GaN crystals and gaN substrates

Abstract

This invention provides a GaN crystal that can be used as a substrate in nitride semiconductor devices with lateral device structures such as GaN-HEMT; and a GaN substrate that can be used in the fabrication of nitride semiconductor devices with lateral device structures such as GaN-HEMT. The GaN crystal has a 5cm² diameter. 2 The surfaces with an inclination of less than 10 degrees relative to the (0001) crystal plane have a Mn concentration of 1.0 × 10⁻⁶. 16 atoms / cm 3 Above and less than 1.0 × 10 19 atoms / cm 3 The total donor impurity concentration is less than 5.0 × 10⁻⁶. 16 atoms / cm 3 .

Description

Technical Field

[0001] This invention relates to a GaN crystal and a GaN substrate, and more particularly to a semi-insulating GaN crystal and a semi-insulating GaN substrate. Background Technology

[0002] GaN (gallium nitride) is a type of group III nitride compound with a wurtzite-type crystal structure belonging to the hexagonal crystal system.

[0003] In recent years, as substrates for GaN-HEMT (High Electron Mobility Transistor), substrates with a semi-insulating GaN layer as the surface layer and single-crystal GaN substrates composed entirely of semi-insulating GaN crystals have been studied (Patent Document 1).

[0004] Semi-insulating GaN refers to high-resistivity GaN, typically with a resistivity of 1×10⁻⁶. 5 Room temperature resistivity above Ωcm.

[0005] To make GaN semi-insulating, it is known that it is only necessary to dop it with impurities such as Fe (iron), Mn (manganese), and C (carbon) that have the function of compensating n-type charge carriers (compensating impurities).

[0006] According to the content described in Non-Patent Literature 1, when the Mn concentration is 2×10⁻⁶ using the HVPE (Hydride Vapor Phase Epitaxy) method... 17 cm -3 When GaN crystals are homoepitaxially grown on a GaN substrate, the concentration of Si as a donor impurity is 6 × 10⁻⁶. 16 cm -3 It is believed that the Si element at this concentration was unintentionally introduced into the crystal under the HVPE growth environment, and therefore it can be said that it is independent of the Mn concentration.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2012-246195

[0010] Non-patent literature

[0011] Non-patent literature 1: Japanese Journal of Applied Physics, Vol. 58, SC1047 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] In order to obtain a GaN substrate for use in GaN-HEMT, the inventors investigated Mn-doped semi-insulating GaN. The results showed that while increasing the Mn doping level resulted in higher resistivity in the GaN crystal, it also increased the through-dislocation density compared to undoped GaN crystals, and the GaN crystal itself became more brittle, thus degrading crystal quality.

[0014] Thus, currently, we have not yet obtained Mn-doped GaN crystals with sufficiently high resistivity and good crystal quality comparable to undoped GaN crystals.

[0015] The objective of this invention is to obtain a GaN crystal that can be used as a substrate in nitride semiconductor devices with lateral device structures such as GaN-HEMT.

[0016] Furthermore, the objective of this invention is to obtain a GaN substrate that can be used to fabricate nitride semiconductor devices with lateral device structures such as GaN-HEMT.

[0017] Technical solutions to the problem

[0018] The inventors conducted in-depth research and discovered that maintaining a balance between the concentration of Mn, which acts as a compensating impurity contributing to high resistivity, and the concentration of donor impurities, which hinder the high resistivity effect brought about by the compensating impurities, is crucial in GaN crystals. They found that optimizing this balance can solve the aforementioned problem. Specifically, they discovered that by growing GaN crystals using the HVPE method with Mn doping, a low concentration of donor impurities can be achieved, while simultaneously doping with Mn at an appropriate concentration, resulting in GaN crystals with semi-insulating properties and good quality. This led to the development of the present invention.

[0019] That is, the main idea of ​​this invention is as follows:

[0020] [1] A GaN crystal, characterized in that the GaN crystal has a 5cm diameter. 2 The surfaces with an inclination of less than 10 degrees relative to the (0001) crystal plane have a Mn concentration of 1.0 × 10⁻⁶. 16 atoms / cm 3 Above and less than 1.0 × 10 19 atoms / cm 3 The total donor impurity concentration is less than 5.0 × 10⁻⁶. 16 atoms / cm 3 .

[0021] [2] According to the GaN crystal described in [1], the Mn concentration is 6.0 × 10⁻⁶. 18 atoms / cm 3 the following.

[0022] [3] According to the GaN crystal described in [1] or [2], the Mn concentration is 1.0 × 10⁻⁶. 17 atoms / cm 3 above.

[0023] [4] The GaN crystal according to any one of [1] to [3] has a full width at half maximum (FWHM) of the (004) XRD rocking curve measured on the (0001) surface side of less than 40 arcsec.

[0024] [5] The GaN crystal according to any one of [1] to [4], wherein the density of penetrating dislocations on the (0001) surface is less than 1.0 × 10⁻⁶. 7 cm -2 .

[0025] [6] A GaN crystal, characterized in that the GaN crystal has a 5cm... 2 The above-mentioned surfaces have an inclination of less than 10 degrees relative to the (0001) crystal plane and are semi-insulating, and satisfy one or more of the following (A) and (B):

[0026] (A) The full width at half maximum (FWHM) of the (0004) XRD rocking curve measured on the (0001) surface side is less than 40 arcsec;

[0027] (B) The density of penetrating dislocations on the (0001) surface is less than 1×10⁻⁶. 7 cm -2 .

[0028] [7] The GaN crystal described in [6] is doped with Mn.

[0029] [8] The GaN crystal according to [6] or [7] has a total donor impurity concentration of less than 5.0 × 10⁻⁶. 16 atoms / cm 3 .

[0030] [9] A GaN substrate, which is composed of GaN crystals as described in any one of [1] to [8].

[0031]

[10] A GaN substrate, characterized in that it has a main surface having a surface tilted at less than 10 degrees relative to the (0001) crystal plane, and a Mn concentration of 1.0 × 10⁻⁶. 16 atoms / cm 3 Above and less than 1.0 × 10 19 atoms / cm 3 The total donor impurity concentration is less than 5.0 × 10⁻⁶. 16 atoms / cm 3 .

[0032]

[11] The GaN substrate according to [9] or

[10] is a single-crystal GaN substrate.

[0033]

[12] The GaN substrate according to

[10] or

[11] is formed by stacking on a support substrate.

[0034]

[13] A method for manufacturing an epitaxial wafer, comprising the following steps: preparing a GaN substrate as described in any one of

[10] to

[12] ; and epitaxially growing one or more nitride semiconductor layers on the prepared substrate.

[0035]

[14] An epitaxial wafer comprising a GaN substrate as described in any one of

[10] to

[12] and one or more nitride semiconductor layers epitaxially grown on the substrate.

[0036]

[15] A method for manufacturing a nitride semiconductor device, comprising the following steps: preparing a GaN substrate as described in any one of

[10] to

[12] ; and epitaxially growing one or more nitride semiconductor layers on the prepared substrate.

[0037]

[16] A method for manufacturing a GaN-HEMT includes the following steps: preparing a GaN substrate as described in any one of

[10] to

[12] ; and epitaxially growing one or more nitride semiconductor layers on the prepared substrate.

[0038]

[17] A GaN substrate, which is a GaN substrate formed by stacking GaN crystals on a supporting substrate, characterized in that,

[0039] The GaN crystal has a 5cm 2 The above surfaces have an inclination of less than 10 degrees relative to the (0001) crystal plane.

[0040] The Mn concentration at a position less than 2 μm away from the interface between the GaN crystal and the supporting substrate along the

[0001] direction is less than 20 times the Mn concentration at a position more than 2 μm away from the interface along the

[0001] direction.

