GaN crystal and method for producing GaN crystal

Abstract

The present invention relates to a GaN crystal comprising a Zn-doped GaN layer, in which the Zn concentration in the Zn-doped GaN layer is 1.0 * 10 < 16 > atoms / cm < 3 > or more and 1.0 * 10 < 20 > atoms / cm < 3 > or less, and the full width at half maximum of the rocking curve by (004) X-ray diffraction is 50 arcsec or less, or the full width at half maximum of the rocking curve by (201) X-ray diffraction is 50 arcsec or less.

Description

Technical Field

[0001] The present invention relates to a gallium nitride (GaN) crystal and a method for manufacturing the same. Background Art

[0002] In recent years, GaN-based high electron mobility transistors (HEMTs) (hereinafter sometimes referred to as “GaN-HEMTs”) have been actively developed as device applications for high frequencies of several tens of GHz to several hundreds of GHz.

[0003] GaN-HEMT is made by growing GaN crystals on a substrate. As substrates for GaN-HEMT, silicon, silicon carbide (SiC), GaN, etc. have been studied, but GaN-HEMT using GaN substrates can be expected to have superior performance compared to those using other substrates.

[0004] Although GaN-HEMT repeatedly switches current on and off at high frequencies, it is ideal that no current flows at all in the OFF state. Therefore, the GaN substrate used for GaN-HEMT is required to have high resistance, and the GaN substrate is semi-insulated to form a semi-insulating substrate (SI substrate).

[0005] As a method for making a GaN substrate semi-insulating, a method of doping with transition metal elements is known. Transition metal elements act as acceptors, and therefore have the effect of compensating for background donors that are unintentionally introduced into the GaN substrate and reducing the carrier concentration in the GaN substrate. Such transition metal elements are called compensating impurities.

[0006] For example, in the invention described in Non-Patent Document 1, GaN crystal doped with iron (Fe) and manganese (Mn) as compensation impurities is obtained. In addition, in Patent Documents 1 and 2, GaN crystal doped with zinc (Zn) as compensation impurity is obtained.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2011-020896

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 60-65798

[0011] Non-patent literature

[0012] Non-patent literature 1: M Iwinska et al., “Iron and manganese as dopants used in the crystallization of highly resistive HVPE-GaN on native seeds”, Japanese Journal of Applied Physics, Vol. 58, SC1047, 2019 Summary of the invention

[0013] Problems to be solved by the invention

[0014] When Fe is used as a compensating impurity, the resistivity of the obtained GaN crystal is small, and when used as an SI substrate for devices, there is a hidden danger of increased leakage current of the device. In addition, when Mn is used as a compensating impurity, the resistivity of the obtained GaN crystal is large, but there is a tendency to diffuse easily in the GaN crystal. Therefore, when used as an SI substrate for devices, there is a hidden danger of increased on-resistance caused by current collapse.

[0015] As a compensating impurity other than Fe and Mn, Patent Document 1 discloses a GaN crystal obtained by a flux method using Zn. Patent Document 2 discloses a GaN crystal layer obtained by doping Zn by MOCVD using an organic zinc compound as a dopant precursor.

[0016] However, when the Zn-doped GaN crystal is used as the SI substrate, it is not possible to realize a GaN crystal that satisfies all three requirements: high specific resistance, suppression of current collapse, and high crystal quality.

[0017] Therefore, a first object of the present invention is to provide a GaN crystal having excellent crystal quality and achieving high specific resistance and suppression of the occurrence of current collapse, and a method for producing the same.

[0018] In addition, when the Zn-doped GaN crystal is used as an SI substrate, the crystal quality has room for improvement. In addition, if a Zn-doped GaN crystal layer is obtained by MOCVD, the crystal growth rate is extremely slow and a GaN self-supporting substrate cannot be obtained.

[0019] Therefore, a second object of the present invention is to provide a GaN crystal having excellent crystal quality and capable of being a self-supporting substrate, and a method for manufacturing the same.

[0020] Solutions to the problem

[0021] That is, the gist of the present invention is as follows.

[0022] [1] A GaN crystal comprising a Zn-doped GaN layer,

[0023] In the Zn-doped GaN layer, the Zn concentration is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (004) X-ray diffraction is 50 arcsec or less.

[0024] [2] A GaN crystal comprising a Zn-doped GaN layer,

[0025] In the Zn-doped GaN layer, the Zn concentration is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (201) X-ray diffraction is 50 arcsec or less.

[0026] [3] The GaN crystal according to [1] or [2] above, wherein:

[0027] In the above Zn-doped GaN layer, the C concentration is 1.0×10 18 atoms / cm 3 the following.

[0028] [4] The GaN crystal according to any one of [1] to [3] above, wherein:

[0029] The Zn-doped GaN layer has a thickness of 50 μm or more.

[0030] [5] The GaN crystal according to any one of [1] to [4] above, wherein

[0031] The alkali metal concentration on the crystal surface of the Zn-doped GaN layer is 10 ppm or less.

[0032] [6] The GaN crystal according to any one of [1] to [5] above, wherein

[0033] The Zn-doped GaN layer does not contain alkali metal inclusions.

[0034] [7] The GaN crystal according to any one of [1] to [6] above, wherein:

[0035] When the Zn-doped GaN layer is irradiated with light having energy greater than the band gap energy of GaN, the peak of light emitted does not exist in the region of 2.64 to 2.82 eV.

[0036] [8] The GaN crystal according to any one of [1] to [7] above, wherein:

[0037] The resistivity of the Zn-doped GaN layer at 300K is 1×10 9 Ωcm or more.

[0038] [9] The GaN crystal according to any one of [1] to [8] above, wherein

[0039] The Zn-doped GaN layer has a surface having an inclination of 10 degrees or less with respect to the (0001) crystal plane.

[0040]

[10] The GaN crystal according to any one of [1] to [9] above, wherein:

[0041] In the Zn-doped GaN layer, the total donor impurity concentration is less than 5.0×10 16 atoms / cm 3 .

[0042]

[11] The GaN crystal according to any one of [1] to

[10] above, wherein:

[0043] In the Zn-doped GaN layer, the contents of O (oxygen) and Si (silicon) are both 1.0×10 15 atoms / cm 3 above.

[0044]

[12] A GaN crystal comprising a Zn-doped GaN layer,

[0045] The resistivity of the Zn-doped GaN layer at 300K is 1×10 9 Ωcm or more.

[0046]

[13] A method for producing a GaN crystal containing a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 A method of Zn-doping a GaN layer in a GaN crystal, the method comprising:

[0047] Metallic Zn was used as the doping precursor.

[0048]

[14] A method for producing a GaN crystal containing a Zn concentration of 1.0×1016 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 A method for producing a GaN crystal having a Zn-doped GaN layer having a thickness of 50 μm or more, the method comprising:

[0049] An organic Zn compound was used as a doping precursor.

[0050]

[15] The method for producing a GaN crystal according to

[13] or

[14] above, wherein:

[0051] The above-mentioned vapor phase growth method is the HVPE method.

[0052] In addition, the gist of aspect A corresponding to the above-mentioned first object of the present invention is as follows.

[0053] [1] A GaN crystal comprising a Zn-doped GaN layer,

[0054] In the Zn-doped GaN layer, the Zn concentration is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, the C concentration is 1.0×10 18 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (004) X-ray diffraction is 50 arcsec or less.

[0055] [2] A GaN crystal comprising a Zn-doped GaN layer,

[0056] In the Zn-doped GaN layer, the Zn concentration is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, the C concentration is 1.0×10 18 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (201) X-ray diffraction is 50 arcsec or less.

[0057] [3] The GaN crystal according to [1] or [2] above, wherein:

[0058] The alkali metal concentration on the crystal surface of the Zn-doped GaN layer is 10 ppm or less.

[0059] [4] The GaN crystal according to any one of [1] to [3] above, wherein:

[0060] The Zn-doped GaN layer does not contain alkali metal inclusions.

[0061] [5] The GaN crystal according to any one of [1] to [4] above, wherein

[0062] When the Zn-doped GaN layer is irradiated with light having energy greater than the band gap energy of GaN, the peak of light emitted does not exist in the region of 2.64 to 2.82 eV.

[0063] [6] The GaN crystal according to any one of [1] to [5] above, wherein

[0064] The Zn-doped GaN layer has a thickness of 50 μm or more.

[0065] [7] The GaN crystal according to any one of [1] to [6] above, wherein:

[0066] The resistivity of the Zn-doped GaN layer at 300K is 1×10 9 Ωcm or more.

[0067] [8] The GaN crystal according to any one of [1] to [7] above, wherein:

[0068] The Zn-doped GaN layer has a surface having an inclination of 10 degrees or less with respect to the (0001) crystal plane.

[0069] [9] The GaN crystal according to any one of [1] to [8] above, wherein

[0070] In the Zn-doped GaN layer, the total donor impurity concentration is less than 5.0×10 16 atoms / cm 3 .

[0071]

[10] The GaN crystal according to any one of [1] to [9] above, wherein:

[0072] In the Zn-doped GaN layer, the O (oxygen) concentration and the Si (silicon) concentration are both 1.0×10 15 atoms / cm 3 above.

[0073]

[11] A method for producing a GaN crystal containing a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 A method of Zn-doping a GaN layer in a GaN crystal, the method comprising:

[0074] Metallic Zn was used as the doping precursor.

[0075]

[12] The method for manufacturing a GaN crystal according to

[11] above, wherein:

[0076] The above-mentioned vapor phase growth method is the HVPE method.

[0077] In addition, the gist of aspect B corresponding to the above-mentioned second object of the present invention is as follows.

[0078] [1] A GaN crystal comprising a Zn-doped GaN layer,

[0079] In the Zn-doped GaN layer, the Zn concentration is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, the thickness is 50 μm or more, and the full width at half maximum of the rocking curve based on (004) X-ray diffraction is 50 arcsec or less.

[0080] [2] A GaN crystal comprising a Zn-doped GaN layer,

[0081] In the Zn-doped GaN layer, the Zn concentration is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, the thickness is 50 μm or more, and the full width at half maximum of the rocking curve based on (201) X-ray diffraction is 50 arcsec or less.

[0082] [3] The GaN crystal according to [1] or [2] above, wherein:

[0083] The alkali metal concentration on the crystal surface of the Zn-doped GaN layer is 10 ppm or less.

[0084] [4] The GaN crystal according to any one of [1] to [3] above, wherein:

[0085] The Zn-doped GaN layer does not contain alkali metal inclusions.

[0086] [5] The GaN crystal according to any one of [1] to [4] above, wherein

[0087] When the Zn-doped GaN layer is irradiated with light having energy greater than the band gap energy of GaN, the peak of light emitted does not exist in the region of 2.64 to 2.82 eV.

[0088] [6] The GaN crystal according to any one of [1] to [5] above, wherein

[0089] In the above Zn-doped GaN layer, the C concentration is 1.0×10 18 atoms / cm 3 the following.

[0090] [7] The GaN crystal according to any one of [1] to [6] above, wherein:

[0091] The resistivity of the Zn-doped GaN layer at 300K is 1×10 9 Ωcm or more.

[0092] [8] The GaN crystal according to any one of [1] to [7] above, wherein:

[0093] The Zn-doped GaN layer has a 5 cm 2 The above surfaces have an inclination of 10 degrees or less with respect to the (0001) crystal plane.

[0094] [9] The GaN crystal according to any one of [1] to [8] above, wherein

[0095] In the Zn-doped GaN layer, the total donor impurity concentration is less than 5.0×10 16 atoms / cm 3 .

[0096]

[10] The GaN crystal according to any one of [1] to [9] above, wherein:

[0097] In the Zn-doped GaN layer, the O (oxygen) concentration and the Si (silicon) concentration are both 1.0×10 15 atoms / cm 3 above.

[0098]

[11] A method for producing a GaN crystal containing a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 A method for producing a GaN crystal having a Zn-doped GaN layer having a thickness of 50 μm or more, the method comprising:

[0099] An organic Zn compound was used as a doping precursor.

[0100]

[12] The method for manufacturing a GaN crystal according to

[11] above, wherein:

[0101] The above-mentioned vapor phase growth method is the HVPE method.

[0102] Effects of the Invention

[0103] The present invention can provide a GaN crystal having excellent crystal quality, high specific resistance and suppressed current collapse, and is therefore very suitable as a substrate for a nitride semiconductor device having a horizontal device structure such as a GaN-HEMT.

[0104] In addition, the present invention can provide a GaN crystal having excellent crystal quality and a thickness of at least a certain value. The GaN crystal of the present invention can be used as a self-supporting substrate with a high specific resistance, and is therefore very suitable as a substrate for a nitride semiconductor device having a horizontal device structure such as a GaN-HEMT. BRIEF DESCRIPTION OF THE DRAWINGS

[0105] Figure 1 This is a plan view showing a case where the (0001) surface of the GaN crystal of this embodiment is divided into cells of 5 mm×5 mm by a square lattice.

[0106] Figure 2 This is a cross-sectional view showing one form of the GaN crystal according to the present embodiment.

[0107] Figure 3 This is a cross-sectional view showing one form of the GaN crystal according to the present embodiment.

[0108] Figure 4 are process cross-sectional views for explaining the method for manufacturing the GaN crystal of this embodiment, respectively, Figure 4 (a) refers to the state of the c-plane GaN seed crystal, Figure 4 (b) refers to the state where a GaN layer is stacked on a c-plane GaN seed crystal. Figure 4 (c) is a state where the GaN layer as a stacked structure is thinned.

