JP2015040169A - Periodic table group 13 metal nitride crystals - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a periodic table group 13 metal nitride crystal which is high in purity and quality and causes little defect.SOLUTION: A periodic table group 13 metal nitride crystal is obtained by crystal growth in the presence of a supercritical and/or subcritical nitrogen-containing solvent and has at least two luminescence peaks in the range of 3.430 to 3.480 eV in the emission spectrum observed by the low-temperature photoluminescence method. The periodic table group 13 metal nitride crystal is preferably a gallium nitride crystal and is obtained by growing a crystal on a ground substrate with a nonpolar or semi-polar surface as the principal plane. The periodic table group 13 metal nitride crystal has a plurality of first luminescence peaks in the range of 3.435-3.460 eV in the emission spectrum and a second luminescence peak of a half band width of 12 meV or smaller in the range of 3.465-3.480 eV in the emission spectrum.

Description

  The present invention relates to a periodic table Group 13 metal nitride crystal. Specifically, the present invention relates to a periodic table group 13 metal nitride crystal obtained by crystal growth in the presence of a nitrogen-containing solvent in a supercritical and / or subcritical state. The present invention also relates to a specific periodic table group 13 metal nitride crystal obtained by growing on a base substrate having a nonpolar plane or a semipolar plane as a main surface.

  Periodic table group 13 metal nitride crystals such as gallium nitride (GaN) are used as materials for various semiconductor devices such as light-emitting elements, electronic elements, and semiconductor sensors. In order to obtain a high-quality semiconductor device using a periodic table group 13 metal nitride crystal, it is necessary that the periodic table group 13 metal nitride crystal has good crystallinity without distortion. For that purpose, it is important that the periodic table group 13 metal nitride crystal does not contain unnecessary impurities and / or defects and has high purity.

As a method for producing a periodic table group 13 metal nitride crystal, a hydride vapor phase epitaxy method (HVPE method), an ammonothermal method, and the like are known. The HVPE method is a method in which Ga chloride and a hydride of group V element (NH ₃ ) are introduced into a furnace in a hydrogen gas stream, thermally decomposed, and crystals generated by the thermal decomposition are deposited on the substrate. In the HVPE method, the raw material gas is continuously introduced into the system and discharged during the crystal growth, so that moisture adsorbed on the raw material surface and the furnace inner wall can be discharged out of the system. For this reason, the HVPE method has an advantage that a periodic table group 13 metal nitride crystal having a relatively high purity can be obtained because oxygen impurities derived from moisture are hardly taken into the grown crystal.

  The ammonothermal method is a method for producing a desired crystal material using a solvent containing nitrogen such as ammonia in a supercritical state and / or a subcritical state and a dissolution-precipitation reaction of raw materials. When applied to crystal growth, crystals are precipitated by generating a supersaturated state due to a temperature difference utilizing the temperature dependence of the raw material solubility in a nitrogen-containing solvent such as ammonia. Specifically, a crystal raw material or seed crystal is placed in a pressure-resistant container such as an autoclave and sealed, and heated with a heater or the like to form a high-temperature region and a low-temperature region in the pressure-resistant container. Crystals can be produced by dissolving and growing crystals on the other hand. The ammonothermal method is advantageous in that the raw material utilization efficiency is better than that of the HVPE method, and the manufacturing cost can be suppressed. For this reason, the ammonothermal method is expected to be used in various fields. For example, a technique using the ammonothermal method has been proposed for a method for manufacturing a light emitting element or a method for manufacturing a large-diameter nitride semiconductor. Yes.

  For example, Patent Documents 1 and 2 describe a method of growing a gallium nitride crystal by an ammonothermal method. Patent Document 1 describes that ammonothermal growth is performed using ammonium fluoride. In Patent Document 2, examination of temperature conditions and pressure conditions for growing a gallium nitride crystal is performed.

Special Table 2007-509507 JP 2008-120672 A

  However, the gallium nitride crystal grown by the ammonothermal method as described in Patent Documents 1 and 2 contains a large amount of impurities such as oxygen, and has a high purity periodic group 13 metal nitride. There was a problem that it was difficult to reliably obtain crystals. In the ammonothermal method, a technique for solving such a problem has not yet been found, and further technical examination is required.

  In order to solve such problems of the prior art, the present inventors have proceeded with studies for the purpose of providing a high-quality periodic table group 13 metal nitride crystal with high purity and few defects. .