[0041] Invention Effects

[0042] According to the present invention, a GaN crystal is provided that exhibits semi-insulation properties and good crystal quality even when the concentration of Mn, used as a compensating impurity, is relatively low. Therefore, a GaN crystal suitable for use as a substrate in lateral nitride semiconductor devices such as GaN-HEMTs is provided; and a GaN substrate suitable for manufacturing lateral nitride semiconductor devices such as GaN-HEMTs is provided. Attached Figure Description

[0043] Figure 1 This is a three-dimensional view of a GaN crystal representing an embodiment.

[0044] Figure 2 This is a plan view showing the (0001) surface of the GaN crystal in the embodiment divided into 5mm × 5mm cells using a square grid.

[0045] Figure 3 This is a perspective view of a single-crystal GaN substrate illustrating an embodiment.

[0046] Figure 4 This is a cross-sectional view of a single-crystal GaN substrate used in an embodiment.

[0047] Figure 5 This is a cross-sectional view of a single-crystal GaN substrate used in an embodiment.

[0048] Figure 6 This is a schematic diagram showing the basic configuration of an HVPE apparatus suitable for GaN crystal growth in an embodiment.

[0049] Figure 7 This is a graph showing the relationship between the susceptor temperature of the HVPE device and the impurity concentration of the grown GaN crystal.

[0050] Figure 8 This is a graph showing the relationship between the temperature of the Ga storage section and the Mn, Si, and O concentrations of the grown GaN crystal.

[0051] Explanation of reference numerals in the attached figures

[0052] 1: HVPE device; 2: reactor; 3: gallium storage unit; 4: base; 5: first heater; 6: second heater; 7: sleeve; 10: crystal; 11: (0001) surface; 12: (000-1) surface; 100: substrate; 101: (0001) surface; 102: (000-1) surface; 110: first region; 120: second region. Detailed Implementation

[0053] In GaN crystals, the crystal axes parallel to

[0001] and [000-1] are called c-axis, the crystal axis parallel to <10-10> is called m-axis, and the crystal axis parallel to <11-20> is called a-axis. The crystal planes orthogonal to the c-axis are called c-planes, the crystal planes orthogonal to the m-axis are called m-planes, and the crystal planes orthogonal to the a-axis are called a-planes.

[0054] In this specification, when referring to crystal axes, crystal planes, crystal orientations, etc., unless otherwise specified, they refer to the crystal axes, crystal planes, crystal orientations, etc. of GaN crystals.

[0055] The Miller index (hkil) of hexagonal crystal has the relationship h + k = -i, so (hkl) is sometimes labeled with 3 digits. For example, if (0004) is labeled with 3 digits, it is (004).

[0056] In this specification, the numerical range represented by “~” refers to the range including the values ​​recorded before and after “~” as the lower and upper limits. “A~B” means above A and below B.

[0057] Embodiments of the present invention will now be described with appropriate reference to the accompanying drawings. Embodiments of the present invention include, but are not limited to, the following methods.

[0058] 1. GaN crystal

[0059] The first embodiment of the present invention relates to a GaN crystal.

[0060] The GaN crystal of the first embodiment (hereinafter also referred to as "GaN crystal") has a 5cm diameter. 2 The above-described surfaces have an inclination of 10 degrees or less (including 0 degrees) relative to the (0001) crystal plane. In this specification, the term "surface with an inclination of 10 degrees or less (including 0 degrees) relative to the (0001) crystal plane" is sometimes abbreviated as "(0001) surface". The GaN crystal described above can have various thicknesses and can take various forms, such as a self-supporting substrate, an epitaxial layer grown on another GaN crystal, or a GaN layer stacked on a supporting substrate using bonding technology. The shape of the GaN crystal in the first embodiment is arbitrary, but a shape that yields the GaN substrate described later is preferred.

[0061] (0001) The surface area can be 18 cm². 2 Above or 75cm 2 165cm or above 2 The above, in addition, can be 350cm 2 the following.

[0062] The GaN crystal of the first embodiment can be a crystal grown in any direction, but it is preferably a crystal grown on a surface with an inclination of 10 degrees or less (including 0 degrees) relative to the (0001) crystal plane.

[0063] The (0001) surface of the GaN crystal in the first embodiment is preferably the main surface (large area surface). Furthermore, the area ratio of the (0001) surface in the crystal growth surface is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and the upper limit is 100%.

[0064] If the area of ​​the (0001) surface is large, then as described later, the donor impurity concentration can be suppressed to a low level, and semi-insulating properties can be achieved even if the Mn concentration is relatively low. The same applies when the area ratio of the (0001) surface in the crystal growth plane is within the range described above.

[0065] Figure 1 The crystal 10 shown is an example of a GaN crystal according to the first embodiment.

[0066] Crystal 10 has a (0001) surface 11 as Ga polarity and a (000-1) surface 12 as N polarity. That is, crystal 10 is an example of GaN crystal with the (0001) surface as the main surface, in which crystal growth is performed on the (0001) surface.

[0067] In crystal 10, the tilt of the (0001) surface 11 relative to the (0001) crystal plane can be 0 degrees or more and less than 0.5 degrees, 0.5 degrees or more and less than 1 degree, 1 degree or more and less than 1.5 degrees, 1.5 degrees or more and less than 2.5 degrees, 2.5 degrees or more and less than 5 degrees, 5 degrees or more and less than 10 degrees, etc. The tilt is preferably less than 2.5 degrees.

[0068] The surface of crystal 10 is such a crystal plane that it is closely related to the suppression or control of unintentional donor impurities during its growth.

[0069] Explanation is not required. Figure 1 All surfaces of the (0001) surface 11 shown have an inclination within the aforementioned numerical range. In this case, the (0001) surface (or (0001) surface 11) is referred to as "main surface A", and the main surface A has an area of ​​at least 5 cm². 2 The above-mentioned area can be any inclined (0001) surface with the above-mentioned numerical range. The total area of ​​the (0001) surface 11 or the area of ​​the inclined (0001) surface with the above-mentioned numerical range can be 18 cm². 2 Above or 75cm 2 165cm or above 2 The above, or 350cm, is also acceptable. 2 the following.

[0070] Thickness t is typically above 1 μm, with no particular upper limit, but usually below 4 mm. Thickness t can be above 5 μm and below 200 μm, above 200 μm and below 500 μm, above 500 μm and below 1 mm, above 1 mm, etc.

[0071] (0001) Surface 11 is preferably shaped to contain a circle having a diameter of 20 mm or more. Furthermore, it is preferably shaped to obtain the GaN substrate described later. Therefore, it is preferably shaped to contain a circle having a diameter greater than the diameter R of the substrate 100 described later.

[0072] The GaN crystal in the first embodiment is doped with Mn, and the Mn concentration is 1.0 × 10⁻⁶. 16 atoms / cm 3 Above and less than 1.0 × 10 19 atoms / cm 3 And the total donor impurity concentration is less than 5.0 × 10⁻⁶. 16 atoms / cm 3 Mn, as a compensating impurity, contributes to high resistivity, while donor impurities hinder the high resistivity effect brought about by compensating impurities. Furthermore, from the perspective of impurity energy levels, doping with Mn is superior to doping with other compensating impurities such as Fe. This is because the energy level of Mn is deeper than that of Fe, thus the trapped electrons require greater energy to return to the conduction band.

[0073] The total donor impurity concentration is preferably less than 4.0 × 10⁻⁶. 16 atoms / cm 3 More preferably less than 2.0 × 10 16 atoms / cm 3 Furthermore, in other forms of GaN crystals, it is preferable that at least one of the Mn concentration and the total donor impurity concentration satisfies the above-described range, and it is particularly preferable that at least the donor impurity concentration satisfies the above-described range.

[0074] Total donor impurity concentration refers to the sum of the concentrations of donor impurities contained in the GaN crystal of the first embodiment. Impurities that contribute to GaN's role as a donor include O (oxygen), Si (silicon), S (sulfur), Ge (germanium), and Sn (tin).

