n-type GaN crystal, GaN wafer, and method for manufacturing GaN crystal, GaN wafer, and nitride semiconductor devices.

Abstract

To fulfill the following demand: if GaN crystals having a (004) XRD rocking curve FWHM of 20 arcsec or less, which is equivalent to that of GaN crystals grown by the ammonothermal method, can be grown by HVPE with high productivity, it is expected to contribute to promoting the development of nitride semiconductor devices produced using c-plane GaN wafers as substrates and a reduction in cost.SOLUTION: In this n-type GaN crystal, the donor dopant contained at the highest concentration is Ge. The n-type GaN crystal has a resistivity at room temperature of less than 0.03 Ω cm and has a (004) XRD rocking curve FWHM of less than 20 arcsec. The n-type GaN crystal has two principal surfaces each having an area of 3 cm2 or more, and one of the surfaces has Ga polarity and is inclined at an angle of 0 to 10 degrees relative to the (0001) crystal plane. Additionally, the n-type GaN crystal has a diameter of 20 mm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention primarily relates to n-type GaN crystals, GaN wafers, and methods for manufacturing GaN crystals, GaN wafers, and nitride semiconductor devices. [Background technology]

[0002] GaN (gallium nitride) is a type of III-V compound semiconductor and has a wurtzite-type crystal structure belonging to the hexagonal crystal system. Representative growth techniques for bulk GaN crystals include HVPE (Hydride Vapor Phase Epitaxy), high-pressure solution growth, amonothermal growth, and Na flux growth (Non-Patent Literature 1). HVPE offers significantly higher GaN crystal growth rates compared to other techniques, and almost all commercially available GaN wafers are grown using HVPE.

[0003] There is a report that GaN crystals were grown using HVPE on a 1-inch diameter c-plane GaN seed wafer grown by the amonothermal method, and an 18mm diameter c-plane GaN wafer was cut from the GaN crystals (Non-Patent Literature 2). There is a report (Non-Patent Literature 3) that GaN crystals were grown using HVPE on c-plane GaN seed wafers grown by the amonothermal method, and that Si (silicon) doped GaN crystals were further grown using HVPE on c-plane seed wafers cut from the HVPE-grown GaN crystals. The (002)XRD rocking curve FWHM of the Si-doped GaN crystal was reported to be 32 arcsec. There is a report (Non-Patent Literature 4) that germanium-doped GaN crystals were grown on a c-plane GaN seed wafer grown by the amonothermal method using HVPE. The (002)XRD rocking curve FWHM of the Ge-doped GaN crystal was 67 arcsec.

[0004] There is a report (Non-Patent Literature 5) of growing a 5.6 mm thick GaN crystal in HVPE on an m-plane GaN seed wafer grown by the acidic amonothermal method, and cutting a 2-inch diameter m-plane GaN wafer from the HVPE-grown GaN crystal. A (200)XRD rocking curve FWHM of 13 arcsec was obtained at the center of the 2-inch HVPE wafer. A conductive c-plane GaN wafer is known that consists of GaN crystals grown by an acidic amonothermal method using NH4F (ammonium fluoride) and NH4I (ammonium iodide) as mineralizing agents, and has a (004)XRD rocking curve FWHM of approximately 10 arcsec (Patent Document 1). In the above, XRD refers to X-ray diffraction, and FWHM refers to Full Width at Half Maximum. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] WO2018 / 030311A1 [Non-patent literature]

[0006] [Non-Patent Document 1] H. Amano, Japanese Journal of Applied Physics 52 (2013) 050001 [Non-Patent Document 2] JZ Domagala, et al., Journal of Crystal Growth 456 (2016) 80 [Non-Patent Document 3] M. Iwinska, et al., Journal of Crystal Growth 456 (2016) 91 [Non-Patent Document 4] M. Iwinska, et al., Journal of Crystal Growth 480 (2017) 102 [Non-Patent Document 5] Y. Tsukada, et al., Japanese Journal of Applied Physics 55 (2016) 05FC01 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The inventors believe that if GaN crystals with a (004)XRD rocking curve FWHM of 20 arcsec or less, comparable to GaN crystals grown by the amonothermal method, can be grown using HVPE, which offers excellent mass productivity, it will contribute to accelerating the development and reducing the cost of nitride semiconductor devices produced using c-plane GaN wafers as substrates. [Means for solving the problem]

[0008] The present invention relates in part to n-type GaN crystals, in part to GaN wafers, in part to a method for manufacturing GaN wafers, in part to a method for manufacturing epitaxial wafers, in part to an epitaxial wafer, in part to a method for manufacturing nitride semiconductor devices, and in part to a method for manufacturing bulk GaN crystals.

[0009] Embodiments of the present invention include, but are not limited to, the following [A1] to [A26]. [A1] An n-type GaN crystal characterized in that the donor impurity present at the highest concentration is Ge, it has a room-temperature resistivity of less than 0.03 Ω·cm, and its (004)XRD rocking curve FWHM is less than 20 arcsec, less than 18 arcsec, less than 16 arcsec, less than 14 arcsec, or less than 12 arcsec. [A2] The n-type GaN crystal described in [A1], wherein the crystal has two principal surfaces facing opposite directions, and each of the two principal surfaces has an area of ​​3 cm². 2The above describes an n-type GaN crystal in which one of the two main surfaces is Ga polar and has an inclination of 0 degrees or more and 10 degrees or less with respect to the (0001) crystal plane. [A3] The n-type GaN crystal described in [A2] having a diameter of 20 mm or more, 45 mm or more, 95 mm or more, or 145 mm or more. [A4] An n-type GaN crystal having two principal planes facing opposite directions, one of which is Ga polar and has an inclination of 0 degrees or more to 10 degrees with respect to the (0001) crystal plane, characterized in that the donor impurity present at the highest concentration is Ge, it has a room-temperature resistivity of less than 0.03 Ω·cm, and when the (004)XRD rocking curve is measured every 1 mm along at least one line on the one principal plane over a length of 40 mm, the maximum value of the (004)XRD rocking curve FWHM between all measurement points is 20 arcsec or less. [A5] The n-type GaN crystal according to [A4], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, 12 arcsec or less, or 10 arcsec or less. [A6] An n-type GaN crystal having two principal planes facing opposite directions, one of which is Ga polar and has an inclination of 0 degrees or more to 10 degrees with respect to the (0001) crystal plane, characterized in that the donor impurity present at the highest concentration is Ge, it has a room temperature resistivity of less than 0.03 Ω·cm, and when the (004)XRD rocking curve is measured every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on one of the principal planes, the maximum value of the (004)XRD rocking curve FWHM between all measurement points on each line is 20 arcsec or less. [A7] The average value of the (004) XRD locking curve FWHM between all measurement points on each line is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, 1 The n-type GaN crystal described in [A6], wherein the arcsec interval is 2 arcsec or less or 10 arcsec or less. An n-type GaN crystal according to any one of [A2] to [A7], having a room-temperature resistivity of less than 0.02 Ω·cm, less than 0.015 Ω·cm, or less than 0.010 Ω·cm. [A9]A carrier concentration of 1×10 18 cm -3 or more, 2×10 18 cm -3 or more, 3×10 18 cm -3 or more, or 4×10 18 cm -3 or more. An n-type GaN crystal according to any one of [A2] to [A7]. [A10]An n-type GaN crystal according to any one of [A2] to [A9], satisfying one or more conditions selected from the following (a) to (c) with respect to the impurity concentration: (a) The Si concentration is 5×10 16 atoms / cm 3 or more; (b) The O concentration is 3×10 16 atoms / cm 3 or less; (c) The H concentration is 1×10 17 atoms / cm 3 or less. [A11]An n-type GaN crystal according to [A10], satisfying all of the conditions (a) to (c) with respect to the impurity concentration. [A12]An n-type GaN crystal according to any one of [A2] to [A11], having an O concentration of 3×10 16 atoms / cm 3 or less, 2×10 16 atoms / cm 3 or less, or 1×10 16 atoms / cm 3 or less. [A13]An n-type GaN crystal according to any one of [A2] to [A12], having a Ge concentration of 1×10 18 atoms / cm 3 or more, and a Si concentration of 4×10 17 atoms / cm 3 or more. [A14]The concentration of each impurity excluding Ge, Si, O, and H is 5×10 15atoms / cm 3 The n-type GaN crystal described in any of [A2] to [A13] above, which is as follows: [A15] An n-type GaN crystal according to any of [A2] to [A14] above, which is a GaN crystal grown with HVPE. [A16] A GaN wafer made of an n-type GaN crystal as described in any of [A2] to [A15] above. [A17] A GaN wafer in which a first region made of an n-type GaN crystal as described in any of [A2] to [A15] is provided on the Ga polar side, and a second region with a lower carrier concentration than the n-type GaN crystal is provided on the N polar side. [A18] The GaN wafer according to [A17], wherein the thickness of the first region is 5 μm or more and 250 μm or less. [A19] The GaN wafer described in [A17] or [A18], wherein the second region satisfies one or more conditions selected from (a) to (c) below with respect to the impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [A20] The GaN wafer according to [A19], wherein the second region satisfies all of the above conditions (a) to (c) regarding the impurity concentration. [A21] The oxygen concentration in the second region is 3 × 10 16 atoms / cm 3 Below, 2 x 10 16 atoms / cm 3 The following or 1 x 10 16 atoms / cm 3 The following is a GaN wafer as described in any of [A17] to [A20] above. [A22] The concentrations of each impurity in the second region, excluding Si, O, and H, are 5 × 10 15 atoms / cm 3A GaN wafer as described in any of the above [A17] to [A21], which is as follows: [A23] A GaN wafer according to any one of [A17] to [A22], having a regrowth interface between the first region and the second region. [A24] A method for manufacturing an epitaxial wafer, comprising the steps of preparing a GaN wafer according to any of [A16] to [A23] above, and epitaxially growing one or more nitride semiconductor layers on the prepared GaN wafer. [A25] A GaN wafer as described in any of [A16] to [A23] above, and the GaN wafer An epitaxial wafer comprising one or more nitride semiconductor layers epitaxially grown on an EVA. [A26] A method for manufacturing a nitride semiconductor device, comprising the steps of preparing a GaN wafer as described in any of [A16] to [A23] above, and epitaxially growing one or more nitride semiconductor layers on the prepared GaN wafer.

[0010] Embodiments of the present invention further include the following [B1] to [B29]. [B1] n-type GaN crystal having a room-temperature resistivity of less than 0.03 Ω·cm, a (004)XRD rocking curve FWHM of less than 20 arcsecs, and satisfying one or more conditions selected from (a) to (c) below regarding impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [B2] The n-type GaN crystal described in [B1] above, wherein the crystal has two principal surfaces facing opposite directions, and each of the two principal surfaces has an area of ​​3 cm². 2 The above describes an n-type GaN crystal in which one of the two main surfaces is Ga polar and has an inclination of 0 degrees or more and 10 degrees or less with respect to the (0001) crystal plane. [B3] The n-type GaN crystal described in [B2] having a diameter of 20 mm or more, 45 mm or more, 95 mm or more, or 145 mm or more. [B4] An n-type GaN crystal having two principal planes facing opposite directions, one of which is Ga polar and has an inclination of 0 to 10 degrees with respect to the (0001) crystal plane, characterized in that it has a room-temperature resistivity of less than 0.03 Ω·cm, when the (004)XRD rocking curve is measured every 1 mm along at least one line on the one principal plane over a length of 40 mm, the maximum value of the (004)XRD rocking curve FWHM between all measurement points is 20 arcsec or less, and satisfies one or more conditions selected from (a) to (c) below regarding the impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [B5] The n-type GaN crystal according to [B4], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, or 12 arcsec or less. [B6] An n-type GaN crystal having two principal planes facing opposite directions, one of which is Ga polar and has an inclination of 0 to 10 degrees with respect to the (0001) crystal plane, characterized in that it has a room-temperature resistivity of less than 0.03 Ω·cm, when the (004)XRD rocking curve is measured every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on one principal plane, the maximum value of the (004)XRD rocking curve FWHM between all measurement points on each line is 20 arcsec or less, and satisfies one or more conditions selected from (a) to (c) below regarding the impurity concentration: (a) Si concentration is 5 × 1016 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [B7] The n-type GaN crystal according to [B6], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points on each line is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, or 12 arcsec or less. [B8] An n-type GaN crystal according to any of [B2] to [B7] above, having a room-temperature resistivity of less than 0.02 Ω·cm, less than 0.015 Ω·cm, or less than 0.010 Ω·cm. [B9] Carrier concentration is 1 × 10 18 cm -3 or more, or 2 x 10 18 cm -3 The above is an n-type GaN crystal as described in any of [B2] to [B7] above. [B10] An n-type GaN crystal according to any of [B2] to [B9] above, satisfying all of the above conditions (a) to (c) with respect to the impurity concentration. [B11]O concentration is 3 × 10 16 atoms / cm 3 Below, 2 x 10 16 atoms / cm 3 The following or 1 x 10 16 atoms / cm 3 The n-type GaN crystal described in any of the above [B2] to [B10] is as follows: [B12] An n-type GaN crystal according to any of [B2] to [B11] above, wherein the donor impurity present at the highest concentration is Si. [B13] The n-type GaN crystal according to [B12], wherein the total concentration of donor impurities excluding Si is 10% or less, 5% or less, or 1% or less of the Si concentration. [B14] The n-type GaN crystal described in [B13], wherein the carrier concentration is 90% or more of the Si concentration. [B15] The concentration of each impurity except Si, O, and H is 5 × 10 15 atoms / cm 3 The n-type GaN crystal described in any of the above [B2] to [B14] is as follows: [B16] Ge concentration is 1 × 10 18 atoms / cm 3 Furthermore, the Si concentration is 4 × 10 17 atoms / cm 3 The above is an n-type GaN crystal as described in any of [B2] to [B12] above. [B17] The concentration of each impurity except Ge, Si, O, and H is 5 × 10 15 atoms / cm 3 The n-type GaN crystal described in [B16] above is as follows: [B18] An n-type GaN crystal according to any of [B2] to [B17] above, which is a GaN crystal grown with HVPE. [B19] A GaN wafer made of an n-type GaN crystal as described in any of [B2] to [B18] above. [B20] A GaN wafer in which a first region made of an n-type GaN crystal as described in any of [B2] to [B18] is provided on the Ga polar side, and a second region with a lower carrier concentration than the n-type GaN crystal is provided on the N polar side. [B21] The GaN wafer according to [B20], wherein the thickness of the first region is 5 μm or more and 250 μm or less. [B22] The GaN wafer described in [B20] or [B21], wherein the second region satisfies one or more conditions selected from (a) to (c) below with respect to the impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [B23] The GaN wafer according to [B22], wherein the second region satisfies all of the above conditions (a) to (c) regarding the impurity concentration. [B24] The O concentration in the second region is 3×10 16 atoms / cm 3 or less, 2×10 16 atoms / cm 3 or less or 1×10 16 atoms / cm 3 or less, and the GaN wafer according to any one of [B20] to [B23]. [B25] The concentration of each impurity other than Si, O, and H in the second region is 5×10 15 atoms / cm 3 or less, and the GaN wafer according to any one of [B20] to [B24]. [B26] The GaN wafer according to any one of [B20] to [B25], having a regrowth interface between the first region and the second region. [B27] A method for manufacturing an epitaxial wafer, comprising the step of preparing a GaN wafer according to any one of [B19] to [B26], and the step of epitaxially growing one or more nitride semiconductor layers on the prepared GaN wafer. [B28] An epitaxial wafer comprising the GaN wafer according to any one of [B19] to [B26] and one or more nitride semiconductor layers epitaxially grown on the GaN wafer. [B29] A method for manufacturing a nitride semiconductor device, comprising the step of preparing a GaN wafer according to any one of [B19] to [B26], and the step of epitaxially growing one or more nitride semiconductor layers on the prepared GaN wafer.