[0109] Figure 5 are process cross-sectional views for explaining a method for producing a c-plane GaN seed crystal used in producing a GaN crystal according to the present embodiment, respectively, Figure 5 (a) refers to the state of the seed wafer, Figure 5 (b) refers to the state where the GaN film is grown on the c-plane GaN seed crystal. Figure 5 (c) refers to a state where the GaN laminate is processed to obtain at least one c-plane GaN seed crystal.

[0110] Figure 6 It is a schematic diagram showing the basic structure of the HVPE apparatus.

[0111] Figure 7This is the emission spectrum obtained when the GaN crystal obtained in Example A-1 is irradiated with 3.81 eV light.

[0112] Figure 8 This is the emission spectrum obtained when the GaN crystal obtained in Example B-1 is irradiated with 3.81 eV light.

[0113] Explanation of symbols

[0114] 1 Seed wafer

[0115] 2 GaN thick film

[0116] 3 c-plane GaN seed

[0117] 5 c-plane GaN seed

[0118] 6 GaN layers

[0119] 10 Zn-doped GaN crystal

[0120] 11 (0001) Surface

[0121] 20 HVPE device

[0122] 21 Reactor

[0123] 22 Gallium storage battery

[0124] 23 Base

[0125] 24 First Heater

[0126] 25 Second Heater

[0127] 100 GaN crystal

[0128] 101 (0001) Surface

[0129] 102 (000-1) Surface

[0130] 110 First Area

[0131] 120 Second Area DETAILED DESCRIPTION

[0132] Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments and can be implemented with various modifications within the scope of the gist of the invention.

[0133] In the present disclosure, the crystal axis parallel to the

[0001] axis is referred to as the c-axis, the crystal axis parallel to the <10-10> axis is referred to as the m-axis, and the crystal axis parallel to the <11-20> axis is referred to as the a-axis. The crystal plane orthogonal to the c-axis is referred to as the c-plane, the crystal plane orthogonal to the m-axis is referred to as the m-plane, and the crystal plane orthogonal to the a-axis is referred to as the a-plane.

[0134] The Miller index (hkil) of the hexagonal crystal has the relationship of h+k=-i, and therefore, it is sometimes expressed as (hkl) using a three-digit number. For example, if (0004) is expressed as (004) using a three-digit number.

[0135] In this specification, when referring to a crystal axis, a crystal plane, a crystal orientation, etc., unless otherwise specified, they refer to the crystal axis, crystal plane, crystal orientation, etc. in a GaN substrate or a GaN layer, respectively.

[0136] In this specification, each concentration such as Zn concentration, C concentration, O concentration, and Si concentration at a specific position is a value determined from each detection amount using secondary ion mass spectrometry (SIMS).

[0137] In the present specification, when the expression "to" is used, it is used as an expression including the numerical values ​​or physical property values ​​before and after it. That is, "A to B" means A or more and B or less.

[0138] 《GaN Crystal (1)》

[0139] The GaN crystal of this embodiment includes a Zn-doped GaN layer.

[0140] In the Zn-doped GaN layer, the Zn concentration is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (004) X-ray diffraction is 50 arcsec or less.

[0141] In addition, the Zn concentration in the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (201) X-ray diffraction may be 50 arcsec or less.

[0142] The Zn-doped GaN layer may satisfy the following two conditions: the full width at half maximum of the rocking curve based on (004) X-ray diffraction is less than 50 arcsec, and the full width at half maximum of the rocking curve based on (201) X-ray diffraction is less than 50 arcsec.

[0143] For the GaN crystal of this embodiment, as embodiment A, the C concentration in the Zn-doped GaN layer is preferably 1.0×10 18 atoms / cm 3 In addition, as embodiment B, the thickness of the Zn-doped GaN layer is preferably 50 μm or more.

[0144] The above-mentioned method A and method B are described below in sequence.

[0145] However, the GaN crystal of this embodiment is not limited to the above-mentioned form A and form B.

[0146] That is, the GaN crystal of this embodiment does not necessarily have to satisfy the C concentration of the Zn-doped GaN layer of 1.0×10 18 atoms / cm 3 At least one of the following (method A), and the thickness of the Zn-doped GaN layer is 50 μm or more (method B). Moreover, in a preferred embodiment of the GaN crystal of this embodiment, even if the C concentration of the Zn-doped GaN layer in the GaN crystal is not satisfied at the same time, 18 atoms / cm 3 In both the following cases (Form A) and the case where the thickness of the Zn-doped GaN layer is 50 μm or more (Form B), the same as the preferred forms in Form A and Form B are also applicable.

[0147] 〈Method A〉

[0148] [GaN Crystal of First Embodiment]

[0149] The GaN crystal of the first embodiment of the aspect A is characterized in that it includes a Zn-doped GaN layer, and the Zn concentration in the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, the C concentration is 1.0×10 18 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (004) X-ray diffraction is 50 arcsec or less.

[0150] The Zn-doped GaN layer is formed of a GaN crystal layer doped with Zn. By containing Zn at a specific concentration, the resistance of the GaN layer can be increased. By setting the C concentration to be below the upper limit, the occurrence of current collapse caused by C can be suppressed.

[0151] In one embodiment of the GaN crystal of the first embodiment, the Zn concentration in the entire crystal is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, the C concentration is 1.0×10 18 atoms / cm 3 That is, the GaN crystal is composed of only the Zn-doped GaN layer.

[0152] In another embodiment of the GaN crystal of the first embodiment, the GaN crystal has a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, C concentration is 1.0×10 18 atoms / cm 3 The following Zn-doped GaN layer. In this case, the thickness of the Zn-doped GaN layer in the c-axis direction does not need to be consistent with the thickness of the entire GaN crystal in the c-axis direction.

[0153] For example, if the thickness of the Zn-doped GaN layer is 100 μm on the surface of the GaN crystal, the thickness of the Zn-doped GaN layer is sufficient if the thickness of the GaN crystal is 400 μm. Of course, the thickness of the Zn-doped GaN layer is not limited to the above thickness, and any case of being thicker or thinner than the above thickness is not excluded. In addition, the entire thickness direction of the GaN crystal may be composed of the Zn-doped GaN layer. In this case, the Zn concentration in the GaN crystal as a whole is equivalent to 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, C concentration is 1.0×10 18 atoms / cm 3 The following situation.

[0154] The Zn concentration is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3Below, C concentration is 1.0×10 18 atoms / cm 3 The Zn-doped GaN layer below can have various thicknesses and can be in various forms such as a self-supporting substrate, an epitaxial layer grown on other GaN crystals, or a GaN layer stacked on a supporting substrate using bonding technology.

[0155] For example, from the viewpoint of processability such as being able to obtain a self-supporting GaN substrate by processing, the thickness of the Zn-doped GaN layer is preferably 50 μm or more, more preferably 80 μm or more, and further preferably 100 μm or more. The upper limit of the thickness is not particularly limited, and is preferably 200 μm or less, for example.

[0156] The Zn concentration of the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 As a compensating impurity, Zn contributes to high resistance. By setting the Zn concentration to 1.0×10 16 atoms / cm 3 As described above, a high specific resistance of the Zn-doped GaN layer can be achieved. In addition, by setting the Zn concentration of the Zn-doped GaN layer to 1.0×10 20 atoms / cm 3 The following can keep the crystal quality good.

[0157] In addition, from the perspective of impurity energy levels, doping with Zn is superior to doping with other compensating impurities such as Fe (iron). The reason is that since the energy level of Zn is deeper than that of Fe, a larger energy is required to return the captured electrons to the conduction band.

[0158] The Zn concentration of the Zn-doped GaN layer is 1.0×10 20 atoms / cm 3 Below, below, preferably 6.0×10 19 atoms / cm 3 Below, 5.0×10 19 atoms / cm 3 Below, 3.0×10 19 atoms / cm 3 Below, 1.0×10 19 atoms / cm 3 Below, 5.0×10 18 atoms / cm 3 the following.

[0159] In addition, the Zn concentration of the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above, below, preferably 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.

[0160] The C concentration of the Zn-doped GaN layer is 1.0×10 18 atoms / cm 3 As follows. C as a compensating impurity can contribute to high resistance. On the other hand, if a certain amount of C is contained, there is a risk of causing current collapse when the GaN crystal containing the Zn-doped GaN layer is used in a device. Therefore, from the perspective of reducing the risk of causing current collapse, it is preferred that the C concentration of the Zn-doped GaN layer is low.

[0161] The C concentration of the Zn-doped GaN layer is 1.0×10 18 atoms / cm 3 Below, below, preferably 8.0×10 17 atoms / cm 3 Below, 5.0×10 17 atoms / cm 3 Below, 3.0×10 17 atoms / cm 3 Below, 1.0×10 17 atoms / cm 3 Below, 5.0×10 16 atoms / cm 3 Below, 2.0×10 16 atoms / cm 3 The lower limit of the C concentration in the GaN crystal is not particularly limited, but is usually equal to the detection limit.

[0162] As impurities that function as donors to GaN, O (oxygen), Si (silicon), S (sulfur), Ge (germanium), Sn (tin), etc. are known, and are called donor impurities.

[0163] Donor impurities hinder the effect of increasing the resistance brought about by compensating impurities. Therefore, the total concentration of the donor impurities contained in the Zn-doped GaN layer, i.e., the total donor impurity concentration, is preferably less than 5.0×10 16 atoms / cm 3 , more preferably less than 4.0×10 16 atoms / cm 3 , and more preferably less than 2.0×10 16 atoms / cm 3 The less the donor impurities, the better. Therefore, the lower limit of the total donor impurity concentration is not particularly limited.

[0164] As described later, the Zn-doped GaN layer in this embodiment can be grown, for example, preferably by a vapor phase growth method, more preferably by a hydride vapor phase epitaxy (HVPE) method. Although O (oxygen) and Si (silicon) are not intentionally added as donor impurities to the Zn-doped GaN layer obtained by the above method, the Zn-doped GaN layer can be grown at a rate of 10 15 atoms / cm 3 That is, the concentration of O (oxygen) and the concentration of Si (silicon) in the Zn-doped GaN layer can both be 1.0×10 15 atoms / cm 3 above.

[0165] On the other hand, only when the above-mentioned donor impurities are intentionally doped, other donor impurities other than O and Si are contained in the Zn-doped GaN layer at a non-negligible concentration. It should be noted that "intentional doping" refers to the case where the element as a target element is added as a raw material in the form of a simple substance or a compound in order to dope the Zn-doped GaN layer.

[0166] Therefore, unless the Zn-doped GaN layer is intentionally doped with donor impurities other than O and Si, the total donor impurity concentration of the Zn-doped GaN layer can be considered to be equal to the sum of the O concentration and the Si concentration. Whether the Zn-doped GaN layer is doped with donor impurities other than O and Si can be confirmed by elemental analysis or the like.

[0167] As long as there is no obstacle in practical use, the Zn-doped GaN layer may contain compensating impurities other than Zn and C, such as Fe (iron), Co (cobalt), Ni (nickel), etc. Alternatively, it may be substantially free of compensating impurities other than Zn and C. In this case, the total concentration of compensating impurities other than Zn and C is, for example, 1×1016 atoms / cm 3 the following.

[0168] In addition to the donor impurities and compensating impurities mentioned above, the Zn-doped GaN layer may also contain H (hydrogen), the concentration of which may be, for example, 10 16 ~10 17 atoms / cm 3 about.

[0169] The full width at half maximum of the rocking curve of the Zn-doped GaN layer based on (004) X-ray diffraction is less than 50 arcsec. The rocking curve refers to the diffraction intensity distribution when the direction of the incident X-ray and the position of the detector are fixed in the X-ray diffraction measurement and only the crystal as a sample is rotated. It is one of the indicators of crystal quality.

[0170] The smaller the half-value width of the rocking curve, the less the crystal defects and the better the crystal quality. The half-value width is preferably less than 40 arcsec, more preferably less than 30 arcsec, and further preferably less than 20 arcsec. The lower limit of the half-value width is not particularly limited, and is usually more than 5 arcsec. It should be noted that the half-value width in this specification has the same meaning as the half-value width generally referred to. That is, it refers to the maximum intensity f relative to the peak max , indicating half its intensity 1 / 2f max The distance between the locations.

[0171] The full width at half maximum can be adjusted by the growth method of the GaN crystal layer in the Zn-doped GaN layer (gas phase method or liquid phase method, etc.), the crystal properties of the seed crystal substrate used when growing the GaN crystal layer, the crystal growth conditions, the selection of the growth surface, or the impurity content, etc.

[0172] The rocking curve measurement based on (004) X-ray diffraction uses CuKα1 radiation. In the measurement, the X-ray tube is operated at, for example, a voltage of 45 kV and a current of 40 mA. When the X-ray is incident on the (0001) surface, the incident plane of the X-ray can be perpendicular to the a-axis or the m-axis.

[0173] The beam size of X-rays can be set as follows: when the incident angle (the angle between the reflection surface and the X-rays) is set to 90°, that is, when the X-rays are perpendicularly incident on the (004) reflection surface, the size of the irradiation area on the (0001) surface becomes 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 rotation axis of the sample in the rocking curve measurement, and ω represents the angle between the incident X-rays and the crystal surface.

