystal was separated from the seed and the surface of its

[0001] side (the side bonded to the seed) was observed, a plurality of V-grooves parallel to each other were formed at equal intervals. The direction of the V-grooves was parallel to the linear opening of the pattern mask provided on the seed surface before crystal growth, and the pitch between the V-grooves was the same as the pitch between the linear openings. This indicates that this GaN crystal grew in the manner shown in FIG. 11, and the remnants of the voids formed as a result are the V-grooves, that is, the side surfaces of the V-grooves were part of the inner surface of the voids. The depth of the V-groove measured by the laser microscope was 1.9 mm at the deepest part. Considering the observation results before regrowth, it was thought that the GaN crystal began to be coreless when it grew 1-2 mm in the [000-1] direction.

[0085] (4) Processing of wafers The GaN single crystal grown by the ammonothermal method was sliced parallel to the C-plane to obtain a plurality of blank wafers. An external photograph of a double-sided polished C-plane GaN wafer with a thickness of 350 μm, which was fabricated by processing one of them, is shown in Fig. 13. In the C-plane GaN wafer shown in Fig. 13, both the gallium-polarity surface and the nitrogen-polarity surface are CMP-finished, but the damaged layer on the nitrogen-polarity surface can also be removed by alkaline etching. The alkaline-etched nitrogen-polarity surface becomes a matte surface on which fine cones are densely formed.

[0086] (5) Evaluation of wafers <epd> The C-plane GaN wafer fabricated by the above procedure was etched with 89% sulfuric acid heated to 270°C for 1 hour. After etching, the gallium-polarity surface of the C-plane GaN wafer was observed using an optical microscope (ECLIPSE LV100 manufactured by Nikon Corporation). A 2 mm × 2 mm square region on the gallium-polarity surface was divided into 400 sub-regions, each of which was a 100 μm × 100 μm square, and the number of etch pits contained in each sub-region was examined. As a result, 372 sub-regions, corresponding to 93% of the 400, were pit-free (EP D = 0 cm -2 ). Among the 28 sub-regions where etch pits were found, the EPD in the sub-region with the highest EPD was 1.1×10 5 cm -2 . The average value of EPD among the 400 sub-regions was 1.7×10 3 cm -2 .

[0087] Furthermore, a 3 mm × 3 mm square region encompassing the above 2 mm × 2 mm square region was divided into 900 sub-regions, each of which was a 100 μm × 100 μm square, and the number of etch pits contained in each sub-region was examined. As a result, 829 sub-regions, corresponding to 92% of the 900, were pit-free (EPD = 0 cm -2 ). Among the 71 sub-regions where etch pits were found, the EPD in the sub-region with the highest EPD was 1.5×10 5 c m -2 . The average value of EPD among the 900 sub-regions was 2.0×10 3 cm -2 . was

[0088] Furthermore, a 3.5 mm × 3.5 mm square region containing the above 3 mm × 3 mm square region was divided into 1225 sub-regions, each being a 100 μm × 100 μm square, and the number of etch pits contained in each sub-region was examined. As a result, 1141 sub-regions, which is 93% of 1225, were pit-free (EPD = 0 cm -2 ). Among the 84 sub-regions where etch pits were found, the EPD in the sub-region with the highest EPD was 1.5×10 5 cm -2 . The average value of EPD among the 1225 sub-regions was 1.9 ×10 3 cm -2 . This 3.5 mm × 3.5 mm square region did not overlap with the linear etch pit array described later.

[0089] Furthermore, a 4 mm × 4 mm square region containing the above 3.5 mm × 3.5 mm square region was divided into 1600 sub-regions, each being a 100 μm × 100 μm square, and the number of etch pits contained in each sub-region was examined. As a result, 1395 sub-regions, which is 87% of 1600, were pit-free (EPD = 0 cm -2 ). Among the 205 sub-regions where etch pits were found, the EPD in the sub-region with the highest EPD was 2.0×10 5 cm -2 . The average value of EPD among the 1600 sub-regions was 8. 3×10 3 cm -2 . This 4 mm × 4 mm square region partially overlapped with the linear etch pit array described later. On the other hand, a 1.3 mm × 1.3 mm pit-free region was also observed in this 4 mm × 4 mm square region.