As a result of intensive studies to solve the above problems, the present inventors have found that in the periodic table group 13 metal nitride crystals obtained by a specific method, a low-temperature photoluminescence method (hereinafter also referred to as a low-temperature PL method). It has been found that there is a feature in the peak shape of the emission spectrum observed. Further, the inventors of the present invention have found that among the group 13 metal nitride crystals of the periodic table obtained by the ammonothermal method, the emission spectrum measured by the low temperature PL method is at least 2 in the range of 3.430 eV to 3.480 eV. It has been found that a periodic table group 13 metal nitride crystal having two emission peaks has high purity and has few defects such as vacancies and dislocations, and has led to the present invention.
Specifically, the present invention has the following configuration.

[1] A Group 13 metal nitride crystal of a periodic table obtained by crystal growth in the presence of a nitrogen-containing solvent in a supercritical and / or subcritical state, and having an emission spectrum observed by a low-temperature photoluminescence method A group 13 metal nitride crystal of the periodic table having at least two emission peaks in the range of 3.430 eV to 3.480 eV.
[2] The first emission peak is in the range of 3.435 to 3.460 eV of the emission spectrum, and the second emission peak is in the range of 3.465 to 3.480 eV of the emission spectrum. Periodic table of Group 13 metal nitride crystals.
[3] The periodic table group 13 metal nitride crystal according to [1] or [2] obtained by crystal growth on a base substrate having a nonpolar plane or a semipolar plane as a main surface.
[4] The periodic table group 13 metal nitride crystal according to any one of [1] to [3], which is obtained by crystal growth on a base substrate having a nonpolar plane as a main surface.
[5] The periodic table group 13 metal nitride crystal according to any one of [2] to [4], wherein the half width of the second emission peak is 12 meV or less.
[6] The periodic table group 13 of any one of [2] to [5], wherein the emission spectrum has a plurality of the first emission peaks in a range of 3.435 to 3.460 eV of the emission spectrum. Metal nitride crystals.
[7] The periodic table group 13 metal nitride crystal according to any one of [1] to [6], wherein the periodic table group 13 metal nitride crystal is a gallium nitride crystal.

  According to the present invention, it is possible to obtain a periodic table group 13 metal nitride crystal having high purity and few defects. That is, in the present invention, the crystallinity is very good, and a high-quality periodic table group 13 metal nitride crystal can be obtained. Such a periodic table group 13 metal nitride crystal is suitably used as a material for various semiconductor devices.

FIG. 1 is a schematic view of a crystal manufacturing apparatus that can be used in the present invention. FIG. 2 is an emission spectrum of the periodic table group 13 metal nitride crystal produced in Example 1. FIG. 3 is an emission spectrum of the periodic table group 13 metal nitride crystal produced in Example 2. 4 is an emission spectrum of the periodic table group 13 metal nitride crystal produced in Example 3. FIG. FIG. 5 is an emission spectrum of the periodic table group 13 metal nitride crystal produced in Comparative Example 1. 6 is an emission spectrum of a periodic table group 13 metal nitride crystal produced in Comparative Example 2. FIG. FIG. 7 is an emission spectrum of the periodic table group 13 metal nitride crystal produced in Comparative Example 3. FIG. 8 is an emission spectrum of the periodic table group 13 metal nitride crystal produced in Comparative Example 4. FIG. 9 is an emission spectrum of the periodic table group 13 metal nitride crystal produced in Comparative Example 5. FIG. 10 is an emission spectrum of the periodic table group 13 metal nitride crystal produced in Comparative Example 6.

(Definition)
Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. Moreover, in this specification, wtppm means weight ppm.