[0011] Embodiments of the present invention further include the following [C1] to [C44]. [C1]In an n-type GaN crystal having two main surfaces facing in opposite directions, one of the two main surfaces is Ga-polar and has an inclination with respect to the (0001) crystal plane of 0 degrees or more and 10 degrees or less, the n-type GaN crystal having a diameter of 45 mm or more, the (004) XRD rocking curve FWHM being less than 20 arcsec, less than 18 arcsec, less than 16 arcsec, less than 14 arcsec or less than 12 arcsec, and satisfying one or more conditions selected from the following (a) to (c) with respect to the impurity concentration: (a) The Si concentration is 5 × 10 16 atoms / cm 3 or more; (b) The O concentration is 3 × 10 16 atoms / cm 3 or less; (c) The H concentration is 1 × 10 17 atoms / cm 3 or less. [C2] The n-type GaN crystal according to [C1], having a diameter of 95 mm or more or 145 mm or more. [C3]In an n-type GaN crystal having two main surfaces facing in opposite directions, one of the two main surfaces is Ga-polar and has an inclination with respect to the (0001) crystal plane of 0 degrees or more and 10 degrees or less, when measuring the (004) XRD rocking curve every 1 mm over a length of 40 mm along at least one line on the one main surface, the maximum value of the (004) XRD rocking curve FWHM between all measurement points is 20 arcsec or less, and satisfying one or more conditions selected from the following (a) to (c) with respect to the impurity concentration: (a) The Si concentration is 5 × 10 16 atoms / cm 3 or more; (b) The O concentration is 3 × 10 16 atoms / cm 3 or less; (c) The H concentration is 1 × 10 17 atoms / cm 3 or less. [C4] The n-type GaN crystal according to [C3], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, 12 arcsec or less, or 10 arcsec or less. [C5] An n-type GaN crystal having two principal planes facing opposite directions, one of which is Ga polar and has an inclination of 0 to 10 degrees with respect to the (0001) crystal plane, characterized in that when the (004)XRD rocking curve is measured every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on the one principal plane, the maximum value of the (004)XRD rocking curve FWHM between all measurement points on each line is 20 arcsec or less, and one or more conditions selected from (a) to (c) below regarding the impurity concentration are satisfied: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [C6] The n-type GaN crystal according to [C5], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points on each line is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, 12 arcsec or less, or 10 arcsec or less. [C7] An n-type GaN crystal according to any of [C1] to [C6] above, satisfying all of the above conditions (a) to (c) with respect to the impurity concentration. [C8]Si concentration is 5 × 10 17 atoms / cm 3 The following is an n-type GaN crystal as described in any of [C1] to [C7] above. [C9] The concentration of each impurity except Si, O, and H is 5 × 10 15 atoms / cm 3The following is an n-type GaN crystal as described in any of [C1] to [C8] above. [C10]O concentration is 3 × 10 16 atoms / cm 3 Below, 2 x 10 16 atoms / cm 3 The following or 1 x 10 16 atoms / cm 3 The following is an n-type GaN crystal as described in any of [C1] to [C9] above. [C11] 5×10 17 cm -3 An n-type GaN crystal according to any one of [C1] to [C10], having at least one of a carrier concentration less than 0.04 Ω·cm and a room-temperature resistivity of 0.04 Ω·cm or more. [C12] An n-type GaN crystal grown with HVPE, as described in any of [C1] to [C11] above. [C13] A GaN wafer made of an n-type GaN crystal as described in any of [C1] to [C12] above. [C14] The C14 has a back layer made of an n-type GaN crystal as described in any of [C1] to [C12] above, and a front layer made of GaN with a minimum thickness of 20 μm or more, formed on the main surface on the Ga polar side of the n-type GaN crystal via a regrowth interface, wherein at least a portion of the front layer within a distance of 5 μm from the top surface is included in a high carrier concentration region, and the lower limit of the carrier concentration in the high carrier concentration region is 1 × 10⁻⁶ 18 cm -3 The above-mentioned area is a double-layer GaN wafer. [C15] The two-layer GaN wafer according to [C14], wherein at least a portion of the top layer within 20 μm from the top surface is included in the high carrier concentration region. [C16] The high carrier concentration region has a lower limit of carrier concentration of 2 × 10 18 cm -3 The above is 3 x 10 18 cm -3 or more, or 4 x 10 18 cm -3 A two-layer GaN wafer as described in [C14] or [C15] above, wherein the region is as described above. [C17] A two-layer GaN wafer according to any of [C14] to [C16], wherein the surface layer satisfies one or more conditions selected from (a) to (c) below with respect to the impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [C18] The two-layer GaN wafer according to [C17], wherein the front layer satisfies all of the above conditions (a) to (c) regarding the impurity concentration. [C19] The oxygen concentration in the outer layer is 3 × 10 16 atoms / cm 3 Below, 2 x 10 16 atoms / cm 3 The following or 1 x 10 16 atoms / cm 3 A two-layer GaN wafer as described in any of the above [C14] to [C18], which is as follows: [C20] A two-layer GaN wafer according to any one of [C14] to [C19], wherein the high carrier concentration region is doped with Si. [C21] The concentrations of each impurity in the surface layer, excluding Si, O, and H, are 5 × 10 15 atoms / cm 3 The following is the two-layer GaN wafer described in [C20] above. [C22] A two-layer GaN wafer according to any one of [C14] to [C20], wherein the high carrier concentration region is doped with Ge. [C23] The concentrations of each impurity in the surface layer, excluding Ge, Si, O, and H, are 5 × 10 15 atoms / cm 3 The following is the two-layer GaN wafer described in [C22] above. [C24] In the high carrier concentration region, the variation in the carrier concentration or the total concentration of donor impurities along the c-axis is within ±25%, ±20%, ±15%, or ±10% from the median, wherein the two-layer GaN wafer is as described in any of [C14] to [C23]. [C25] A back layer made of an n-type GaN crystal as described in any of [C1] to [C12], and a front layer made of GaN with a minimum thickness of 20 μm or more, formed on the main surface on the Ga polar side of the n-type GaN crystal via a regrowth interface, wherein at least a portion of the front layer within a distance of 5 μm from the top surface is included in the carrier compensation region, and the lower limit of the total concentration of compensating impurities in the carrier compensation region is 1 × 10⁻⁶ 17 atoms / cm 3 The above-mentioned area is a double-layer GaN wafer. [C26] The two-layer GaN wafer according to [C25], wherein at least a portion of the top layer within 20 μm from the top surface is included in the carrier compensation region. [C27] The carrier compensation region has a lower limit of 2 × 10⁻¹⁰ total concentration of compensated impurities. 17 atoms / cm 3 The above 5 x 10 17 atoms / cm 3 The above is 1 x 10 18 atoms / cm 3 The above is 2 x 10 18 atoms / cm 3 or more, or 5 x 10 18 atoms / cm 3 A two-layer GaN wafer as described in [C25] or [C26] above, wherein the region is as described above. [C28] The surface layer is selected from (a) to (c) below with respect to the impurity concentration of one or more of the above. A two-layer GaN wafer according to any of the above [C25] to [C27] that satisfies the following conditions: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3The following applies: [C29] In the carrier compensation region, the variation in the total concentration of compensating impurities along the c-axis direction is within ±25%, ±20%, ±15%, or ±10% from the median value, wherein the two-layer GaN wafer is as described in any of [C25] to [C28]. [C30] A double-layer GaN wafer according to any of [C14] to [C29], wherein the thickness of the double-layer GaN wafer is greater than 300 μm, and the maximum thickness of the front layer is 300 μm or less, 250 μm or less, or 200 μm or less. [C31] A two-layer GaN wafer according to any one of [C14] to [C30], wherein the minimum thickness of the surface layer is 50 μm or more, 75 μm or more, or 100 μm or more. [C32] A two-layer GaN wafer according to any of [C14] to [C31], wherein the difference between the maximum and minimum thickness of the surface layer is 200 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, or 10 μm or less. [C33] A method for manufacturing an epitaxial wafer, comprising the steps of preparing a wafer according to any of [C13] to [C32] above, and epitaxially growing one or more nitride semiconductor layers on the prepared wafer. [C34] An epitaxial wafer comprising a wafer as described in any of [C13] to [C32] above, and one or more nitride semiconductor layers epitaxially grown on the GaN wafer. [C35] A method for manufacturing a nitride semiconductor device, comprising the steps of preparing a wafer according to any of [C13] to [C32] above, and epitaxially growing one or more nitride semiconductor layers on the prepared wafer. [C36] The C36 step is to prepare a GaN wafer as described in [C13] above, and to epitaxially grow a GaN layer with a thickness of 20 μm or more on the main surface on the Ga polar side of the prepared GaN wafer, wherein the GaN layer is provided with a high carrier concentration region or a carrier compensation region, and the lower limit of the carrier concentration in the high carrier concentration region is 1 × 10⁻⁶ 18 cm -3 The above region is the carrier compensation region, and the lower limit of the total concentration of compensated impurities is 2 × 10⁻⁶17 atoms / cm 3 The above-mentioned area is a method for manufacturing a double-layer GaN wafer. [C37] The manufacturing method according to [C36], wherein in the step of epitaxial growth, the GaN layer is grown with HVPE. [C38] The manufacturing method according to [C36] or [C37], wherein the thickness of the GaN layer is 500 μm or less. [C39] The GaN layer is provided with the high carrier concentration region, and the lower limit of the carrier concentration in the high carrier concentration region is 2 × 10 18 cm -3 The above is 3 x 10 18 cm -3 or more, or 4 x 10 18 cm -3 A manufacturing method according to any of the above regions [C36] to [C38]. [C40] The manufacturing method according to any one of [C36] to [C39], wherein the GaN layer is provided with the high carrier concentration, and the high carrier concentration region is doped with Ge. [C41] The manufacturing method according to any one of [C36] to [C40], wherein the GaN layer is provided with the high carrier concentration, and the high carrier concentration region is intentionally doped with Si. [C42] The GaN layer is provided with the carrier compensation region, and the lower limit of the total concentration of compensation impurities in the carrier compensation region is 5 × 10 17 atoms / cm 3 The above is 1 x 10 18 atoms / cm 3 The above is 2 x 10 18 atoms / cm 3 or more, or 5 x 10 18 atoms / cm 3 A manufacturing method according to any of the above regions [C36] to [C38]. [C43] The manufacturing method according to any one of [C36] to [C42], further comprising the step of thinning the laminate obtained in the epitaxial growth step. [C44] A method for producing a bulk GaN crystal, comprising the steps of preparing a GaN wafer as described in [C13] and epitaxially growing GaN on the prepared GaN wafer.

[0012] Embodiments of the present invention further include the following [D1] to [D19]. [D1] A c-plane GaN wafer characterized in that the donor impurity present at the highest concentration is Ge, the conductivity type is n-type and it has a room temperature resistivity of less than 0.03 Ω·cm, and (004) the XRD rocking curve FWHM is less than 20 arcsec, less than 18 arcsec, less than 16 arcsec, less than 14 arcsec, or less than 12 arcsec. [D2] Area 3cm 2 A c-plane GaN wafer according to [D1], having the above-mentioned main surface. [D3] A c-plane GaN wafer according to [D1] having a diameter of 20 mm or more, 45 mm or more, 95 mm or more, or 145 mm or more. [D4] A c-plane GaN wafer characterized in that the donor impurity present at the highest concentration is Ge, the conductivity type is n-type and it has a room-temperature resistivity of less than 0.03 Ω·cm, and when the (004)XRD rocking curve is measured every 1 mm along at least one line on one main surface over a length of 40 mm, the maximum value of the (004)XRD rocking curve FWHM between all measurement points is 20 arcsec or less. [D5] The c-plane GaN wafer according to [D4], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, 12 arcsec or less, or 10 arcsec or less. [D6]The donor impurity contained at the highest concentration is Ge, the conductivity type is n-type and it has a room temperature resistivity of less than 0.03 Ω·cm, and when the (004) XRD rocking curve is measured every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on one main surface, the maximum value of the (004) XRD rocking curve FWHM between all the measurement points on each line is 20 arcsec or less. A c-plane GaN wafer characterized by this. [D7]The c-plane GaN wafer according to [D6] above, where the average value of the (004) XRD rocking curve FWHM between all the measurement points on each of the above lines is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, 12 arcsec or less, or 10 arcsec or less. [D8]The variation width of the x-direction component of the off-cut angle on the line extending in the x-direction passing through the center of the front surface, and the variation width of the y-direction component of the off-cut angle on the line extending in the y-direction perpendicular to the x-direction passing through the center of the front surface are each 0.15 degrees or less, 0.1 degrees or less, or 0.08 degrees or less within a section of length 40 mm. The c-plane GaN wafer according to any one of [D1] to [D7] above. [D9]Having a room temperature resistivity of less than 0.02 Ω·cm, less than 0.015 Ω·cm, or less than 0.010 Ω·cm. The c-plane GaN wafer according to any one of [D1] to [D8] above. [D10] The carrier concentration is 1×10 18 cm -3 or more, 2×10 18 cm -3 or more, 3×10 18 cm -3 or more, or 4×10 18 cm [[ID=2I]] -3 or more. The c-plane GaN wafer according to any one of [D1] to [D8] above. [D11] The c-plane GaN wafer according to any one of [D1] to [D10] above, satisfying one or more conditions selected from the following (a) to (c) regarding the impurity concentration: (a) The Si concentration is 5×10 16 atoms / cm 3 or more; (b) The O concentration is 3×10 16atoms / cm 3 is as follows; (c) The H concentration is 1×10 17 atoms / cm 3 or less. [D12] The c-plane GaN wafer according to [D11], satisfying all of the above conditions (a) to (c) regarding the impurity concentration. [D13] The O concentration is 3×10 16 atoms / cm 3 or less, 2×10 16 atoms / cm 3 or less, or 1×10 16 atoms / cm 3 or less, the c-plane GaN wafer according to any one of [D1] to [D12] among those described. [D14] The Ge concentration is 1×10 18 atoms / cm 3 or more, and the Si concentration is 4×10 17 atoms / cm 3 or more, the c-plane GaN wafer according to any one of [D1] to [D13] among those described. [D15] The concentration of each impurity excluding Ge, Si, O, and H is 5×10 15 atoms / cm 3 or less, the c-plane GaN wafer according to any one of [D1] to [D14] among those described. [D16] The c-plane GaN wafer consisting of a GaN crystal grown by HVPE, according to any one of [D1] to [D15] among those described. [D17] A method for manufacturing an epitaxial wafer, comprising the step of preparing a c-plane GaN wafer according to any one of [D1] to [D16], and the step of epitaxially growing one or more nitride semiconductor layers on the prepared c-plane GaN wafer. [D18] An epitaxial wafer comprising a GaN wafer according to any one of [D1] to [D16] among those described, and one or more nitride semiconductor layers epitaxially grown on the GaN wafer. [D19] A method for manufacturing a nitride semiconductor device, comprising the steps of preparing a GaN wafer as described in any of [D1] to [D16] above, and epitaxially growing one or more nitride semiconductor layers on the prepared GaN wafer.

[0013] Embodiments of the present invention further include the following [E1] to [E20]. [E1] A c-plane GaN wafer characterized by having an n-type conductivity and a room-temperature resistivity of less than 0.03 Ω·cm, (004) an XRD rocking curve FWHM of less than 20 arcsec, and satisfying one or more conditions selected from (a) to (c) below regarding the impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [E2] Area 3cm 2 The c-plane GaN wafer according to [E1], having the above-mentioned main surface. [E3] A c-plane GaN wafer according to [E1] having a diameter of 20 mm or more, 45 mm or more, 95 mm or more, or 145 mm or more. [E4] A c-plane GaN wafer characterized by having an n-type conductivity and a room-temperature resistivity of less than 0.03 Ω·cm, measuring the (004)XRD locking curve every 1 mm along at least one line over a length of 40 mm on one main surface, with the maximum value of the (004)XRD locking curve FWHM between all measurement points being 20 arcsec or less, and satisfying one or more conditions selected from (a) to (c) below regarding the impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [E5] The c-plane GaN wafer according to [E4], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, or 12 arcsec or less. [E6] A c-plane GaN wafer characterized by having an n-type conductivity and a room-temperature resistivity of less than 0.03 Ω·cm, measuring the (004)XRD locking curve every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on one main surface, such that the maximum value of the (004)XRD locking curve FWHM between all measurement points on each line is 20 arcsec or less, and satisfying one or more conditions selected from (a) to (c) below regarding the impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [E7] The c-plane GaN wafer according to [E6], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points on each line is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, or 12 arcsec or less. [E8] A c-plane GaN wafer according to any one of [E1] to [E7], wherein the variation range of the x-component of the offcut angle on a line extending in the x-direction through the center of the front surface and the variation range of the y-component of the offcut angle on a line extending in the y-direction perpendicular to the x-direction through the center of the front surface are 0.15 degrees or less, 0.1 degrees or less, or 0.08 degrees or less, respectively, within a 40 mm length section. [E9] A c-plane GaN wafer according to any of [E1] to [E8], having a room-temperature resistivity of less than 0.02 Ω·cm, less than 0.015 Ω·cm, or less than 0.010 Ω·cm. [E10] A carrier concentration of 1 × 10 18 cm -3 or more, or 2 x 10 18 cm -3 The c-plane GaN wafer described in any of [E1] to [E8] above. [E11] A c-plane GaN wafer according to any of [E1] to [E10] above, satisfying all of the above conditions (a) to (c) with respect to the impurity concentration. [E12]O concentration is 3 × 10 16 atoms / cm 3 Below, 2 x 10 16 atoms / cm 3 The following or 1 x 10 16 atoms / cm 3 The c-plane GaN wafer described in any of the above [E1] to [E11], which is as follows: [E13] A c-plane GaN wafer according to any of [E1] to [E12] above, wherein the donor impurity present at the highest concentration is Si. [E14] The c-plane GaN wafer according to [E13], wherein the total concentration of donor impurities other than Si is 10% or less, 5% or less, or 1% or less of the Si concentration. [E15] The c-plane GaN wafer according to [E14], wherein the carrier concentration is 90% or more of the Si concentration. [E16] The concentration of each impurity except Si, O, and H is 5 × 10 15 atoms / cm 3 The c-plane GaN wafer described in any of the above [E1] to [E15] is as follows: [E17] A c-plane GaN wafer according to any of [E1] to [E16] above, comprising a GaN crystal grown with HVPE. [E18] A method for manufacturing an epitaxial wafer, comprising the steps of preparing a c-plane GaN wafer as described in any of [E1] to [E17] above, and epitaxially growing one or more nitride semiconductor layers on the prepared GaN wafer. [E19] An epitaxial wafer comprising a c-plane GaN wafer as described in any of [E1] to [E17] above, and one or more nitride semiconductor layers epitaxially grown on the c-plane GaN wafer. [E20] A method for manufacturing a nitride semiconductor device, comprising the steps of preparing a c-plane GaN wafer as described in any of [E1] to [E17] above, and epitaxially growing one or more nitride semiconductor layers on the prepared c-plane GaN wafer.

[0014] Embodiments of the present invention further include the following [F1] to [F25]. [F1] A c-plane GaN wafer characterized by having an n-type conductivity, a diameter of 45 mm or more, (004) an XRD rocking curve FWHM of less than 20 arcsec, less than 18 arcsec, less than 16 arcsec, less than 14 arcsec, or less than 12 arcsec, and satisfying one or more conditions selected from (a) to (c) below regarding the impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [F2] A c-plane GaN wafer according to [F1] having a diameter of 95 mm or more or 145 mm or more. [F3] The conductivity type is n-type, and when the (004)XRD locking curve is measured every 1 mm along at least one line on one main surface over a length of 40 mm, the total measurement A c-plane GaN wafer characterized in that the maximum value of the (004)XRD rocking curve FWHM between fixed points is 20 arcsec or less, and one or more conditions selected from (a) to (c) below regarding the impurity concentration are satisfied: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [F4] The c-plane GaN wafer according to [F3], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, 12 arcsec or less, or 10 arcsec or less. [F5] A c-plane GaN wafer characterized by having an n-type conductivity, measuring the (004)XRD locking curve every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on one main surface, such that the maximum value of the (004)XRD locking curve FWHM between all measurement points on each line is 20 arcsec or less, and satisfying one or more conditions selected from (a) to (c) below regarding impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [F6] The c-plane GaN wafer according to [F5], wherein the average value of the (004)XRD rocking curve FWHM between all measurement points on each line is 18 arcsec or less, 16 arcsec or less, 14 arcsec or less, 12 arcsec or less, or 10 arcsec or less. [F7] A c-plane GaN wafer according to any of [F1] to [F6], wherein the variation range of the x-direction component of the offcut angle on a line extending in the x-direction through the center of the front surface and the variation range of the y-direction component of the offcut angle on a line extending in the y-direction perpendicular to the x-direction through the center of the front surface are 0.15 degrees or less, 0.1 degrees or less, or 0.08 degrees or less, respectively, within a 40 mm length section. A c-plane GaN wafer according to any one of [F1] to [F7], satisfying all of the conditions (a) to (c) with respect to the impurity concentration. [F9] The Si concentration is 5×10 17 atoms / cm 3 A c-plane GaN wafer according to any one of [F1] to [F8], wherein the Si concentration is 5×10 atoms / cm or less. [F10] The concentration of each impurity excluding Si, O and H is 5×10 15 atoms / cm 3 A c-plane GaN wafer according to any one of [F1] to [F9], wherein the concentration of each impurity excluding Si, O and H is 5×10 atoms / cm or less. [F11] The O concentration is 3×10 16 atoms / cm 3 hereinafter, 2×10 16 atoms / cm 3 hereinafter or 1×10 16 atoms / cm 3 A c-plane GaN wafer according to any one of [F1] to [F10], wherein the O concentration is 3×10 atoms / cm or less, 2×10 atoms / cm or less, or 1×10 atoms / cm or less. [F12] A c-plane GaN wafer according to any one of [F1] to [F11], having at least one of a carrier concentration of less than 5×10 cm and a room temperature resistivity of 0.04 Ω·cm or more. 17 cm -3 A c-plane GaN wafer according to any one of [F1] to [F11], having at least one of a carrier concentration of less than 5×10 cm and a room temperature resistivity of 0.04 Ω·cm or more. [F13] A c-plane GaN wafer according to any one of [F1] to [F12], comprising a GaN crystal grown by HVPE. [F14] A method for manufacturing an epitaxial wafer, comprising the steps of preparing a c-plane GaN wafer according to any one of [F1] to [F13], and epitaxially growing one or more nitride semiconductor layers on the prepared c-plane GaN wafer. [F15] An epitaxial wafer comprising a c-plane GaN wafer according to any one of [F1] to [F13], and one or more nitride semiconductor layers epitaxially grown on the c-plane GaN wafer. [F16] A method for manufacturing a nitride semiconductor device, comprising the steps of preparing a c-plane GaN wafer according to any one of [F1] to [F13], and epitaxially growing one or more nitride semiconductor layers on the prepared c-plane GaN wafer. [F17] The F17 comprises the steps of preparing a c-plane GaN wafer as described in any of [F1] to [F13] above, and epitaxially growing a GaN layer with a thickness of 20 μm or more on the main surface on the Ga polar side of the prepared c-plane GaN wafer, wherein the GaN layer is provided with a high carrier concentration region or a carrier compensation region, and the lower limit of the carrier concentration in the high carrier concentration region is 1 × 10⁻⁶ 18 cm -3 The above region is the carrier compensation region, and the lower limit of the total concentration of compensated impurities is 2 × 10⁻⁶ 17 atoms / cm 3 The above-mentioned area is a method for manufacturing a double-layer GaN wafer. [F18] The manufacturing method according to [F17], wherein in the step of epitaxial growth, the GaN layer is grown with HVPE. [F19] The manufacturing method according to [F17] or [F18], wherein the thickness of the GaN layer is 500 μm or less. [F20] The GaN layer is provided with the high carrier concentration region, and the lower limit of the carrier concentration in the high carrier concentration region is 2 × 10 18 cm -3 The above is 3 x 10 18 cm -3 or more, or 4 x 10 18 cm -3 A manufacturing method according to any of the above regions [F17] to [F19]. [F21] The manufacturing method according to any one of [F17] to [F20], wherein the GaN layer is provided with the high carrier concentration region, and the high carrier concentration region is doped with Ge. [F22] The manufacturing method according to any one of [F17] to [F21], wherein the GaN layer is provided with the high carrier concentration region, and the high carrier concentration region is intentionally doped with Si. [F23] The GaN layer is provided with the carrier compensation region, and the lower limit of the total concentration of compensation impurities in the carrier compensation region is 5 × 10 17 atoms / cm 3 The above is 1 x 10 18 atoms / cm 3 The above is 2 x 10 18 atoms / cm 3or more, or 5 x 10 18 atoms / cm 3 A manufacturing method according to any of the above regions [F17] to [F19]. [F24] A manufacturing method according to any one of [F17] to [F23], further comprising the step of thinning the laminate obtained in the epitaxial growth step. [F25] A method for producing a bulk GaN crystal, comprising the steps of preparing a c-plane GaN wafer according to any of [F1] to [F13] above, and epitaxially growing GaN on the prepared c-plane GaN wafer.