[0090] Furthermore, a 5 mm × 5 mm square region encompassing the above-mentioned 4 mm × 4 mm square region was divided into 2,500 sub-regions, each being a 100 μm × 100 μm square, and the number of etch pits contained in each sub-region was examined. As a result, 2,210 sub-regions, which is 88% of 2,500, were pit-free (EPD = 0 cm -2 ). Among the 290 sub-regions where etch pits were found, the EPD in the sub-region with the highest EPD was 2.0×10 5 cm -2 . The average value of EPD among the 2,500 sub-regions was 7.2×10 3 cm -2 .

[0091] Figure 14 is an optical microscope image of the above-mentioned 5 mm × 5 mm square region. The complex mixture of white and gray patterns is due to the nitrogen polar surface becoming rough by the aforementioned etching process. As shown in Figure 14, in this 5 mm × 5 mm square region, a linear etch pit array with a width W d of 260 - 270 μm was observed. In the C-plane GaN wafer fabricated in Experiment 1, such a linear etch pit array was formed at a 4 mm period over the entire gallium polar surface. The extending direction of the linear etch pit array was consistent with the extending direction of the linear opening in the pattern mask provided on the HVPE seed. On the other hand, the position of the linear etch pit array and the linear opening was shifted by 2 mm in the direction orthogonal to the extending direction. This suggests that when the GaN crystal growing on the nitrogen polar surface of the HVPE seed coalesces above the pattern mask, a linear dislocation array parallel to the linear opening is formed.

[0092] In the 5 mm × 5 mm square region shown in Figure 14, even in the region overlapping with the linear etch pit array, the maximum number of etch pits contained in one sub-region (100 μm × 100 μm) was 20. That is, the density of the etch pits constituting the linear etch pit array was at most 2×10 5 cm -2 was. The entire straight-edge When examining a strip-shaped region with a length of 5 mm and a width of 200 μm that overlaps with the tip pit array, the average value of EPD between 100 sub-regions within the strip-shaped region was 1.2×10 5 cm -2 was.

[0093] Another one of the plurality of blank wafers obtained in the above 5.1.(4) was processed to fabricate a C-plane GaN wafer with a thickness of 350 μm, etched with 89% sulfuric acid heated to 270°C for 2 hours, and then a part (4×7 mm 2 ) of its gallium-polar surface was observed with an optical microscope. As a result, a rectangular pit-free region of 1.62 mm×1.88 mm and a rectangular pit-free region of 1.47 mm×1.92 mm were found. The distance between these two pit-free regions was about 0.5 mm.

[0094] <X-ray topography> Using an X-ray diffractometer [XRT-300 manufactured by Rigaku Corporation], X-ray topography analysis of the C-plane GaN wafer fabricated in Experiment 1 was performed. The transmission X-ray topography image obtained using (11-20) diffraction is shown in Fig. 15. Since the X-ray source used was MoKα and the thickness of the sample was 350 μm, μ·t = 10.2. Therefore, the X-ray topography image in Fig. 15 is an anomalous transmission image. Transmission X-ray topography images could be obtained for any part of the C-plane GaN wafer fabricated in Experiment 1.

[0095] <XRC-FWHM of (002) reflection> Using an X-ray diffractometer [PANalytical X’Pert Pro MRD manufactured by Spectris Corporation] the XRC-FWHM of the (002) reflection in the C-plane GaN wafer fabricated in Experiment 1 was measured. A Ge(220) 2-crystal monochromator was used for the incident optical system of the X-ray diffractometer. The beam size of the X-ray on the sample surface was set to be 0.2 mm × 3 mm when the incident angle of the X-ray was 90° (the incident direction of the X-ray was perpendicular to the sample surface). During measurement, the direction in which the beam size became 3 mm was made perpendicular to the X-ray incident plane. The incident plane is a plane that is perpendicular to the reflection plane and contains the incident ray and the reflected ray. Measurements were carried out at 0.2 mm intervals on the virtual line segment X parallel to the m-axis and the virtual line segment Y parallel to the a-axis, each passing through the approximate center of the gallium polar plane, as shown in Fig. 16. That is, at each of a plurality of measurement points arranged at 0.2 mm intervals on each line segment, an ω scan was performed to obtain XRC, and its FWHM was determined. The X-ray incident plane in the ω scan at each measurement point on line segment X was made parallel to line segment X. The X-ray incident plane in the ω scan at each measurement point on line segment Y was made parallel to line segment Y. The length of line segment X exceeded 90% of the size of the gallium polar plane in the m-axis direction. The length of line segment Y exceeded 90% of the size of the gallium polar plane in the a-axis direction.