[0075] As described below, the GaN crystal of the first embodiment can be grown using HVPE (Hydride Vapor Phase Epitaxy). Therefore, in this GaN crystal, although unintentionally added, it can be grown at a rate of 10... 15 atoms / cm 3The concentration of O (oxygen) and Si (silicon) is on the order of magnitude or higher. On the other hand, in the GaN crystal of the first embodiment, there are donor impurities other than O and Si present at a non-negligible concentration, which is only when these donor impurities are intentionally doped. To explain, "intentional doping" means that in order to dope the element to be doped into the GaN crystal, the element used as a raw material is added as a monomer or a compound, etc.

[0076] Therefore, unless intentionally doped with donor impurities other than O and Si, the total donor impurity concentration of the GaN crystal in the first embodiment can be considered equal to the sum of the O concentration and the Si concentration. Whether the GaN crystal is doped with donor impurities other than O and Si can be confirmed by elemental analysis or the like.

[0077] The GaN crystal of the first embodiment is characterized by a large difference between the Mn concentration and the total donor impurity concentration, and a low total donor impurity concentration, so the resistivity is not easily affected by changes in the donor impurity concentration.

[0078] Furthermore, a notable feature of the GaN crystal in the first embodiment is that, due to the low total donor impurity concentration, a high resistivity can be achieved with a relatively low Mn concentration.

[0079] In the first embodiment, the Mn concentration of the GaN crystal can be 6.0 × 10⁻⁶. 18 atoms / cm 3 Below, 5.0×10 18 atoms / cm 3 Below, 3.0×10 18 atoms / cm 3 Below, 1.0×10 18 atoms / cm 3 Below, 8.0×10 17 atoms / cm 3 The following can also be 1.0×10 16 atoms / cm 3 Above, 3.0×10 16 atoms / cm 3 Above, 5.0×10 16 atoms / cm 3 Above, 1.0×10 17 atoms / cm 3 Above, 3.0×10 17 atoms / cm 3 Above, 5.0×10 17 atoms / cm 3 above.

[0080] If the total donor impurity concentration is less than 5.0 × 10 16 atoms / cm 3 The room temperature resistivity of GaN crystal is 1×10⁻⁶ when the Mn concentration is 1×10⁻⁶. 17 atoms / cm 3 It can reach 1×10 11 Ωcm and above, further reaching 2×10 11 Ωcm and above, further reaching 5×10 11 Above Ωcm. Furthermore, the room temperature resistivity of GaN crystals is above 1×10⁻⁶ Mn concentration. 18 atoms / cm 3 It can reach 5×10 12 Ωcm, at a Mn concentration of 3×10 18 atoms / cm 3 It can reach 7×10 12 Ωcm.

[0081] To achieve the same resistivity, reducing the concentration of Mn required in GaN crystals is beneficial for suppressing the decrease in crystal quality and thermal conductivity caused by the addition of Mn.

[0082] It should be noted that the concentrations of donor impurities, compensating impurities, and other elements in GaN crystals can be determined using secondary ion mass spectrometry (SIMS).

[0083] The GaN crystal of the first embodiment may contain C, one of the compensating impurities, at a concentration that meets the detection limit using secondary ion mass spectrometry (SIMS) (approximately 5 × 10⁻⁶). 15 atoms / cm 3 The value is above 1, and preferably less than 1×10. 17 atoms / cm 3 More preferably, less than 5×10 16 atoms / cm 3 The concentration.

[0084] The GaN crystal of the first embodiment may contain compensating impurities other than Mn and C, such as Fe (iron), Co (cobalt) or Ni (nickel), provided that it does not pose a practical obstacle.

[0085] In addition to the impurities mentioned above, the GaN crystal of the first embodiment may also contain H (hydrogen), and its concentration may be, for example, 10. 16 ~10 17 atoms / cm 3 Order of magnitude (specifically 1×10) 16 atoms / cm 3 Above and less than 1×10 18atoms / cm 3 ).

[0086] The full width at half maximum (FWHM) of the (0004) XRD rocking curve measured on the (0001) surface side of the GaN crystal is preferably 40 arcsec or less, more preferably 30 arcsec or less, even more preferably 20 arcsec or less, even more preferably 18 arcsec or less, even more preferably 16 arcsec or less, even more preferably 14 arcsec or less, and even more preferably 12 arcsec or less. Here, FWHM is generally synonymous with the term "half-peak width". This FWHM can be adjusted by the GaN crystal growth method (vapor phase or liquid phase, etc.), the crystal characteristics of the seed substrate used to grow the GaN crystal, the crystal growth conditions, the selection of the growth surface, or the impurity content, etc.

[0087] (0004) The XRD rocking curve is one of the indicators of crystal quality, and it is measured using CuKα1 radiation. During the measurement, the X-ray tube is operated, for example, at a voltage of 45 kV and a current of 40 mA.

[0088] In the XRD rocking curve determination of (0004), when X-rays are incident on the (0001) surface, the incident surface of the X-rays can be made perpendicular to the a-axis or the m-axis.

[0089] The X-ray beam size can be set as follows: when the incident angle (the angle formed by the reflecting surface and the X-ray) is set to 90°, that is, when the X-ray is incident perpendicularly onto the (0004) surface, which serves as the reflecting surface, the size of the irradiated area on the (0001) surface 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 refers to the axis of rotation of the sample in the rocking curve measurement.

[0090] With the X-ray beam size set in this way, ω is approximately 36.5° in the (0004) XRD rocking curve measurement, therefore the size of the irradiated area is approximately 1.7 × 5 mm. 2 .

[0091] The penetration dislocation density (hereinafter referred to as "dislocation density") of the GaN crystal in the first embodiment is typically less than 1 × 10⁻⁶. Furthermore, it has the same meaning as the dark spot density of the cathodoluminescence (CL) method described in the experimental examples below. 7 cm -2 Preferably less than 5×10 6 cm -2 More preferably, less than 1×10 6 cm -2 More preferably, less than 5 × 10 5 cm -2More preferably, less than 1×10 5 cm -2 The dislocation density can be adjusted by the following methods: the growth method of GaN crystal (vapor phase method, liquid phase method, etc.), the crystal characteristics of the seed substrate used to grow GaN crystal, crystal growth conditions, the selection of the growth surface, or the content of impurities, etc.

[0092] In a particularly preferred example, the (0001) surface of the GaN crystal of the first embodiment is as follows: Figure 2 As shown, when the grid is divided into 5mm×5mm cells by square grids, there is at least one 100μm×100μm square region without penetrating dislocations in each 5mm×5mm cell.

[0093] There are three types of penetrating dislocations: edge, spiral, and mixed. However, this specification does not distinguish between them and refers to them collectively as penetrating dislocations.

[0094] The presence and density of through dislocations in the GaN crystal of the first embodiment can be investigated by etching with 89% sulfuric acid heated to 270°C for 1 time. The etch pits formed on the (0001) surface by this etching correspond to through dislocations, and their density is equivalent to the density of through dislocations. This situation is confirmed by investigating the correspondence between the etch pits formed when a conductive GaN crystal grown using HVPE is etched under the same conditions and the dark spots appearing in the cathodoluminescence (CL) image.

[0095] Other forms of GaN crystals in the first embodiment satisfy one or more of the preferred ranges selected from the preferred ranges of the full width at half maximum (FWHM) of the (0004) XRD rocking curve measured on the (0001) surface side of the GaN crystal and the preferred range of the penetrating dislocation density on the (0001) surface. It should be noted that the GaN crystals in these other embodiments preferably apply the conditions of the GaN crystals of the first embodiment described above, as well as the conditions of the GaN crystals described in other forms.

[0096] There are no particular limitations on the method for obtaining the GaN crystals described above. Specifically, they can be obtained through the GaN crystal growth methods described later.