[0174] When the X-ray beam size is set in this way, in the rocking curve measurement based on (004) X-ray diffraction, ω is about 36.5°, so the size of the irradiation area is about 1.7×5 mm. 2 .

[0175] In addition, similarly to the measurement of (004), the rocking curve measurement of other crystal planes may be performed. For example, the measurement of (201) is often performed.

[0176] The full width at half maximum in the rocking curve of (004) becomes an indicator of the uniformity of the surface parallel to the c-axis, that is, the c-plane. On the other hand, the full width at half maximum in the rocking curve of (201) becomes an indicator of the rotational uniformity of the surface not parallel to the c-axis, that is, the c-plane, about the c-axis.

[0177] The rocking curve measurement of the plane parallel to the c-axis is called on-axis measurement, and the rocking curve measurement of the plane not parallel to the c-axis is called off-axis measurement. The former is related to the dislocation density with screw dislocation components, and the latter is related to the dislocation density with edge dislocation components. In order to evaluate the crystal quality, it is preferred to perform both on-axis measurement and off-axis measurement.

[0178] The alkali metal concentration on the crystal surface of the Zn-doped GaN layer in this embodiment is preferably 10 ppm or less. The Zn-doped GaN layer satisfies the above requirements, which means that there is no region with a locally high alkali metal concentration in the Zn-doped GaN layer. Since there is no region with a locally high alkali metal concentration, the influence on the lattice length of the GaN crystal can be suppressed, and cracking of the GaN crystal containing the Zn-doped GaN layer when it is made into a substrate can be suppressed.

[0179] It should be noted that the ppm indicating the concentration in this specification refers to ppma (parts per million atomic) based on the number of atoms.

[0180] The alkali metal concentration on the crystal surface is more preferably 8 ppm or less, further preferably 5 ppm or less, the less the better, but is usually 0.1 ppm or more. It should be noted that the alkali metal concentration in this specification refers to the alkali metal concentration in any 100 μm×100 μm square grid on the crystal surface, for example, it can be measured by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX).

[0181] The Zn-doped GaN layer in this embodiment preferably does not contain alkali metal inclusions. Alkali metal inclusions, when present inside a crystal, refer to closed spaces containing alkali metals formed in the Zn-doped GaN layer, and when present on the surface of a crystal, refer to such closed spaces being exposed on the surface of the crystal to form recesses.

[0182] If a GaN crystal containing a Zn-doped GaN layer inside the crystal and containing alkali metal inclusions on the crystal surface is used as a substrate, when a GaN crystal layer is epitaxially grown thereon, the alkali metal contained in the closed space, such as Na, will volatilize, etc., and there is a risk of causing the substrate to crack due to volume expansion or reducing the crystal quality of the epitaxially grown GaN crystal layer. It is known that such a closed space is generally generated in the crystal when a GaN crystal is obtained by a flux method. The presence or absence of alkali metal inclusions can be distinguished by an optical microscope or SEM.

[0183] It is also preferred that the peak of the light emitted by the Zn-doped GaN layer in this embodiment when irradiated with light having an energy greater than the band gap energy of GaN does not exist in the region of 2.64 to 2.82 eV. It is known that in the flux method, for example, when a GaN crystal produced by the Na flux method is irradiated with the above light, there is generally broad light emission with a peak at 2.64 to 2.82 eV, and by having the above peak, it can be inferred that the GaN crystal is obtained by the Na flux method.

[0184] As described above, GaN crystals produced by the flux method have a risk of having regions with high alkali metal concentrations or alkali metal inclusions on the crystal surface, and are sometimes not ideal as semi-insulating GaN crystals for devices requiring high reliability.

[0185] In contrast, the Zn-doped GaN layer produced by the vapor phase growth method emits light having a peak in the region of 2.88 to 2.98 eV when irradiated with the same light. This light emission comes from Zn and can be distinguished from that from Na. Therefore, by not having a light emission peak in the region of 2.64 to 2.82 eV and having a light emission peak in the region of 2.88 to 2.98 eV when irradiated with the above light, it is possible to distinguish whether it is a Zn-doped GaN layer obtained by the Na flux method or a Zn-doped GaN layer obtained by the vapor phase method.

[0186] As described above, the GaN crystal of the first embodiment can be made of a GaN crystal having a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 The following Zn-doped GaN crystal composition is composed of only the above-mentioned Zn-doped GaN layer, but it can also be set as a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3The structure of the Zn-doped GaN layer is as follows.

[0187] In the case where the GaN crystal has a Zn-doped GaN layer and a seed layer, such as Figure 2 As shown, the GaN crystal of the first embodiment includes a first region 110 and a second region 120 .

[0188] Figure 2 A cross section is shown when the GaN crystal 100 is cut along a plane perpendicular to the (0001) surface 101 .

[0189] In the GaN crystal 100 , the first region 110 including the (0001) surface 101 is preferably formed of a Zn-doped GaN layer.

[0190] The GaN crystal 100 has a second region 120 on the (000-1) surface 102 side. The second region 120 may be composed of a GaN crystal having a room temperature resistivity of less than 1×10 5 A GaN crystal layer with a thickness of Ωcm, that is, a GaN crystal layer that is not semi-insulating, is formed.

[0191] The total concentration of compensating impurities in the second region 120 is generally lower than that in the first region 110. The second region 120 may have a region near a boundary with the first region 110 where the total concentration of compensating impurities increases stepwise or continuously as it approaches the first region 110.

[0192] The GaN crystal 100 having the first region 110 and the second region 120 may be manufactured by forming the second region 120 on the first region 110 by epitaxial growth, or by forming the first region 110 on the second region 120 by epitaxial growth.

[0193] An example of the GaN crystal according to the first embodiment has a (0001) surface 101 of Ga polarity and a (000-1) surface 102 of N polarity.

[0194] In the case where the GaN crystal 100 has a seed layer and a Zn-doped GaN layer, as Figure 2 As shown, the surface of the first region 110 as the Zn-doped GaN layer becomes a (0001) surface 101 , and the surface of the second region 120 as the seed layer becomes a (000-1) surface 102 .

[0195] In the case where the GaN crystal 100 is composed of only a Zn-doped GaN layer, as shown in FIG. Figure 3 As shown, one surface of the Zn-doped GaN layer serving as the first region 110 becomes a (0001) surface 101 , and the other surface becomes a (000-1) surface 102 .

[0196] The Zn-doped GaN layer in the first embodiment preferably has a surface with an inclination of 10 degrees or less relative to the (0001) crystal plane. In this specification, "a surface with an inclination of 10 degrees or less relative to the (0001) crystal plane" is sometimes referred to as "(0001) surface". In addition, the inclination of 10 degrees or less is a concept that also includes 0 degrees.

[0197] The shape of the GaN crystal in the first embodiment is arbitrary, but is preferably a shape that allows a GaN substrate described later to be obtained.

[0198] The area of ​​the (0001) surface of the Zn-doped GaN layer can be, for example, 1 cm 2 Above, or can be 5cm 2 Above, or can be 10cm 2 Above, or can be 18cm 2 Above, or can be 75cm 2 Above, or can be 165cm 2 The upper limit is not particularly limited, for example, it can be 350 cm 2 the following.

[0199] The GaN crystal of the first embodiment may be a GaN crystal grown in any direction, and is preferably a GaN crystal grown on a plane having an inclination of 10 degrees or less (including 0 degrees) with respect to the (0001) crystal plane.

[0200] The (0001) surface of the GaN crystal of the first embodiment is preferably the main surface, i.e., the large-area surface. In addition, the area ratio of the (0001) surface in the crystal growth surface is preferably 60% or more, more preferably 70% or more, and further preferably 80% or more, and the upper limit is 100%.

[0201] As described later, the larger the area of ​​the (0001) surface, the lower the total donor impurity concentration can be, and semi-insulating properties can be achieved even at a relatively low Zn concentration. The same is true when the area ratio of the (0001) surface in the crystal growth plane is within the above range.

[0202] In the case where the GaN crystal of the first embodiment is disc-shaped, its diameter is usually more than 20 mm, and can be set to more than 25 mm, more than 40 mm, more than 50 mm, and more than 90 mm in stages as follows. In addition, the above diameter can also be set to any size such as 25 to 27 mm (about 1 inch), 50 to 55 mm (about 2 inches), 100 to 105 mm (about 4 inches), 150 to 155 mm (about 6 inches). In the case where the GaN crystal is in a shape other than a disc, a disc-shaped shape with the same area as its main surface can be used to achieve a size within the above range.

[0203] When a GaN substrate is produced, the thickness t of the GaN crystal is set to a value that does not make it difficult to handle the GaN substrate according to the diameter. For example, when the diameter of the GaN crystal is about 2 inches, the thickness of the GaN crystal is preferably 250 to 500 μm, more preferably 300 to 450 μm.

[0204] In GaN crystals, Figure 2 In the case of the structure in which the second region 120 formed by the seed layer and the first region 110 formed by the Zn-doped GaN layer are stacked, the thickness t1 of the first region 110 as the Zn-doped GaN layer is preferably 50 to 200 μm, more preferably 80 to 200 μm, and further preferably 100 to 150 μm.

[0205] When the GaN crystal of the first embodiment is used as a GaN substrate, of the two large-area surfaces of the GaN crystal, the (0001) surface 101 is used as the front surface for epitaxial growth of the nitride semiconductor layer. The (0001) surface 101 is mirror-finished, and its root mean square roughness (RMS) measured by an atomic force microscope (AFM) is usually less than 2 nm, preferably less than 1 nm, and more preferably less than 0.5 nm in a measurement range of 2 μm×2 μm.

[0206] The (000-1) surface 102 is the back surface, and therefore, can be subjected to mirror finish or matte (rough surface) finish.

[0207] The edge of the GaN substrate formed of the GaN crystal of the first embodiment may be chamfered.

[0208] The GaN substrate may be provided with various markings as needed, such as an orientation flat or cutout for indicating the orientation of the crystal, an index flat for making it easy to distinguish the front and back surfaces, and the like.

[0209] The shape of the GaN substrate is not particularly limited, and the shapes of the (0001) surface and the (000-1) surface may be disc-shaped, square, rectangular, hexagonal, octagonal, elliptical, etc., or may be irregular shapes.

[0210] In order to reduce leakage current when GaN crystal is used as a high resistance substrate in a device, the specific resistance of the Zn-doped GaN layer at 300K in the first embodiment is preferably 1×10 9 Ωcm or more.

[0211] The specific resistance at 300K is more preferably 5×10 9Ωcm or more, more preferably 1×10 10 Ωcm or more, more preferably 5×10 10 Ωcm or more, particularly preferably 1×10 11 The upper limit is not particularly limited because the specific resistance is higher than Ωcm. Furthermore, the higher the specific resistance, the more preferable it is.

[0212] The Zn-doped GaN layer in the first embodiment preferably has a p-type carrier type. In the case of poor crystal quality of GaN crystal, even if Zn is doped in the GaN layer, it cannot fully compensate for the electrons caused by unexpected impurities such as Si and O, and there is a tendency to become n-type. Therefore, the p-type carrier type of the Zn-doped GaN layer means that the crystallinity of the GaN single crystal layer constituting the GaN crystal is good.

[0213] [GaN Crystal of Second Embodiment]

[0214] The GaN crystal of the second embodiment of the aspect A is characterized in that it includes a Zn-doped GaN layer, and the Zn concentration of the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, the C concentration is 1.0×10 18 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (201) X-ray diffraction is 50 arcsec or less.

[0215] As described in the half-width of the rocking curve of the Zn-doped GaN layer based on (201) X-ray diffraction in the first embodiment, the half-width of the rocking curve of the Zn-doped GaN layer based on (004) X-ray diffraction in the second embodiment becomes an indicator for observing the rotational uniformity of the surface that is not parallel to the c-axis, that is, the c-plane, around the c-axis.

[0216] The smaller the half-value full width of the rocking curve based on (201) X-ray diffraction, the better the crystal quality. The half-value full width of the Zn-doped GaN layer is 50 arcsec or less, preferably 40 arcsec or less, more preferably 30 arcsec or less, and further preferably 20 arcsec or less. The lower limit of the half-value full width is not particularly limited, but is usually 5 arcsec or more.

[0217] Preferred aspects of the Zn-doped GaN layer and GaN crystal except for the full width at half maximum of the rocking curve are the same as those described in [GaN crystal of first embodiment].

[0218] The full width at half maximum of the rocking curve of the Zn-doped GaN layer based on (004) and (201) X-ray diffraction is preferably 50 arcsec or less, more preferably 40 arcsec or less, further preferably 30 arcsec or less, and particularly preferably 20 arcsec or less.

[0219] 〈Method B〉

[0220] [GaN Crystal of First Embodiment]

[0221] The GaN crystal of the first embodiment of the aspect B is characterized in that it includes a Zn-doped GaN layer, and the Zn concentration in the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, the thickness is 50 μm or more, and the full width at half maximum of the rocking curve based on (004) X-ray diffraction is 50 arcsec or less.

[0222] The Zn-doped GaN layer is formed of a crystal layer of GaN doped with Zn. By containing a specific concentration of Zn, the resistance of the GaN crystal can be increased. Furthermore, by having a thickness of more than a certain level, it can be used as a self-supporting substrate, and thus has excellent handleability.