[0015] Embodiments of the present invention further include the following [G1] to [G29]. [G1] The conductivity type is n-type, and the dislocation density on one of the main surfaces is 2 × 10 5 cm -2 Below, 1 x 10 5 cm -2 The following, or 5 x 10 4 cm -2 A c-plane GaN wafer characterized by the following: and satisfying one or more conditions selected from (a) to (c) below regarding impurity concentration: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [G2] A c-plane GaN wafer as described in [G1], satisfying all of the above conditions (a) to (c) with respect to the impurity concentration. [G3]O concentration is 3 × 10 16 atoms / cm 3 Below, 2 x 10 16 atoms / cm 3 The following or 1 x 10 16 atoms / cm 3 The c-plane GaN wafer described in [G1] or [G2] above, which is as follows: [G4] A c-plane GaN wafer according to any of [G1] to [G3], wherein the variation range of the x-component of the offcut angle on a line extending in the x-direction through the center of the front surface and the variation range of the y-component of the offcut angle on a line extending in the y-direction perpendicular to the x-direction through the center of the front surface are 0.15 degrees or less, 0.1 degrees or less, or 0.08 degrees or less, respectively, within a 40 mm length section. [G5] 5×10 17 cm -3 A c-plane G according to any of [G1] to [G4] having at least one of the following: a carrier concentration of less than 0.04 Ω·cm and a room-temperature resistivity of 0.04 Ω·cm or more. aN wafer. [G6] Si concentration is 5 × 10 17 atoms / cm 3 The c-plane GaN wafer described in any of [G1] to [G5] above, which is as follows: [G7] The concentration of each impurity except Si, O, and H is 5 × 10 15 atoms / cm 3 The c-plane GaN wafer described in [G6] above is as follows: [G8] A c-plane GaN wafer according to any of [G1] to [G4], having a room-temperature resistivity of less than 0.03 Ω·cm, less than 0.02 Ω·cm, less than 0.015 Ω·cm, or less than 0.010 Ω·cm. [G9] Carrier concentration is 1 × 10 18 cm -3 The above is 2 x 10 18 cm -3 The above is 3 x 10 18 cm -3 or more, or 4 x 10 18 cm -3 The above is a c-plane GaN wafer as described in any of [G1] to [G4] above. [G10] Ge concentration is 1 × 10 18 atoms / cm 3 Furthermore, the Si concentration is 4 × 10 17 atoms / cm 3 The c-plane GaN wafer described above in [G8] or [G9]. [G11] A c-plane GaN wafer according to any of [G8] to [G10] above, wherein the donor impurity present at the highest concentration is Ge. [G12] The concentration of each impurity except Ge, Si, O, and H is 5 × 10 15 atoms / cm 3 The c-plane GaN wafer described in [G10] or [G11] above, which is as follows: [G13] A c-plane GaN wafer according to either [G8] or [G9], wherein the donor impurity present at the highest concentration is Si. [G14] The c-plane GaN wafer according to [G13], wherein the total concentration of donor impurities excluding Si is 10% or less, 5% or less, or 1% or less of the Si concentration. [G15] The c-plane GaN wafer according to [G14], wherein the carrier concentration is 90% or more of the Si concentration. [G16] The concentration of each impurity except Si, O, and H is 5 × 10 15 atoms / cm 3 The c-plane GaN wafer described in any of [G13] to [G15] above, which is as follows: [G17] A c-plane GaN wafer according to any of [G1] to [G16], comprising a GaN crystal grown with HVPE. [G18] A method for manufacturing an epitaxial wafer, comprising the steps of preparing a c-plane GaN wafer as described in any of [G1] to [G17] above, and epitaxially growing one or more nitride semiconductor layers on the prepared c-plane GaN wafer. [G19] An epitaxial wafer comprising a c-plane GaN wafer as described in any of [G1] to [G17] above, and one or more nitride semiconductor layers epitaxially grown on the c-plane GaN wafer. [G20] A method for manufacturing a nitride semiconductor device, comprising the steps of preparing a c-plane GaN wafer as described in any of [G1] to [G17] above, and epitaxially growing one or more nitride semiconductor layers on the prepared c-plane GaN wafer. [G21] The method comprises the steps of preparing a c-plane GaN wafer as described in any of [G1] to [G7] above, and epitaxially growing a GaN layer with a thickness of 20 μm or more on the main surface on the Ga polar side of the prepared c-plane GaN wafer, wherein the GaN layer is provided with a high carrier concentration region or a carrier compensation region, and the lower limit of the carrier concentration in the high carrier concentration region is 1 × 10⁻⁶ 18 cm -3 The above region is the carrier compensation region, and the lower limit of the total concentration of compensated impurities is 2 × 10⁻⁶ 17 atoms / cm 3 The above-mentioned area is a method for manufacturing a double-layer GaN wafer. [G22] The manufacturing method according to [G21], wherein in the step of epitaxial growth, the GaN layer is grown with HVPE. [G23] The manufacturing method according to [G21] or [G22], wherein the thickness of the GaN layer is 500 μm or less. [G24] The GaN layer is provided with the high carrier concentration region, and the lower limit of the carrier concentration in the high carrier concentration region is 2 × 10 18 cm -3 The above is 3 x 10 18 cm -3 or more, or 4 x 10 18 cm -3 The above areas are those described in any of the above [G21] to [G23]. Manufacturing method for the product. [G25] The manufacturing method according to any one of [G21] to [G24], wherein the GaN layer is provided with the high carrier concentration region, and the high carrier concentration region is doped with Ge. [G26] The manufacturing method according to any one of [G21] to [G25], wherein the GaN layer is provided with the high carrier concentration region, and the high carrier concentration region is intentionally doped with Si. [G27] The GaN layer is provided with the carrier compensation region, and the lower limit of the total concentration of compensation impurities in the carrier compensation region is 5 × 10 17 atoms / cm 3 The above is 1 x 10 18 atoms / cm 3 The above is 2 x 10 18 atoms / cm3 or more, or 5 x 10 18 atoms / cm 3 A manufacturing method according to any of the above regions [G21] to [G23]. [G28] A manufacturing method according to any one of [G21] to [G27], further comprising the step of thinning the laminate obtained in the epitaxial growth step. [G29] A method for producing a bulk GaN crystal, comprising the steps of preparing a c-plane GaN wafer according to any of [G1] to [G7] above, and epitaxially growing GaN on the prepared c-plane GaN wafer.

[0016] Embodiments of the present invention further include the following [H1] to [H32]. [H1] An n-type GaN crystal having two principal planes facing opposite directions, one of which is Ga polar and (0001) has an inclination with respect to the crystal plane of 0 degrees or more and 10 degrees or less, characterized in that an anomalous X-ray transmission image of at least one 10 mm × 10 mm square area can be obtained, and that one or more conditions selected from (a) to (c) below regarding the impurity concentration are satisfied: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [H2] An n-type GaN crystal having two principal planes facing opposite directions, one of which is Ga polar and (0001) has an inclination with respect to the crystal plane of 0 degrees or more and 10 degrees or less, characterized in that an anomalous X-ray transmission image of at least one 15 mm × 15 mm square area can be obtained, and that one or more conditions selected from (a) to (c) below regarding the impurity concentration are satisfied: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [H3] An n-type GaN crystal having two principal planes facing opposite directions, one of which is Ga polar and (0001) tilted to the crystal plane at 0 degrees or more and 10 degrees or less, characterized in that an anomalous X-ray transmission image of at least one 20 mm × 20 mm square area can be obtained, and that one or more conditions selected from (a) to (c) below regarding the impurity concentration are satisfied: (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all; (b) O concentration is 3 × 10 16 atoms / cm 3 The following: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: [H4] An n-type GaN crystal according to any of the above [H1] to [H3], satisfying all of the above conditions (a) to (c) with respect to the impurity concentration. [H5]O concentration is 3 × 10 16 atoms / cm 3 Below, 2 x 10 16 atoms / cm 3 The following or 1 x 10 16 atoms / cm 3 The following is an n-type GaN crystal as described in any of [H1] to [H4] above. [H6] 5×10 17 cm -3 An n-type GaN crystal according to any one of [H1] to [H5], having at least one of the following: a carrier concentration of less than 0.04 Ω·cm and a room-temperature resistivity of 0.04 Ω·cm or more. [H7]Si concentration is 5 × 10 17 atoms / cm 3 The following is an n-type GaN crystal as described in any of [H1] to [H6] above. [H8] The concentration of each impurity except Si, O, and H is 5 × 10 15 atoms / cm 3 The n-type GaN crystal described in [H7] above is as follows: [H9] An n-type GaN crystal according to any of [H1] to [H5] above, having a room-temperature resistivity of less than 0.03 Ω·cm, less than 0.02 Ω·cm, less than 0.015 Ω·cm, or less than 0.010 Ω·cm. [H10] Carrier concentration is 1 × 10 18 cm -3 The above is 2 x 10 18 cm -3 The above is 3 x 10 18 cm -3 or more, or 4 x 10 18 cm -3 The above is an n-type GaN crystal as described in any of [H1] to [H5] above. [H11] Ge concentration is 1 × 10 18 atoms / cm 3 Furthermore, the Si concentration is 4 × 10 17 atoms / cm 3 The above is the n-type GaN crystal described in [H9] or [H10]. [H12] An n-type GaN crystal according to any of [H9] to [H11] above, wherein the donor impurity present at the highest concentration is Ge. [H13] The concentration of each impurity except Ge, Si, O, and H is 5 × 10 15 atoms / cm 3 The n-type GaN crystal described in [H11] or [H12] above, which is as follows: [H14] The n-type GaN crystal according to [H9] or [H10], wherein the donor impurity present at the highest concentration is Si. [H15] The n-type GaN crystal according to [H14], wherein the total concentration of donor impurities excluding Si is 10% or less, 5% or less, or 1% or less of the Si concentration. [H16] The n-type GaN crystal according to [H15], wherein the carrier concentration is 90% or more of the Si concentration. [H17] The concentration of each impurity except Si, O, and H is 5 × 10 15 atoms / cm 3The following is an n-type GaN crystal as described in any of [H14] to [H16] above. [H18] An n-type GaN crystal according to any of [H1] to [H17] above, comprising a GaN crystal grown with HVPE. [H19] A GaN wafer, an n-type GaN crystal as described in any of [H1] to [H18] above. [H20] The n-type GaN crystal according to [H19], wherein the variation range of the x-component of the offcut angle on a line extending in the x-direction through the center of the front surface and the variation range of the y-component of the offcut angle on a line extending in the y-direction perpendicular to the x-direction through the center of the front surface are 0.15 degrees or less, 0.1 degrees or less, or 0.08 degrees or less, respectively, within a 40 mm length section. [H21] A method for manufacturing an epitaxial wafer, comprising the steps of preparing an n-type GaN crystal as described in [H19] or [H20] above, and epitaxially growing one or more nitride semiconductor layers on the prepared n-type GaN crystal. [H22] An epitaxial wafer comprising an n-type GaN crystal as described in [H19] or [H20] above, and one or more nitride semiconductor layers epitaxially grown on the n-type GaN crystal. [H23] A method for manufacturing a nitride semiconductor device, comprising the steps of preparing an n-type GaN crystal as described in [H19] or [H20] above, and epitaxially growing one or more nitride semiconductor layers on the prepared n-type GaN crystal. [H24] The procedure comprises the steps of preparing a GaN wafer which is an n-type GaN crystal as described in any of [H1] to [H8] above, and epitaxially growing a GaN layer with a thickness of 20 μm or more on the main surface on the Ga polar side of the prepared GaN wafer, wherein the GaN layer is provided with a high carrier concentration region or a carrier compensation region, and the lower limit of the carrier concentration in the high carrier concentration region is 1 × 10⁻⁶ 18 cm -3 The above region is the carrier compensation region, and the lower limit of the total concentration of compensated impurities is 2 × 10⁻⁶ 17 atoms / cm 3 The above-mentioned area is a method for manufacturing a double-layer GaN wafer. [H25] The manufacturing method according to [H24], wherein in the step of epitaxial growth, the GaN layer is grown with HVPE. [H26] The manufacturing method according to [H24] or [H25], wherein the thickness of the GaN layer is 500 μm or less. [H27] The GaN layer is provided with the high carrier concentration region, and the lower limit of the carrier concentration in the high carrier concentration region is 2 × 10 18 cm -3 The above is 3 x 10 18 cm -3 or more, or 4 x 10 18 cm -3 A manufacturing method described in any of the above [H24] to [H26], which falls within the above region. [H28] The manufacturing method according to any one of [H24] to [H27], wherein the GaN layer is provided with the high carrier concentration region, and the high carrier concentration region is doped with Ge. [H29] The manufacturing method according to any one of [H24] to [H28], wherein the GaN layer is provided with the high carrier concentration region, and the high carrier concentration region is intentionally doped with Si. [H30] The GaN layer is provided with the carrier compensation region, and the lower limit of the total concentration of compensation impurities in the carrier compensation region is 5 × 10 17 atoms / cm 3 The above is 1 x 10 18 atoms / cm 3 The above is 2 x 10 18 atoms / cm 3 or more, or 5 x 10 18 atoms / cm 3 The manufacturing method described in [H24] above, relating to the above area. [H31] The manufacturing method according to any one of [H24] to [H30], further comprising the step of thinning the laminate obtained in the epitaxial growth step. [H32] A method for producing a bulk GaN crystal, comprising the steps of preparing a GaN wafer which is an n-type GaN crystal as described in any of [H1] to [H8] above, and epitaxially growing GaN on the prepared GaN wafer. [Effects of the Invention]

[0017] According to one preferred embodiment, a GaN crystal grown in HVPE is provided, having a (004)XRD rocking curve full width at half maximum of 20 arcsec or less. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a perspective view showing an n-type GaN crystal according to an embodiment. [Figure 2] Figure 2 is a plan view showing an n-type GaN crystal according to the embodiment. [Figure 3] Figure 3 is a plan view showing an n-type GaN crystal according to the embodiment. [Figure 4] Figure 4 is a perspective view showing a GaN wafer according to an embodiment. [Figure 5] Figure 5 is a cross-sectional view showing a GaN wafer according to an embodiment. [Figure 6] Figure 6 is a plan view showing a GaN wafer according to an embodiment. [Figure 7] Figure 7 is a plan view showing a GaN wafer according to an embodiment. [Figure 8] Figure 8 is a perspective view showing an example of a bilayer GaN wafer. [Figure 9] Figure 9 is a schematic diagram showing the basic configuration of an HVPE device. [Figure 10] Figure 10(a) is a cross-sectional view showing the seed and edge cover set on the susceptor, and Figure 10(b) is a cross-sectional view showing the state in which a GaN crystal has grown on the seed shown in Figure 10(a). [Figure 11] Figure 11 is a cross-sectional view showing the seed and edge cover set on the susceptor. [Figure 12] Figure 12 is a diagram showing the basic configuration of a crystal growth apparatus used for growing GaN crystals by the amonothermal method. [Figure 13]Figure 13 is a cross-sectional view showing a GaN crystal layer grown on the N-polarity surface of the first c-plane GaN wafer using the amonothermal method. [Figure 14] Figure 14 shows the configuration of the sample prepared in Experiment 6 and the observation direction of the three-photon excitation image in Experiment 6. [Figure 15] Figure 15 is a diagram illustrating that the offcut angle of a c-plane GaN wafer can be decomposed into two components perpendicular to each other. [Figure 16] Figure 16 shows a transmission X-ray topography image of a 20 mm × 20 mm square area obtained in Experiment 7 from a c-plane GaN wafer (Sample E-7) made of GaN crystals grown with HVPE (photograph used as a substitute for diagram). [Modes for carrying out the invention]

[0019] In GaN crystals, the (0001) and (000-1) crystal planes are collectively called c-planes, the {10-10} crystal plane is called the m-plane, and the {11-20} crystal plane is called the a-plane. The crystal axis perpendicular to the c-plane is called the c-axis, the crystal axis perpendicular to the m-plane is called the m-axis, and the crystal axis perpendicular to the a-plane is called the a-axis. In this specification, when referring to crystal axes, crystal planes, crystal orientations, etc., it means the crystal axes, crystal planes, crystal orientations, etc. of a GaN crystal unless otherwise specified. The Miller indices (hkil) of a hexagonal crystal are sometimes written with three digits, (hkl), because the relationship h+k=-i holds. For example, (0004) is written with three digits as (004). The present invention will be described below with reference to the drawings as appropriate, in accordance with the embodiments.