First, the relationship between the axes and planes of the hexagonal crystal structure will be described. In this specification, the “principal surface” of the seed crystal or the periodic table group 13 metal nitride crystal is the widest surface in the seed crystal or periodic table group 13 metal nitride crystal. Refers to the surface to be done. In this specification, the “C plane” is a plane equivalent to the {0001} plane in a hexagonal crystal structure (wurtzite type crystal structure), and is a polar plane. For example, it refers to the (0001) plane and the (000-1) plane opposite to it, and gallium nitride corresponds to the Ga plane or N plane, respectively. Further, in this specification, the “M plane” refers to {1-100} plane, {01-10} plane, {-1010} plane, {−1100} plane, {0-110} plane, {10-10 } Non-polar planes comprehensively represented as planes, specifically (1-100) plane, (01-10) plane, (-1010) plane, (-1100) plane, (0-110). ) Plane and (10-10) plane. Further, in this specification, the “A plane” means {2-1-10} plane, {-12-10} plane, {-1-120} plane, {-2110} plane, {1-210} plane. , {11-20} plane which is comprehensively represented as a plane. Specifically, (11-20) plane, (2-1-10) plane, (-12-10) plane, (-1-120) plane, (-2110) plane, (1-210) plane, Means. In this specification, “c-axis”, “m-axis”, and “a-axis” mean axes perpendicular to the C-plane, M-plane, and A-plane, respectively.
In the present specification, the “nonpolar plane” means a plane in which both of the periodic table group 13 metal element and the nitrogen element are present on the surface, and the abundance ratio thereof is 1: 1. Specifically, the M surface and the A surface can be mentioned.
In this specification, the “semipolar plane” means, for example, when the group 13 metal nitride of the periodic table is a hexagonal crystal and its main surface is represented by (hklm), m = 0 except for the {0001} plane It's not a side. That is, it refers to a plane that is inclined with respect to the (0001) plane and is not a nonpolar plane. It means a surface where only one of the group 13 metal elements and nitrogen element or the C surface is present on the surface, and the abundance ratio is not 1: 1. h, k, l and m are each independently preferably an integer of -5 to 5, more preferably an integer of -2 to 2, and preferably a low index surface. . Examples of semipolar planes that can be preferably used as the main surface of the Group 13 metal nitride crystal of the periodic table include {10-11} plane, {10-1-1} plane, {10-12} plane, {10-1- 2} plane, {20-21} plane, {202-1} plane, {20-2-1} plane, {10-12} plane, {10-1-2} plane, {11-21} plane, {11-2-1} plane, {11-22} plane, {11-2-2} plane, {11-24} plane, {11-2-4} plane, and the like, particularly {10 The -11} plane and the {202-1} plane can be cited as preferable planes.
In addition, the plane orientation of each crystal plane such as the C plane, M plane, A plane, etc. shall be generically referred to when tilted at an arbitrary angle from the above crystal plane, and preferably ± 10 ° from the arbitrary crystal plane. More preferably, it is a case of tilting in a range of ± 7 °.

(Group 13 metal nitride crystal of the periodic table)
Examples of the periodic table group 13 metal nitride crystal (hereinafter sometimes referred to as group 13 nitride crystal) include a periodic table group 13 nitride crystal typified by gallium nitride (GaN). Furthermore, examples of the periodic table group 13 metal nitride include GaN, AlN, InN, and mixed crystals thereof. Examples of mixed crystals include AlGaN, InGaN, AlInN, and AlInGaN. Among these, a mixed crystal containing GaN and Ga is preferable, and GaN is more preferable.

  The periodic table group 13 metal nitride crystal of the first aspect of the present invention is a periodic table group 13 metal nitride obtained by crystal growth in the presence of a nitrogen-containing solvent in a supercritical and / or subcritical state. It is a crystal and has at least two emission peaks in the range of 3.430 eV to 3.480 eV of an emission spectrum observed by a low temperature photoluminescence method (low temperature PL method). Thus, by having at least two emission peaks in the range of 3.430 eV to 3.480 eV of the emission spectrum observed by the low temperature PL method, the periodic table group 13 metal nitride crystal has a purity. It is possible to increase and reduce defects such as vacancies and dislocations.

In addition, the periodic table group 13 metal nitride crystal according to the second aspect, which is another aspect of the present invention, is formed on a base substrate made of a nitride crystal whose main surface is a nonpolar plane or a semipolar plane. A group 13 metal nitride crystal obtained by epitaxially growing a group nitride crystal, and having an emission spectrum in the range of 3.430 eV to 3.480 eV observed by a low temperature photoluminescence method (low temperature PL method). Have at least two emission peaks. In the second aspect, the periodic table group 13 metal nitride crystal is obtained by epitaxially growing a group 13 nitride crystal on a base substrate made of a nitride crystal having a nonpolar plane as a main surface. More preferably, it is a Group 13 metal nitride crystal.
Thus, by having at least two emission peaks in the range of 3.430 eV to 3.480 eV of the emission spectrum observed by the low temperature PL method, the periodic table group 13 metal nitride crystal has a purity. It is possible to obtain a crystal that is high and has few defects such as vacancies and dislocations. Any of the aspects of the present invention can be obtained by epitaxially growing a group 13 nitride crystal on a base substrate.