[0223] In one embodiment of the GaN crystal of the first embodiment, the Zn concentration in the entire crystal is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Hereinafter, the thickness of the entire crystal is 50 μm or more. That is, the GaN crystal is composed of only the Zn-doped GaN layer.

[0224] In another embodiment of the GaN crystal of the first embodiment, the GaN crystal has a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 In this case, the thickness of the Zn-doped GaN layer in the c-axis direction does not need to match the thickness of the entire GaN crystal in the c-axis direction.

[0225] For example, if the thickness of the Zn-doped GaN layer is 100 μm on the surface of the GaN crystal, the thickness of the Zn-doped GaN layer is sufficient, relative to the overall thickness of the GaN crystal of 400 μm. Of course, as long as the thickness of the Zn-doped GaN layer is 50 μm or more, it is not limited to the above example, and does not exclude any of the cases where it is thicker than 100 μm on the surface or thinner than 100 μm on the surface. In addition, the entire thickness direction of the GaN crystal may be composed of a Zn-doped GaN layer. In this case, the Zn concentration in the overall GaN crystal described above is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Below, the case where the thickness of the entire crystal is 50 μm or more.

[0226] The Zn concentration is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 The thickness of the Zn-doped GaN layer below may be 50 μm or more, more preferably 80 μm or more, and further preferably 100 μm or more. The upper limit of the thickness is not particularly limited, but is preferably 200 μm or less, for example.

[0227] The Zn concentration of the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 As a compensating impurity, Zn contributes to high resistance. By setting the Zn concentration to 1.0×10 16 atoms / cm 3 As described above, a high specific resistance of the Zn-doped GaN layer can be achieved. In addition, by setting the Zn concentration of the Zn-doped GaN layer to 1.0×10 20 atoms / cm 3 The following can keep the crystal quality good.

[0228] In addition, from the perspective of impurity energy levels, doping based on Zn is superior to doping based on other compensating impurities such as Fe (iron). The reason is that since the energy level of Zn is deeper than that of Fe, a larger energy is required to return the captured electrons to the conduction band.

[0229] The Zn concentration of the Zn-doped GaN layer is 1.0×10 20 atoms / cm 3 Below, below, preferably 6.0×10 19atoms / cm 3 Below, 5.0×10 19 atoms / cm 3 Below, 3.0×10 19 atoms / cm 3 Below, 1.0×10 19 atoms / cm 3 Below, 5.0×10 18 atoms / cm 3 the following.

[0230] In addition, the Zn concentration of the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above, below, preferably 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.

[0231] The Zn-doped GaN layer may contain C as a compensating impurity. The energy level depth of C is about 0.9 eV, and on the other hand, the inventors' research shows that the energy level depth of Zn is deeper than this value. Therefore, regarding the semi-insulating property of GaN co-doped with Zn and C, since Zn is dominant compared to C, the Zn-doped GaN layer may contain C.

[0232] The C concentration in the Zn-doped GaN layer is not particularly limited, but is preferably 1.0×10 17 atoms / cm 3 Above, below, preferably 3.0×10 17 atoms / cm 3 Above, 5.0×10 17 atoms / cm 3 Above, 8.0×10 17 atoms / cm 3 Above, 1.0×10 18 atoms / cm 3 above.

[0233] On the other hand, from the viewpoint of avoiding unexpected deterioration of crystal quality, the C concentration of the Zn-doped GaN layer is preferably 5.0×10 19 atoms / cm 3Below, below, preferably 2.0×10 19 atoms / cm 3 Below, 1.0×10 19 atoms / cm 3 Below, 8.0×10 18 atoms / cm 3 Below, 5.0×10 18 atoms / cm 3 the following.

[0234] As impurities that function as donors to GaN, O (oxygen), Si (silicon), S (sulfur), Ge (germanium), Sn (tin), etc. are known, and are called donor impurities.

[0235] Donor impurities hinder the effect of increasing the resistance brought about by compensating impurities. Therefore, the total concentration of the donor impurities contained in the Zn-doped GaN layer, i.e., the total donor impurity concentration, is preferably less than 5.0×10 16 atoms / cm 3 , more preferably less than 4.0×10 16 atoms / cm 3 , and more preferably less than 2.0×10 16 atoms / cm 3 The less the donor impurities, the better. Therefore, the lower limit of the total donor impurity concentration is not particularly limited.

[0236] As described later, the Zn-doped GaN layer in this embodiment can be grown, for example, preferably by a vapor phase growth method, more preferably by a hydride vapor phase epitaxy (HVPE) method. Although O (oxygen) and Si (silicon) are not intentionally added as donor impurities to the Zn-doped GaN layer obtained by the above method, the Zn-doped GaN layer can be grown at a rate of 10 15 atoms / cm 3 That is, the concentration of O (oxygen) and the concentration of Si (silicon) in the Zn-doped GaN layer can both be 1.0×10 15 atoms / cm 3 above.

[0237] On the other hand, only when the above-mentioned donor impurities are intentionally doped, other donor impurities other than O and Si are contained in the Zn-doped GaN layer at a non-negligible concentration. It should be noted that "intentional doping" refers to the case where the element as a target element is added as a raw material in the form of a simple substance or a compound in order to dope the Zn-doped GaN layer.

[0238] Therefore, unless the Zn-doped GaN layer is intentionally doped with donor impurities other than O and Si, the total donor impurity concentration of the Zn-doped GaN layer can be considered to be equal to the sum of the O concentration and the Si concentration. Whether the Zn-doped GaN layer is doped with donor impurities other than O and Si can be confirmed by elemental analysis or the like.

[0239] As long as there is no obstacle in practical use, the Zn-doped GaN layer may contain compensating impurities other than Zn and C, such as Fe (iron), Co (cobalt), Ni (nickel), etc. Alternatively, it may be substantially free of compensating impurities other than Zn and C. In this case, the total concentration of compensating impurities other than Zn and C is, for example, 1×10 16 atoms / cm 3 the following.

[0240] In addition to the donor impurities and compensating impurities mentioned above, the Zn-doped GaN layer may also contain H (hydrogen), the concentration of which may be, for example, 10 16 ~10 17 atoms / cm 3 about.

[0241] The full width at half maximum of the rocking curve of the Zn-doped GaN layer based on (004) X-ray diffraction is less than 50 arcsec. The rocking curve refers to the diffraction intensity distribution when the direction of the incident X-ray and the position of the detector are fixed in the X-ray diffraction measurement and only the crystal as a sample is rotated. It is one of the indicators of crystal quality.

[0242] The smaller the half-value width of the rocking curve, the less the crystal defects and the better the crystal quality. The half-value width is preferably less than 40 arcsec, more preferably less than 30 arcsec, and further preferably less than 20 arcsec. The lower limit of the half-value width is not particularly limited, and is usually more than 5 arcsec. It should be noted that the half-value width in this specification has the same meaning as the half-value width generally referred to. That is, it refers to the maximum intensity f relative to the peak max , indicating half its intensity 1 / 2f max The distance between the locations.

[0243] The full width at half maximum can be adjusted by the growth method of the GaN crystal layer in the Zn-doped GaN layer (gas phase method or liquid phase method, etc.), the crystal properties of the seed crystal substrate used when growing the GaN crystal layer, the crystal growth conditions, the selection of the growth surface, or the impurity content, etc.

[0244] The rocking curve measurement based on (004) X-ray diffraction uses CuKα1 radiation. In the measurement, the X-ray tube is operated at, for example, a voltage of 45 kV and a current of 40 mA. When the X-ray is incident on the (0001) surface, the incident plane of the X-ray can be perpendicular to the a-axis or the m-axis.

[0245] The beam size of X-rays can be set as follows: when the incident angle (angle between the reflection surface and the X-rays) is set to 90°, that is, when the X-rays are perpendicularly incident on the (004) reflection surface, the size of the irradiation area on the (0001) surface becomes 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 rotation axis of the sample in the rocking curve measurement, and ω represents the angle between the incident X-rays and the crystal surface.

[0246] When the X-ray beam size is set in this way, in the rocking curve measurement based on (004) X-ray diffraction, ω is about 36.5°, so the size of the irradiation area is about 1.7×5 mm. 2 .

[0247] In addition, similarly to the measurement of (004), the rocking curve measurement of other crystal planes can also be performed. For example, the measurement of (201) can be performed well.

[0248] The full width at half maximum in the rocking curve of (004) becomes an indicator of the uniformity of the surface parallel to the c-axis, that is, the c-plane. On the other hand, the full width at half maximum in the rocking curve of (201) becomes an indicator of the rotational uniformity of the surface not parallel to the c-axis, that is, the c-plane, about the c-axis.

[0249] The rocking curve measurement of the plane parallel to the c-axis is called on-axis measurement, and the rocking curve measurement of the plane not parallel to the c-axis is called off-axis measurement. The former is related to the dislocation density with screw dislocation components, and the latter is related to the dislocation density with edge dislocation components. In order to evaluate the crystal quality, it is preferable to perform both on-axis measurement and off-axis measurement.

[0250] The alkali metal concentration on the crystal surface of the Zn-doped GaN layer in this embodiment is preferably 10 ppm or less. The Zn-doped GaN layer satisfies the above requirements, which means that there is no region with a locally high alkali metal concentration in the Zn-doped GaN layer. Since there is no region with a locally high alkali metal concentration, the influence on the lattice constant of the GaN crystal can be suppressed, and cracking of the GaN crystal including the Zn-doped GaN layer when it is made into a substrate can be suppressed.

[0251] It should be noted that ppm indicating concentration in this specification refers to ppma (parts per million atomic) based on the number of atoms.

[0252] The alkali metal concentration on the crystal surface is more preferably 8 ppm or less, further preferably 5 ppm or less, the less the better, but is usually 0.1 ppm or more. It should be noted that the alkali metal concentration in this specification refers to the alkali metal concentration in any 100 μm×100 μm square grid on the crystal surface, for example, it can be measured by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX).

[0253] The Zn-doped GaN layer in this embodiment preferably does not contain alkali metal inclusions. Alkali metal inclusions, when present inside a crystal, refer to closed spaces containing alkali metals formed in the Zn-doped GaN layer, and when present on the surface of a crystal, refer to such closed spaces being exposed on the surface of the crystal to form recesses.

[0254] If a GaN crystal containing a Zn-doped GaN layer inside the crystal and containing alkali metal inclusions on the crystal surface is used as a substrate, when a GaN crystal layer is epitaxially grown thereon, the alkali metal contained in the closed space, such as Na, will volatilize, etc., and there is a risk of causing the substrate to crack due to volume expansion or reducing the crystal quality of the epitaxially grown GaN crystal layer. It is known that such a closed space is generally generated in the crystal when a GaN crystal is obtained by a flux method. The presence or absence of alkali metal inclusions can be distinguished by an optical microscope or SEM.

[0255] It is also preferred that the peak of the light emitted by the Zn-doped GaN layer in this embodiment when irradiated with light having an energy greater than the band gap energy of GaN does not exist in the region of 2.64 to 2.82 eV. It is known that in the flux method, for example, when a GaN crystal produced by the Na flux method is irradiated with the above light, there is generally broad light emission with a peak at 2.64 to 2.82 eV, and by having the above peak, it can be inferred that the GaN crystal is obtained by the Na flux method.

[0256] As described above, GaN crystals produced by the flux method have a risk of having regions with high alkali metal concentrations or alkali metal inclusions on the crystal surface, and are sometimes not ideal as semi-insulating GaN crystals for devices requiring high reliability.

[0257] In contrast, the Zn-doped GaN layer produced by the vapor phase growth method emits light having a peak in the region of 2.88 to 2.98 eV when irradiated with the same light. This light emission comes from Zn and can be distinguished from that from Na. Therefore, by not having a light emission peak in the region of 2.64 to 2.82 eV and having a light emission peak in the region of 2.88 to 2.98 eV when irradiated with the above light, it is possible to distinguish whether it is a Zn-doped GaN layer obtained by the Na flux method or a Zn-doped GaN layer obtained by the vapor phase method.

[0258] As described above, the GaN crystal of the first embodiment can be made of a GaN crystal having a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 The following Zn-doped GaN crystal composition is composed of only the above-mentioned Zn-doped GaN layer, but it can also be set as a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 The structure of the Zn-doped GaN layer is as follows.

[0259] In the case where the GaN crystal has a Zn-doped GaN layer and a seed layer, such as Figure 2 As shown, the GaN crystal of the first embodiment includes a first region 110 and a second region 120 .

[0260] Figure 2 A cross section is shown when the GaN crystal 100 is cut along a plane perpendicular to the (0001) surface 101 .

[0261] In the GaN crystal 100 , the first region 110 including the (0001) surface 101 is preferably formed of a Zn-doped GaN layer.

[0262] The GaN crystal 100 has a second region 120 on the (000-1) surface 102 side. The second region 120 may be composed of a GaN crystal having a room temperature resistivity of less than 1×10 5 A GaN crystal layer with a thickness of Ωcm, that is, a GaN crystal layer that is not semi-insulating, is formed.

[0263] The total concentration of compensating impurities in the second region 120 is generally lower than that in the first region 110. The second region 120 may have a region near a boundary with the first region 110 where the total concentration of compensating impurities increases stepwise or continuously as it approaches the first region 110.

[0264] The GaN crystal 100 having the first region 110 and the second region 120 may be manufactured by forming the second region 120 on the first region 110 by epitaxial growth, or by forming the first region 110 on the second region 120 by epitaxial growth.