[0097] 2. GaN substrate

[0098] The second embodiment of the present invention relates to a GaN substrate.

[0099] The GaN substrate of the second embodiment has a main surface with a tilt of less than 10 degrees relative to the (0001) crystal plane, and an Mn concentration of 1.0 × 10⁻⁶. 16 atoms / cm 3 Above and less than 1.0 × 10 19 atoms / cm3 The total donor impurity concentration is less than 5.0 × 10⁻⁶. 16 atoms / cm 3 The surface with an inclination of less than 10 degrees relative to the (0001) crystal plane is preferably 5 cm. 2 That's all. In particular, the GaN substrate in the second embodiment is preferably a single-crystal GaN substrate, and more preferably a self-supporting substrate composed only of single-crystal GaN.

[0100] The GaN substrate of the second embodiment may be suitably obtained from the GaN crystal of the first embodiment, but is not limited to being obtained from the GaN crystal of the first embodiment.

[0101] Alternatively, when growing a GaN crystal on a support substrate and obtaining a GaN substrate from the GaN crystal, the GaN substrate can also be a GaN substrate composed of a support substrate and a GaN crystal stacked together. In this case, the GaN crystal portion only needs to satisfy the above requirements.

[0102] The GaN substrate of the second embodiment is preferably at least partially composed of the GaN crystal of the first embodiment described above. In this case, the GaN substrate of the second embodiment can exhibit the same effects as the GaN crystal of the first embodiment described above.

[0103] like Figure 3 The substrate 100 shown is an example of a GaN substrate according to the second embodiment, having a (0001) surface 101 as Ga polarity and a (000-1) surface 102 as N polarity.

[0104] The diameter R' of the substrate 100 is typically 20 mm or more, typically 25–27 mm (about 1 inch), 50–55 mm (about 2 inches), 100–105 mm (about 4 inches), or 150–155 mm (about 6 inches), etc.

[0105] The thickness t' of the substrate 100 is set to a value that makes it easy to process the substrate 100, based on the diameter R'. For example, when the diameter R' of the substrate 100 is about 2 inches, the thickness t' is preferably 250 to 500 μm, more preferably 300 to 450 μm.

[0106] Of the two large-area surfaces of the substrate 100, the (0001) surface 101 is used for the epitaxial growth of the nitride semiconductor layer. The (0001) surface 101 is mirror polished, and its root mean square (RMS) roughness, as measured by AFM, is typically less than 2 nm in the measurement range of 2 μm × 2 μm, preferably less than 1 nm, and more preferably less than 0.5 nm.

[0107] (000-1) Surface 102 is the back side, so it can be either mirror polished or matte (rough) polished.

[0108] The edges of substrate 100 can be chamfered.

[0109] The substrate 100 can be marked in various ways as needed: orientation planes or grooves to indicate crystal orientation, or indicator planes to easily identify the surface and back side, etc.

[0110] The substrate 100 is disk-shaped, but in the modified example, the shapes of the (0001) surface 101 and the (000-1) surface 102 can be square, rectangle, hexagon, octagon or ellipse, or they can be amorphous.

[0111] Figure 4 The section represents the cut when the substrate 100 is cut by a plane perpendicular to the (0001) surface 101.

[0112] In the substrate 100, the first region 110 including the (0001) surface 101 may be composed of the GaN crystal of the first embodiment described above.

[0113] When the thickness t1 of the first region 110 is less than the thickness t' of the substrate 10, such as Figure 4 As shown, the substrate 100 has a second region 120 on the (000-1) surface 102 side.

[0114] The second region 120 can be characterized by a room temperature resistivity of less than 1×10⁻⁶. 5 The formation of GaN crystals with an Ωcm (i.e., non-semi-insulating GaN crystals) is achieved.

[0115] The total concentration of compensating impurities in the second region 120 is typically lower than that in the first region 110. The second region 120 may have a region near its boundary with the first region 110 where the total concentration of compensating impurities increases in stages or continuously as it approaches the first region 110.

[0116] The substrate 100 having a first region 110 and a second region 120 can be manufactured by epitaxial growth on the first region 110 to form the second region 120 or by epitaxial growth on the second region 120 to form the first region 110.

[0117] In one example, such as Figure 5 As shown, the thickness of the substrate 100 can be equal to the thickness t1 of the first region 110. In other words, the substrate 100 can be made solely of the GaN crystal of the first embodiment.

[0118] The third embodiment of the present invention is a GaN substrate having a 5cm diameter. 2The GaN substrate formed by stacking GaN crystals with a tilt of less than 10 degrees relative to the (0001) crystal plane on a supporting substrate, wherein the Mn concentration of the GaN substrate at a position less than 2 μm away from the interface between the GaN crystal and the supporting substrate along the

[0001] direction is less than 20 times the Mn concentration at a position more than 2 μm away from the interface along the

[0001] direction.

[0119] The GaN crystal in the GaN substrate of the third embodiment may also be the GaN crystal of the first embodiment. Furthermore, the GaN substrate of the third embodiment may also be a GaN substrate equivalent to the GaN substrate of the second embodiment.

[0120] Positions less than 2 μm away from the interface along the (0001) direction and positions more than 2 μm away refer to a coaxial comparison along the normal direction of the interface between the GaN crystal and the supporting substrate. Specifically, with the interface as a reference, the Mn concentration at any position greater than 0 μm and less than 2 μm away along this normal direction is compared with the Mn concentration at any position more than 2 μm away.

[0121] The inventors have discovered that when the Mn concentration at a position less than 2 μm away from the GaN crystal and the supporting substrate along the

[0001] direction is less than 20 times the Mn concentration at a position more than 2 μm away from the interface along the

[0001] direction, crack formation can be suppressed during subsequent processes such as polishing. Furthermore, it has been confirmed that the increase in through-dislocation density introduced by crystal growth can also be suppressed.

[0122] Typically, when Mn-doped GaN crystals are grown from a supporting substrate, the Mn concentration at the interface tends to be high. This is thought to be due to the introduction of manganese vapor into the seed substrate. For example, the reason is believed to be that the target Mn concentration is 3.0 × 10⁻⁶. 17 atoms / cm 3 In this case, the ambient temperature of the Mn metal needs to be set to 800°C. However, during the process of reaching 800°C, manganese vapor is supplied to the seed substrate before the growth of the GaN crystal begins. As a result, when the Mn at the interface is concentrated, an increase in the density of through dislocations is observed. However, the inventors have found that this situation can be suppressed by satisfying the above-mentioned benchmark.

[0123] The ratio of the Mn concentration at a location less than 2 μm away from the interface along the

[0001] direction to the Mn concentration at a location more than 2 μm away from the interface along the

[0001] direction is preferably 20 times or less, more preferably 10 times or less, even more preferably 5 times or less, and particularly preferably 2 times or less.

[0124] Furthermore, when the thickness of the GaN substrate is 10.0 μm or more, as a variation of the third embodiment, the condition in the third embodiment that "the Mn concentration at a position less than 2 μm away from the interface between the GaN crystal and the supporting substrate along the (0001) direction is 20 times or less than the Mn concentration at a position more than 2 μm away from the interface along the

[0001] direction" can be applied as "the ratio of the Mn concentration measured at a position 1.0 μm away from the interface between the GaN crystal and the supporting substrate along the

[0001] direction to the average value of the Mn concentration measured at 1.0 μm intervals (9 positions) at positions from 2.0 μm to 10.0 μm away from the interface along the

[0001] direction is 20 times or less." This ratio is preferably 10 times or less, more preferably 5 times or less, and even more preferably 2 times or less.