[0096] As a result of measuring over 69 mm on the line segment X parallel to the m-axis, among 346 measurement points, only 1 point had an XRC-FWHM of 40 arcsec or more, and the XRC-FWHM was less than 40 arcsec at 345 points, which is approximately 100% of all measurement points. On line segment X, there was a section with a length of 64 mm where the XRC-FWHM was less than 40 arcsec at all measurement points within the section. Among 346 measurement points, 7 points had an XRC-FWHM of 30 arcsec or more, and the XRC-FWHM was less than 30 arcsec at 339 points, which is 98% of all measurement points. On line segment X, there was a section with a length of 35.2 mm where the XRC-FWHM was less than 30 arcsec at all measurement points within the section.

[0097] As a result of measurement over 54.6 mm on the line segment Y parallel to the a-axis, out of 274 measurement points, only 1 point had an XRC-FWHM of 40 arcsec or more, and for 273 points, which is approximately 100% of all the measurement points, the XRC-FWHM was less than 40 arcsec. On the line segment Y, there was a section with a length of 49.6 mm where the XRC-FWHM was less than 40 arcsec for all the measurement points within that section. Among the 274 measurement points, 11 points had an XRC-FWHM of 30 arcsec or more, and for 263 points, which is 96% of all the measurement points, the XRC-FWHM was less than 30 arcsec. On the line segment X, there was a section with a length of 26.4 mm where the XRC-FWHM was less than 30 arcsec for 131 points, which is 98% of the 133 measurement points within that section.

[0098] <XRC-FWHM of the <(004) reflection>> Using an X-ray diffractometer [PANalytical X’Pert Pro MRD manufactured by Spectris Co., Ltd.], the XRC-FWHM of the <(004) reflection> in the C-plane GaN wafer fabricated in Experiment 1 was measured. For the incident-side optical system, an X-ray mirror and a Ge(440) four-crystal monochromator were used. The resolution of the optical system was 5 - 6 arcsec. The X-ray beam size on the sample surface was set to be 0.2 mm × 5 mm when the incident angle of the X-ray was 90° (the incident direction of the X-ray was perpendicular to the sample surface). During the measurement, the direction in which the beam size became 5 mm was made perpendicular to the X-ray incident plane.

[0099] On a 70-mm long line segment parallel to the m-axis passing through approximately the center of the gallium-polar surface, ω scans were performed at 1-mm intervals to measure the XRC-FWHM of the <(004) reflection>. In each ω scan, the X-ray incident plane was made parallel to the m-axis. The measured values of the XRC-FWHM at all the measurement points are shown in Table 1 below. The average and standard deviation of the XRC-FWHM among all the measurement points were 11.7 arcsec and 3.8 arcsec, respectively.

Table 1

[0100] Furthermore, ω scans were performed at 1 mm intervals on a line segment 59 mm in length parallel to the a-axis passing through the approximate center of the gallium polar plane, and the XRC-FWHM of the (004) reflection was measured. In each ω scan, the X-ray incident plane was parallel to the a-axis. The measured values of XRC-FWHM at all measurement points are shown in Table 2 below. The average and standard deviation of XRC-FWHM among all measurement points were 13.0 arcsec and 4.2 arcsec, respectively.