[0265] An example of the GaN crystal according to the first embodiment has a (0001) surface 101 of Ga polarity and a (000-1) surface 102 of N polarity.

[0266] In the case where the GaN crystal 100 has a seed layer and a Zn-doped GaN layer, as Figure 2 As shown, the surface of the first region 110 as the Zn-doped GaN layer becomes a (0001) surface 101 , and the surface of the second region 120 as the seed layer becomes a (000-1) surface 102 .

[0267] In the case where the GaN crystal 100 is composed of only a Zn-doped GaN layer, as shown in FIG. Figure 3 As shown, one surface of the Zn-doped GaN layer serving as the first region 110 becomes a (0001) surface 101 , and the other surface becomes a (000-1) surface 102 .

[0268] The Zn-doped GaN layer in the first embodiment preferably has a surface with an inclination of 10 degrees or less relative to the (0001) crystal plane. In this specification, "a surface with an inclination of 10 degrees or less relative to the (0001) crystal plane" is sometimes referred to as "(0001) surface". In addition, the inclination of 10 degrees or less is a concept that also includes 0 degrees.

[0269] The shape of the GaN crystal in the first embodiment is arbitrary, but is preferably a shape that allows a GaN substrate described later to be obtained.

[0270] The area of ​​the (0001) surface of the Zn-doped GaN layer can be, for example, 1 cm 2 Above, or can be 5cm 2 Above, or can be 10cm 2 Above, or can be 18cm 2 Above, or can be 75cm 2 Above, or can be 165cm 2 The upper limit is not particularly limited, for example, it can be 350 cm 2the following.

[0271] The GaN crystal of the first embodiment may be a GaN crystal grown in any direction, and is preferably a GaN crystal grown on a plane having an inclination of 10 degrees or less (including 0 degrees) with respect to the (0001) crystal plane.

[0272] The (0001) surface of the GaN crystal of the first embodiment is preferably the main surface, i.e., the large-area surface. In addition, the area ratio of the (0001) surface in the crystal growth surface is preferably 60% or more, more preferably 70% or more, and further preferably 80% or more, and the upper limit is 100%.

[0273] As described later, the larger the area of ​​the (0001) surface, the lower the total donor impurity concentration can be, and semi-insulating properties can be achieved even at a relatively low Zn concentration. The same is true when the area ratio of the (0001) surface in the crystal growth plane is within the above range.

[0274] In the case where the GaN crystal of the first embodiment is disc-shaped, its diameter is usually more than 20 mm, and can be set to more than 25 mm, more than 40 mm, more than 50 mm, and more than 90 mm in stages as follows. In addition, the above diameter can also be set to any size such as 25 to 27 mm (about 1 inch), 50 to 55 mm (about 2 inches), 100 to 105 mm (about 4 inches), 150 to 155 mm (about 6 inches). In the case where the GaN crystal is in a shape other than a disc, a disc-shaped shape with the same area as its main surface can be used to achieve a size within the above range.

[0275] When a GaN substrate is produced, the thickness t of the GaN crystal is set to a value that does not make it difficult to handle the GaN substrate according to the diameter. For example, when the diameter of the GaN crystal is about 2 inches, the thickness of the GaN crystal is preferably 250 to 500 μm, more preferably 300 to 450 μm.

[0276] In GaN crystals, Figure 2 In the case of the structure in which the second region 120 formed by the seed layer and the first region 110 formed by the Zn-doped GaN layer are stacked, the thickness t1 of the first region 110 as the Zn-doped GaN layer is greater than 50 μm, preferably 80 to 200 μm, and more preferably 100 to 150 μm.

[0277] When the GaN crystal of the first embodiment is used as a GaN substrate, of the two large-area surfaces of the GaN crystal, the (0001) surface 101 is used as the front surface for epitaxial growth of the nitride semiconductor layer. The (0001) surface 101 is mirror-finished, and its root mean square roughness (RMS) measured by an atomic force microscope (AFM) is usually less than 2 nm, preferably less than 1 nm, and more preferably less than 0.5 nm in a measurement range of 2 μm×2 μm.

[0278] The (000-1) surface 102 is the back surface, and therefore, can be subjected to mirror finish or matte (rough surface) finish.

[0279] The edge of the GaN substrate formed of the GaN crystal of the first embodiment may be chamfered.

[0280] The GaN substrate may be provided with various markings as needed, such as an orientation flat or cutout for indicating the orientation of the crystal, an index flat for making it easy to distinguish the front and back surfaces, and the like.

[0281] The shape of the GaN substrate is not particularly limited, and the shapes of the (0001) surface and the (000-1) surface may be disc-shaped, square, rectangular, hexagonal, octagonal, elliptical, etc., or may be irregular shapes.

[0282] In order to reduce leakage current when GaN crystal is used as a high resistance substrate in a device, the specific resistance of the Zn-doped GaN layer at 300K in the first embodiment is preferably 1×10 9 Ωcm or more.

[0283] The specific resistance at 300K is more preferably 5×10 9 Ωcm or more, more preferably 1×10 10 Ωcm or more, more preferably 2×10 10 Ωcm or more, particularly preferably 3×10 10 The upper limit is not particularly limited because the specific resistance is higher than Ωcm. Furthermore, the higher the specific resistance, the more preferable it is.

[0284] The Zn-doped GaN layer in the first embodiment preferably has a p-type carrier type. In the case of poor crystal quality of GaN crystal, even if Zn is doped in the GaN layer, it cannot fully compensate for the electrons caused by unexpected impurities such as Si and O, and there is a tendency to become n-type. Therefore, the p-type carrier type of the Zn-doped GaN layer means that the crystallinity of the GaN single crystal layer constituting the GaN crystal is good.

[0285] [GaN Crystal of Second Embodiment]

[0286] The GaN crystal of the second embodiment of the aspect B is characterized in that it includes a Zn-doped GaN layer, and the Zn concentration of the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Hereinafter, the thickness of the Zn-doped GaN layer is 50 μm or more, and the full width at half maximum of the rocking curve of the Zn-doped GaN layer by (201) X-ray diffraction is 50 arcsec or less.

[0287] Preferred aspects of the GaN crystal of the second embodiment are the same as those described in [GaN crystal of the first embodiment].

[0288] As described in the half-width of the rocking curve of the Zn-doped GaN layer based on (201) X-ray diffraction in the first embodiment, the half-width of the rocking curve of the Zn-doped GaN layer based on (004) X-ray diffraction in the first embodiment becomes an indicator for observing the rotational uniformity of the surface that is not parallel to the c-axis, that is, the c-plane, around the c-axis.

[0289] The smaller the half-value full width of the rocking curve based on (201) X-ray diffraction, the better the crystal quality. The half-value full width of the Zn-doped GaN layer is 50 arcsec or less, preferably 40 arcsec or less, more preferably 30 arcsec or less, and further preferably 20 arcsec or less. The lower limit of the half-value full width is not particularly limited, but is usually 5 arcsec or more.

[0290] Preferred aspects of the Zn-doped GaN layer and GaN crystal except for the full width at half maximum of the rocking curve are the same as those described in [GaN crystal of first embodiment].

[0291] The full width at half maximum of the rocking curve of the Zn-doped GaN layer based on (004) and (201) X-ray diffraction is preferably 50 arcsec or less, more preferably 40 arcsec or less, further preferably 30 arcsec or less, and particularly preferably 20 arcsec or less.

[0292] 《GaN Crystal (2)》

[0293] Another GaN crystal of this embodiment includes a Zn-doped GaN layer.

[0294] The resistivity of the Zn-doped GaN layer at 300K is 1×10 9Ωcm or more. In addition, the Zn concentration in the Zn-doped GaN layer is preferably 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 the following.

[0295] The resistivity of the Zn-doped GaN layer at 300K is more preferably 5×10 9 Ωcm or more, more preferably 1×10 10 Ωcm or more, more preferably 5×10 10 Ωcm or more, particularly preferably 1×10 11 The upper limit is not particularly limited because the specific resistance is higher than Ωcm. Furthermore, the higher the specific resistance, the more preferable it is.

[0296] The GaN crystal of this embodiment can suppress the reduction in crystal quality and reduce the unexpected adverse effects on device characteristics when the Zn concentration is extremely high and exceeds the upper limit by setting the Zn concentration in the Zn-doped GaN layer within the range of the above-mentioned upper and lower limits and achieving a high resistivity above a certain level.

[0297] Other preferred aspects of the GaN crystal of this embodiment are the same as the preferred aspects of the above-mentioned "GaN crystal (1)".

[0298] 《Method for manufacturing GaN crystal》

[0299] The manufacturing method of the GaN crystal of this embodiment is to manufacture a GaN crystal containing a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 The following is the method of doping the GaN crystal with Zn layer.

[0300] Here, when the GaN crystal of the above-mentioned form A is obtained as the GaN crystal, metal Zn is used as the doping precursor. In addition, when the GaN crystal of the above-mentioned form B is obtained as the GaN crystal, an organic Zn compound is used as the doping precursor.

[0301] Hereinafter, each manufacturing method will be described in detail.

[0302] 〈Method A〉

[0303] (Method for producing GaN crystal)

[0304] The Zn-doped GaN layer of the GaN crystal of the first embodiment and the second embodiment of aspect A can be produced by, for example, a vapor phase growth method or a liquid phase growth method.

[0305] Examples of the vapor phase growth method include the HVPE method, and examples of the liquid phase growth method include the acidic ammonothermal method and the alkaline ammonothermal method. Among these, the HVPE method is preferred from the viewpoint of ease of production.

[0306] Therefore, the third embodiment in aspect A of the present invention relates to a method for producing a GaN crystal.

[0307] The method for producing a GaN crystal in the third embodiment of the method A is to produce a GaN crystal having a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 The following method of Zn-doping a GaN layer is characterized in that metallic Zn is used as a doping precursor.

[0308] The method for producing GaN crystal preferably comprises the following first step (i). The method can be applied to the production of a GaN substrate having an N polarity region and a Ga polarity region sandwiching a regrown interface, and more preferably the resistivity is increased in at least a portion of the Ga polarity region.

[0309] (i) In the first step, a Zn-doped GaN layer is formed by growing a (0001)-oriented GaN layer on a c-plane GaN substrate seed crystal by a vapor phase epitaxy method.

[0310] It should be noted that, in the present specification, “on the substrate” and “on the surface of the substrate” have the same meaning, and “on the substrate seed crystal” and “on the surface of the substrate seed crystal” have the same meaning, respectively.

[0311] Hereinafter, the above-mentioned first step will be described in more detail.

[0312] In the first step, Figure 4 As shown in FIG. 2( b), a GaN layer 6 having a (0001) orientation is grown by a vapor phase growth method, preferably by an HVPE method. Figure 4 The GaN layer 6 is grown on the Ga polar surface of the c-plane GaN seed crystal 5 shown in (a), and a GaN crystal as a stacked structure is obtained. The growth thickness t 6g It is preferably 50 μm or more. At this time, a regrown interface is formed between the c-plane GaN seed crystal 5 and the GaN layer 6 .

[0313] The method for obtaining the c-plane GaN seed crystal used in the first step is not particularly limited. Figure 5 After the seed crystal wafer 1 is prepared as shown in (a), Figure 5As shown in (b), a (0001) oriented GaN thick film 2 made of unintentionally doped GaN is grown thereon by a vapor phase epitaxy method, preferably by an HVPE method. Figure 5 (c) As shown in FIG. 2 , the GaN thick film 2 is processed to obtain one or more c-plane GaN seed crystals 3 as substrates. An example of the seed crystal wafer 1 is a c-plane sapphire wafer, and preferably a peeling layer can be provided on the main surface. In addition, a GaN thick film can be further grown on the c-plane GaN seed crystal 3 obtained in this way by HVPE method or the like, and the processed c-plane GaN substrate can be used as the c-plane GaN seed crystal used in the first step.

[0314] Usually, the Ga polar surface of the c-plane GaN seed crystal 5 is processed to be flat by a flattening process, i.e., by appropriately applying grinding, polishing, a processing technique using a chemical polishing agent and a polishing pad called CMP, etc. before growing the GaN layer 6. The Ga polar surface after flattening can be processed to a rough surface by a roughening process, i.e., by etching, before growing the GaN layer 6.

[0315] In the first step, at least a portion of the GaN layer 6 is doped with Zn as a compensating impurity.

[0316] It should be noted that in addition to Zn, doping with Fe or the like as a compensating impurity is not excluded.

[0317] The doping of Zn can be performed by a conventionally known method, for example, preferably by a vapor phase growth method, more preferably by an HVPE method. When the vapor phase growth method is used, as described above, metal Zn is used as a doping precursor. Specifically, metal Zn is used in the form of vapor Zn obtained by heating.

[0318] In the vapor phase growth method, the effect of using metal Zn as a doping precursor will be described in comparison with the prior art.

[0319] Conventionally, there is a known method of using an organic Zn compound as a doping precursor when growing a GaN layer by an organic metal vapor phase growth (MOCVD) method. In this method, although a Zn-doped GaN crystal layer with excellent crystal quality can be obtained, since an organic Zn compound is used as a doping precursor in the MOCVD method, C at a certain concentration or above is inevitably contained in the Zn-doped GaN layer.