[0125] In addition, as another variation, the condition that "the Mn concentration measured 1.0 μm away from the interface between the GaN crystal and the supporting substrate along the

[0001] direction is 20 times or less relative to the average value of the Mn concentration measured at 10 μm intervals from 2.0 μm to the outermost surface along the

[0001] direction from the interface" can also be applied. This ratio is preferably 10 times or less, more preferably 5 times or less, and even more preferably 2 times or less.

[0126] There are no particular limitations on the method for manufacturing GaN substrates with Mn concentration characteristics as described above. Specifically, examples include: methods for starting GaN crystal growth in a temperature region with low manganese vapor supply, as described later; and methods for heating Mn raw materials using a heater different from that used for Ga raw materials.

[0127] The third embodiment of the present invention includes variations, and may also be a preferred embodiment of the second embodiment described above. Furthermore, matters described as the first and second embodiments above can be applied as preferred embodiments in the third embodiment.

[0128] 3. GaN crystal growth methods

[0129] An example of a method for manufacturing a GaN crystal according to the first embodiment is shown below. The GaN crystal of the first embodiment is typically grown using HVPE.

[0130] The HVPE apparatus suitable for growing GaN crystals according to the first embodiment and the conditions applied when using the apparatus to grow GaN crystals according to the first embodiment will be described below.

[0131] 3.1.HVPE device

[0132] The basic configuration of the HVPE apparatus suitable for growing GaN crystals according to the first embodiment is as follows: Figure 6 As shown schematically.

[0133] Reference Figure 6 The HVPE apparatus 1 includes: a hot-wall reactor 2, a gallium storage section 3 and a base 4 disposed within the reactor, and a first heater 5 and a second heater 6 disposed outside the reactor. The first heater 5 and the second heater 6 respectively surround the reactor 2 in an annular shape.

[0134] Reactor 2 is a quartz tubular chamber. Reactor 2 contains a first section Z1, primarily heated by the first heater 5, and a second section Z2, primarily heated by the second heater 6. Exhaust pipe P E It is connected to the reactor end on the Z2 side of the second partition.

[0135] The gallium storage section 3 configured in the first partition Z1 is a container with a gas inlet and a gas outlet, which can be formed of carbon or quartz, or a combination of carbon and quartz components.

[0136] The base 4, located in the second partition Z2, is made of graphite, but is not limited to it. It can be made of metals with excellent heat resistance and corrosion resistance, such as W (tungsten) or Mo (molybdenum). Alternatively, it can be made by coating the surface of a heat-resistant ceramic such as SiC with pyrolytic graphite. The mechanism for rotating the base 4 can be arbitrarily configured.

[0137] In the second section Z2, a sleeve 7 is inserted into reactor 2 to prevent the inner wall of reactor 2 from contacting the gas flowing inside reactor 2. The sleeve 7 is formed of flexible graphite sheets or cylindrical graphite coated with pyrolytic carbon, and has an outer diameter slightly smaller than the inner diameter of reactor 2. The sleeve 7 can be in contact with or completely sealed to reactor 2, or there can be a slight gap. The placement of the sleeve 7 is considered effective in reducing the Si concentration of the grown GaN crystal. This is because the presence of the sleeve 7 inhibits the introduction of Si elements from reactor 2, formed from the quartz tube, into the GaN crystal.

[0138] When growing GaN crystals using the HVPE apparatus 1, metallic gallium is added to the gallium storage section 3, seed crystals are placed on the substrate 4, and the first section Z1 and the second section Z2 are heated by the first heater 5 and the second heater 6, respectively. Simultaneously, NH3 (ammonia) diluted with a carrier gas is supplied to the second section Z2 through the ammonia inlet pipe P1, and HCl (hydrogen chloride) diluted with a carrier gas is supplied to the gallium storage section 3 through the hydrogen chloride inlet pipe P2. The HCl reacts with the metallic gallium in the gallium storage section 3, and the resulting GaCl (gallium chloride) is transported to the second section Z2 through the gallium chloride inlet pipe P3. In the second section Z2, NH3 reacts with GaCl, and the resulting GaN crystallizes on the seed crystal.

[0139] When growing GaN crystals on Mn-doped seed crystals, N2 or similar substances are introduced into a dopant inlet pipe P4 containing metallic Mn before being introduced into reactor 2. Mn can also be doped by introducing HCl or H2 into the dopant inlet pipe P4, but N2 is preferred, especially to suppress the concentration of Si as a donor impurity. When N2 is selected as the carrier gas, it is assumed that the Mn surface within the dopant inlet pipe P4 forms nitrides, and the vaporized Mn nitrides are released as a dopant source into the second partition Z2.

[0140] The vapor pressure of manganese is positively correlated with temperature. Therefore, the concentration of Mn in GaN crystals can be adjusted by changing the temperature of the partition Z1 containing Mn.

[0141] The portions of the ammonia inlet tube P1, hydrogen chloride inlet tube P2, gallium chloride inlet tube P3, and dopant inlet tube P4 exposed to high temperatures within the reactor can be made of quartz.

[0142] In particular, regarding the nozzle of the gallium chloride inlet tube P3, since it is located in the second zone Z2, which is heated to a higher temperature than the first zone Z1, and H2, as a byproduct of the GaCl generation reaction, flows therein, it is preferably formed of a carbon material such as pyrolytic graphite or W (tungsten) rather than quartz.

[0143] The inventors conducted experiments using an HVPE apparatus with the same basic structure as HVPE apparatus 1. The results showed that when the nozzle of the gallium chloride inlet tube was changed from a quartz tube to a pyrolytic graphite tube, only N2 was used in the carrier gas, and the Si concentration of the GaN crystal grown unintentionally was halved. It should be noted that the O concentration of the GaN crystal was not affected by this nozzle change.

[0144] Figure 6 The nozzles of the ammonia inlet pipe P1 and the gallium chloride inlet pipe P3 are independent, but in a preferred embodiment, a double-tube nozzle can be used, with the former as the outer tube and the latter as the inner tube. In this case, the outer tube diameter can be increased to be the same as the inner diameter of the reactor.

[0145] Figure 6 In the gallium chloride inlet tube P3 and the dopant inlet tube P4, the nozzles are independent. However, in a preferred embodiment, to ensure that the grown GaN crystal is uniformly doped with Mn, GaCl can be mixed with the dopant source and then released into the second partition Z2 through a shared nozzle. Therefore, for example, the nozzle of the dopant inlet tube P4 can be configured inside the gallium chloride inlet tube P3.

[0146] In such Figure 6In the HVPE apparatus 1 shown, the reactor 2 can be changed from a transverse to a longitudinal configuration without altering its basic structure. The reactor that is changed to a longitudinal configuration can be either a configuration in which the feed gas flows downwards within the reactor, or a configuration in which the gas flows in the opposite direction.

[0147] 3.2. Seed Crystals

[0148] When growing the GaN crystal in the embodiment, the seed crystal is preferably a c-plane single-crystal GaN substrate. Furthermore, the seed crystal is preferably an undoped GaN substrate.

[0149] c-plane single-crystal GaN substrates, wherein unintentionally doped c-plane single-crystal GaN substrates typically have a density of less than 1 × 10⁻⁶. 7 cm -2 The dislocation density is high, thus enabling the growth of a Mn-doped GaN layer with good surface flatness on its (0001) surface.

[0150] When using GaN / sapphire templates as seed crystals, the morphology of the Mn-doped GaN layer is inferior to that of an undoped GaN layer grown on the same seed crystal. In contrast, the inventors have grown undoped GaN layers with an Mn concentration of approximately 2 × 10⁻⁶ on c-plane single-crystal GaN substrates. 17 cm -3 The surfaces of the GaN layers were all flat, and no morphological differences discernible by differential interference microscopy were observed between them. Therefore, it can be confirmed that if a c-plane single-crystal GaN substrate is used as a seed crystal to grow Mn-doped GaN crystals, flat growth comparable to that of undoped GaN crystals can be achieved.