[0020] 1.n-type GaN crystal 1.1. Form and Dimensions The crystal 10 shown in Figure 1 is an example of an n-type GaN crystal according to the embodiment. The crystal 10 has two principal surfaces (large-area surfaces) facing opposite directions, namely a first principal surface 11 and a second principal surface 12. One of the first principal surface 11 and the second principal surface 12 is Ga polar, and the other is N polar. Preferably, the first principal surface 11 and the second principal surface 12 are parallel to each other.

[0021] When the first principal surface 11 is Ga polar and the second principal surface 12 is N polar, the inclination of the first principal surface 11 with respect to the (0001) crystal plane is 0 degrees or more and 10 degrees or less. This inclination may be 0.2 degrees or more, and may also be less than 5 degrees, less than 2.5 degrees, less than 2 degrees, less than 1.5 degrees, less than 1 degree, or less than 0.5 degrees. (0001) The inclination of the first principal surface 11 with respect to the crystal plane is, in other words, the angle between the

[0001] direction of the crystal 10 and the normal vector of the first principal surface 11. When the first principal surface 11 is N polar and the second principal surface 12 is Ga polar, the inclination of the first principal surface 11 with respect to the (000-1) crystal plane is 0 degrees or more and 10 degrees or less. This inclination may be less than 5 degrees, less than 2.5 degrees, less than 2 degrees, less than 1.5 degrees, less than 1 degree, or less than 0.5 degrees.

[0022] The area of ​​the first main surface 11 and the second main surface 12 is 3 cm² each. 2 It is preferable that the above conditions are met. Diameter D of crystal 10 C These are typically 20mm or more, and may be 45mm or more, 95mm or more, or 145mm or more, typically 25-27mm (about 1 inch), 50-55mm (about 2 inches), 100-105mm (about 4 inches), 150-155mm (about 6 inches), etc. The shapes of the first principal surface 11 and the second principal surface 12 are not limited to circles, but can be changed to squares, rectangles or other quadrilaterals, regular hexagons or other polygons, regular octagons or other polygons, or any other arbitrary shape.

[0023] The crystal 10 may be an ingot or a wafer, or it may be an epitaxial layer grown on another GaN crystal, or a film bonded to a support substrate. In other words, the crystal 10 may or may not be self-supporting. When crystal 10 is an ingot, its thickness t C The thickness is preferably 1.5 mm or more, more preferably 2 mm or more, and even more preferably 3 mm or more. When crystal 10 is a wafer, its thickness t C These can be 200 μm or more but less than 500 μm, 500 μm or more but less than 750 μm, 750 μm or more but less than 1 mm, 1 mm or more but less than 2 mm, etc. When crystal 10 is an epitaxial layer grown on another GaN crystal or a film bonded to a support substrate, its thickness t C These can be 5 μm or more but less than 50 μm, 50 μm or more but less than 100 μm, 100 μm or more but less than 150 μm, 150 μm or more but 250 μm or less, etc.

[0024] 1.2. Properties Crystal 10 consists of GaN grown using HVPE. GaN grown in a typical HVPE apparatus equipped with a quartz reactor usually satisfies one or more of the following conditions regarding impurity concentration, selected from (a) to (c): (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all. (b) O concentration is 3 × 10 16 atoms / cm 3 The following applies: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: Crystal 10 may satisfy all of the above conditions (a) to (c).

[0025] Crystal 10 is an n-type semiconductor containing donor impurities. In one example, though not limited to, the room-temperature resistivity (specific resistivity at room temperature) of crystal 10 is less than 0.03 Ω·cm, preferably less than 0.02 Ω·cm, more preferably less than 0.015 Ω·cm, and even more preferably less than 0.010 Ω·cm. The donor impurities that crystal 10 may contain include Group 14 elements such as Si (silicon) and Ge (germanium), and Group 16 elements such as O (oxygen) and S (sulfur). The donor impurity present in crystal 10 at the highest concentration is preferably Si or Ge.

[0026] For example, by making the total concentration of donor impurities excluding Si sufficiently lower than the Si concentration, the carrier concentration of crystal 10 can be controlled by adjusting the Si concentration. To achieve this, it is preferable to set the total concentration of donor impurities excluding Si to 10% or less, more preferably 5% or less, or even 1% or less of the Si concentration. When the total concentration of donor impurities excluding Si is 10% or less of the Si concentration, the carrier concentration of crystal 10 may be 90% or more of the Si concentration. When adding Ge to crystal 10, it is effective in reducing Ge concentration variations by making the molar ratio of H2 in the carrier gas used during growth relatively high, but consequently the Si concentration of crystal 10 will be 10 17 atoms / cm 3 It could be more than one unit.

[0027] To sufficiently reduce the resistivity of crystal 10, the carrier concentration of crystal 10 at room temperature should be 1 × 10⁻⁶. 18 cm -3 Furthermore, 2 x 10 18 cm -3 It is preferable that the carrier concentration be 3 × 10⁻⁶. 18 cm -3 In addition, 4x10 18 cm -3 The above may also be used. From the viewpoint of electrical properties, there is no particular upper limit to the carrier concentration, but in order to avoid worsening the productivity of crystal 10, the carrier concentration should be 1 × 10 19 cm -3 It can be set to the following: 8x10 18 cm -3 Below, and furthermore, 5 x 10 18 cm -3 The following settings may also be used, as high concentrations of doping increase the frequency of abnormal growth.

[0028] 1.3. Crystal Quality The quality of crystal 10 can be evaluated using the (004)XRD rocking curve FWHM, which is measured by an ω scan using CuKα1 emission. The better the crystal quality, the narrower the (004)XRD rocking curve FWHM. (004) In XRD rocking curve measurement, the X-ray tube was operated at a voltage of 45kV and a current of 40mA, and a monochromatic CuK was obtained using a Ge(440)4 crystal symmetric monochromator. α The X-rays are incident on the first principal plane 11. The direction from which the X-rays are incident on the first principal plane 11 is not particularly limited; for example, the incident plane of the X-rays may be perpendicular to the a-axis.

[0029] The X-ray beam size is calculated by taking the angle of incidence (the angle between the reflecting surface and the X-ray) as 90°. In other words, when X-rays are incident perpendicularly to the (004) surface, which is the reflective surface, the size of the irradiation area on the first main surface 11 is set to 5 mm in the direction parallel to the ω axis and 1 mm in the direction perpendicular to the ω axis. The ω axis is the rotation axis of the sample in rocking curve measurement. When the X-ray beam size is set in this way, the (004)XRD rocking curve measurement of GaN shows that ω is approximately 36.5°, so the size of the irradiation area on the first main surface 11 is approximately 1.7 × 5 mm. 2 That is the case. The (004)XRD locking curve FWHM measured in this manner may be less than 20 arcsec, even less than 18 arcsec, even less than 16 arcsec, even less than 14 arcsec, and even less than 12 arcsec.

[0030] When the diameter of the first main surface 11 exceeds 40 mm, as shown in Figure 2, by performing an ω scan at 1 mm intervals along a line L on the first main surface 11 over a length of 40 mm under the above conditions, 40 measurement points P are arranged at 1 mm intervals along the line L. M (004) An XRD locking curve can be obtained at each measurement point P. MIn the ω scan, the ω axis is set perpendicular to line L. That is, the X-rays are incident on the crystal 10 so that the X-ray incident plane is parallel to line L.

[0031] In a preferred example, when such measurement is performed along at least one line on the first main surface 11, the maximum value of the (004)XRD rocking curve FWHM between all measurement points may be 20 arcsec or less. The average value of the (004)XRD locking curve FWHM across all measurement points may be 18 arcsec or less, further 16 arcsec or less, further 14 arcsec or less, further 12 arcsec or less, and further 10 arcsec or less.

[0032] When the diameter of the first main surface 11 exceeds 40 mm, an ω scan can be performed on the first main surface 11 at 1 mm intervals over a length of 40 mm along two mutually perpendicular lines L1 and L2, as illustrated in Figure 3, under the above conditions. This allows for obtaining (004)XRD rocking curves at 40 measurement points arranged at 1 mm intervals on each line L1 and L2. In this case, the ω axis is set perpendicular to line L1 for each measurement point on line L1, and the ω axis is set perpendicular to line L2 for each measurement point on line L2.

[0033] In a preferred example, when such measurements are taken along at least two mutually perpendicular lines on the first main surface 11, the maximum value of the (004)XRD rocking curve FWHM between all measurement points on each line may be 20 arcsec or less. That is, the maximum value between 40 measurement points on one of the two lines and the maximum value between 40 measurement points on the other line may both be 20 arcsec or less. The average value of the (004)XRD locking curve FWHM between all measurement points on each line may be 18 arcsec or less, further 16 arcsec or less, further 14 arcsec or less, further 12 arcsec or less, and further 10 arcsec or less.

[0034] From crystal 10, an anomalous X-ray transmission image of at least one 10 mm × 10 mm square area can be obtained using the Lang method of X-ray topography. In the Lang method, the X-ray source is placed on one main surface side of the plate-shaped test specimen, and the X-ray detector is placed on the other main surface side. Anomalous X-ray transmission, also known as the Bormann effect, is a phenomenon in which X-rays penetrate crystals of a thickness that would normally be impassable due to absorption. For example, if a transmission image is obtained from a 344 μm thick GaN crystal using X-ray topography with a MoKα (wavelength 0.71073 Å) X-ray source, it is an anomalous transmission image. This is because the absorption coefficient μ of GaN is 290.40 cm² when the X-ray source is MoKα. -1 Therefore, when the wafer thickness t is 344 μm, μ·t = 10.0, and if there is no abnormal transmission, a transmission image cannot be obtained under the condition μ·t ≥ 10. Since anomalous transmission patterns are not observed when the crystal integrity is low, GaN crystals that exhibit anomalous transmission patterns in X-ray topography can be considered to be of good quality. Preferably, an anomalous X-ray transmission image of at least one 15 mm × 15 mm square area is obtained from the crystal 10, and more preferably, an anomalous X-ray transmission image of at least one 20 mm × 20 mm square area is obtained.

[0035] 2. GaN wafers In this specification, a GaN wafer with an offcut of 10 degrees or less from the (0001) crystal plane or the (000-1) crystal plane is referred to as a c-plane GaN wafer.

[0036] 2.1. Form and Dimensions The wafer 20 shown in Figure 4 is an example of a GaN wafer according to the embodiment. Wafer 20 is a c-plane GaN wafer, and its two main surfaces (large-area surfaces) facing opposite directions, namely the first main surface 21 and the second main surface 22, have one Ga polarity and the other N polarity. The main surface on the Ga polarity side is sometimes called the Ga polarity surface, and the main surface on the N polarity side is sometimes called the N polarity surface. When the first principal surface 21 is Ga polar, the inclination of the first principal surface 21 with respect to the (0001) crystal plane is 0 degrees or more and 10 degrees or less. This inclination may be 0.2 degrees or more, and may also be less than 5 degrees, less than 2.5 degrees, less than 1.5 degrees, less than 1 degree, or less than 0.5 degrees. When the first principal surface 21 is N polar, the inclination of the first principal surface 21 with respect to the (000-1) crystal plane is 0 degrees or more and 10 degrees or less. This inclination may be less than 5 degrees, less than 2.5 degrees, less than 1.5 degrees, less than 1 degree, or less than 0.5 degrees. The first main surface 21 and the second main surface 22 are preferably parallel to each other.

[0037] Diameter D of wafer 20 W These are typically 45mm or longer, and may be 95mm or longer, or even 145mm or longer, typically 50-55mm (approximately 2 inches), 100-105mm (approximately 4 inches), 150-155mm (approximately 6 inches), etc. Wafer thickness t W is diameter D W Accordingly, the wafer 20 is designed to be self-supporting and handleable. For example, the diameter D of the wafer 20 W When it is about 2 inches, the thickness t W The diameter of the wafer 20 is preferably 250 to 500 μm, more preferably 300 to 450 μm. W When it is about 4 inches, the thickness t W The diameter D of the wafer 20 is preferably 400 to 800 μm, more preferably 500 to 650 μm. W When it is about 6 inches, the thickness t W The particle size is preferably 500 to 850 μm, and more preferably 600 to 750 μm.

[0038] The off-cut angle of the wafer 20 can be decomposed into two components that are mutually orthogonal within the first main surface 21: an x-direction component and a y-direction component. Referring to Figure 15, when the normal direction of the first main surface 21 is the z-direction and the vector parallel to the c-axis is vector Vc, the off-cut angle of the wafer 20 is equal to the inclination θ of vector Vc from the z-axis. This vector Vc is the x-direction component of vector Vc xAnd the vector Vc is the component in the y direction. y It can be decomposed into two parts. The orthogonal projection of vector Vc on the xz plane is vector Vc x Therefore, the orthogonal projection of vector Vc on the yz plane is vector Vc y That is the case. When vector Vc is decomposed in this way, vector Vc x The inclination from the z-axis is the x-component θ of the off-cut angle θ. x And the vector Vc y The inclination from the z-axis is the y-axis component of the off-cut angle θ θ y That is the case.

[0039] In wafer 20, the variation range of the x-direction component of the offcut angle on a line extending in the x-direction through the center of the first main surface 21, and on a line extending in the y-direction through the center of the first main surface 21 The variation range of the y-direction component of the off-cut angle may be 0.15 degrees or less, preferably 0.1 degrees or less, and more preferably 0.08 degrees or less, within a 40 mm length interval. In this evaluation, portions less than 5 mm from the outer edge when the wafer 20 is viewed from above may be excluded. The range of variation is the difference between the maximum and minimum values. For example, a range of variation of 0.15 degrees or less means that the variation from the median is within ±0.075 degrees. The x-direction may be parallel to one of the a-planes, in which case the y-direction is parallel to one of the m-planes.

[0040] The first main surface 21 of the wafer 20 is the main surface, or "front surface," intended for use in epitaxial growth of nitride semiconductors when manufacturing nitride semiconductor devices using the wafer 20 as a substrate. The first main surface 21 is mirror-finished, and its root mean square (RMS) roughness, as measured by AFM, is preferably less than 2 nm in a measurement range of 2 μm × 2 μm, and may be less than 1 nm or less than 0.5 nm. The second main surface 22 is the "back surface" and may be mirror-finished or matte-finished.

[0041] The edges of wafer 20 may be chamfered. The wafer 20 may be marked with various markings as needed, such as orientation flats or notches to indicate the crystal orientation, and index flats to facilitate identification of the front and back surfaces. The main surface of the wafer 20 is circular, but it is not limited to a circular shape; it can be changed to a square, rectangle, hexagon, octagon, or any other arbitrary shape.

[0042] 2.2. Properties Wafer 20 consists of a GaN crystal grown with HVPE. GaN grown in a typical HVPE apparatus equipped with a quartz reactor usually satisfies one or more of the following conditions regarding impurity concentration, selected from (a) to (c): (a) Si concentration is 5 × 10 16 atoms / cm 3 That's all. (b) O concentration is 3 × 10 16 atoms / cm 3 The following applies: (c) H concentration is 1 × 10 17 atoms / cm 3 The following applies: Wafer 20 may satisfy all of the above conditions (a) to (c).

[0043] For reference, GaN grown with HVPE has an infrared absorption spectrum of 3150-3250 cm⁻¹. -1 The absorption coefficient is 0.5 cm within this range. -1 The absence of absorption peaks exceeding this value distinguishes GaN grown by the amonothermal method from GaN grown by the amonothermal method. This infrared absorption peak is related to the gallium vacancies that are present in high concentrations in GaN grown by the amonothermal method [S. Suihkonen, et al., Applied Physics Letters 108, 202105 (2016); W. Jiang, et al., Applied Physics Express 10, 075506 (2017)].

[0044] Intentional doping of wafer 20 can be performed as needed. Therefore, in one example, wafer 20 can be formed solely from unintentionally doped GaN (UID-GaN). Since unintentional donor impurity doping and the formation of nitrogen vacancies inevitably occur, the conductivity type of UID-GaN is n-type. In UID-GaN, the Si concentration is 5 × 10 17 atoms / cm 3 Below, the oxygen concentration is 3 × 10 16 atoms / cm 3 Below, 2 x 10 16 atoms / cm 3 The following or 1 x 10 16 atoms / cm 3 Below, the concentrations of each impurity, excluding Si, O, and H, are 5 × 10 15 atoms / cm 3 The following are possible: In UID-GaN, the carrier concentration is 5 × 10 17 cm -3 It may be less than 0.04 Ω·cm, and the room-temperature resistivity may be 0.04 Ω·cm or more.

[0045] For example, intentional doping can reduce the room-temperature resistivity of wafer 20 to less than 0.03 Ω·cm, further to less than 0.02 Ω·cm, further to less than 0.015 Ω·cm, and further to less than 0.010 Ω·cm. To sufficiently reduce the resistivity, the carrier concentration of wafer 20 at room temperature should be 1 × 10⁻⁶ 18 cm -3 Furthermore, 2 x 10 18 cm -3 It is preferable that the carrier concentration be 3 × 10⁻⁶. 18 cm -3 In addition, 4x10 18 cm -3 The above may also be used. From the viewpoint of electrical characteristics, there is no particular upper limit to the carrier concentration, but in order to avoid degrading the productivity of wafer 20, the carrier concentration should be 1 × 10⁻⁶. 19 cm -3 It can be set to the following: 8x10 18 cm -3Below, and furthermore, 5 x 10 18 cm -3 The following settings may also be used, as high concentrations of doping increase the frequency of abnormal growth in GaN crystals.

[0046] The dopant added to wafer 20 to reduce resistivity is preferably a donor impurity, and therefore, the conductivity type of wafer 20 when its resistance is reduced by doping is preferably n-type. This is because donor impurities generally exhibit a higher activation rate than acceptor impurities. The activation rate is the ratio of the carrier concentration to the dopant concentration in doped GaN. Elements that can act as donor impurities include Group 14 elements such as Si (silicon) and Ge (germanium), and Group 16 elements such as O (oxygen) and S (sulfur).

[0047] When doped with donor impurities, the donor impurities present in wafer 20 at the highest concentration are preferably Si or Ge, mainly for the following two reasons. Firstly, Si and Ge, along with O, are donor impurities with high activation rates. Secondly, while facet growth is necessary to obtain O-doped GaN, Si or Ge-doped GaN can be obtained by c-plane growth.

[0048] Faceted growth is a technique for growing a

[0001] -oriented GaN film such that the growth surface is full of pits. In contrast, growing such a GaN film so that the growth surface is flat is called c-plane growth. Because threading dislocations tend to accumulate at the bottom of pits, the distribution of threading dislocations becomes non-uniform in GaN films formed by facet growth. Manufacturers of nitride semiconductor devices often do not prefer c-plane GaN wafers cut from such GaN films. (004) GaN crystals with an XRD rocking curve FWHM of 20 arcsec or less have a low density of threading dislocations, so when grown on the c-plane under appropriate conditions, the grown surface can be flat, hillock-free, and have extremely good morphology. Si and Ge can be considered donor impurities that can take advantage of this characteristic.