Table 2

[0101] <Impurity concentration> On the gallium polar plane side of the C-plane GaN wafer fabricated in Experiment 1, the concentrations of fluorine, iodine, and hydrogen from the surface to a depth of 10 μm were measured by SIMS. The concentrations in the portion with a depth of 1 μm or more were below the detection limit for fluorine and iodine (the detection limit is 10 14 ~10 15 atoms / cm 3 level), and the hydrogen was 2 × 10 18 atoms / cm 3 .

[0102] <Infrared absorption spectrum> When the infrared absorption spectrum of the C-plane GaN wafer fabricated in Experiment 1 was measured, multiple absorption peaks attributed to gallium vacancy-hydrogen complexes were observed at 3100 - 3500 cm -1 . Among these multiple absorption peaks, there were four peaks with peak top wavelengths at around 3150 cm , around 3164 cm -1 , around 3176 cm -1 , and around 3188 cm -1 . -1

[0103] (6) Evaluation of ingot The X-ray diffraction characteristics of the regrown GaN crystal obtained in 5.1.(3) above were evaluated using an X-ray diffractometer [PANalytical X’Pert Pro MRD manufactured by Spectris Co., Ltd.] with the GaN crystal still bonded to the seed. A Ge(22 0)2 crystal monochromator was used in the incident optical system of the X-ray diffractometer. On a virtual line drawn on the azugron surface (nitrogen polar surface) of the GaN crystal grown on the nitrogen polar surface of the HVPE seed, XRC was measured at 0.2 mm intervals. This line was orthogonal to the stripe direction of the pattern mask formed on the nitrogen polar surface of the HVPE seed and had a length of 51.4 mm. The X-ray incident plane in the ω scan at each measurement point was parallel to this line. As a result of examining the FWHM of XRC measured on this line, it was less than 40 arcsec at all 258 measurement points. There were 35 out of 258 measurement points where XRC-FWHM was 30 arcsec or more, and XRC-FWHM was less than 30 arcsec at 223 points, which accounted for 86% of all measurement points.

[0104] 5.2. Experiment 2 (1) Preparation of seeds HVPE seeds of the same quality as those used in Experiment 1 were prepared. The HVPE seeds prepared in Experiment 2 were disk-shaped C-plane GaN wafers with a diameter of 2 inches. (2) Formation of pattern mask Similar to Experiment 1, a 200-nm-thick pattern mask composed of a laminated film of TiW and Pt was formed on the nitrogen polar surface of the HVPE seed. However, the pattern of the pattern mask was a rhombic lattice type having a first linear opening and a second linear opening extending in different directions. The extending direction of the first linear opening was inclined by 12° from one of the intersection lines of the M plane and the nitrogen polar surface in the HVPE seed. The angle formed by the extending direction of the first linear opening and the extending direction of the second linear opening was 60°. The widths of both the first linear opening and the second linear opening were set to 50 μm. The pitch between the first linear openings was set to 4 mm, and the pitch between the second linear openings was set to 12 mm.

[0105] (3) Growth of GaN crystals by the ammonothermal method On the HVPE seed on which the above pattern mask was formed, a GaN single crystal was grown by the ammonothermal method. The crystal growth apparatus and crystal growth conditions used were the same as those in Experiment 1. However, the growth time was set to 35 days, and regrowth was not performed. The GaN crystal grew 2.9 mm in the [000-1] direction in 35 days. Therefore, the growth rate was 82 μm / day. The growth front was flattened, and coreless was almost completed. From the results of observing the wafer obtained by slicing the grown crystal, it was considered that the GaN crystal started to become coreless when it grew 1 to 1.5 mm in the [000-1] direction.

[0106] (4) Processing of the wafer After slicing the GaN single crystal grown by the ammonothermal method parallel to the C plane, polishing and CMP finishing were performed on both main surfaces of the obtained blank wafer to obtain a C-plane GaN wafer having a substantially regular hexagonal main surface and a thickness of 350 μm.