[0320] In contrast, in the manufacturing method of this embodiment, by using metal Zn as a doping precursor, the concentration of C unintentionally included in the Zn-doped GaN layer can be reduced compared to the conventional method, for example, the C concentration can be reduced to 1.0×10 18 atoms / cm3 In particular, when the HVPE method is used, the C concentration in the Zn-doped GaN layer can be reduced to the detection limit.

[0321] C functions as a compensating impurity and therefore contributes to the improvement of the resistivity. On the other hand, there is a risk that current collapse of the device will occur due to C. Therefore, when it is desired to reduce the risk of current collapse, the manufacturing method of this embodiment is very suitable.

[0322] It should be noted that it is known that Fe and Mn are used as compensating impurity elements when doping compensating impurities by vapor phase growth method. However, it is known that the vapor pressure varies depending on the type of compensating impurity, and the ease of introduction into GaN crystal varies depending on the element. Therefore, it is not a simple assumption that the doping conditions previously applied to Fe and Mn can be directly applied to Zn and can also be appropriately doped. Therefore, it is necessary to apply conditions that are effective in the case of Zn.

[0323] When vapor Zn is used as a raw material gas used in a vapor phase growth method, the growth rate is preferably 20 μm / hr or more from the viewpoint of high productivity, and is preferably 100 μm / hr or less from the viewpoint of stable crystal growth.

[0324] The partial pressure of vapor Zn is adjusted so as to achieve the above-mentioned Zn concentration.

[0325] The growth thickness of the GaN layer 6 is t 6g It only needs to be set according to the designed thickness of the Ga polar side region of the GaN crystal to be produced.

[0326] In the case of GaN crystal, even if the diameter of the wafer is 4 inches or 6 inches, the growth thickness of the GaN layer 6 can be reduced to t 6g Suppressed to 500 μm or less.

[0327] After the first process, you can Figure 4 As shown in (c), a thinning step is provided to thin the GaN layer 6 as a stacked structure.

[0328] exist Figure 4 In (c), the thickness of the c-plane GaN seed crystal 5 increases from the initial thickness t 5i Reduce to final thickness t 5f , and the thickness of the GaN layer 6 increases from the initial thickness, i.e., the growth thickness t 6g Reduce to final thickness t 6f However, in the thinning step, only one of the c-plane GaN seed crystal 5 and the GaN layer 6 may be processed.

[0329] When the offcut orientation of the GaN crystal to be produced is the same as the offcut of the c-plane GaN seed crystal 5 , the back surface of the c-plane GaN seed crystal 5 , that is, the N-polar surface of the stacked structure can be used as a reference for the surface orientation during thinning.

[0330] When the off-cut orientation of the GaN crystal to be manufactured is different from the off-cut of the c-plane GaN seed crystal 5, that is, when at least one of the off-cut angle and the off-cut direction is different, the crystal orientation of the GaN layer 6 that becomes the stacked structure can be confirmed by an X-ray diffraction device before thinning.

[0331] The processing technique used in the thinning step can be appropriately selected from grinding, polishing, CMP, dry etching, wet etching, and the like.

[0332] By using the manufacturing method described above, the GaN crystal of this embodiment can be produced with a good yield.

[0333] Next, refer to Figure 6 An example of an HVPE apparatus that can be used in the first step included in the above-mentioned production method will be described.

[0334] Figure 6 The HVPE apparatus 20 shown includes a hot wall reactor 21, a gallium storage cell 22 and a susceptor 23 disposed in the reactor 21, and a first heater 24 and a second heater 25 disposed outside the reactor 21. The first heater 24 and the second heater 25 surround the reactor 21 in an annular shape.

[0335] The reactor 21 is a quartz tube chamber. The reactor 21 has a first zone Z1 mainly heated by the first heater 24 and a second zone Z2 mainly heated by the second heater 25. E It is connected to the end of the reactor 21 on the second zone Z2 side.

[0336] The gallium storage cell 22 disposed in the first zone Z1 is a quartz container having a gas inlet and a gas outlet.

[0337] The susceptor 23 disposed in the second zone Z2 is formed of, for example, graphite. Any mechanism for rotating the susceptor 23 may be provided.

[0338] In order to grow GaN using the HVPE device 20, after placing a seed crystal on the susceptor 23, the reactor 21 is heated by the first heater 24 and the second heater 25, and NH3 (ammonia) diluted with a carrier gas is supplied to the second region Z2 through the ammonia introduction pipe P1, and HCl (hydrogen chloride) diluted with a carrier gas is supplied to the gallium storage tank 22 through the hydrogen chloride introduction pipe P2. The HCl reacts with the metal gallium in the gallium storage tank 22, and the generated GaCl (gallium chloride) is transported to the second region Z2 through the gallium chloride introduction pipe P3.

[0339] In the second zone Z2 , NH 3 reacts with GaCl, and the generated GaN is crystallized on the seed crystal placed on the susceptor 23 .

[0340] When the grown GaN is intentionally doped, a doping gas diluted with a carrier gas is introduced into the second zone Z2 in the reactor 21 through the dopant introduction pipe P4 .

[0341] The ammonia introduction pipe P1 , the hydrogen chloride introduction pipe P2 , the gallium chloride introduction pipe P3 , and the dopant introduction pipe P4 are formed of quartz at portions disposed in the reactor 21 .

[0342] As the carrier gas for diluting NH 3 , HCl and each gas in the doping gas, H 2 (hydrogen), N 2 (nitrogen) or a mixed gas of H 2 and N 2 can be preferably used.

[0343] Preferred conditions for growing GaN using the HVPE apparatus 20 are as follows.

[0344] The temperature of the gallium storage cell 22 is, for example, 500 to 1000° C., preferably 700° C. or higher, and preferably 900° C. or lower.

[0345] The temperature of the susceptor 23 is, for example, 900 to 1100° C., preferably 930° C. or higher, more preferably 950° C. or higher, and preferably 1050° C. or lower, more preferably 1020° C. or lower.

[0346] The ratio of the NH 3 partial pressure (V) to the GaCl partial pressure (III) in the reactor 21, that is, the V / III ratio, is, for example, 1 to 20, preferably 2 or more, more preferably 3 or more, and preferably 10 or less.

[0347] If the V / III ratio is too large or too small, the morphology of the growth surface of GaN will be deteriorated. The deterioration of the morphology of the growth surface will cause the crystal quality to decrease.

[0348] For certain impurities, the efficiency of introduction into GaN crystals is highly dependent on the crystal orientation of the growth surface. The uniformity of the concentration of the impurities is reduced inside the GaN crystal grown under the condition of poor growth surface morphology. This is caused by the presence of facets with various orientations on the growth surface with poor morphology.

[0349] A typical example of an impurity whose introduction efficiency into GaN crystal varies significantly depending on the crystal orientation of the growth surface is O (oxygen). Since O is a donor impurity, a decrease in the uniformity of its concentration will cause a decrease in the uniformity of the resistivity.

[0350] In addition, using too low a V / III ratio will increase the nitrogen vacancy concentration of the grown GaN crystal. The effect of nitrogen vacancies on GaN crystals, GaN substrates using the GaN crystals, or nitride semiconductor devices formed on the GaN substrates is still unclear, but since they are point defects, it can be considered that the concentration should be as low as possible.

[0351] The growth rate of GaN is preferably 40 to 200 μm / h, and the product of the partial pressure of NH3 and the partial pressure of GaCl in the reactor can be used as a parameter to control the growth rate. Too high a growth rate will deteriorate the surface morphology of the grown GaN.

[0352] When the GaN layer 6 is doped in the first step described above, in order to prevent the morphology of the growth surface from being deteriorated, it is preferred that the supply rate of the doping gas be gradually increased to a given value over several minutes or tens of minutes from the start of supply.

[0353] For the same reason, it is preferred to start supplying the doping gas when the GaN layer 6 has grown for at least several μm. Specifically, when forming the GaN layer by the first step, it is preferred that the doping gas is not supplied for at least 5 μm, preferably at least 10 μm, of the initial growth of the GaN layer, so that the GaN layer grows as an undoped layer. Thus, no new dislocations are generated at the interface between the undoped layer and the doped layer, and the quality of the seed crystal can be maintained.

[0354] The method of adding compensating impurities such as Zn to the GaN layer 6 is not limited, but a method of introducing a doping gas into an HVPE apparatus is generally used.

[0355] The doping gas used for Zn doping is as described above. For example, when using vapor Zn as the raw material gas, metal Zn is placed in the introduction pipe as a doping precursor and heated, thereby preparing vapor Zn on the spot for use. When preparing vapor Zn on the spot, it is preferred to purge Zn vapor for the first few minutes in such a way that the concentration of Zn gas becomes uniform. For example, it is conceivable to start the supply of GaCl after 5 minutes of purging Zn vapor.

[0356] When Zn is doped after the undoped layer, it is preferred to gradually increase the concentration of hydrogen chloride. By gradually increasing the concentration of hydrogen chloride, it is possible to prevent the formation of a steep undoped layer / Zn doped layer interface in the crystal, thereby improving the crystal quality. Specifically, it is desirable to linearly increase the concentration of hydrogen chloride required for the desired Zn doping concentration over 3 minutes.

[0357] GaN grown using the HVPE apparatus 20 may contain O and Si at a concentration detectable by SIMS (secondary ion mass spectrometry) even when it is not intentionally doped.

[0358] The Si source is quartz (SiO 2 ) used for the reactor 21 and the piping in the reactor 21 , and the O source is either or both of the above-mentioned quartz and moisture remaining in or intruding into the reactor 21 .

[0359] exist Figure 6 The components not shown in the figure are included. For the components arranged in the reactor 21, in addition to quartz and carbon, components made of SiC (silicon carbide), SiNx (silicon nitride), BN (boron nitride), aluminum oxide, W (tungsten), Mo (molybdenum), etc. can be used. Therefore, the concentration of impurity elements other than Si, O and H in GaN grown using the HVPE device 20 can be independently 5×10 15 atoms / cm 3 the following.

[0360] Hereinabove, an example of a method for producing a GaN crystal having a stacked structure has been described as a method for producing a GaN crystal according to the present embodiment, but the GaN crystal is not limited to a GaN crystal having a stacked structure.

[0361] For example, in the first step, the GaN layer 6 is grown to a certain thickness to form a GaN thick film, and the GaN thick film is sliced ​​to obtain a GaN crystal. In this case, the obtained GaN crystal consists only of the GaN layer 6 described above.

[0362] When the specific doping region with high Zn concentration is selected as the region for slicing the GaN crystal, the Zn concentration in the entire region of the obtained GaN crystal increases. That is, a GaN crystal consisting of only a Zn-doped GaN layer without a c-plane GaN seed crystal 5 can be obtained.

[0363] 〈Method B〉

[0364] (Method for producing GaN crystal)

[0365] The Zn-doped GaN layer of the GaN crystal of the first embodiment and the second embodiment of aspect B can be produced by, for example, a vapor phase growth method or a liquid phase growth method.

[0366] Examples of the vapor phase growth method include the HVPE method, and examples of the liquid phase growth method include the acidic ammonothermal method and the alkaline ammonothermal method. Among these, the HVPE method is preferred from the viewpoint of ease of production.

[0367] Therefore, the third embodiment in aspect B of the present invention relates to a method for producing a GaN crystal.

[0368] The method for producing a GaN crystal in the third embodiment of the method B is to produce a GaN crystal having a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 The following method for forming a Zn-doped GaN layer with a thickness of 50 μm or more is characterized in that an organic Zn compound is used as a doping precursor.

[0369] The method for producing GaN crystal preferably comprises the following first step (i). The method can be applied to the production of a GaN substrate having an N polarity region and a Ga polarity region sandwiching a regrown interface, and more preferably the resistivity is increased in at least a portion of the Ga polarity region.

[0370] (i) In the first step, a Zn-doped GaN layer is formed by growing a (0001)-oriented GaN layer on a c-plane GaN substrate seed crystal by a vapor phase epitaxy method.

[0371] It should be noted that, in the present specification, “on the substrate” and “on the surface of the substrate” have the same meaning, and “on the substrate seed crystal” and “on the surface of the substrate seed crystal” have the same meaning, respectively.

[0372] Hereinafter, the above-mentioned first step will be described in more detail.

[0373] In the first step, Figure 4 As shown in FIG. 2( b), a GaN layer 6 having a (0001) orientation is grown by a vapor phase growth method, preferably by an HVPE method. Figure 4 The GaN layer 6 is grown on the Ga polar surface of the c-plane GaN seed crystal 5 shown in (a), and a GaN crystal as a stacked structure is obtained. The growth thickness t 6g At this time, a regrown interface is formed between the c-plane GaN seed crystal 5 and the GaN layer 6 .

[0374] The method for obtaining the c-plane GaN seed crystal used in the first step is not particularly limited. Figure 5 After the seed crystal wafer 1 is prepared as shown in (a), Figure 5 As shown in (b), a (0001) oriented GaN thick film 2 made of unintentionally doped GaN is grown thereon by a vapor phase epitaxy method, preferably by an HVPE method. Figure 5 (c) As shown in FIG. 2 , the GaN thick film 2 is processed to obtain one or more c-plane GaN seed crystals 3 as substrates. An example of the seed crystal wafer 1 is a c-plane sapphire wafer, and preferably a peeling layer can be provided on the main surface. In addition, a GaN thick film can be further grown on the c-plane GaN seed crystal 3 obtained in this way by HVPE method or the like, and the processed c-plane GaN substrate can be used as the c-plane GaN seed crystal used in the first step.