[0049] In a preferred example, by making the total concentration of donor impurities excluding Si sufficiently lower than the Si concentration, the carrier concentration of wafer 20 can be controlled by adjusting the Si concentration. To achieve this, it is preferable that the total concentration of donor impurities excluding Si be 10% or less, more preferably 5% or less, and even more preferably 1% or less of the Si concentration. When the total concentration of donor impurities excluding Si is 10% or less of the Si concentration, the carrier concentration of wafer 20 may be 90% or more of the Si concentration. When Ge is intentionally added to wafer 20, it is effective in reducing Ge concentration unevenness by making the molar ratio of H2 in the carrier gas used during growth relatively high, but consequently the Si concentration of wafer 20 is 10, even when Si is not intentionally added. 17 atoms / cm 3 It could be more than one unit.

[0050] In one embodiment, only a portion of the wafer 20 may be intentionally doped. In the example shown in Figure 5, wafer 20 is made of intentionally doped GaN (ID-GaN). The first region R1, made of (nally doped GaN), is located on the Ga polarity first main surface 21 side, and the second region R2, made of UID-GaN, is located on the N polarity second main surface 22 side. The first region R1 has a higher carrier concentration and lower resistivity than the second region R2. An intermediate region (not shown) having a carrier concentration intermediate between the first region R1 and the second region R2 may be provided. In this intermediate region, the carrier concentration may increase continuously or stepwise from the N polar side to the Ga polar side.

[0051] The thickness t1 of the first region R1 can be, for example, 5 μm or more and less than 50 μm, 50 μm or more and less than 100 μm, 100 μm or more and less than 150 μm, or 150 μm or more and 250 μm or less. A regrowth interface may exist between the first region R1 and the second region R2. That is, the wafer 20 shown in Figure 5 may be manufactured by first completing a c-plane GaN wafer made of UID-GaN, and then growing an ID-GaN layer on the Ga polarity side main surface of the c-plane GaN wafer using HVPE.

[0052] In the wafer 20 shown in Figure 5, the room-temperature resistivity in the first region R1 may be less than 0.03 Ω·cm, less than 0.02 Ω·cm, less than 0.015 Ω·cm, or less than 0.010 Ω·cm. The carrier concentration at room temperature in the first region R1 is preferably 1 × 10⁻⁶. 18 cm -3 The above is fua2×10 18 cm -3 That's all. 3 × 10 18 cm -3 In addition, 4x10 18 cm -3 That's fine too. The intentional dopant contained in the first region R1 is preferably a donor impurity, and the donor impurity present in the first region R1 at the highest concentration is Si or Ge. In a preferred example, the total concentration of donor impurities excluding Si in the first region R1 can be 10% or less, more precisely 5% or less, or even 1% or less of the Si concentration. In the second region R2, the Si concentration is 5 × 10 17 atoms / cm 3 Below, the oxygen concentration is 3 × 10 16 atoms / cm 3 Below, 2 x 10 16 atoms / cm 3 The following or 1 x 10 16 atoms / cm 3 Below, the concentrations of each impurity, excluding Si, O, and H, are 5 × 10 15 atoms / cm 3 The following are possible: In the second region R2, the carrier concentration is 5 × 1017 It may be less than 0.04 Ω·cm, and the room-temperature resistivity may be 0.04 Ω·cm or more.

[0053] 2.3. Crystal Quality The crystal quality of wafer 20 can be evaluated using the (004)XRD rocking curve FWHM, which is measured by ω scanning using CuKα1 radiation. The better the crystal quality, the narrower the (004)XRD rocking curve FWHM. (004) In XRD rocking curve measurement, the X-ray tube was operated at a voltage of 45kV and a current of 40mA, and a monochromatic CuK was obtained using a Ge(440)4 crystal symmetric monochromator. α The line is incident on the first main surface 21.

[0054] The X-ray beam size is set such that, when the incident angle (the angle between the reflecting surface and the X-ray) is 90°, that is, when the X-ray is incident perpendicularly to the reflecting surface (004), the size of the irradiation area on the first main surface 21 is 5 mm in the direction parallel to the ω axis and 1 mm in the direction perpendicular to the ω axis. The ω axis is the rotation axis of the sample in rocking curve measurement. When the X-ray beam size is set in this way, the (004)XRD rocking curve measurement of GaN shows that ω is approximately 36.5°, so the irradiation area on the first main surface 21 is approximately 1.7 × 5 mm². 2 That is the case.

[0055] As shown in Figure 6, by performing an ω scan every 1 mm along a line L over a length of 40 mm on the first main surface 21 of the wafer 20, the lines L are arranged at a 1 mm pitch. There are 40 measurement points P M (004) An XRD rocking curve can be obtained at each measurement point P. M In ω scanning, the ω axis is set perpendicular to line L. In other words, X-rays are incident on the wafer 20 so that the X-ray incident plane and line L are parallel.

[0056] On wafer 20, when measurements are taken along at least one line on the first main surface 21, the maximum value of the (004)XRD rocking curve FWHM between all measurement points is 20 arcsec or less. The average value of the (004)XRD locking curve FWHM across all measurement points may be 18 arcsec or less, further 16 arcsec or less, further 14 arcsec or less, further 12 arcsec or less, and further 10 arcsec or less.

[0057] Furthermore, on the first main surface 21 of the wafer 20, by performing ω scans at 1 mm intervals over a length of 40 mm along two mutually perpendicular lines L1 and L2, as illustrated in Figure 7, under the above conditions, (004)XRD rocking curves at 40 measurement points arranged at 1 mm pitch can be obtained on each line L1 and L2. In this case, the ω axis is set perpendicular to line L1 for each measurement point on line L1, and the ω axis is set perpendicular to line L2 for each measurement point on line L2.

[0058] In a preferred example, when such measurements are taken along at least two mutually perpendicular lines on the first main surface 21, the maximum value of the (004)XRD rocking curve FWHM between all measurement points on each line may be 20 arcsec or less. That is, the maximum value between 40 measurement points on one of the two lines and the maximum value between 40 measurement points on the other line may both be 20 arcsec or less. The average value of the (004)XRD locking curve FWHM between all measurement points on each line may be 18 arcsec or less, further 16 arcsec or less, further 14 arcsec or less, further 12 arcsec or less, and further 10 arcsec or less.

[0059] The dislocation density on the first main surface 21 of the wafer 20 is preferably 2 × 10⁻¹⁰ 5 cm -2 More preferably 1 × 10 5 cm -2 More preferably 5 × 10 4 cm -2The following is possible. When evaluating the dislocation density, portions less than 5 mm from the outer edge when the wafer 20 is viewed from above may be excluded.

[0060] 2.4.Applications The wafer 20 can be preferably used as a substrate for the manufacture of various nitride semiconductor devices. Nitride semiconductor devices are semiconductor devices in which the main part of the device structure is formed from nitride semiconductors. Nitride semiconductors are also called nitride-based III-V group compound semiconductors, group III nitride-based compound semiconductors, or GaN-based semiconductors, and include GaN, as well as compounds in which some or all of the gallium in GaN is replaced with other group 13 elements of the periodic table (B, Al, In, etc.). Typical examples of nitride semiconductor devices that can be manufactured using wafer 20 include light-emitting devices such as light-emitting diodes (LEDs) and laser diodes (LDs), and electronic devices such as rectifiers, bipolar transistors, field-effect transistors, and HEMTs (High Electron Mobility Transistors), but are not limited to these.

[0061] When manufacturing nitride semiconductor devices, one or more nitride semiconductor layers are epitaxially grown on the first main surface 21 of a wafer 20 to form an epitaxial wafer with a semiconductor device structure. Preferred epitaxial growth methods include, but are not limited to, vapor phase methods such as MOCVD, MBE, pulsed deposition, sputtering, and HVPE. Semiconductor processing may include etching, ion implantation, and the application of structures such as electrodes and protective films. After the process is completed, the epitaxial wafer is thinned as needed and then cut into nitride semiconductor device chips. In this thinning process, the second main surface 22 side of the wafer 20 is ground, polished and / or etched.

[0062] When wafer 20 consists solely of UID-GaN, electrodes are typically not formed on the surface of wafer 20. In one example, after an epitaxial wafer is formed using wafer 20 consisting solely of UID-GaN, the entire wafer 20 can be removed from the epitaxial wafer by grinding, polishing, and / or etching. When the wafer 20 has a first region R1 formed of ID-GaN on the first main surface 21 side and a second region R2 formed of UID-GaN on the second main surface 22 side, as shown in Figure 5, in one example, after an epitaxial wafer is formed using the wafer 20, the second region R2 is removed from the wafer 20 by grinding, polishing and / or etching, and an electrode can be formed on the surface of the exposed first region R1. When wafer 20 consists solely of ID-GaN, in one example, electrodes may be formed on the second main surface 22 of wafer 20 after an epitaxial wafer has been formed using wafer 20. These electrodes may be formed after the thinning process of the epitaxial wafer.

[0063] Wafer 20 can also be used as a material that constitutes part of a double-layer GaN wafer. The two-layer wafer 40 shown in Figure 8 is an example of a two-layer GaN wafer, and the back layer L consists of at least a portion of the wafer 20. b And, the surface layer L made of GaN epitaxially grown on the main surface of the Ga polar side of wafer 20 f It has the following: Front layer L f and the back layer L b A regrowth interface 43 exists between them.

[0064] The two-layer wafer 40, like the wafer 20, is intended to be used as a substrate in the manufacture of nitride semiconductor devices. Therefore, its thickness is the same as that of a normal GaN wafer: preferably 250 to 500 μm, more preferably 300 to 450 μm, when the diameter is about 2 inches; preferably 400 to 800 μm, more preferably 500 to 650 μm, when the diameter is about 4 inches; and preferably 500 to 850 μm, more preferably 600 to 750 μm, when the diameter is about 6 inches.

[0065] Front layer L f The thickness of the layer is preferably uniform, but not required. In a two-layer wafer 40, when the regrowth interface 43 is inclined with respect to the main surface 41 on the Ga polar side, the top layer L f The thickness of the surface layer L varies along the direction of the inclination. f The minimum thickness, i.e., the thickness at the point of minimum thickness, is at least 20 μm, preferably 50 μm or more, and may be 75 μm or more, 100 μm or more, etc. When the thickness of the two-layer wafer 40 exceeds 300 μm, the top layer L f The maximum thickness, i.e., the thickness at the point of maximum thickness, is preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 200 μm or less. Front layer L f The difference between the maximum and minimum thickness is 200 μm or less, preferably 100 μm or less, more preferably 50 μm or less, even more preferably 25 μm or less, and even more preferably 10 μm or less.

[0066] Front layer L f Therefore, at least the portion within 5 μm of the top surface is included in the high carrier concentration region or the carrier compensation region. (Front layer L) f The upper surface, in other words, is the main surface 41 on the Ga polarity side of the two-layer wafer 40. In a preferred example, the surface layer L f Of these, the portion within a distance Z from the top surface is included in the high carrier concentration region or the carrier compensation region. Here, Z is the front layer L f As long as it does not exceed the minimum thickness, it may be between 20 μm and less than 50 μm, between 50 μm and less than 100 μm, between 100 μm and less than 150 μm, between 150 μm and 250 μm, etc.

[0067] The high carrier concentration region has a lower limit of 1 × 10⁻⁶ carrier concentration. 18 cm -3 The above is the region. In the high carrier concentration region, the lower limit of the carrier concentration is 2 × 10⁻⁶. 18 cm -3 The above is 3 x 10 18 cm -3Above, or 4 x 10 18 cm -3 These are possible areas. The donor impurities that are preferably added in the high carrier concentration region are Si and Ge. The high carrier concentration region has a lower limit of 4 × 10⁻⁶ carrier concentration. 18 cm -3 The above conditions are met, and the lower limit of the total concentration of donor impurities is 5 × 10⁻⁶. 18 atoms / cm 3 The above 6 x 10 18 atoms / cm 3 or more, or 8 x 10 18 atoms / cm 3 These are possible areas. The total concentration of donor impurities in the high carrier concentration region should be 5 × 10 to avoid a significant decrease in crystal quality. 19 atoms / cm 3 Furthermore, 2 x 10 19 atoms / cm 3 Furthermore, 1 x 10 19 atoms / cm 3 The following may be considered: In the high carrier concentration region, the variation in carrier concentration along the c-axis is preferably within ±25%, more preferably within ±20%, even more preferably within ±15%, and even more preferably within ±10% from the median. If measuring the carrier concentration is difficult, it may be substituted with the total concentration of donor impurities.

[0068] The carrier compensation region is defined as having a lower limit of 2 × 10⁻⁶ total concentration of compensated impurities. 17 atoms / cm 3 The above is the region. In the carrier compensation region, the lower limit of the total concentration of compensated impurities is 5 × 10⁻⁶. 17 atoms / cm 3 The above is 1 x 10 18 atoms / cm 3 The above is 2 x 10 18 atoms / cm 3 or more, or 5 x 10 18 atoms / cm 3 These are possible areas. Compensating impurities are impurities that compensate for n-type carriers in GaN crystals. Preferred compensating impurities are carbon (C) and transition metal elements, with examples of transition metal elements including iron (Fe), manganese (Mn), cobalt (Co), chromium (Cr), vanadium (V), nickel (Ni), and copper (Cu). The total concentration of compensating impurities in the carrier compensation region is set to 5 × 10 to avoid a significant decrease in crystal quality. 19 atoms / cm 3 Furthermore, 2 x 10 19 atoms / cm 3 Furthermore, 1 x 10 19 atoms / cm 3 The following may be considered: In the carrier compensation region, the variation in the total concentration of compensating impurities along the c-axis is preferably within ±25%, more preferably within ±20%, even more preferably within ±15%, and even more preferably within ±10% from the median value.

[0069] When manufacturing a two-layer wafer 40, first a wafer 20 is prepared, and then a GaN layer is epitaxially grown on the main surface of the Ga polar side of the wafer 20 to obtain a laminate. Preferably, the wafer 20 is made only of UID-GaN. There are no limitations on the method for growing the GaN layer; MOCVD is acceptable, but HVPE is preferred. The growth thickness of the GaN layer is preferably 500 μm or less. By intentionally doping at least a portion of the GaN layer, a high carrier concentration region or a carrier compensation region can be provided. A thinning step is provided as needed to thin the laminate obtained by growing the GaN layer. In the thinning step, either the N-polar side of the wafer 20 or the Ga-polar side of the GaN layer, or both, are ground, polished, and / or etched.

[0070] The two-layer wafer 40 has a deliberately doped high carrier concentration region or carrier compensation region on the front layer L fWhile this may only be possible with certain materials, in terms of function as a substrate for manufacturing nitride semiconductor devices, it is not inferior to a GaN wafer that has been intentionally doped as a whole. This is because the manufacturing process for nitride semiconductor devices generally includes an epitaxial wafer thinning process, and in this process, the GaN wafer used as a substrate is processed from the back side, and a considerable portion of it is removed. In the two-layer wafer 40, during the manufacturing process of nitride semiconductor devices, the back layer L b Even if it is completely removed, the remaining surface layer L f Its role as a substrate supporting the structure of nitride semiconductor device chips The surface layer L f The minimum thickness is at least 20 μm, preferably 50 μm or more.

[0071] In addition to the above, wafer 20 can also be used as a seed wafer when growing bulk GaN crystals using various methods such as HVPE, THVPE (Tri-Halide Vapor Phase Epitaxy), OVPE (Oxide Vapor Phase Epitaxy), amonothermal method, Na flux method, and others. Wafer 20 formed solely of UID-GaN is particularly suitable for this application.

[0072] 3. Method for growing GaN crystals The following describes a method for growing GaN crystals that can be preferably used in the production of n-type GaN crystals or GaN wafers according to the embodiment, or in the method for manufacturing GaN wafers according to the embodiment. 3.1. HVPE equipment Figure 9 shows the basic configuration of an HVPE apparatus that can be used for manufacturing n-type GaN crystals or GaN wafers according to the embodiment, or for manufacturing GaN wafers according to the embodiment. Referring to Figure 9, the HVPE apparatus 100 comprises a hot-wall type reactor 101, a gallium reservoir 102 and a susceptor 103 located inside the reactor, and a first heater 104 and a second heater 105 located outside the reactor. The first heater 104 and the second heater 105 each surround the reactor 101 in an annular manner.

[0073] Reactor 101 is a quartz tube chamber. Inside reactor 101 are a first zone Z1, which is mainly heated by the first heater 104, and a second zone Z2, which is mainly heated by the second heater 105. Exhaust pipe P E It is connected to the reactor end on the second zone Z2 side. The gallium reservoir 102 located in the first zone Z1 is a quartz container having a gas inlet and a gas outlet. The susceptor 103 located in the second zone Z2 is formed of, for example, graphite. A mechanism for rotating the susceptor 103 can be provided as desired.

[0074] A seed is placed on susceptor 103. Preferably, as shown in Figure 10(a), an edge cover that covers the edge of the seed is placed on the susceptor together with the seed. The edge cover is formed of, for example, graphite, and its height h is set so that the position of the upper surface of the GaN thick film grown on the seed does not rise above the upper edge of the edge cover at the end of its growth, as shown in Figure 10(b). As shown in Figure 11, the edge cover may cover not only the edges of the seed but also the outer periphery of the main surface of the seed.

[0075] When growing thick GaN crystal films on large-area seed substrates, edge covering plays a crucial role. Based on the inventors' experience, when using a 2-inch diameter circular GaN wafer as a seed, the use of an edge cover was essential to grow a GaN layer of sufficient thickness to cut the wafer without cracking. On the other hand, when a GaN wafer with a rectangular main surface but a larger area than a 2-inch diameter circle was used as a seed, it was possible to grow a GaN film of a thickness that could be cut from the wafer without cracking, even without edge covering. However, the GaN thick film grown without edge covering had poor surface morphology, with ridges protruding in the c-axis direction forming along the outer edge, large pits densely forming on the inner wall surface of these ridges, and fine cracks observed on the surface of these ridges. When this GaN thick film was sliced ​​along the c-plane, cracks extending from the edge to the center were observed. A crash occurred, and we were unable to obtain the desired wafer.

[0076] Returning to Figure 9, when growing GaN crystals, the reactor 101 is heated by the first heater 104 and the second heater 105, and NH3 (ammonia) diluted with a carrier gas is supplied to the second zone Z2 through the ammonia introduction tube P1. HCl (hydrogen chloride) diluted with a carrier gas is also supplied to the gallium reservoir 102 through the hydrogen chloride introduction tube P2. This HCl reacts with metallic gallium in the gallium reservoir 102, and the resulting GaCl (gallium chloride) is transported to the second zone Z2 through the gallium chloride introduction tube P3. In the second zone Z2, NH3 and GaCl react, and the resulting GaN crystallizes on the seed placed on the susceptor 103.

[0077] When doping GaN crystals growing on a seed with impurities, the doping gas, diluted with a carrier gas, is guided through the dopant introduction tube P4 to the second zone Z2 in the reactor 101. The ammonia inlet tube P1, hydrogen chloride inlet tube P2, gallium chloride inlet tube P3, and dopant inlet tube P4 can be made of quartz in the portion that is placed inside the reactor 101.

[0078] In Figure 9, the distance from the nozzle to the susceptor 103 is the same for both the ammonia inlet pipe P1 and the gallium chloride inlet pipe P3. However, this is not limited to the case where the nozzle of the ammonia inlet pipe P1 is opened at a position further away from the susceptor 103 (upstream) than the nozzle of the gallium chloride inlet pipe P3. Alternatively, the nozzles of the ammonia inlet tube P1 and the gallium chloride inlet tube P3, which are separate in Figure 9, may be integrated to form a double-tube nozzle with the former as the outer tube and the latter as the inner tube.