[0107] (5) Evaluation of the wafer Using an X-ray diffractometer [PANalytical X’Pert Pro MRD manufactured by Spectris Co., Ltd.] the XRC-FWHM of the (002) reflection in the C-plane GaN wafer fabricated in this Experiment 2 was measured. For the incident optical system of the X-ray diffractometer, a Ge(220) 2-crystal monochromator was used. The beam size of the X-ray on the sample surface was set to be 0.2 mm × 3 mm when the incident angle of the X-ray was 90°. During the measurement, the direction in which the beam size became 3 mm was made perpendicular to the X-ray incident plane. Measurements were taken at intervals of 0.2 mm on line segment X parallel to the m-axis and line segment Y parallel to the a-axis, each passing through the approximate center of the gallium polar plane shown in Fig. 17. Similar to Experiment 1, the X-ray incident plane in the ω scan at each measurement point on line segment X was parallel to line segment X, and the X-ray incident plane in the ω scan at each measurement point on line segment Y was parallel to line segment Y. The length of line segment X exceeded 90% of the size of the gallium polar plane in the m-axis direction. The length of line segment Y exceeded 90% of the size of the gallium polar plane in the a-axis direction.

[0108] As a result of measuring over 45 mm on line segment X parallel to the m-axis, the XRC-FWHM was below 40 arcsec at all 226 measurement points. There were 3 out of 226 measurement points where the XRC-FWHM was 30 arcsec or more, and the XRC-FWHM was below 30 arcsec at 223 points, which accounted for 99% of all measurement points.

[0109] As a result of measuring over 53.8 mm on line segment Y parallel to the a-axis, the XRC-FWHM was below 40 arcsec at all 270 measurement points. There was 1 out of 270 measurement points where the XRC-FWHM was 30 arcsec or more, and the XRC-FWHM was below 30 arcsec at 269 points, which accounted for approximately 100% of all measurement points. On line segment Y, there was a section with a length of 46.6 mm where the XRC-FWHM was below 30 arcsec at all measurement points within the interval.

[0110] When calculating the radius of curvature of the C-plane in the direction parallel to line segment X from the change rate of the peak top angle of the XRC measured on line segment X, it was 550 m (in this calculation, the change rate of the peak top angle of the XRC was obtained using the least squares method from the measured values at all 226 measurement points). Separately, two points 10 mm apart from each other were selected from 226 measurement points on line segment X, and the radius of curvature of the C-plane was calculated from the difference Δω in the peak top angle of XRC between the two points using the aforementioned formula 1 (R = ΔL / Δω). Then, no matter how the two points were selected, the absolute value of the radius of curvature of the C-plane in the direction parallel to line segment X did not fall below 78 m. In other words, the absolute value of the radius of curvature was 78 m when calculated by selecting the two points with the largest Δω.

[0111] When calculating the radius of curvature of the C-plane in the direction parallel to line segment Y from the rate of change of the peak top angle of XRC measured on line segment Y, it was 79 m (in this calculation, the rate of change of the peak top angle of XRC was obtained from the measured values at all 270 measurement points using the least squares method). Separately, two points 10 mm apart from each other were selected from 270 measurement points on line segment Y, and the radius of curvature of the C-plane was calculated from the difference Δω in the peak top angle of XRC between the two points using the aforementioned formula 1 (R = ΔL / Δω). Then, no matter how the two points were selected, the absolute value of the radius of curvature of the C-plane in the direction parallel to line segment Y did not fall below 52 m. In other words, the absolute value of the radius of curvature was 52 m when calculated by selecting the two points with the largest Δω.

[0112] (6) Evaluation of the ingot The X-ray diffraction characteristics of the GaN crystal obtained in the above 5.2.(3) were evaluated using an X-ray diffractometer [PANalytical X’Pert Pro MRD manufactured by Spectris Co., Ltd.] with the GaN crystal still bonded to the seed. In the incident optical system of the X-ray diffractometer, a Ge(220)2 crystal monochromator was used. XRC was measured at 0.2 mm intervals on a virtual line drawn on the as-grown surface (nitrogen polar surface) of the GaN crystal grown on the nitrogen polar surface of the HVPE seed. The line segment was the first linear opening of the pattern mask formed on the nitrogen polar surface of the HVPE seed The angle formed with the extending direction of the mouth was 78 degrees, and it was parallel to one of the m axes, with a length of 41 mm. The X-ray incident plane in the ω scan at each measurement point was made parallel to this line segment.