[0151] The inventors believe that the morphology of the growth surface may affect the O (oxygen) concentration of the GaN crystal. Even under the same growth environment, the O concentration entering a GaN layer grown along the

[0001] direction can differ by more than 50 times between a flat and an uneven growth surface. This decrease in O concentration occurs when the growth surface is a flat surface parallel to the (0001) crystal plane.

[0152] The seed crystal can be a GaN substrate obtained using a gas-phase method such as HVPE, or a GaN substrate obtained using a liquid-phase method such as ammonothermal method. Regarding the ammonothermal method, it can be either an acidic ammonothermal method or an alkaline ammonothermal method.

[0153] In a preferred embodiment, a c-plane single-crystal GaN substrate can be used as a seed crystal. This substrate is grown using NH4F (or HF) and NH4I (or HI) as mineralizing agents via an acidic ammonothermal method, resulting in a (0004) XRD rocking curve full width at half maximum (FWHM) of less than 20 arcsec. For details regarding the manufacturing process of this c-plane single-crystal GaN substrate, please refer to Publication No. WO2018 / 030311. When using a GaN substrate manufactured using a liquid-phase method such as ammonothermal methods as a seed crystal, compared to using a GaN substrate manufactured using HVPE, a Mn-doped GaN crystal with a lower penetration dislocation density can be obtained.

[0154] 3.3. Carrier Gas

[0155] When growing GaN crystals according to the embodiments using HVPE, the use of H2 (hydrogen) as the carrier gas is undesirable. It is preferable to use only inert gases such as N2 (nitrogen) or rare gases as the carrier gas. N2 is a preferred inert gas.

[0156] The reason why H2 is not preferred as a carrier gas is that H2 helps decompose quartz, which is used as a reactor and piping material, and is considered to be the main reason for unintentional Si doping in the grown GaN crystal.

[0157] 3.4. Temperature conditions

[0158] In use such Figure 6 When using the HVPE apparatus 1 shown, the temperature of the first partition Z1 has little effect on the impurity concentration of the grown GaN crystal.

[0159] Based on experiments using an HVPE apparatus with the same basic structure as HVPE apparatus 1 (using only N2 as the carrier gas), when the base temperature was fixed at 1030°C and the temperature of the gallium storage section was varied between 440°C and 840°C, no substantial changes were observed in the Si, O, C, and H concentrations of the GaN crystal grown without intentional doping. Furthermore, the growth rate of the GaN crystal also remained essentially unchanged.

[0160] However, when the temperature of the gallium storage section is set above 900°C, an increase in Si and C concentrations can be observed in the grown GaN crystal.

[0161] On the other hand, the temperature T2 of the second partition Z2 has a significant impact on the impurity concentration of the grown GaN crystal.

[0162] Figure 7 The figure shows the relationship between the base temperature and the impurity concentration of the grown GaN crystal obtained from experiments using an HVPE apparatus with the same basic structure as HVPE apparatus 1.

[0163] In this experiment, the temperature of the gallium storage section was fixed at 840°C, while the base temperature varied between 985°C and 1070°C. Only N2 was used as the carrier gas, and GaCl and NH3 were supplied to the reactor at flow rates of 40 sccm and 500 sccm, respectively, to grow GaN crystals on a single-c-plane GaN substrate without intentional doping.

[0164] like Figure 7 As shown, the O concentration of the grown GaN crystal was adjusted by increasing the substrate temperature from 985℃ to 1005℃, and from 10... 17 atoms / cm 3 Quantity up to 10 16 atoms / cm 3 The magnitude was reduced by an order of magnitude, further decreasing to 10 by increasing the base temperature. 15 atoms / cm 3 The order of magnitude. This is presumably because the higher the temperature, the better the surface flatness of the grown GaN layer, making it more difficult for O to penetrate.

[0165] On the other hand, the Si concentration of the grown GaN crystal tends to increase with increasing substrate temperature, but does not exceed 5 × 10⁻⁶. 15 atoms / cm 3 .

[0166] The C concentration of the grown GaN crystal also showed a tendency to increase with increasing substrate temperature.

[0167] 3.5. Mn doping

[0168] The inventors used an HVPE apparatus with the same basic structure as HVPE apparatus 1, supplied 50 sccm of N2 carrier gas to a dopant inlet tube containing metallic Mn, and changed the temperature T1 of the first partition Z1 during the experiment. The results showed that the Mn concentration of the GaN crystal grown on the single-c GaN substrate at 1030°C was as follows: Figure 8 The land shown is in 1×10 16 atoms / cm 3 Up to 3×10 19 atoms / cm 3 Between these values, the temperature T1 varies approximately proportionally.

[0169] In this experiment, not only the carrier gas supplied to the dopant introduction tube P4, but also the entire carrier gas supplied to the reactor was N2. In fact, since the dopant introduction tube P4 is very close to the Ga storage section 3, both the dopant introduction tube and the Ga storage section can be heated by the same heater. Therefore, the target Mn doping amount is 2.2 × 10⁻⁶. 18atoms / cm 3 At that time, the set temperature of the dopant introduction tube was 900℃.

[0170] Thus, if the set temperature of the dopant introduction tube is set to 900°C before the growth of the GaN crystal begins, the Mn precursor is transported to the substrate surface, resulting in an increase in the Mn concentration during the initial stage of crystal growth. On the other hand, it is determined that even if the temperature T1 is 500°C, the growth rate of the GaN crystal will not decrease. Therefore, by setting the temperature T1 to 500°C before the start of growth and heating it to the target set temperature, such as 900°C, after the start of growth, the Mn concentration during the initial stage of growth can be suppressed. From this perspective, the temperature T1 before the start of growth is preferably in the range of 400°C to 600°C, and more preferably in the range of 450°C to 550°C. This method is one of the effective means for realizing the third embodiment of the present invention.

[0171] Regarding the growth method of GaN crystals, the conditions other than those mentioned above can be applied using the conventional conditions in HVPE.

[0172] 4. Applications of the substrate

[0173] The GaN substrate (especially a single-crystal GaN substrate) of the second or third embodiment (hereinafter collectively referred to as the second embodiment, etc.) is preferably used for the manufacture of nitride semiconductor devices, especially nitride semiconductor devices with lateral device structures. Specifically, the nitride semiconductor device can be manufactured by a method having the following steps: preparing the above-described GaN substrate; and epitaxially growing one or more nitride semiconductor layers on the prepared substrate.

[0174] Nitride semiconductors, also known as group III-V nitride compound semiconductors, group III nitride compound semiconductors, GaN-based semiconductors, etc., are compounds formed by replacing some or all of the gallium in GaN with other elements in group 13 of the periodic table (B, Al, In, etc.).

[0175] A representative example of nitride semiconductor devices with lateral device structures is GaN-HEMT (High Electron Mobility Transistor). However, lateral device structures can also be used in electronic devices other than HEMTs, such as bipolar transistors, as well as in light-emitting devices such as light-emitting diodes (LEDs) and laser diodes (LDs).

[0176] In the substrate made of GaN crystal of the first embodiment, in addition to the single-crystal GaN substrate of the second embodiment, there is also a substrate formed by laminating a GaN layer made of GaN crystal of the first embodiment onto a support substrate using a bonding technique. This substrate can also be used for the same purposes as the single-crystal GaN substrate of the second embodiment.

[0177] Furthermore, the GaN crystal of the first embodiment and the GaN substrate of the second embodiment, etc., can be used as an epitaxial wafer by stacking the crystal or one or more nitride semiconductor layers epitaxially grown on the substrate. The method for manufacturing the epitaxial wafer is not particularly limited; for example, it can be manufactured by a method comprising the following steps: preparing the aforementioned GaN substrate; and epitaxially growing one or more nitride semiconductor layers on the prepared substrate.