[0079] In Figure 9, the nozzles of the gallium chloride inlet tube P3 and the dopant inlet tube P4 are depicted as independent, but this is not limiting. For example, in order to uniformly dope the growing GaN crystal, the nozzle of the dopant inlet tube P4 may be opened into the gallium chloride inlet tube P3 so that the GaCl and doping gas are mixed and then released into the second zone Z2 through a common nozzle.

[0080] When doping growing GaN crystals with Si, the doping gases used are SiH4 (silane), SiH3Cl (monochlorosilane), and SiH2Cl. s Dichlorosilane, SiHCl3 (trichlorosilane), or SiCl4 (tetrachlorosilane) can preferably be used. When doping growing GaN crystals with Ge, the doping gases include GeH4 (Germanic), GeH3Cl (Monochlorogermanic), and GeH2Cl. s (Dichlorogermane), GeHCl3 (trichlorogermane), or GeCl4 (tetrachlorogermane) can preferably be used. Growing GaN crystals may contain oxygen (O) and silicon (Si) even without intentional doping. The unintended Si likely originates from quartz constituting the reactor or piping, while the unintended O originates from either or both of this quartz and moisture that entered the reactor from the outside.

[0081] In addition to quartz and carbon, the components placed inside the reactor 101, including those omitted in Figure 9, are SiC (silicon carbide) and SiN. xMaterials formed from silicon nitride (BN), boron nitride (BN), alumina, tungsten (W), molybdenum (Mo), etc., can be used. In this way, the concentrations of each impurity, excluding Si, O, and H, in the GaN crystal grown on the seed will be 5 × 10⁻⁶ unless intentional doping is performed. 15 atoms / cm 3 The following are possible:

[0082] 3.2. Seed A preferred example of a seed used for growing n-type GaN crystals or GaN wafers according to the embodiment is a c-plane GaN wafer grown by an acidic amonothermal method using NH4F and NH4I as mineralizers. For information on how to manufacture the same, please refer to the aforementioned Patent Document 1 (WO2018 / 030311A1). This c-plane GaN wafer is often 10 18 atoms / cm 3 Despite having an oxygen concentration above the mid-range, the oxygen concentration on the main surface of its Ga polar side is 3 × 10⁻⁶. 16 atoms / cm 3 The following GaN crystals can be grown using HVPE with almost no strain generation. The inclination of the main surface with respect to the (0001) crystal plane is preferably in the range of 0 to 1 degree, more preferably in the range of 0 to 0.5 degrees.

[0083] 3.3. Growth conditions The preferred conditions for growing GaN crystals on a seed using HVPE are as follows: The temperature of the gallium reservoir is, for example, 500 to 1000°C, preferably 700°C or higher, and preferably 900°C or lower. The susceptor temperature is, for example, 900 to 1100°C, preferably 930°C or higher, more preferably 950°C or higher, and also preferably 1050°C or lower, more preferably 1020°C or lower.

[0084] The V / III ratio, which is the ratio of the partial pressure of NH3 to the partial pressure of GaCl in the reactor, can be, for example, 1 to 20, but is preferably 2 or more, more preferably 3 or more, and also preferably 10 or less. A V / III ratio that is too high or too low can cause deterioration of the surface morphology of the growing GaN. This deterioration of surface morphology leads to a decrease in crystal quality and an unintended increase in the concentration of oxygen incorporated into the GaN crystal.

[0085] For some impurities, the efficiency of their incorporation into the GaN crystal strongly depends on the orientation of the facets exposed on the growing GaN surface. In GaN crystals where the surface morphology is poor during growth, the uniformity of the concentration of such impurities is low, because facets of various orientations exist on surfaces with poor morphology. A typical example of such impurities is O (oxygen), but the inventors have found that Ge (germanium) exhibits a similar tendency. As will be described later, this is related to the fact that when intentionally growing Ge-doped GaN crystals, it is better not to lower the molar ratio of H2 in the carrier gas too much.

[0086] Furthermore, using a V / III ratio that is too low increases the nitrogen vacancy concentration in the growing GaN crystal. The impact of nitrogen vacancies on GaN wafers and nitride semiconductor devices formed on GaN wafers is not yet clear, but since they are point defects, their concentration should be kept as low as possible.

[0087] The growth rate of GaN crystals can be controlled using the product of the NH3 partial pressure and GaCl partial pressure in the reactor as a parameter. This rate is, for example, 20 to 200 μm / h, preferably 30 μm / h or more, more preferably 40 μm / h or more, and also preferably 120 μm / h or less, more preferably 100 μm / h or less, and even more preferably 80 μm / h or less. The inventors have found that when growing GaN crystals using HVPE on a high-quality seed consisting of GaN crystals grown by the acidic amonothermal method, if the growth rate is set too low, a problem occurs in which regions where growth is locally stopped are formed on the growth surface.

[0088] When a low growth rate of 20 μm / h to 50 μm / h is adopted, it is possible to effectively prevent the generation of new threading dislocations at the interface between the seed, which consists of a GaN crystal grown by the acidic amonothermal method, and the GaN crystal grown on the seed using HVPE. To increase production efficiency, the growth rate may be increased during the growth process. When the initial growth rate is set to 40 μm / h and then increased to 80 μm / h or 120 μm / h, experiments conducted by the inventors suggested that the threading dislocation density of GaN crystals grown at 80 μm / h was no different from that of seeds made from GaN crystals grown by the acidic amonothermal method, and that even in GaN crystals grown at 120 μm / h, the threading dislocation density was at most twice that of such seeds. When increasing the growth rate, it should be done within a range that does not degrade the surface morphology of the growing GaN crystal. The problems that may arise due to the deterioration of surface morphology are as described above.

[0089] For the carrier gas used to dilute NH3, HCl, and the doping gas, H2 (hydrogen gas), N2 (nitrogen gas), or a mixture of H2 and N2 can preferably be used. The molar ratio of H2 in the carrier gas affects the impurity concentration of the growing GaN crystal. The molar ratio of H2 in the carrier gas, as used here, is calculated based on the flow rates of each type of gas supplied as carrier gas from outside the reactor into the reactor.

[0090] For reference, Table 1 below shows the results of an investigation into how the impurity concentration of Si-doped GaN and Ge-doped GaN grown by HVPE at approximately the same growth rate and with the same V / III ratio on the Ga polar surface of c-plane GaN wafers cut from GaN crystals grown on a sapphire substrate using HVPE changes depending on the molar ratio of H2 in the carrier gas. The doping gases used were SiH2Cl2 for Si doping and GeCl4 for Ge doping.

[0091] [Table 1]

[0092] As can be seen from Table 1, the oxygen concentration in Si-doped GaN crystals can be less than 10% of the Si concentration when the molar ratio of H2 in the carrier gas is 0 (zero). Since the only donor impurity other than Si is essentially oxygen, this is equivalent to the total concentration of donor impurities other than Si being less than 10% of the Si concentration. If the molar ratio of H2 in the carrier gas is increased, the oxygen concentration in Si-doped GaN becomes even lower, and can be less than 1% of the Si concentration when the molar ratio is 0.7.

[0093] On the other hand, in Ge-doped GaN crystals, when the molar ratio of H2 in the carrier gas is 0 (zero), the Ge concentration is more than 10 times higher than when the molar ratio is 0.7, and the ratio of Ge concentration to Si concentration is also higher. Therefore, at first glance, the molar ratio of H2 in the carrier gas is lower. This may seem preferable, but it is not necessarily so. As can be seen from the fact that when the molar ratio of H2 in the carrier gas is 0 (zero), the O concentration is an order of magnitude higher than when the molar ratio is 0.7, the inventors have confirmed that when the molar ratio is 0, the surface morphology of the growing GaN is poor, and this is also the reason why the Ge concentration is high. Since both O and Ge are donor impurities, GaN crystals grown under conditions where the molar ratio of H2 in the carrier gas is too low may experience a problem of reduced carrier concentration uniformity. Therefore, when Ge doping, the molar ratio of H2 in the carrier gas is preferably around 0.3 to 0.7. In Ge-doped GaN crystals grown under these conditions, the Ge concentration is 1 × 10⁻⁶. 18 atoms / cm 3 In the above case, the Si concentration is 4 × 10 17 atoms / cm 3 That concludes the explanation.

[0094] Regardless of whether the crystal is doped with Si or Ge, the oxygen concentration of GaN crystals grown with HVPE tends to decrease as the molar ratio of H2 in the carrier gas increases, resulting in a concentration of 2 × 10⁻⁶. 16 atoms / cm 3 Furthermore, 1 x 10 16 atoms / cm 3 The following is possible. This is thought to be because the surface morphology of the growing GaN crystal is improved. The crystal quality of the c-plane GaN wafer used as a seed also affects the surface morphology of the GaN crystal grown on it. High-quality seed wafers can be used to grow GaN crystals with lower oxygen concentrations. When growing GaN crystals on a seed, doping gas may be supplied from the beginning, but preferably, supply is started after the GaN layer has grown to a thickness of at least 10 μm. Furthermore, it is preferable to gradually increase the supply rate of the doping gas to a predetermined value over several minutes to several tens of minutes from the start of supply.

[0095] 4. Experimental Results The experiments conducted by the inventors are described below. In the experiment, a crystal growth apparatus, whose basic configuration is shown in Figure 12, was used to grow GaN crystals using the amonothermal method. This crystal growth apparatus consists of an autoclave and a capsule made of Pt-Ir alloy placed inside it. The capsule has a dissolution zone and a growth zone that are separated from each other by Pt baffles. When growing GaN crystals, a feedstock is placed in the dissolution zone along with a mineralizing agent (not shown), and a seed is suspended in the growth zone by Pt wire. A gas line, connected to a vacuum pump, ammonia cylinder, and nitrogen cylinder, is connected to the autoclave and capsule via valves. When filling the capsule with NH3 (ammonia), the amount of NH3 supplied from the ammonia cylinder can be monitored using a mass flow meter.

[0096] The amount of NH3 placed in the capsule determines the pressure inside the capsule when it is heated to a predetermined temperature. To balance the pressure inside and outside the capsule, NH3 is sealed not only inside the capsule but also in the space between the autoclave and the capsule. Once the seed, feedstock, and mineralizer are installed and the introduction of NH3 is complete, the capsule is sealed and heated from the outside of the autoclave with a heater (not shown) to bring the interior to a supercritical state. To create a temperature gradient between the dissolution zone and the growth zone, the top and bottom of the autoclave are heated separately by multiple heaters.

[0097] 4.1. Experiment 1 (1) Preparing the seed First, a first c-plane GaN wafer with a thickness of 0.4 mm was prepared by growing it using an amonothermal method with NH4F and NH4I as mineralizers. On the mirror-finished N-polarity surface of the first c-plane GaN wafer, using the lift-off method, A selective growth mask with a stripe pattern was formed using a two-layer sputtered film consisting of a 100 nm thick TiW underlayer and a 100 nm thick Pt surface layer. The linear openings in the selective growth mask had a width of 50 μm and a pitch of 2 mm between them. The stripe direction was parallel to the a-plane of the GaN crystal constituting the wafer.

[0098] Using a first c-plane GaN wafer on which such a selective growth mask was formed on the N-polarity surface as a seed, GaN crystals were grown by the amonothermal method. In the amonothermal process, polycrystalline GaN was used as the feedstock, and NH4F and NH4I were used as mineralizers. The polycrystalline GaN was produced by contacting elemental Ga with HCl gas under heating to generate gaseous GaCl, and then reacting the gaseous GaCl with NH3 gas. The amount of mineralizing agent used was 1.0% molar ratio to the NH3 solvent for both NH4F and NH4I. The NH4I mineralizing agent was synthesized by reacting HI (hydrogen iodide) gas with NH3 in a Pt-Ir capsule, which served as the reaction vessel.

[0099] In the amonothermal process, the average temperature T1 of the dissolution zone and T2 of the growth zone was between 600°C and 620°C, the temperature difference T1-T2 (T1>T2) between the two zones was between 5°C and 10°C, and the capsule pressure was between 200 MPa and 230 MPa. These conditions were maintained for more than 30 days. On the N polarity surface of the first c-plane GaN wafer, GaN crystals grew in layers, as shown in Figure 13, with a thickness t of 3 mm. Voids formed in the areas adjacent to the selective growth mask, and the height h of these voids, i.e., the distance from the top surface of the selective growth mask to the top edge of the void, was between 0.5 mm and 1 mm. Note that GaN crystals also grew on the Ga polarity surface of the first c-plane GaN wafer, but this is omitted from Figure 13.

[0100] Next, the grown GaN crystal layer was processed to form a second c-plane GaN wafer with a thickness of 0.4 mm. The Ga polarity surface of the second c-plane GaN wafer was planarized by grinding, and then finished with CMP to remove the damaged layer. When the full width at half maximum of the (004)XRD rocking curve was measured on a c-plane GaN wafer fabricated using the same method as this second c-plane GaN wafer, a value of less than 10 arcsec was obtained.

[0101] (2) Fabrication of Ge-doped c-plane GaN wafers The Ga polarity surface obtained by cutting the second c-plane GaN wafer described above has an area of ​​approximately 7 cm². 2Using a 0.4 mm thick c-plane GaN wafer as a seed, a GaN thick film was grown on its Ga polar surface using a vapor phase growth apparatus with a basic configuration common to the HVPE apparatus shown in Figure 9. The procedure was generally as follows. First, I placed the seed on the susceptor. I did not use an edge cover. Next, N2, H2, and NH3 were supplied into the reactor so that their partial pressures were 0.25 atm, 0.73 atm, and 0.02 atm, respectively, while the reactor was heated by a heater installed on the outside of the reactor.

[0102] After the susceptor temperature reached 1002°C, the susceptor temperature was kept constant while GaN was grown. The temperature of the GaN reservoir was set to 800°C. The carrier gas supplied to the reactor consisted of 69% H2 and the remainder N2, according to a molar ratio. For the first 60 minutes after growth begins, the partial pressures of GaCl and NH3 are 7.7 × 10⁻⁶. -3 ATM and 2.3 × 10 -2 The reactor was supplied with a constant current (ATM), and no intentional doping gas was supplied.

[0103] 60 minutes after growth begins, GeCl4 (tetrachlorogermane) is supplied to the reactor. The process was initiated. The supply rate of GeCl4 was gradually increased over a period of 5 minutes. After the supply rate of GeCl4 reaches a predetermined value, GaCl, NH3, and GeCl4 are supplied, with their respective partial pressures being 7.7 × 10⁻⁶. -3 atm, 2.3 × 10 -2 atm and 1.7 × 10 -7 We supplied the reactor with atm (atm) and grew a Ge-doped GaN thick film to a thickness of approximately 2.7 mm. The growth rate of the Ge-doped GaN thick film, calculated from its thickness and growth time, was approximately 33 μm / min.

[0104] Next, the Ge-doped GaN thick film was sliced ​​parallel to the c-plane, and the Ga polar surface of the resulting wafer was planarized by grinding and then subjected to CMP finishing. Slice damage on the N polar surface side of the wafer was removed by etching. Furthermore, the wafer was cut to obtain a wafer with a thickness of 335 μm and a main surface area of ​​approximately 7 cm². 2 We have completed the Ge-doped c-plane GaN wafer (hereinafter also referred to as "Sample E-1").

[0105] (3) Evaluation <(004)XRD Locking Curve FWHM> The (004)XRD rocking curve of sample E-1 was measured at a location away from the edge on the Ga polar surface. For the measurement, the line-focus CuKα source of the X-ray diffractometer [Panalytical X'Pert Pro MRD, manufactured by Spectris Co., Ltd.] was operated at 45kV and 40mA, and CuKα 1-rays were obtained using a Ge(440)4 crystal symmetric monochromator. The optical system used was a parallel optical system, with a 1 / 2 slit, an X-ray mirror, and a 1mm x 1mm cross slit on the incident side. The detector used was a semiconductor pixel detector, PIXcel. 3D The 0D mode of (registered trademark) was used. The angular resolution was 5-6 arcsec.

[0106] The X-ray beam size was set such that, when the incident angle was 90°, that is, when the X-rays were incident perpendicularly to the Ga polar surface of the sample substrate, the size of the irradiation area on the Ga polar surface was 5 mm in the direction parallel to the ω axis and 1 mm in the direction perpendicular to the ω axis. In the rocking curve measurement, X-rays were incident on the sample from a direction perpendicular to the a-axis of the GaN crystal. In other words, the incident plane of the X-rays was parallel to the a-plane of the GaN crystal. The FWHM of the (004)XRD rocking curve was 8.5 arcsec.

[0107] <Electrical Characteristics> The room-temperature resistivity of sample E-1, and the carrier concentration and carrier mobility at room temperature determined by Hall assay, were 0.012 Ω·cm and 1.5 × 10⁻⁶, respectively.18 cm -3 and 347cm 2 It was / V·s.

[0108] <Impurity concentration> The impurity concentration of sample E-1 was measured by dynamic SIMS, and the Ge concentration was found to be 1.4 × 10⁻⁶. 18 atoms / cm 3 , Si concentration is 7.0 × 10 17 atoms / cm 3 , O concentration is 6.8 × 10 15 atoms / cm 3 The concentrations of H, Cl, and C were below the detection limit. The detection limit concentration in this SIMS measurement is 1 × 10⁻⁶ for Ge. 15 atoms / cm 3 , Si is 5 × 10 14 atoms / cm 3 , O is 4 × 10 15 atoms / cm 3 , H (hydrogen) is 2 × 10 16 atoms / cm 3 , Cl (chlorine) is 1 × 10 14 atoms / cm 3 , C (carbon) is 3 × 10 15 atoms / cm 3 That was the case.

[0109] 4.2. Experiment 2 As a seed, a Ga polar plane area of ​​approximately 6 cm² was used, possessing crystal quality equivalent to the second c-plane GaN wafer fabricated in Experiment 1. 2 A 0.4mm thick c-plane GaN wafer is prepared using NH4 as a mineralizing agent. The seeds were fabricated from GaN crystals grown using the amonothermal method with F and NH4I. A thick GaN film was grown on the Ga polar surface of this seed using HVPE with the same vapor phase growth apparatus used in Experiment 1. The procedure was generally as follows. First, the seeds were placed on the susceptor of the vapor phase growth apparatus. The edge cover was not used. Next, N2, H2, and NH3 were supplied into the reactor so that their partial pressures were 0.67 atm, 0.31 atm, and 0.02 atm, respectively, while the inside of the reactor was heated by a heater installed on the outside of the reactor.

[0110] After the susceptor temperature reached 1000°C, the susceptor temperature was kept constant while GaN was grown. The temperature of the GaN reservoir was set to 900°C. The carrier gas supplied to the reactor during growth consisted of 69% H2 and the remainder N2, in molar ratio. For the first 60 minutes after growth begins, the partial pressures of GaCl and NH3 are 7.9 × 10⁻⁶ -3 ATM and 2.4 × 10 -2 The reactor was supplied with a constant current (ATM), and no intentional doping gas was supplied.