  As the base substrate, a crystal layer different from the group 13 nitride crystal to be epitaxially grown can be used, but a crystal layer made of the same kind of crystal is preferably used as the base substrate. For example, when the Group 13 nitride crystal to be epitaxially grown is a GaN crystal, the base substrate is also preferably made of GaN.

The periodic table group 13 metal nitride crystal according to the first aspect of the present invention is a so-called alloy in which a periodic table group 13 metal nitride crystal is grown in the presence of a nitrogen-containing solvent in a supercritical and / or subcritical state. It was obtained by the monothermal method. For this reason, this group 13 metal nitride crystal of the periodic table can be grown at a high growth rate by efficiently using the raw material. That is, according to the present invention, it is possible to produce high quality crystals efficiently and at low cost.
In addition, the periodic table group 13 metal nitride crystal of the second aspect of the present invention is a gas phase method such as HVPE method or MOCVD method, a liquid phase method such as Na flux method, liquid phase epitaxy method (LPE method), etc. In particular, it can be obtained by a so-called ammonothermal method in which a Group 13 metal nitride crystal of the periodic table is grown in the presence of a nitrogen-containing solvent in a supercritical and / or subcritical state. Is preferred.

The periodic table group 13 metal nitride crystal of any aspect of the present invention has at least two emission peaks in the range of 3.430 eV to 3.480 eV of the emission spectrum observed by the low temperature photoluminescence method. There are features. Here, “having at least two emission peaks” means that there are two or more peak tops observed separately in the emission spectrum.
In the present invention, the “emission spectrum observed by the low temperature photoluminescence method” means that a He—Cd laser beam having an absolute temperature of 30 K or less and a wavelength of 325 nm is irradiated with a beam intensity of 38 W / cm ² and a periodic table group 13 metal nitride. The photoluminescence spectrum observed when a crystal sample is irradiated. This emission spectrum can be observed using a spectrometer (trade name C5094) manufactured by Hamamatsu Photonics and a detector (trade name BT-CCD PMA-50) manufactured by Hamamatsu Photonics. In the following description, the “emission spectrum observed by the low-temperature photoluminescence method” may be simply referred to as “emission spectrum”.

  2 and 5 show typical emission spectra of gallium nitride crystals manufactured by the ammonothermal method. The emission spectrum of FIG. 2 is an emission spectrum of a gallium nitride crystal manufactured in Example 1 described later, and the emission spectrum of FIG. 5 is an emission spectrum of a gallium nitride crystal manufactured in Comparative Example 1 described later.

The emission spectrum of FIG. 2 has a plurality of separated emission peaks. Among these peaks, the peak I _{2, A} (second emission peak) having a peak top in the vicinity of 3.472 eV is an emission peak due to donor-bound exciton DBE (Donor Bound Exciton) of the gallium nitride crystal returning to the valence band. . In addition, two peaks (first emission peaks) existing in the range of 3.435 to 3.460 eV are emission peaks due to transition of donor-bound excitons to the electron orbit of impurities. The light emission at the first emission peak is light emission called TES (Two Electron Satellites) light emission.
In the reference PHYSICAL REVIEW B 66, 233311 (2002), the correspondence between each peak and the kind of impurities is examined for Two Electron Satellites and is shown in TABLE 1. According to this, since the first peaks in FIG. 2 exist at 3.456 eV and 3.446 eV, both indicate that O is contained in the crystal as an impurity.

In the emission spectrum of FIG. 2, the second emission peak has a sharp shape as described above, and the first emission peak and the second emission peak can be clearly distinguished. On the other hand, the emission peak of the emission spectrum of FIG. 5 is a broad single peak in which a plurality of emission peaks overlap, and the first emission peak and the second emission peak cannot be distinguished.
The inventors of the present application have examined in detail the correlation between the peak shape of such an emission spectrum and the impurity concentration of the Group 13 metal nitride crystal of the periodic table. The periodic table group 13 metal nitride crystals (Examples 1 to 3) whose spectrum has at least two emission peaks have a uniform high purity, whereas the emission peak of the emission spectrum is a broad single peak. It has been found that any gallium nitride crystal (Comparative Examples 1 to 6) has low purity.