[0113] As a result of examining the FWHM of XRC measured on this line segment, it was less than 40 arcsec for all 206 measurement points. There were 3 out of 206 measurement points where the XRC-FWHM was 30 arcsec or more, and the XRC-FWHM was less than 30 arcsec at 203 points, which accounted for 98% of all the measurement points. On this line segment, there was a section with a length of 21.6 mm where the XRC-FWHM was less than 30 arcsec for all the measurement points within this section.

[0114] As described above, the present invention has been described with reference to specific embodiments. However, 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 variously modified within the scope not departing from the gist of the invention, and can be combined with the features described in other embodiments within the practicable range.

Explanation of Reference Numerals

[0115] 10 GaN single crystal 11 Gallium polar plane 12 Nitrogen polar plane 13 Side surface 14 Linear dislocation array 15 Orientation flat 20 C-plane GaN wafer 21 Gallium polar plane 22 Nitrogen polar plane 23 Side surface 30 Pattern mask 31 Linear opening 40 GaN crystal 50 Void 100 Crystal growth apparatus 101 Autoclave 102 Growth container 102a Raw material dissolution zone 102b Crystal growth zone 103 Baffle 104 Platinum wire 105 Vacuum pump 106 Ammonia cylinder 107 Nitrogen cylinder 108 Valve 109 Mass flow meter< / epd>

Claims

1. In a GaN single crystal having a gallium-polar surface which is a main surface on one side and a nitrogen-polar surface which is a main surface on the opposite side, at least one square region is found on the gallium-polar surface, and the length of each of the four sides constituting the outer periphery of the at least one square region is 2 mm or more. When the at least one square region is divided into a plurality of sub-regions each being a square of 100 μm × 100 μm, 80% or more of the plurality of sub-regions are pit-free regions (regions where the etch pit density is 0 cm －２ of the region), each of the gallium-polar surface and the nitrogen-polar surface has a size including a square of 10 mm × 10 mm, and an abnormal transmission image of a 10 mm × 10 mm square region can be obtained in X-ray topography, The pit-free region (region where the etch pit density is 0 cm−2) is a GaN single crystal which is a region where no etch pits are observed after etching for 1 hour or more using 89% sulfuric acid heated to 270 °C as an etchant.

2. Among the plurality of sub-regions, the ratio of the pit-free region (region where the etch pit density is 0 cm －２ of the region) is 85% or more. The GaN single crystal according to claim 1.

3. Among the plurality of sub-regions, the ratio of the pit-free region (region where the etch pit density is 0 cm －２ of the region) is 90% or more. The GaN single crystal according to claim 1.

4. In the sub-region having the highest EPD among the plurality of sub-regions, the EPD is 1 × 10 ６ cm －２ less than. The GaN single crystal according to any one of claims 1 to 3.

5. The average value of the EPD between the plurality of sub-regions is 1 × 10 ４ cm －２ less than. The GaN single crystal according to any one of claims 1 to 4.

6. In the sub-region among the plurality of sub-regions where the EPD is the highest, the EPD is less than 2×10 ５ cm －２ The GaN single crystal according to claim 3.

7. The average value of the EPD among the plurality of sub-regions is less than 3×10 ３ cm －２ The GaN single crystal according to claim 3 or 6.

8. The at least one square region has a length of each of the four sides constituting its outer periphery of 3.5 mm or less. The GaN single crystal according to claim 3, 6 or 7.

9. A square pit-free region (etch pit density is 0 cm －２ The GaN single crystal according to any one of claims 1 to 8, in which at least one is found on the gallium polar surface.

10. In a GaN single crystal having a gallium polar surface as one main surface and a nitrogen polar surface as the other main surface, each main surface has a size including a 10 mm×10 mm square, and a square pit-free region (etch pit density is 0 cm －２ The region) is characterized in that at least one is found on the gallium polar surface. The pit-free region (the region where the etch pit density is 0 cm−2) is a region where no etch pits are observed after etching for 1 hour or more using 89% sulfuric acid heated to 270°C as an etchant. The GaN single crystal.

Images