[0111] Sixty minutes after growth began, the supply of SiH2Cl2 to the reactor was started. The supply rate of SiH2Cl2 was gradually increased over a period of five minutes. After the supply rate of SiH2Cl2 reaches a predetermined value, GaCl, NH3, and SiH2Cl2 are supplied, with their respective partial pressures being 7.9 × 10⁻⁶. -3 atm, 2.4 × 10 -2 atm and 1.9 × 10 -8 The reactor was supplied with a current atm, and a Si-doped GaN thick film was grown to a thickness of approximately 2.38 mm. The growth rate of the Si-doped GaN thick film, calculated from its thickness and growth time, was 40 μm / h.

[0112] Next, the Si-doped GaN thick film was sliced ​​parallel to the c-plane, and the Ga polar surface of the resulting wafer was planarized by grinding and then subjected to CMP finishing. Slice damage on the N polar surface side of the wafer was removed by etching. Furthermore, the wafer was cut to obtain a wafer with a thickness of 335 μm and a main surface area of ​​approximately 6 cm². 2 We have completed the Si-doped c-plane GaN wafer (hereinafter also referred to as "Sample E-2").

[0113] The (004)XRD rocking curve of sample E-2 was measured at a position away from the edge on the Ga polar surface, in the same manner as in Experiment 1. The result showed that its FWHM was 10.0 arcsec. The room-temperature resistivity of sample E-2, and the carrier concentration and carrier mobility at room temperature, determined by Hall assay, were 0.013 Ω·cm and 1.3 × 10⁻⁶, respectively. 18 cm -3 and 391cm 2 It was / V·s.

[0114] When the impurity concentration of sample E-2 was measured using dynamic SIMS, the Si concentration was found to be 1.4 × 10⁻⁶. 18 atoms / cm 3 The concentrations of O (oxygen), H (hydrogen), Cl (chlorine), and C (carbon) were below the detection limit. The detection limit concentration in this SIMS measurement was 5 × 10⁻⁶ for Si. 14 atoms / cm 3 , O is 4 × 10 15 atoms / cm 3 H is 2 × 10 16 atoms / cm 3 Cl is 1 × 10 14 atoms / cm 3 C is 3 x 10 15 atoms / cm 3 That was the case. In sample E-2, the total concentration of donor impurities excluding Si was less than 1% of the Si concentration, and the carrier concentration was 93% of the Si concentration.

[0115] 4.3. Experiment 3 As a seed, a Ga polar plane area of ​​approximately 33 cm² was used, which had the same crystal quality as the second c-plane GaN wafer fabricated in Experiment 1. 2 A 0.4mm thick c-plane GaN wafer is prepared using NH4 as a mineralizing agent. The seeds were fabricated from GaN crystals grown using the amonothermal method with 4F and NH4I. A thick GaN film was grown on the Ga polar surface of this seed using HVPE with a vapor phase growth apparatus of the same type as that used in Experiment 1. The procedure was generally as follows. First, the seeds were placed on the susceptor of the vapor phase growth apparatus, and the seeds were surrounded by a 6mm high graphite edge cover. The edge cover was made to be in close contact with the edges of the seeds.

[0116] Next, N2, H2, and NH3 were supplied into the reactor so that their partial pressures were 0.73 atm, 0.24 atm, and 0.024 atm, respectively, while the inside of the reactor was heated by a heater installed on the outside of the reactor. After the susceptor temperature reached 1000°C, the susceptor temperature was kept constant while GaN was grown. The temperature of the Ga boat was set to 900°C. The carrier gas supplied to the reactor during growth consisted of 75% H2 and the remainder N2, according to a molar ratio.

[0117] For the first 60 minutes after growth begins, the partial pressures of GaCl and NH3 are 7.9 × 10⁻⁶ -3 ATM and 2.4 × 10 -2 The reactor was supplied with a constant current (ATM), and no intentional doping gas was supplied. Sixty minutes after growth began, the supply of SiH2Cl2 to the reactor was started. The supply rate of SiH2Cl2 was gradually increased over a period of five minutes. After the supply rate of SiH2Cl2 reaches a predetermined value, GaCl, NH3, and SiH2Cl2 are supplied, with their respective partial pressures being 7.9 × 10⁻⁶. -3 atm, 2.4 × 10 -2 atm and 1.6 × 10 -3 The reactor was supplied with a current atm, and a Si-doped GaN thick film was grown to a thickness of approximately 2 mm. The growth rate of the Si-doped GaN thick film, calculated from its thickness and growth time, was 35 μm / h.

[0118] Next, the grown GaN thick film was sliced ​​parallel to the c-plane, and the Ga polar surface of the resulting wafer was planarized by grinding and then subjected to CMP finishing. Slice damage on the N polar surface side of the wafer was removed by etching. Furthermore, the wafer was cut to obtain a wafer with a thickness of 360 μm and a main surface area of ​​approximately 30 cm².2 We have completed the Si-doped c-plane GaN substrate (hereinafter also referred to as "Sample E-3").

[0119] The (004)XRD locking curve was measured on the Ga polarity side of sample E-3. First, ω scans were performed every 1 mm along a line passing approximately through the center of the Ga polar plane and perpendicular to the m-axis over a length of 40 mm, thereby obtaining (004)XRD rocking curves at 40 measurement points arranged at 1 mm intervals along the line. The measurement conditions at each measurement point were the same as in Experiment 1, except that the X-rays were incident on the sample from a direction perpendicular to the m-axis of the GaN crystal. The maximum value of the (004)XRD rocking curve FWHM across 40 measurement points was 19.3 arcsec, and the average value was 10.5 arcsec.

[0120] Next, by performing ω scans every 1 mm along a line passing approximately through the center of the Ga polarity plane and perpendicular to the a-axis over a length of 40 mm, (004)XRD rocking curves were obtained at 40 measurement points arranged at 1 mm intervals along the line. The measurement conditions at each measurement point were the same as in Experiment 1. The maximum value of the (004)XRD rocking curve FWHM across 40 measurement points was 16.2 arcsec, and the average value was 10.4 arcsec. The carrier concentration of sample E-3, measured at the center of the Ga polar surface, was 1.5 × 10⁻⁶. 18 cm -3 That was the case.

[0121] 4.4. Experiment 4 As a seed, a Ga polar plane area of ​​approximately 32 cm² was used, with crystal quality equivalent to the second c-plane GaN wafer fabricated in Experiment 1. 2 A 0.56 mm thick c-plane GaN wafer was fabricated from GaN crystals grown using the amonothermal method with NH4F and NH4I as mineralizers. A thick GaN film was grown on the Ga polar plane of this seed using HVPE with a vapor phase growth apparatus of the same type as that used in Experiment 1. The procedure was generally as follows. First, the seeds were placed on the susceptor of the vapor phase growth apparatus, and the edges of the seeds and the outer periphery of the Ga polar surface were covered with a 4mm high graphite edge cover.

[0122] Next, N2, H2, and NH3 were supplied into the reactor at partial pressures of 0.30 atm, 0.65 atm, and 0.052 atm, respectively, while the inside of the reactor was heated by a heater installed on the outside of the reactor. GaN growth was initiated when the susceptor temperature reached 960°C. Ten minutes after growth began, the supply of SiH2Cl2 to the reactor was started. The supply rate of SiH2Cl2 was gradually increased over 30 minutes.

[0123] The growth conditions from the start of growth to 3 hours afterward were: gallium reservoir temperature 800°C, susceptor temperature 960°C, and GaCl partial pressure 6.0 × 10⁻⁶. -3 atm, NH3 voltage division 4.1 × 10 -2 atm, SiH2Cl2 partial pressure 2.1 × 10⁻¹⁰ -8 The temperature was atm. After 3 hours, the susceptor temperature was raised to 998°C. The carrier gas supplied to the reactor consisted of 40% H2 and the remainder N2 in molar ratio. In this manner, a Si-doped GaN thick film was grown to a thickness of approximately 2.2 mm. The growth rate was 37 μm / h.

[0124] Next, the grown GaN thick film was sliced ​​parallel to the c-plane, and the Ga polar surface of the resulting wafer was planarized by grinding and then subjected to CMP finishing. Slice damage on the N polar surface side of the wafer was removed by etching. Furthermore, the wafer was cut to obtain a wafer with a thickness of 400 μm and a main surface area of ​​approximately 16 cm². 2 We have completed the c-plane GaN wafer (hereinafter also referred to as "Sample E-4").

[0125] The (004)XRD locking curve was measured on the Ga polarity side of sample E-4. By performing ω scans every 1 mm over a length of 40 mm along a single line passing through the center of the Ga polar plane and perpendicular to the m-axis, (004)XRD rocking curves were obtained at 40 measurement points arranged at 1 mm intervals along the line. The measurement conditions at each measurement point were the same as in Experiment 1, except that the X-rays were incident on the sample from a direction perpendicular to the m-axis of the GaN crystal. The maximum value of the (004)XRD rocking curve FWHM across 40 measurement points was 17.8 arcsec, and the average value was 11.2 arcsec.

[0126] The carrier concentration of sample E-4, measured at the center of the Ga polar surface, was 1.5 × 10⁻⁶. 18 cm -3 That was the case. Using almost the same conditions as when sample E-4 was grown, except for increasing the supply of SiH2Cl2, the crystal quality was equivalent to sample E-4, and the carrier concentration at the center of the Ga polar plane was 2.8 × 10⁻⁶. 18 cm -3 It was also possible to grow c-plane GaN substrates.

[0127] 4.5. Experiment 5 As a seed, a Ga polar plane area of ​​approximately 33.8 cm² was used, which has the same crystal quality as the second c-plane GaN wafer fabricated in Experiment 1. 2 A 0.55 mm thick c-plane GaN wafer was fabricated from GaN crystals grown using the amonothermal method with NH4F and NH4I as mineralizers. A thick GaN film was grown on the Ga polar plane of this seed using HVPE with a vapor phase growth apparatus of the same type as that used in Experiment 1. The procedure was generally as follows. First, the seeds were placed on the susceptor of the vapor phase growth apparatus, and the edges of the seeds and the outer periphery of the Ga polar surface were covered with a 4mm high graphite edge cover.

[0128] Next, N2, H2, and NH3 were supplied into the reactor at partial pressures of 0.30 atm, 0.65 atm, and 0.052 atm, respectively, while the inside of the reactor was heated by a heater installed on the outside of the reactor. GaN growth was initiated when the susceptor temperature reached 1005°C. The growth conditions were: gallium reservoir temperature 800°C, susceptor temperature 1005°C, and GaCl partial pressure 9.0 × 10⁻⁶. -3 atm, NH3 voltage division 4.1 × 10 -2 The reactor was set to atm, and the carrier gas supplied to the reactor consisted of 38% H2 and the remainder N2, according to a molar ratio.

[0129] Furthermore, 5 hours after growth began, the supply of GeCl4 to the reactor was started. The GeCl4 partial pressure was gradually increased to 1.9 × 10⁻⁶ over 30 minutes. -7 The rate was increased up to 100, and then kept constant thereafter. In this manner, a Ge-doped GaN thick film was grown to a thickness of approximately 3 mm. The growth rate was 47 μm / h.

[0130] Next, the grown GaN thick film was sliced ​​parallel to the c-plane, and the Ga polar surface of the resulting wafer was planarized by grinding and then subjected to CMP finishing. Slice damage on the N polar surface side of the wafer was removed by etching. Furthermore, by cutting the wafer, a wafer with a thickness of 400 μm and a main surface area of ​​approximately 19.5 cm² was obtained. 2 We have completed the c-plane GaN wafer (hereinafter also referred to as "Sample E-5").

[0131] The (004)XRD locking curve was measured on the Ga polar side of sample E-5. First, by performing ω scans every 1 mm along a line passing through the center of the Ga polar plane and perpendicular to the m-axis over a length of 40 mm, (004)XRD rocking curves were obtained at 40 measurement points arranged at 1 mm intervals along the line. The measurement conditions at each measurement point were the same as in Experiment 1, except that the X-rays were incident on the sample from a direction perpendicular to the m-axis of the GaN crystal. The maximum value of the (004)XRD rocking curve FWHM across 40 measurement points was 9.4 arcsec, and the average value was 7.5 arcsec.

[0132] Next, by performing ω scans every 1 mm along a line passing approximately through the center of the Ga polarity plane and perpendicular to the a-axis over a length of 40 mm, (004)XRD rocking curves were obtained at 40 measurement points arranged at 1 mm intervals along the line. The measurement conditions at each measurement point were the same as in Experiment 1. The maximum value of the (004)XRD rocking curve FWHM across 40 measurement points was 11.0 arcsec, and the average value was 7.9 arcsec. The carrier concentration of sample E-5, measured at the center of the Ga polar surface, was 4.9 × 10⁻⁶. 18 cm -3 That was the case.

[0133] Furthermore, using a PL (photoluminescence) imaging system [PLI-200, manufactured by Photon Design Co., Ltd.], the number of dark spots in the PL image observed within a 230 μm × 230 μm square area at multiple measurement points on the Ga polar surface of sample E-5 was counted. PL images were acquired using a mercury lamp as the excitation source, with an excitation wavelength of 313 nm and a detection wavelength of 365 ± 5 nm. The detector was a 2048 × 2048 pixel CMOS camera, so the pixel resolution was approximately 0.11 μm. The measurement points were located at the grid points of a square grid with sides of 2.88 mm, and there were 381 such points. The average scotoma density across 381 measurement points is 3.3 × 10⁻⁶. 4 cm -2 Then, a scotoma was observed. The number of measurement points that were not measured amounted to 54% of the total. In calculating the average value, the scotoma density at measurement points where no scotoma was observed was 0 cm². -2 Assuming that only one scotoma was observed at the measurement point, the dislocation density was 230 × 230 μm². 2 Since there is one per unit, 1.9 × 10 3 cm -2 That's what I decided. After measuring the dark spot density using PL imaging as described above, sample E-5 was etched with 89% sulfuric acid heated to 270°C for 1 hour. The etch pits formed on its Ga polar surface corresponded one-to-one with the dark spots in the PL image. The inventors have separately confirmed that the etch pits formed by this method also correspond one-to-one with the dark spots appearing in the cathodoluminescence image.

[0134] The aforementioned Ge-doped GaN thick film, approximately 3 mm thick, was sliced ​​simultaneously with sample E-5, and processed in the same manner as sample E-5 to produce a 400 μm thick sample with a main surface area of ​​approximately 20 cm². 2 The variation in the offcut angle within the main plane of a c-plane GaN wafer was investigated. When a direction parallel to one of the a-planes was selected as the x-direction, and a direction perpendicular to the x-direction was defined as the y-direction, the variation range of the x-direction component of the offcut angle was 0.04 degrees (±0.02 degrees from the center value) on a 4 cm line extending in the x-direction through the center of the Ga polar plane, and the variation range of the y-direction component of the offcut angle was 0.06 degrees (±0.03 degrees from the center value) on a 4 cm line extending in the y-direction through the center of the Ga polar plane.

[0135] 4.6. Experiment 6 As a seed, a c-plane GaN wafer with crystal quality equivalent to the second c-plane GaN wafer fabricated in Experiment 1 was prepared from GaN crystals grown by the amonothermal method using NH4F and NH4I as mineralizers. Samples E-6a to E-6e were prepared by growing GaN crystals on the Ga polarity main surface of this seed using HVPE under different conditions with a vapor phase growth apparatus of the same type as that used in Experiment 1.

[0136] When growing GaN crystals using HVPE, the susceptor temperature was set to approximately 1000°C, the Ga reservoir temperature to 800°C, and the carrier gas supplied to the reactor consisted of 69% H2 and the remainder N2 in molar ratio. For all of samples E-6a to E-6e, the first layer, which was initially grown on the seed, was formed at a growth rate of approximately 40 μm / h.

[0137] Sample E-6a is a sample in which only the first layer was grown on a seed. Sample E-6b was fabricated by growing a second layer with a thickness of 40 μm at a growth rate of 80 μm / h, following the growth of the first layer. Sample E-6c was fabricated by growing a second layer with a thickness of 40 μm at a growth rate of 120 μm / h, following the growth of the first layer. Sample E-6d was prepared by growing a first layer, followed by growing a 21 μm thick second layer doped with SiH2Cl2 (dichlorosilane). Sample E-6e was prepared by growing a first layer, followed by growing a 21 μm thick second layer doped with GeCl4 (tetrachlorogermane).

[0138] The HVPE growth conditions for each sample are shown in Table 2 below.

[0139] [Table 2]

[0140] In all of samples E-6a to E-6e, the top surface of the GaN crystal grown on the seed with HVPE was mirror-flat to the naked eye. When cross-sections of samples E-6d and E-6e were observed with a fluorescence microscope, the flatness of the interface between the first and second layers was found to be good. The carrier concentrations in the second layer of samples E-6d and E-6e, as evaluated by Raman spectroscopy, were both 1 × 10⁻⁶. 18 cm -3 That was the case.

[0141] Using a multiphoton excitation microscope (Nikon Corporation's High-Speed ​​Multiphoton Confocal Laser Microscope System A1R-MP+), three-photon excitation images (3PPL images) of samples E-6a to E-6e were observed from the surface side of the HVPE-GaN crystal, as shown in Figure 14 (however, sample E-6a does not have a second layer). A Ti-sapphire mode-locked laser with a wavelength of 800 nm was used as the excitation source, driven with a pulse width of 140 fs and a repetition rate of 80 MHz.

[0142] The following was discovered from the 3PPL image observation: The only penetrating dislocations present in the first layer of sample E-6a were those propagated from the seed. No new penetrating dislocations were observed at the interface between the seed and the first layer, nor within the first layer itself. In sample E-6b, the penetrating dislocation in the first layer propagated into the second layer without branching at the interface between the first and second layers. No new penetrating dislocations were observed in the middle of the second layer. Unlike sample E-6b, in sample E-6c, all of the penetrating dislocations propagating from the first layer to the second layer bifurcated at the interface between the first and second layers. In other words, the number of penetrating dislocations in the second layer was twice that of the first layer.

[0143] In sample E-6d, some through-dislocations bifurcated at the interface between the first and second layers as they propagated from the first to the second layer, but the proportion of such through-dislocations was only about one in 100. No new through-dislocations were observed in the middle of the second layer. In sample E-6e, some threading dislocations also bifurcated at the interface between the first and second layers as they propagated from the first to the second layer, but the proportion of such threading dislocations was about 1 in 50. That was the extent of it. No new penetrating dislocations were observed in the middle of the second layer. These 3PPL observations for samples E-6d and E-6e suggest that Si or Ge doping has little effect on the penetration dislocation density.

[0144] 4.7. Experiment 7 As a seed, a Ga polar plane area of ​​approximately 24.8 cm² was used, which had the same crystal quality as the second c-plane GaN wafer fabricated in Experiment 1. 2 A 0.53 mm thick c-plane GaN wafer was fabricated from GaN crystals grown by the amonothermal method using NH4F and NH4I as mineralizers. In the manufacturing process of these GaN crystals, a selective growth mask was used that formed a slanted square lattice pattern of linear apertures with a line width of 20 μm. The slanted square lattice pattern was formed by superimposing two stripe patterns, each parallel to the a-plane and at a 60-degree angle to each other. One of the two stripe patterns had a pitch of 2 mm, and the other had a pitch of 15 mm. A GaN thick film was grown on the Ga polar surface of this seed using HVPE with a vapor phase growth apparatus of the same type as that used in Experiment 1. The procedure was generally as follows. First, the seeds were placed on the susceptor of the vapor phase growth apparatus, and the edges of the seeds and the outer periphery of the Ga polar surface were covered with a 4mm high graphite edge cover.