Conventionally, in order to make it easy to grow at a high speed as much as possible with an emphasis on industrial productivity, an iodine compound that tends to increase the solubility difference between the raw material dissolution region / crystal growth region using a high pressure range (200 MPa) that can be dissolved is used. The main mineralizer has been selected. When a crystal grown under such conditions is measured at low temperature PL, for example, as shown in Comparative Examples 2 and 3, a single broad (wide half-value width) peak is observed, and as a commonly used semiconductor, there are too many carriers. It was in the state of.
On the other hand, in the present invention, at least two luminescences in the range of 3.430 eV to 3.480 eV of the emission spectrum observed by the low temperature photoluminescence method are obtained by setting the growth conditions to low pressure and using only a fluorine compound as the mineralizer. A group 13 metal nitride crystal having a peak in the periodic table was successfully obtained. That is, the periodic table group 13 metal nitride crystal obtained in the present invention has high purity and has few defects such as vacancies and dislocations.

  The plurality of peaks in the emission spectrum vary depending on the type of impurities incorporated in the Group 13 metal nitride crystal of the periodic table, but the first emission peak existing in the range of 3.435 to 3.460 eV and 3.465 to 3 It is preferable to include a second emission peak existing in the range of .480 eV. The periodic table group 13 metal nitride crystal having the first emission peak and the second emission peak in such a range has an extremely high purity and few defects such as vacancies and dislocations.

  Each of the first emission peak and the second emission peak may be a single emission peak, or may have a plurality of emission peaks. The emission spectrum may have a plurality of first emission peaks in the range of 3.435 to 3.460 eV. Thereby, a periodic table group 13 metal nitride crystal having high purity and few defects can be obtained. In addition, it is preferable that the 2nd light emission peak which exists in the range of 3.465-3.480eV of an emission spectrum is a single light emission peak.

The half width of the second emission peak of the emission spectrum is preferably 12 meV or less, more preferably meV or less, and further preferably 10 meV or less.
Here, the “half-value width of the second emission peak” is a half height between the baseline and the peak of the second emission peak when the background level is the baseline of the second emission peak. This refers to the peak width at this position.
That the half width of the second emission peak is 12 meV or less means that the shape of the second emission peak is sharp, and the half width of the second emission peak is in such a range. Group metal nitride crystals have a very high purity.

The oxygen concentration of the group 13 metal nitride crystal of the periodic table is preferably 1 × 10 ²⁰ atoms / cm ³ or less, more preferably 5 × 10 ¹⁹ atoms / cm ³ or less, and 1 × 10 ¹⁹ atoms / cm ^3. More preferably, it is not more than cm ³ . A periodic table group 13 metal nitride crystal having an oxygen concentration in the above range has high purity and high crystal stability.

It is preferable that the periodic table group 13 metal nitride crystal of any aspect of the present invention is grown on a base substrate having a nonpolar plane or a semipolar plane as a main surface. Among them, the periodic table group 13 metal nitride crystal is more preferably a crystal grown on a base substrate having a nonpolar plane as a main surface. That is, it is preferable that the periodic table group 13 metal nitride crystal of the present invention is grown on a base substrate having an M plane as a main surface. The main surface in this case may be an M surface having an off angle. The range of the off angle is preferably within ± 15 °, more preferably within ± 10 °, and further preferably within ± 5 °.
In general, a Group 13 nitride crystal grown on a base substrate having a polar surface as a main surface is considered to be less likely to incorporate impurities, and it has been considered that it is easy to obtain a relatively high-purity crystal. . On the other hand, Group 13 nitride crystals grown on a base substrate having a nonpolar plane or a semipolar plane as a main surface are easy to incorporate impurities such as oxygen, and have a high purity and low defect. It was extremely difficult to obtain. However, by studying the present inventors, the crystal growth conditions are appropriately adjusted as described below, and for the first time, an extremely high purity and crystal stability can be achieved on a base substrate having a nonpolar or semipolar surface as a main surface. It became possible to obtain a high group 13 nitride crystal.

(Manufacturing method of periodic table group 13 metal nitride crystal)
The periodic table group 13 metal nitride crystal of any aspect of the present invention is preferably obtained by an ammonothermal method. The ammonothermal method is a method for producing a desired material using a solvent in a supercritical state and / or a subcritical state and utilizing a dissolution-precipitation reaction of raw materials. Specifically, the periodic table group 13 metal nitride crystal of the present invention is filled with a periodic table group 13 metal nitride crystal raw material in a raw material dissolution region of the reaction vessel, and is supercritical and / or in the reaction vessel. It is obtained by a growth process in which a periodic table group 13 metal nitride crystal is grown in the presence of a nitrogen-containing solvent in a subcritical state.