[0375] Usually, the Ga polar surface of the c-plane GaN seed crystal 5 is processed to be flat by a flattening process, i.e., by appropriately applying grinding, polishing, a processing technique using a chemical polishing agent and a polishing pad called CMP, etc. before growing the GaN layer 6. The Ga polar surface after flattening can be processed to a rough surface by a roughening process, i.e., by etching, before growing the GaN layer 6.

[0376] In the first step, at least a portion of the GaN layer 6 is doped with Zn as a compensating impurity.

[0377] It should be noted that in addition to Zn, doping with Fe or the like as a compensating impurity is not excluded.

[0378] The doping of Zn can be performed by a conventionally known method, for example, preferably by a vapor phase growth method, more preferably by an HVPE method. When the vapor phase growth method is used, as described above, an organic Zn compound is used as a doping precursor.

[0379] In the vapor phase growth method, the effect of using an organic Zn compound as a doping precursor will be described in comparison with the prior art.

[0380] In the past, there is a known method of using an organic Zn compound as a doping precursor when growing a GaN layer by an organic metal vapor phase growth (MOCVD) method. In this method, although a Zn-doped GaN crystal layer with excellent crystal quality can be obtained, it is difficult to thicken the GaN crystal layer.

[0381] In contrast, in the manufacturing method of this embodiment, by using a vapor phase growth method, preferably an HVPE method, in crystal growth, and using an organic Zn compound as a doping precursor, it is possible to obtain a crystal layer having a Zn-doped GaN layer with a thickness of 50 μm or more. In particular, by using the HVPE method for crystal growth, it is possible to obtain a crystal with excellent crystal quality that cannot be achieved with the prior art.

[0382] It should be noted that it is known that Fe and Mn are used as compensating impurity elements when doping compensating impurities by vapor phase growth method. However, it is known that the vapor pressure varies depending on the type of compensating impurity, and the ease of introduction into GaN crystal varies depending on the element. Therefore, it is not a simple assumption that the doping conditions previously applied to Fe and Mn can be directly applied to Zn and can also be appropriately doped. Therefore, it is necessary to apply conditions that are effective in the case of Zn.

[0383] Examples of the raw material gas of the organic Zn compound used in the vapor phase growth method include diethyl Zn and dimethyl Zn. From the viewpoint of stable crystal growth, diethyl Zn is more preferable.

[0384] When an organic Zn compound is used as a dopant precursor, the growth rate is preferably 20 μm / hr or more from the viewpoint of high productivity, and is preferably 100 μm / hr or less from the viewpoint of stable crystal growth.

[0385] The partial pressure of the organic Zn compound is adjusted so as to achieve the above-mentioned Zn concentration.

[0386] The growth thickness of the GaN layer 6 is t 6g It only needs to be set according to the designed thickness of the Ga polar side region of the GaN crystal to be produced.

[0387] In the case of GaN crystal, even if the diameter of the wafer is 4 inches or 6 inches, the growth thickness of the GaN layer 6 can be reduced to t 6g Suppressed to 500 μm or less.

[0388] After the first process, you can Figure 4 As shown in (c), a thinning step is provided to thin the GaN layer 6 as a stacked structure.

[0389] exist Figure 4 In (c), the thickness of the c-plane GaN seed crystal 5 increases from the initial thickness t 5i Reduce to final thickness t 5f , and the thickness of the GaN layer 6 increases from the initial thickness, i.e., the growth thickness t 6g Reduce to final thickness t 6fHowever, in the thinning step, only one of the c-plane GaN seed crystal 5 and the GaN layer 6 may be processed.

[0390] When the off-cut orientation of the GaN crystal to be produced is the same as the off-cut orientation of the c-plane GaN seed crystal 5 , the back surface of the c-plane GaN seed crystal 5 , that is, the N-polar surface of the stacked structure can be used as a reference for the surface orientation during thinning.

[0391] When the off-cut orientation of the GaN crystal to be manufactured is different from the off-cut of the c-plane GaN seed crystal 5, that is, when at least one of the off-cut angle and the off-cut direction is different, the crystal orientation of the GaN layer 6 that becomes the stacked structure can be confirmed by an X-ray diffraction device before thinning.

[0392] The processing technique used in the thinning step can be appropriately selected from grinding, polishing, CMP, dry etching, wet etching, and the like.

[0393] By using the manufacturing method described above, the GaN crystal of this embodiment can be produced with a good yield.

[0394] Next, refer to Figure 6 An example of an HVPE apparatus that can be used in the first step included in the above-mentioned production method will be described.

[0395] Figure 6 The HVPE apparatus 20 shown includes a hot wall reactor 21, a gallium storage cell 22 and a susceptor 23 disposed in the reactor 21, and a first heater 24 and a second heater 25 disposed outside the reactor 21. The first heater 24 and the second heater 25 surround the reactor 21 in an annular shape.

[0396] The reactor 21 is a quartz tube chamber. The reactor 21 has a first zone Z1 mainly heated by the first heater 24 and a second zone Z2 mainly heated by the second heater 25. E It is connected to the end of the reactor 21 on the second zone Z2 side.

[0397] The gallium storage cell 22 disposed in the first zone Z1 is a quartz container having a gas inlet and a gas outlet.

[0398] The susceptor 23 disposed in the second zone Z2 is formed of, for example, graphite. Any mechanism for rotating the susceptor 23 may be provided.

[0399] In order to grow GaN using the HVPE device 20, after placing a seed crystal on the susceptor 23, the reactor 21 is heated by the first heater 24 and the second heater 25, and NH3 (ammonia) diluted with a carrier gas is supplied to the second region Z2 through the ammonia introduction pipe P1, and HCl (hydrogen chloride) diluted with a carrier gas is supplied to the gallium storage tank 22 through the hydrogen chloride introduction pipe P2. The HCl reacts with the metal gallium in the gallium storage tank 22, and the generated GaCl (gallium chloride) is transported to the second region Z2 through the gallium chloride introduction pipe P3.

[0400] In the second zone Z2 , NH 3 reacts with GaCl, and the generated GaN is crystallized on the seed crystal placed on the susceptor 23 .

[0401] When the grown GaN is intentionally doped, a doping gas diluted with a carrier gas is introduced into the second zone Z2 in the reactor 21 through the dopant introduction pipe P4 .

[0402] The ammonia introduction pipe P1 , the hydrogen chloride introduction pipe P2 , the gallium chloride introduction pipe P3 , and the dopant introduction pipe P4 are formed of quartz at portions disposed in the reactor 21 .

[0403] As the carrier gas for diluting NH 3 , HCl and each gas in the doping gas, H 2 (hydrogen), N 2 (nitrogen) or a mixed gas of H 2 and N 2 can be preferably used.

[0404] Preferred conditions for growing GaN using the HVPE apparatus 20 are as follows.

[0405] The temperature of the gallium storage cell 22 is, for example, 500 to 1000° C., preferably 700° C. or higher, and preferably 900° C. or lower.

[0406] The temperature of the susceptor 23 is, for example, 900 to 1100° C., preferably 930° C. or higher, more preferably 950° C. or higher, and preferably 1050° C. or lower, more preferably 1020° C. or lower.

[0407] The ratio of the NH 3 partial pressure (V) to the GaCl partial pressure (III) in the reactor 21, that is, the V / III ratio, is, for example, 1 to 20, preferably 2 or more, more preferably 3 or more, and preferably 10 or less.

[0408] If the V / III ratio is too large or too small, the morphology of the growth surface of GaN will be deteriorated. The deterioration of the morphology of the growth surface will cause the crystal quality to decrease.

[0409] For certain impurities, the efficiency of introduction into GaN crystals is highly dependent on the crystal orientation of the growth surface. The uniformity of the concentration of the above impurities is reduced inside the GaN crystal grown under the condition of poor growth surface morphology. This is caused by the presence of small faces in various orientations on the growth surface with poor morphology.

[0410] A typical example of an impurity whose introduction efficiency into GaN crystal varies significantly depending on the crystal orientation of the growth surface is O (oxygen). Since O is a donor impurity, a decrease in the uniformity of its concentration will cause a decrease in the uniformity of the resistivity.

[0411] In addition, using too low a V / III ratio will increase the nitrogen vacancy concentration of the grown GaN crystal. The effect of nitrogen vacancies on GaN crystals, GaN substrates using the GaN crystals, or nitride semiconductor devices formed on the GaN substrates is still unclear, but since they are point defects, it can be considered that the concentration should be as low as possible.

[0412] The growth rate of GaN is preferably 40 to 200 μm / h, and the product of the partial pressure of NH3 and the partial pressure of GaCl in the reactor can be used as a parameter to control the growth rate. Too high a growth rate will deteriorate the surface morphology of the grown GaN.

[0413] When the GaN layer 6 is doped in the first step described above, in order to prevent the morphology of the growth surface from being deteriorated, it is preferred that the supply rate of the doping gas be gradually increased to a given value over several minutes or tens of minutes from the start of supply.

[0414] For the same reason, it is preferred to start supplying the doping gas when the GaN layer 6 has grown for at least several μm. Specifically, when forming the GaN layer by the first step, it is preferred that the doping gas is not supplied for at least 5 μm, preferably at least 10 μm, of the initial growth of the GaN layer, so that the GaN layer grows as an undoped layer. Thus, no new dislocations are generated at the interface between the undoped layer and the doped layer, and the quality of the seed crystal can be maintained.

[0415] The method of adding compensating impurities such as Zn to the GaN layer 6 is not limited, but a method of introducing a doping gas into an HVPE apparatus is generally used.

[0416] As described above, when diethyl zinc, which is an organic metal, is used as the raw material gas, a cylinder of diethyl zinc gas having an arbitrary concentration is prepared and passed at a predetermined flow rate to introduce Zn into the system.

[0417] When Zn is doped after the undoped layer, it is preferred to gradually increase the diethyl Zn flow rate. By gradually increasing the diethyl Zn flow rate, it is possible to prevent the formation of a steep undoped layer / Zn doped layer interface in the crystal, so the crystal quality is improved. Specifically, it is expected that the diethyl Zn flow rate required for the desired Zn doping concentration will rise linearly over 3 minutes.

[0418] GaN grown using the HVPE apparatus 20 may contain O and Si at a concentration detectable by SIMS (secondary ion mass spectrometry) even when it is not intentionally doped.

[0419] The Si source is quartz (SiO 2 ) used for the reactor 21 and the piping in the reactor 21 , and the O source is either or both of the above-mentioned quartz and moisture remaining in or intruding into the reactor 21 .

[0420] exist Figure 6 The components not shown in the figure are included. For the components arranged in the reactor 21, in addition to quartz and carbon, components made of SiC (silicon carbide), SiNx (silicon nitride), BN (boron nitride), aluminum oxide, W (tungsten), Mo (molybdenum), etc. can be used. Therefore, the concentration of impurity elements other than Si, O and H in GaN grown using the HVPE device 20 can be independently 5×10 15 atoms / cm 3 the following.

[0421] Hereinabove, an example of a method for producing a GaN crystal having a stacked structure has been described as a method for producing a GaN crystal according to the present embodiment, but the GaN crystal is not limited to a GaN crystal having a stacked structure.

[0422] For example, in the first step, the GaN layer 6 is grown to a certain thickness to form a GaN thick film, and the GaN thick film is sliced ​​to obtain a GaN crystal. In this case, the obtained GaN crystal consists only of the GaN layer 6 described above.

[0423] When the specific doping region with high Zn concentration is selected as the region for slicing the GaN crystal, the Zn concentration in the entire region of the obtained GaN crystal increases. That is, a GaN crystal consisting of only a Zn-doped GaN layer without a c-plane GaN seed crystal 5 can be obtained.

[0424] 《Applications of GaN Crystals》

[0425] The GaN crystal of this embodiment can be preferably used for manufacturing nitride semiconductor devices, especially nitride semiconductor devices with a horizontal device structure, in any of the methods including method A and method B. Specifically, the nitride semiconductor device can be manufactured by a method having the following steps: a step of preparing the above-mentioned GaN crystal, a step of preparing a substrate from the prepared GaN crystal, and a step of epitaxially growing one or more nitride semiconductor layers on the substrate.

[0426] Nitride semiconductors are also called nitride III-V compound semiconductors, III-nitride compound semiconductors, GaN-based semiconductors, etc. In addition to GaN, they also include compounds in which part or all of the gallium in GaN is replaced by other elements from Group 13 of the periodic table (B, Al, In, etc.).

[0427] A typical example of a nitride semiconductor device with a horizontal device structure is GaN-HEMT, but the horizontal device structure can also be used in electronic devices other than HEMT such as bipolar transistors, and can also be used in light-emitting devices such as light-emitting diodes (LEDs) and laser diodes (LDs).

[0428] Example

[0429] Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

[0430] (Example A-1)

[0431] 1. Epitaxial growth of GaN crystals

[0432] Using a vapor phase growth apparatus equipped with a hot wall reactor made of quartz, GaN crystal was epitaxially grown on a self-supporting GaN seed crystal having a size of 20 mm square and a thickness of 400 μm by the HVPE method.

[0433] In this process, (1) a temperature raising step, (2) a GaN layer growing step, and (3) a cooling step are sequentially performed as described below.

[0434] (1) Heating step

[0435] First, a self-supporting GaN seed crystal is placed in a reactor.