[0145] Next, N2, H2, and NH3 were supplied into the reactor at partial pressures of 0.30 atm, 0.65 atm, and 0.052 atm, respectively, while the inside of the reactor was heated by a heater installed on the outside of the reactor. GaN growth was initiated when the susceptor temperature reached 1005°C. The growth conditions were: gallium reservoir temperature 800°C, susceptor temperature 1005°C, and GaCl partial pressure 9.2 × 10⁻⁶. -3 atm, NH3 voltage division 4.2 × 10 -2 The reactor was set to atm, and the carrier gas supplied to the reactor consisted of 40% H2 and the remainder N2, according to a molar ratio.

[0146] Furthermore, 5 hours after growth began, the supply of GeCl4 to the reactor was started. The GeCl4 partial pressure was gradually increased to 1.6 × 10⁻⁶ over 30 minutes. -7 The pressure was increased to atm and then kept constant. Also, 5 hours after the start of growth, the GaCl partial pressure was gradually increased to 9.4 × 10⁻⁶ over 4 hours. -3 I used "atm". In this manner, a Ge-doped GaN thick film was grown to a thickness of approximately 3 mm. The growth rate was 43 μm / h.

[0147] Next, the grown GaN thick film was sliced ​​parallel to the c-plane, and both main surfaces of the resulting wafer were planarized by grinding and then subjected to CMP finishing. Furthermore, by cutting the wafer, a wafer with a thickness of 400 μm and a main surface area of ​​approximately 15.2 cm² was obtained. 2 We have completed the c-plane GaN wafer (hereinafter also referred to as "Sample E-7"). The carrier concentration of sample E-7, measured at the center of the Ga polar surface, was 2.0 × 10⁻⁶. 18 cm -3 That was the case.

[0148] X-ray topographic analysis of sample E-7 was performed using an X-ray diffractometer [(Rigaku Corporation's high-throughput and high-resolution X-ray topography imaging system XRTmicron)]. Figure 16 shows a transmitted X-ray topographic image of a 20 mm × 20 mm square area obtained using diffraction from the (110) crystal plane. The X-ray source used was MoKα, and the sample thickness was 400 μm, so μ·t = 11.6. Therefore, this X-ray topographic image is an anomalous transmitted image. While there have been previous cases of anomalous X-ray transmission observed in m-plane GaN wafers made of GaN crystals grown with HVPE (WO2015 / 020161), this application appears to be the first to report anomalous X-ray transmission in c-plane GaN wafers grown with HVPE. Referring to Figure 16, the figure shows a stripe consisting of a defect array extending in the left-right direction, and the stripe A defect region is observed extending from the lower left to the upper right, tilted 60 degrees from the tripe. This stripe is parallel to the a-plane and has a pitch of 2 mm, reflecting the pattern of the selective growth mask used in the manufacturing process of the c-plane GaN wafer for seeding. Even with a 350 μm thick c-plane GaN wafer fabricated using essentially the same method except for changing the dopant from Ge to Si, we were able to obtain a transmission X-ray topography image of a 20 mm × 20 mm square area.

[0149] Although the present invention has been described above with reference to specific embodiments, each embodiment is presented as an example and does not limit the scope of the present invention. Each embodiment described herein can be modified in various ways without departing from the spirit of the invention and can be combined with features described in other embodiments to the extent that is feasible. [Explanation of Symbols]

[0150] 10 crystals 11, 21 First principal surface 12, 22 Second principal surface 20 wafers 40 Double-layer wafers 43 Regrowth interface 100 HVPE devices 101 Reactor 102 Gallium accumulation 103 Susceptor 104 First Heater 105 Second heater Z1 First Zone Z2 Second Zone P1 Ammonia Inlet Tube P2 hydrogen chloride inlet pipe P3 gallium chloride inlet tube P4 dopant introduction tube P E exhaust pipe

Claims

1. In an n-type GaN crystal having two principal surfaces facing opposite directions, one of which is Ga polar and (0001) has an inclination of 0 degrees or more and 10 degrees or less with respect to the crystal plane, When the (004)XRD locking curve is measured every 1 mm along at least one line over a length of 40 mm on one of the main surfaces, the maximum value of the (004)XRD locking curve FWHM between all measurement points is 20 arcsec or less, and The following condition (c) must be met regarding the impurity concentration. n-type GaN crystal characterized by: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

2. In an n-type GaN crystal having two principal surfaces facing opposite directions, one of which is Ga polar and (0001) has an inclination of 0 degrees or more and 10 degrees or less with respect to the crystal plane, When the (004)XRD locking curve is measured every 1 mm along at least one line over a length of 40 mm on one of the main surfaces, the average value of the (004)XRD locking curve FWHM between all measurement points is 18 arcsec or less, and The following condition (c) must be met regarding the impurity concentration. n-type GaN crystal characterized by: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

3. The n-type GaN crystal according to claim 1, wherein the average value of the (004)XRD rocking curve FWHM between all the measurement points is 18 arcsec or less.

4. In an n-type GaN crystal having two principal surfaces facing opposite directions, one of which is Ga polar and (0001) has an inclination of 0 degrees or more and 10 degrees or less with respect to the crystal plane, When the (004)XRD locking curve is measured every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on one of the main surfaces, the maximum value of the (004)XRD locking curve FWHM between all measurement points on each line is 20 arcsec or less, and The following condition (c) must be met regarding the impurity concentration. n-type GaN crystal characterized by: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

5. In an n-type GaN crystal having two principal surfaces facing opposite directions, one of which is Ga polar and (0001) has an inclination of 0 degrees or more and 10 degrees or less with respect to the crystal plane, When the (004)XRD locking curve is measured every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on one of the main surfaces, the average value of the (004)XRD locking curve FWHM between all measurement points on each line is 18 arcsec or less, and The following condition (c) must be met regarding the impurity concentration. n-type GaN crystal characterized by: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

6. The n-type GaN crystal according to claim 5, wherein the average value of the (004)XRD rocking curve FWHM between all measurement points on each of the lines is 18 arcsec or less.

7. An n-type GaN crystal according to any one of claims 1 to 6, satisfying condition (b) below with respect to the impurity concentration. (b) The O concentration is 3 × 10 １６ atoms / cm ３ or less.

8. Si concentration is 5 × 10 １７ atoms / cm ３ The n-type GaN crystal according to any one of claims 1 to 7, which is as follows:

9. The concentrations of each impurity, excluding Si, O, and H, are 5 × 10 １５ atoms / cm ３ The n-type GaN crystal according to any one of claims 1 to 8, which is as follows:

10. 5 x 10 １７ cm －３ An n-type GaN crystal according to any one of claims 1 to 9, having at least one of a carrier concentration of less than 0.04 Ω·cm and a room-temperature resistivity of 0.04 Ω·cm or more.

11. A method for producing an n-type GaN crystal according to any one of claims 1 to 10, characterized by comprising the step of growing an n-type GaN crystal with HVPE on a seed of a c-plane GaN wafer grown by an acidic amonothermal method.

12. A GaN wafer made of an n-type GaN crystal according to any one of claims 1 to 10.

13. The device comprises a back layer made of an n-type GaN crystal according to any one of claims 1 to 10, and a front layer made of GaN with a minimum thickness of 20 μm or more, formed on the main surface on the Ga polar side of the n-type GaN crystal via a regrowth interface, wherein at least a portion of the front layer within a distance of 5 μm from the top surface is included in a high carrier concentration region, and the lower limit of the carrier concentration in the high carrier concentration region is 1 × 10⁻⁶ １８ cm －３ The above-mentioned region is a two-layer GaN wafer.

14. The two-layer GaN wafer according to claim 13, wherein at least a portion of the top layer within 20 μm from the top surface is included in the high carrier concentration region.

15. The aforementioned high carrier concentration region has a lower limit of carrier concentration of 2 × 10 １８ cm －３ The two-layer GaN wafer according to claim 13 or 14, relating to the above region.

16. The two-layer GaN wafer according to any one of claims 13 to 15, wherein the surface layer satisfies one or more conditions selected from (a) to (c) below with respect to the impurity concentration: (a) Si concentration is 5 × 10 １６ atoms / cm ３ That's all; (b) O concentration is 3 × 10 １６ atoms / cm ３ The following: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

17. The two-layer GaN wafer according to claim 16, wherein the surface layer satisfies all of the above conditions (a) to (c) regarding the impurity concentration.

18. The oxygen concentration in the aforementioned outer layer is 3 × 10 １６ atoms / cm ３ The following is a two-layer GaN wafer according to any one of claims 13 to 17.

19. The two-layer GaN wafer according to any one of claims 13 to 18, wherein the high carrier concentration region is doped with Si.

20. The concentrations of each impurity in the aforementioned surface layer, excluding Si, O, and H, are 5 × 10 １５ atoms / cm ３ The following is a two-layer GaN wafer according to claim 19.

21. The two-layer GaN wafer according to any one of claims 13 to 19, wherein the high carrier concentration region is doped with Ge.

22. The concentrations of each impurity in the aforementioned surface layer, excluding Ge, Si, O, and H, are 5 × 10 １５ atoms / cm ３ The following is a two-layer GaN wafer according to claim 21.

23. The two-layer GaN wafer according to any one of claims 13 to 22, wherein in the high carrier concentration region, the variation in carrier concentration or total donor impurity concentration along the c-axis is within ±25% of the median value.

24. The device comprises a back layer made of an n-type GaN crystal according to any one of claims 1 to 10, and a front layer made of GaN with a minimum thickness of 20 μm or more, formed on the main surface on the Ga polar side of the n-type GaN crystal via a regrowth interface, wherein at least a portion of the front layer within a distance of 5 μm from the top surface is included in the carrier compensation region, and the lower limit of the total concentration of compensating impurities in the carrier compensation region is 1 × 10⁻⁶ １７ atoms / cm ３ The above-mentioned region is a two-layer GaN wafer.

25. The two-layer GaN wafer according to claim 24, wherein at least a portion of the front layer within 20 μm from the top surface is included in the carrier compensation region.

26. The carrier compensation region has a lower limit of 2 × 10⁻⁶ total concentration of compensated impurities. １７ atoms / cm ３ The above-mentioned region, a two-layer GaN wafer according to claim 24 or 25.

27. The two-layer GaN wafer according to any one of claims 24 to 26, wherein the surface layer satisfies one or more conditions selected from (a) to (c) below with respect to the impurity concentration: (a) Si concentration is 5 × 10 １６ atoms / cm ３ That's all; (b) O concentration is 3 × 10 １６ atoms / cm ３ The following: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

28. The two-layer GaN wafer according to any one of claims 24 to 27, wherein in the carrier compensation region, the variation in the total concentration of compensating impurities along the c-axis direction is within ±25% of the median value.

29. A two-layer GaN wafer according to any one of claims 13 to 28, wherein the thickness of the two-layer GaN wafer is greater than 300 μm, and the maximum thickness of the front layer is 300 μm or less.

30. A two-layer GaN wafer according to any one of claims 13 to 29, wherein the minimum thickness of the surface layer is 50 μm or more.

31. A method for manufacturing an epitaxial wafer, comprising the steps of preparing a wafer according to any one of claims 12 to 30, and epitaxially growing one or more nitride semiconductor layers on the prepared wafer.

32. An epitaxial wafer comprising a wafer according to any one of claims 12 to 30 and one or more nitride semiconductor layers epitaxially grown on the GaN wafer.

33. A method for manufacturing a nitride semiconductor device, comprising the steps of preparing a wafer according to any one of claims 12 to 30, and epitaxially growing one or more nitride semiconductor layers on the prepared wafer.

34. The method comprises the steps of preparing a GaN wafer according to claim 12, and epitaxially growing a GaN layer with a thickness of 20 μm or more on the main surface on the Ga polar side of the prepared GaN wafer, wherein the GaN layer is provided with a high carrier concentration region or a carrier compensation region, and the lower limit of the carrier concentration in the high carrier concentration region is 1 × 10⁻⁶ １８ cm －３ The above region is the carrier compensation region, and the lower limit of the total concentration of compensated impurities is 2 × 10⁻⁶. １７ atoms / cm ３ The above-mentioned method for manufacturing a two-layer GaN wafer.

35. The manufacturing method according to claim 34, wherein in the step of epitaxial growth, the GaN layer is grown with HVPE.

36. The manufacturing method according to claim 34 or 35, wherein the thickness of the GaN layer is 500 μm or less.

37. The GaN layer is provided with the high carrier concentration region, and the lower limit of the carrier concentration in the high carrier concentration region is 2 × 10⁻⁶. １８ cm －３ The manufacturing method according to any one of claims 34 to 36, which falls within the above-mentioned area.

38. The manufacturing method according to any one of claims 34 to 37, wherein the GaN layer is provided with the high carrier concentration, and the high carrier concentration region is doped with Ge.

39. The manufacturing method according to any one of claims 34 to 38, wherein the GaN layer is provided with the high carrier concentration, and the high carrier concentration region is intentionally doped with Si.

40. The GaN layer is provided with the carrier compensation region, and the lower limit of the total concentration of compensation impurities in the carrier compensation region is 5 × 10 １７ atoms / cm ３ The manufacturing method according to any one of claims 34 to 39, which falls within the above-mentioned area.

41. The manufacturing method according to any one of claims 34 to 40, further comprising the step of thinning the laminate obtained in the epitaxial growth step.

42. A method for producing a bulk GaN crystal, comprising the steps of preparing a GaN wafer according to claim 12, and epitaxially growing GaN on the prepared GaN wafer.

43. The conductive type is n-type. When the (004)XRD locking curve is measured every 1 mm along at least one line over a length of 40 mm on one main surface, the maximum value of the (004)XRD locking curve FWHM between all measurement points is 20 arcsec or less, and The following condition (c) must be met regarding the impurity concentration. A c-plane GaN wafer characterized by: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

44. The conductive type is n-type. When the (004)XRD locking curve is measured every 1 mm along at least one line for a length of 40 mm on one main surface, the average value of the (004)XRD locking curve FWHM between all measurement points is 18 arcsec or less, and The following conditions (c) must be met regarding the impurity concentration. A c-plane GaN wafer characterized by: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

45. The c-plane GaN wafer according to claim 43, wherein the average value of the (004)XRD rocking curve FWHM between all the measurement points is 18 arcsec or less.

46. The conductive type is n-type. When the (004)XRD locking curve is measured every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on one main surface, the maximum value of the (004)XRD locking curve FWHM between all measurement points on each line is 20 arcsec or less, and The following condition (c) must be met regarding the impurity concentration. A c-plane GaN wafer characterized by: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

47. The conductive type is n-type. When the (004)XRD locking curve is measured every 1 mm over a length of 40 mm along each of at least two mutually perpendicular lines on one main surface, the average value of the (004)XRD locking curve FWHM between all measurement points on each line is 18 arcsec or less, and The following condition (c) must be met regarding the impurity concentration. A c-plane GaN wafer characterized by: (c) H concentration is 1 × 10 １７ atoms / cm ３ The following applies:

48. The c-plane GaN wafer according to claim 46, wherein the average value of the (004)XRD rocking curve FWHM between all measurement points on each of the lines is 18 arcsec or less.

49. The c-plane GaN wafer according to any one of claims 43 to 48, wherein the variation range of the x-component of the offcut angle on a line extending in the x-direction through the center of the front surface and the variation range of the y-component of the offcut angle on a line extending in the y-direction perpendicular to the x-direction through the center of the front surface are each 0.15 degrees or less within a length of 40 mm.

50. A c-plane GaN wafer according to any one of claims 43 to 49, satisfying condition (b) below with respect to the impurity concentration. (b) O concentration is 3 × 10 １６ atoms / cm ３ The following applies:

51. Si concentration is 5 × 10 １７ atoms / cm ３ The following is a c-plane GaN wafer according to any one of claims 43 to 50.

52. The concentrations of each impurity, excluding Si, O, and H, are 5 × 10 １５ atoms / cm ３ The following is a c-plane GaN wafer according to any one of claims 43 to 51.

53. 5 x 10 １７ cm －３ A c-plane GaN wafer according to any one of claims 43 to 52, having at least one of a carrier concentration of less than 0.04 Ω·cm and a room-temperature resistivity of 0.04 Ω·cm or more.

54. A method for manufacturing an epitaxial wafer, comprising the steps of: preparing a c-plane GaN wafer according to any one of claims 43 to 53; and epitaxially growing one or more nitride semiconductor layers on the prepared c-plane GaN wafer.

55. An epitaxial wafer comprising a c-plane GaN wafer according to any one of claims 43 to 53, and one or more nitride semiconductor layers epitaxially grown on the c-plane GaN wafer.

56. A method for manufacturing a nitride semiconductor device, comprising the steps of: preparing a c-plane GaN wafer according to any one of claims 43 to 53; and epitaxially growing one or more nitride semiconductor layers on the prepared c-plane GaN wafer.

57. The method comprises the steps of preparing a c-plane GaN wafer according to any one of claims 43 to 53, and epitaxially growing a GaN layer with a thickness of 20 μm or more on the main surface on the Ga polar side of the prepared c-plane GaN wafer, wherein the GaN layer is provided with a high carrier concentration region or a carrier compensation region, and the lower limit of the carrier concentration in the high carrier concentration region is 1 × 10⁻⁶ １８ cm －３ The above region is the carrier compensation region, and the lower limit of the total concentration of compensated impurities is 2 × 10⁻⁶. １７ atoms / cm ３ The above-mentioned method for manufacturing a two-layer GaN wafer.

58. The manufacturing method according to claim 57, wherein in the step of epitaxial growth, the GaN layer is grown with HVPE.

59. The manufacturing method according to claim 57 or 58, wherein the thickness of the GaN layer is 500 μm or less.

60. The GaN layer is provided with the high carrier concentration region, and the lower limit of the carrier concentration in the high carrier concentration region is 2 × 10⁻⁶. １８ cm －３ The manufacturing method according to any one of claims 57 to 59, which falls within the above-mentioned area.

61. The manufacturing method according to any one of claims 57 to 60, wherein the GaN layer is provided with the high carrier concentration region, and the high carrier concentration region is doped with Ge.

62. The manufacturing method according to any one of claims 57 to 61, wherein the GaN layer is provided with the high carrier concentration region, and the high carrier concentration region is intentionally doped with Si.

63. The GaN layer is provided with the carrier compensation region, and the lower limit of the total concentration of compensation impurities in the carrier compensation region is 5 × 10 １７ atoms / cm ３ The manufacturing method according to any one of claims 57 to 59, which falls within the above-mentioned area.

64. The manufacturing method according to any one of claims 57 to 63, further comprising the step of thinning the laminate obtained in the epitaxial growth step.

65. A method for producing a bulk GaN crystal, comprising the steps of preparing a c-plane GaN wafer according to any one of claims 43 to 53, and epitaxially growing GaN on the prepared c-plane GaN wafer.

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