[0178] 5. Experimental Results

[0179] 5.1. Experiment 1

[0180] (1) Growth of Mn-doped GaN crystals

[0181] As a seed crystal, it is planned to grow using HVPE with a dislocation density of approximately 2 × 10⁻⁶. 6 ~4×10 6 cm -2 The c-plane single-crystal GaN substrate (a square with one side measuring 20mm).

[0182] On the (0001) surface of the c-plane single-crystal GaN substrate, a material with the same properties as... Figure 6 The HVPE device shown is based on the same basic structure as the HVPE device, and the GaN crystal layer is grown according to the following operating steps.

[0183] First, seed crystals are placed on a base, and then N2 and NH3 are introduced into the reactor at 2700 sccm and 500 sccm respectively, and the reactor is heated.

[0184] Next, after the temperature T1 of the first partition Z1 reaches 500℃ and the temperature T2 of the second partition Z2 reaches 1030℃, the temperature is kept constant, and GaCl and NH3 are supplied at flow rates of 40 sccm and 500 sccm, respectively, thus initiating the growth of the GaN crystal. The only carrier gas supplied during growth is N2; 50 sccm of N2 carrier gas is supplied to the dopant introduction tube, and growth continues until the GaN crystal layer reaches a thickness of 50 μm, resulting in a Mn-doped GaN single crystal with a (0001) surface. The tilt of the crystal growth plane of the Mn-doped single crystal relative to the (0001) crystal plane is 0 degrees. The growth rate of the Mn-doped GaN crystal layer is 1.7 μm / min.

[0185] The following evaluation was conducted on Mn-doped GaN single crystals grown directly on seed substrates.

[0186] (2) Impurity concentration

[0187] When the Mn concentration of the Mn-doped GaN crystal layer was determined using SIMS, the result was 1.0 × 10⁻⁶. 16 atoms / cm 3 Furthermore, the total donor impurity concentration of Si and O is presumed to be the same level as or lower than that of Experiment 2, where the temperature T1 is higher than that of Experiment 1.

[0188] (3) Crystallinity evaluation

[0189] Dislocations, crystal defects in GaN crystals, were observed as dark spots using cathodoluminescence (CL) spectroscopy. Therefore, the dark spot density of the Mn-doped GaN crystal layer was evaluated using the dark spot density obtained by CL spectroscopy. The dark spot density at 2000x magnification was 1.8 × 10⁻⁶. 6 cm -2 Even with Mn doping, no increase in dislocations was observed compared to the c-plane single-crystal GaN substrate prepared as a seed crystal, confirming it as a high-quality Mn-doped GaN crystal.

[0190] 5.2. Experiment 2

[0191] (1) Growth of Mn-doped GaN crystals

[0192] In Experiment 1, the temperature T1 of the first partition Z1 was kept constant at 500℃. Conversely, after maintaining T1 at 500℃ for 5 minutes, the temperature was increased to 600℃ after 10 minutes, and then kept constant at 600℃ until the GaN crystal layer reached a thickness of 50 μm. Other conditions were the same as in Experiment 1. The crystal growth plane of the Mn-doped crystal was tilted 0 degrees relative to the (0001) crystal plane.

[0193] (2) Impurity concentration

[0194] The impurity concentration of the Mn-doped GaN crystal layer obtained using the same method as in Experiment 1 was 2.5 × 10⁻⁶. 16 atoms / cm 3 Si is 5.0 × 10 15 atoms / cm 3 O is 6.0 × 10 15 atoms / cm 3 C is 2.0 × 10 16 atoms / cm 3 H is 3.5 × 10 16 atoms / cm 3 .

[0195] (3) Crystallinity evaluation

[0196] The dark spot density of the Mn-doped GaN crystal layer, evaluated using the same method as in Experiment 1, was 2.3 × 10⁻⁶. 6 cm -2 Even with Mn doping, no increase in dislocations was observed compared to the c-plane single-crystal GaN substrate prepared as a seed crystal, confirming it as a high-quality Mn-doped GaN crystal.

[0197] 5.3. Experiment 3

[0198] (1) Growth of Mn-doped GaN crystals

[0199] In Experiment 1, the temperature T1 of the first partition Z1 was kept constant at 500℃. Conversely, after maintaining T1 at 500℃ for 5 minutes, the temperature was increased to 700℃ after 10 minutes, and then kept constant at 700℃ until the GaN crystal layer reached a thickness of 50 μm. Other conditions were the same as in Experiment 1. The crystal growth plane of the Mn-doped crystal was tilted 0 degrees relative to the (0001) crystal plane.

[0200] (2) Impurity concentration

[0201] The Mn concentration of the Mn-doped GaN crystal layer obtained using the same method as in Experiment 1 was 5.0 × 10⁻⁶. 16 atoms / cm 3 .

[0202] (3) Crystallinity evaluation

[0203] The dark spot density of the Mn-doped GaN crystal layer, evaluated using the same method as in Experiment 1, was 1.8 × 10⁻⁶. 6 cm -2 Even with Mn doping, no increase in dislocations was observed compared to the c-plane single-crystal GaN substrate prepared as a seed crystal, confirming it as a high-quality Mn-doped GaN crystal. Furthermore, the temperature T1 in Experiment 3 was between that in Experiments 2 and 4, suggesting a total donor impurity concentration of 2 × 10⁻⁶ for Si and O. 16 atoms / cm 3 about.

[0204] 5.4. Experiment 4

[0205] (1) Growth of Mn-doped GaN crystals

[0206] In Experiment 1, the temperature T1 of the first partition Z1 was kept constant at 500℃. Conversely, after maintaining T1 at 500℃ for 5 minutes, the temperature was increased to 800℃ after 10 minutes, and then kept constant at 800℃ until the GaN crystal layer reached a thickness of 50 μm. Other conditions were the same as in Experiment 1. The tilt of the Mn-doped crystal growth plane relative to the (0001) crystal plane was 0 degrees.

[0207] (2) Impurity concentration

[0208] The impurity concentration of the Mn-doped GaN crystal layer obtained using the same method as in Experiment 1 was 3.0 × 10⁻⁶. 17 atoms / cm 3 Si is 1.8 × 10 16 atoms / cm 3 O is 1.7 × 10 16 atoms / cm 3 C is 6.0 × 10 15 atoms / cm 3 H is 2.4 × 10 16 atoms / cm 3 .

[0209] (3) Crystallinity evaluation

[0210] The dark spot density of the Mn-doped GaN crystal layer, evaluated using the same method as in Experiment 1, was 1.5 × 10⁻⁶. 6 cm -2 Even with Mn doping, no increase in dislocations was observed compared to the c-plane single-crystal GaN substrate prepared as a seed crystal, confirming it as a high-quality Mn-doped GaN crystal.

[0211] 5.5. Experiment 5

[0212] (1) Growth of Mn-doped GaN crystals

[0213] In Experiment 1, the temperature T1 of the first partition Z1 was kept constant at 500℃. Conversely, after maintaining T1 at 500℃ for 5 minutes, the temperature was increased to 900℃ after 10 minutes, and then kept constant at 900℃ until the GaN crystal layer reached a thickness of 50 μm. Other conditions were the same as in Experiment 1. The crystal growth plane of the Mn-doped crystal was tilted 0 degrees relative to the (0001) crystal plane.

[0214] (2) Impurity concentration

[0215] The cross-section of the Mn-doped GaN crystal was observed using a fluorescence microscope, revealing that the growth layer consisted of two layers. If these layers are designated as layer 1 and layer 2 from the seed side, their thicknesses are 8.5 μm and 41.5 μm, respectively. The impurity concentration of Mn in layer 1 is 1.0 × 10⁻⁶.16 atoms / cm 3 Si is 5.0 × 10 15 atoms / cm 3 O is 6.0 × 10 15 atoms / cm 3 C is 2.0 × 10 16 atoms / cm 3 H is 3.5 × 10 16 atoms / cm 3 Furthermore, the Mn concentration in the second layer is 2.2 × 10⁻⁶. 18 atoms / cm 3 Si is 2.0 × 10 16 atoms / cm 3 O is 1.4 × 10 16 atoms / cm 3 C is 1.8 × 10 16 atoms / cm 3 H is 2.7 × 10 16 atoms / cm 3 That is, the Mn concentration in the first layer is 0.0045 times that in the second layer.