[0436] Next, while ammonia and a carrier gas were supplied to the self-supporting GaN seed crystal, the reactor temperature was raised from room temperature to 1030° C. Nitrogen gas was used as the carrier gas. Through this step, a GaN substrate seed crystal was obtained.

[0437] (2) Zn-doped GaN layer growth steps

[0438] While maintaining the reactor temperature at 1030° C., a mixed gas containing ammonia and gallium chloride as shown in the following growth conditions was supplied as a raw material gas, thereby growing a Zn-doped GaN layer on the GaN substrate seed crystal to a thickness of 850 μm. As a Zn-doping precursor, a Zn-doping precursor obtained by heating metal Zn to 409° C. to form vapor Zn was used.

[0439] The growth rate was set to 83 μm / hr, and the growth conditions were set to reactor pressure 101 kPa, ammonia partial pressure 16.290 kPa, GaCl partial pressure 1.303 kPa, nitrogen partial pressure 83.407 kPa, vapor Zn partial pressure 3.90×10 -5 kPa.

[0440] It should be noted that the Zn vapor was not flowed for the initial 13 minutes of growth to form an undoped layer.

[0441] Here the gas partial pressure (P G ) is the ratio (r) of the volume flow rate of the gas to the total volume flow rate of all gases supplied to the reactor multiplied by the reactor pressure (P R ) and the value obtained, that is, P G =r×P R Represents the value.

[0442] Next, the temperature of the reactor was raised to 1010° C. while continuously supplying the raw material gas and the carrier gas.

[0443] (3) Cooling step

[0444] After the Zn-doped GaN layer growth step (2) is completed, the supply of gallium chloride to the GaN substrate seed crystal is stopped, and the heating of the reactor is stopped to lower the reactor temperature to room temperature. Until the temperature drops to 600°C, the gas flowing in the reactor is set to ammonia and nitrogen, and then to only nitrogen.

[0445] The entire surface of the as-grown GaN crystal taken out from the reactor is mirror-like and flat, and its color is light blue.

[0446] 2. Fabrication of c-plane GaN substrate

[0447] The as-grown GaN crystal obtained in 1. above was laser scored to obtain a square epitaxial substrate with a side length of 7 mm. Then, the +c plane and -c plane were ground and polished to complete the c-plane GaN substrate formed by the GaN crystal containing the Zn-doped GaN layer. It should be noted that in the processing step, the seed portion on the -c plane side was completely removed by grinding.

[0448] The total thickness of the GaN crystal as the c-plane GaN substrate is 400 μm, and it is composed only of the Zn-doped GaN layer.

[0449] 3. Evaluation of c-plane GaN substrate

[0450] <Determination of Zn concentration>

[0451] The Zn concentration of the c-plane GaN substrate obtained above was measured by SIMS.

[0452] As a result, the Zn concentration was 4×10 17 atoms / cm 3 The C concentration is at the limit of detection and is substantially non-existent. The Si concentration is 8×10 14 atoms / cm 3 The O concentration is 8×10 15 atoms / cm 3 It should be noted that the GaN crystal of Example A-1 was grown by the HVPE method, and therefore the alkali metal concentration on the crystal surface was 10 ppm or less, and it can be inferred that the crystal did not contain alkali metal inclusions.

[0453] In addition, the luminescence spectrum of the grown crystal was obtained by photoluminescence. Specifically, the light source used for excitation was a He-Cd laser with a wavelength of 325 nm (energy 3.81 eV), and the GaN crystal of Example A-1 was irradiated. The obtained luminescence spectrum is shown in Figure 7 As a result, there is a peak at 2.98 eV, but no peak exists in the region of 2.64 to 2.82 eV.

[0454] <Measurement of carrier concentration, specific resistance, and carrier type>

[0455] Next, for Hall effect measurement, Ti 30nm and Au 100nm were continuously vacuum-deposited on the surface of the c-plane GaN substrate obtained above. The 4-terminal Van der Pauw method was used in the Hall effect measurement. The result was that the resistivity at 300K was 5.6×10 11 Ωcm.

[0456] In the Hall measurement, the type of carrier cannot be well distinguished.

[0457] <Measurement of rocking curve by X-ray diffraction>

[0458] The rocking curve (XRC) of X-ray diffraction based on (004) reflection and (201) reflection of the c-plane GaN substrate produced above was measured using an X-ray diffraction apparatus (SmartLab manufactured by Rigaku Corporation) using CuKα1 radiation as an X-ray source.

[0459] A Ge(440)4 crystal monochromator was used in the incident optical system of the X-ray diffraction device. The size of the long side limiting slit of the X-ray beam was set to 2 mm. The X-ray tube was operated at a voltage of 45 kV and a current of 40 mA.

[0460] The full width at half maximum (FWHM) of the rocking curve of X-ray diffraction based on (004) reflection was 18.6 arcsec, and the full width at half maximum (FWHM) of the rocking curve of X-ray diffraction based on (201) reflection was 24.7 arcsec.

[0461] (Example B-1)

[0462] 1. Epitaxial growth of GaN crystals

[0463] Using a vapor phase growth apparatus equipped with a hot wall reactor made of quartz, GaN crystal was epitaxially grown on a self-supporting GaN seed crystal having a size of 20 mm square and a thickness of 400 μm by the HVPE method.

[0464] In this process, (1) a temperature raising step, (2) a GaN layer growing step, and (3) a cooling step are sequentially performed as described below.

[0465] (1) Heating step

[0466] First, a self-supporting GaN seed crystal is placed in a reactor.

[0467] Next, while ammonia and a carrier gas were supplied to the self-supporting GaN seed crystal, the reactor temperature was raised from room temperature to 1030° C. Nitrogen gas was used as the carrier gas. Through this step, a GaN substrate seed crystal was obtained.

[0468] (2) Zn-doped GaN layer growth steps

[0469] While maintaining the reactor temperature at 1030° C., a mixed gas containing ammonia and gallium chloride as shown in the following growth conditions was supplied as a raw material gas, thereby growing a Zn-doped GaN layer to a thickness of 250 μm on the GaN substrate seed crystal. As a Zn doping precursor, diethyl Zn at a concentration of 500 ppm diluted with nitrogen was used.

[0470] The growth rate was set to 83 μm / hr, and the growth conditions were set to reactor pressure 101 kPa, ammonia partial pressure 15.683 kPa, GaCl partial pressure 1.255 kPa, nitrogen partial pressure 834.062 kPa, diethyl Zn partial pressure 1.25×10 -3 kPa.

[0471] It should be noted that diethyl Zn was not flowed for the initial 10 minutes of growth to form an undoped layer.

[0472] Here the gas partial pressure (P G ) is the ratio (r) of the volume flow rate of the gas to the total volume flow rate of all gases supplied to the reactor multiplied by the reactor pressure (P R ) and the value obtained, that is, P G =r×P R Represents the value.

[0473] Next, the temperature of the reactor was raised to 1010° C. while continuously supplying the raw material gas and the carrier gas.

[0474] (3) Cooling step

[0475] After the Zn-doped GaN layer growth step (2) is completed, the supply of gallium chloride to the GaN substrate seed crystal is stopped, and the heating of the reactor is stopped to lower the reactor temperature to room temperature. Until the temperature drops to 600°C, the gas flowing in the reactor is set to ammonia and nitrogen, and then to only nitrogen.

[0476] The entire surface of the self-supporting substrate, i.e., the GaN crystal surface, taken out from the reactor was mirror-like and flat, and its color was khaki.

[0477] 2. Fabrication of c-plane GaN substrate

[0478] The self-supporting substrate obtained in 1. above, i.e., the GaN crystal, was laser-scored to obtain a square epitaxial substrate with a side length of 7 mm. Then, the +c plane and -c plane were ground and polished to complete the c-plane GaN substrate formed by the GaN crystal containing the Zn-doped GaN layer. It should be noted that in the processing step, the seed portion on the -c plane side was completely removed by grinding.

[0479] The total thickness of the GaN crystal as the c-plane GaN substrate is 240 μm, and it is composed only of the Zn-doped GaN layer.

[0480] 3. Evaluation of c-plane GaN substrate

[0481] <Determination of Zn concentration>

[0482] The Zn concentration of the c-plane GaN substrate obtained above was measured by SIMS.

[0483] As a result, the Zn concentration is 1×10 19 atoms / cm 3 The C concentration is 2×10 18 atoms / cm 3 . The Si concentration is 8×1015 atoms / cm 3 The O concentration is 8×10 15 atoms / cm 3 It should be noted that the GaN crystal of Example B-1 was grown by the HVPE method, and therefore the alkali metal concentration on the crystal surface was 10 ppm or less, and it can be inferred that the crystal did not contain alkali metal inclusions.

[0484] In addition, the luminescence spectrum of the grown crystal was obtained by photoluminescence. Specifically, the light source used for excitation was a He-Cd laser with a wavelength of 325 nm (energy 3.81 eV), and the GaN crystal of Example B-1 was irradiated. The obtained luminescence spectrum is shown in Figure 8 As a result, there is a peak at 2.95 eV, but no peak exists in the region of 2.64 to 2.82 eV.

[0485] <Measurement of carrier concentration, specific resistance, and carrier type>

[0486] Next, for Hall effect measurement, Ti 30nm and Au 100nm were continuously vacuum-deposited on the surface of the c-plane GaN substrate obtained above. The 4-terminal Van der Pauw method was used in the Hall effect measurement. The result was that the resistivity at 300K was 3.2×10 10 Ωcm.

[0487] In the Hall measurement, the type of carrier cannot be well distinguished.

[0488] <Measurement of rocking curve by X-ray diffraction>

[0489] The rocking curve (XRC) of X-ray diffraction based on (004) reflection and (201) reflection of the c-plane GaN substrate produced above was measured using an X-ray diffraction apparatus (SmartLab manufactured by Rigaku Corporation) using CuKα1 radiation as an X-ray source.

[0490] A Ge(440)4 crystal monochromator was used in the incident optical system of the X-ray diffraction device. The size of the long side limiting slit of the X-ray beam was set to 2 mm. The X-ray tube was operated at a voltage of 45 kV and a current of 40 mA.

[0491] The full width at half maximum (FWHM) of the rocking curve of the X-ray diffraction based on the (004) reflection was 24.5 arcsec. In addition, the full width at half maximum (FWHM) of the rocking curve of the X-ray diffraction based on the (201) reflection was 21.6 arcsec.

[0492] In addition, the present invention is described in detail with reference to specific embodiments, but it should be clear to those skilled in the art that various changes and modifications can be applied without departing from the spirit and scope of the present invention. This application is based on Japanese patent applications (Japanese patent application 2022-140786) filed on September 5, 2022 and Japanese patent applications (Japanese patent application 2022-140787) filed on September 5, 2022, the contents of which are hereby introduced as reference.

Claims

1. A GaN crystal comprising a Zn-doped GaN layer, The Zn concentration in the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (004) X-ray diffraction is 50 arcsec or less.

2. A GaN crystal comprising a Zn-doped GaN layer, The Zn concentration in the Zn-doped GaN layer is 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 Hereinafter, the full width at half maximum of the rocking curve based on (201) X-ray diffraction is 50 arcsec or less.

3. The GaN crystal according to claim 1 or 2, wherein: In the Zn-doped GaN layer, the C concentration is 1.0×10 18 atoms / cm 3 the following.

4. The GaN crystal according to claim 1 or 2, wherein: The thickness of the Zn-doped GaN layer is greater than 50 μm.

5. The GaN crystal according to claim 1 or 2, wherein: The alkali metal concentration on the crystal surface of the Zn-doped GaN layer is less than 10 ppm.

6. The GaN crystal according to claim 1 or 2, wherein: The Zn-doped GaN layer does not contain alkali metal inclusions.

7. The GaN crystal according to claim 1 or 2, wherein: When the Zn-doped GaN layer is irradiated with light having energy greater than the band gap energy of GaN, the peak of light emitted does not exist in the region of 2.64 to 2.82 eV.

8. The GaN crystal according to claim 1 or 2, wherein: The specific resistance of the Zn-doped GaN layer at 300K is 1×10 9 Ωcm or more.

9. The GaN crystal according to claim 1 or 2, wherein: The Zn-doped GaN layer has a surface having an inclination of 10 degrees or less with respect to a (0001) crystal plane.

10. The GaN crystal according to claim 1 or 2, wherein: In the Zn-doped GaN layer, the total donor impurity concentration is less than 5.0×10 16 atoms / cm 3 .

11. The GaN crystal according to claim 1 or 2, wherein: In the Zn-doped GaN layer, the contents of O (oxygen) and Si (silicon) are both 1.0×10 15 atoms / cm 3 above.

12. A GaN crystal comprising a Zn-doped GaN layer, The specific resistance of the Zn-doped GaN layer at 300K is 1×10 9 Ωcm or more.

13. A method for producing a GaN crystal comprising: producing a GaN crystal having a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 A method of Zn-doping a GaN layer in a GaN crystal, the method comprising: Metallic Zn was used as the doping precursor.

14. A method for producing a GaN crystal comprising: producing a GaN crystal having a Zn concentration of 1.0×10 16 atoms / cm 3 Above and 1.0×10 20 atoms / cm 3 A method for producing a GaN crystal having a Zn-doped GaN layer having a thickness of 50 μm or more, the method comprising: An organic Zn compound was used as a doping precursor.

15. The method for producing a GaN crystal according to claim 13 or 14, wherein: The vapor phase growth method is the HVPE method.

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