[0216] Here, for the Mn concentration, under the condition of "the ratio of the Mn concentration measured 1.0 μm away from the interface between the GaN crystal and the supporting substrate along the

[0001] direction to the average value of the Mn concentration measured at 1.0 μm intervals at 9 locations along the

[0001] direction from the interface from 2.0 μm to 10.0 μm", the concentration ratio is 0.75 times.

[0217] Furthermore, when applying the condition of “the ratio of the Mn concentration measured 1.0 μm away from the interface between the GaN crystal and the supporting substrate along the

[0001] direction to the average value of the Mn concentration measured at 10 μm intervals from 2.0 μm to the outermost surface along the

[0001] direction from the interface”, the ratio of the concentrations is 0.0075 times.

[0218] The dark spot density of the Mn-doped GaN crystal layer, evaluated using the same method as in Experiment 1, was 2.3 × 10⁻⁶. 6 cm -2 Even with Mn doping, no increase in dislocations was observed compared to the c-plane single-crystal GaN substrate prepared as a seed crystal, confirming it as a high-quality Mn-doped GaN crystal.

[0219] 5.6. Experiment 6

[0220] (1) Fabrication of GaN substrate

[0221] As seed crystals, a c-plane single-crystal GaN substrate grown using NH4F and NH4I as mineralizing agents via an acidic ammonothermal method was used. Otherwise, a Mn-doped c-plane single-crystal GaN substrate was fabricated following essentially the same procedures as in Experiment 4. The full width at half maximum (FWHM) of the (0004) XRD rocking curve of the c-plane single-crystal GaN substrate grown using the aforementioned ammonothermal method was approximately 10 arcsec. The tilt of the Mn-doped crystal growth plane relative to the (0001) crystal plane was 0 degrees.

[0222] (2)(0004) Full width at half maximum of XRD rocking curve

[0223] The full width at half maximum (FWHM) of the (0004) XRD rocking curve of the Mn-doped GaN substrate prepared in (1) above was measured using an X-ray diffraction apparatus [PANalytical X'Pert Pro MRD manufactured by Spectris].

[0224] In the measurement, the line-focused CuKα radiation source was operated at 45 kV and 40 mA, and CuKα1 radiation was obtained using a Ge(440)4 crystal symmetric monochromator. The optical system used was a parallel optical system, employing a half-slit, an X-ray mirror, and a 1 mm wide × 1 mm high cross slit on the incident side. The detector used was a PIXcel semiconductor pixel detector. 3D (Registered trademark) 0D mode. Angular resolution is 5–6 arcsec.

[0225] X-rays are incident on the (0001) surface of the sample with the incident plane perpendicular to an m-axis. The beam size is set as follows: when the incident angle is set to 90°, i.e., when the X-rays are incident perpendicularly on the Ga polar surface, the size of the irradiated area is 1×5 mm. 2 .

[0226] The value measured at point 1 on the sample surface was 8.6 arcsec. Based on the full width at half maximum (FWHM) value of the (0004) XRD rocking curve, the dislocation density of the fabricated Mn-doped GaN substrate, even with a high estimate, would not exceed 102. 5 cm -2 The order of magnitude was increased, resulting in very high-quality crystals. It should be noted that, except for the different GaN substrate used for the seed crystals, the GaN crystals were grown under the same conditions as in Experiment 4, therefore the impurity concentration is considered to be essentially the same as in Experiment 4.

[0227] The experimental results are shown in Table 1. Note that "-" in Table 1 indicates that no measurement was performed.

[0228] [Table 1]

[0229]

[0230] While the present invention has been described above with reference to specific embodiments, these embodiments are shown as examples and do not limit the scope of the invention. The embodiments described in this specification can be modified in various ways without departing from the spirit of the invention, and can be combined with features described in other embodiments within a feasible range.

Claims

1. A GaN crystal, characterized in that, The GaN crystal has a 5cm diameter. 2 The surfaces with an inclination of less than 10 degrees relative to the (0001) crystal plane have a Mn concentration of 1.0 × 10⁻⁶. 16 atoms / cm 3 Above and less than 1.0 × 10 19 atoms / cm 3 The total donor impurity concentration is less than 5.0 × 10⁻⁶. 16 atoms / cm 3 The concentration of C is 5 × 10 15 atoms / cm 3 Above and less than 1×10 17 atoms / cm 3 The full width at half maximum (FWHM) of the (004) XRD rocking curve measured on the (0001) surface side is less than 40 arcsec.

2. The GaN crystal according to claim 1, wherein the Mn concentration is 6.0 × 10⁻⁶. 18 atoms / cm 3 the following.

3. The GaN crystal according to claim 1 or 2, wherein the Mn concentration is 1.0 × 10⁻⁶. 17 atoms / cm 3 above.

4. The GaN crystal according to claim 1 or 2, wherein the through-dislocation density on the (0001) surface is less than 1.0 × 10⁻⁶. 7 cm -2 .

5. The GaN crystal according to claim 1 or 2, wherein the room temperature resistivity is 1×10⁻⁶. 11 Ωcm or more.

6. A GaN substrate, characterized in that, The GaN substrate has a main surface with a tilt of less than 10 degrees relative to the (0001) crystal plane, and the Mn concentration is 1.0 × 10⁻⁶. 16 atoms / cm 3 Above and less than 1.0 × 10 19 atoms / cm 3 The total donor impurity concentration is less than 5.0 × 10⁻⁶. 16 atoms / cm 3 The concentration of C is 5 × 10 15 atoms / cm 3 Above and less than 1×10 17 atoms / cm 3 The full width at half maximum (FWHM) of the (004) XRD rocking curve measured on the (0001) surface side is less than 40 arcsec.

7. The GaN substrate according to claim 6, wherein it is a single-crystal GaN substrate.

8. The GaN substrate according to claim 6 or 7, wherein it is formed by stacking on a supporting substrate.

9. The GaN substrate according to claim 6 or 7, wherein the room temperature resistivity of the GaN crystal is 1 × 10⁻⁶. 11 Ωcm or more.

10. A method for manufacturing an epitaxial wafer, comprising the steps of: preparing a GaN substrate according to any one of claims 6 to 9; and epitaxially growing one or more nitride semiconductor layers on the prepared substrate.

11. An epitaxial wafer comprising a GaN substrate as described in any one of claims 6 to 9 and one or more nitride semiconductor layers epitaxially grown on the substrate.

12. A method for manufacturing a nitride semiconductor device, comprising the steps of: preparing a GaN substrate according to any one of claims 6 to 9; and epitaxially growing one or more nitride semiconductor layers on the prepared substrate.

13. A method for manufacturing a GaN-HEMT, comprising the steps of: preparing a GaN substrate according to any one of claims 6 to 9; and epitaxially growing one or more nitride semiconductor layers on the prepared substrate.

14. A GaN substrate, which is formed by stacking GaN crystals on a supporting substrate, characterized in that, This GaN crystal has a 5cm 2 The above surfaces have an inclination of less than 10 degrees relative to the (0001) crystal plane. The Mn concentration at a position less than 2 μm away from the interface between the GaN crystal and the supporting substrate along the [0001] direction is less than 20 times the Mn concentration at a position more than 2 μm away from the interface along the [0001] direction.

15. The GaN substrate according to claim 14, wherein the room temperature resistivity of the GaN crystal is 1 × 10⁻⁶. 11 Ωcm or more.

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