In order to produce a periodic table group 13 metal nitride crystal such as GaN with high quality and good yield, it is preferable that the concentration of impurities such as oxygen in the system is low, but the ammonothermal method is a closed system, Impurities that have been mixed in remain in the system without being discharged even during operation. In this respect, it has a disadvantageous feature for high purity as compared with the HVPE method and the like that keeps high purity gas flowing in and out during growth. Moisture adsorbed on the surface of the raw material and the inner wall of the furnace can be desorbed and discharged by raising the temperature while flowing gas in the HVPE method or the like, but it remains in the system in the ammonothermal method.
In response to such problems, the inventors of the present invention succeeded in obtaining crystals with higher purity by using only a fluorine compound as a mineralizer and performing crystal growth under crystal growth conditions with a low growth pressure. did.
Hereinafter, a periodic table group 13 metal nitride crystal raw material that can be used in the present invention and a periodic table group 13 metal nitride crystal growth method using the periodic table group 13 metal nitride crystal raw material will be described.

(Crystal raw material)
In this invention, the periodic table group 13 metal nitride crystal raw material containing the atom which comprises the periodic table group 13 metal nitride crystal which is going to grow by the ammonothermal method is used. For example, when an attempt is made to grow a periodic table group 13 metal nitride crystal of a periodic table group 13 metal, a raw material containing a periodic table group 13 metal is used. Preferably, a polycrystalline raw material or a single crystal raw material of a group 13 metal nitride crystal of the periodic table may be used, and this may be used as a raw material in combination with a metal (metal) of a group 13 atom. The polycrystalline raw material does not need to be a complete nitride, and may contain a metal component in which the group 13 atom is in a metal state (zero valence) depending on conditions. For example, when the group 13 metal nitride crystal to be grown is gallium nitride, a mixture of gallium nitride and metal gallium can be used. Examples of the type of periodic table group 13 metal nitride crystal obtained in the present invention include GaN, InN, AlN, InGaN, AlGaN, and AllnGaN. Preferred is GaN, AlN, AlGaN, AllnGaN, and more preferred is GaN. Therefore, as the group 13 metal nitride crystal raw material of the periodic table, the above-mentioned polycrystalline raw material of crystals and / or these metals can be used in combination.

  The method for producing the crystal raw material is not particularly limited. For example, a nitride polycrystal produced by reacting a metal or an oxide or hydroxide thereof with ammonia in a reaction vessel in which ammonia gas is circulated can be used. In addition, as a metal compound raw material having higher reactivity, a compound having a covalent MN bond such as a halide, an amide compound, an imide compound, or galazan can be used. Furthermore, a nitride polycrystal produced by reacting a metal such as Ga with nitrogen at a high temperature and a high pressure can also be used.

  The amount of water and oxygen contained in the crystal raw material used as the raw material is preferably small. The oxygen content in the polycrystalline raw material is usually 250 wtppm or less, preferably 40 wtppm or less, and particularly preferably 20 wtppm or less. The ease of mixing oxygen into the polycrystalline raw material is related to the reactivity with water or the absorption capacity. The worse the crystallinity of the polycrystalline raw material, the more active groups such as NH groups exist on the surface, which may react with water and partially generate oxides or hydroxides. For this reason, it is usually preferable to use a polycrystalline material having as high crystallinity as possible. The crystallinity can be estimated by the half width of powder X-ray diffraction. The half width of the (100) diffraction line (2θ = about 32.5 ° for hexagonal gallium nitride) is usually 0.25 ° or less, preferably It is 0.20 ° or less, more preferably 0.17 ° or less. In this way, by controlling the oxygen content contained in the crystal raw material, the concentration ratio of hydrogen and oxygen introduced into the crystal can be set to a desired range, and distortion of the crystal is prevented from occurring. be able to.

(Gettering agent)
Further, a gettering agent may be added in the growth system. The gettering agent has a function of adsorbing impurities such as oxygen in the reaction vessel and suppressing the impurities from being taken into the grown crystal. Thereby, a periodic table group 13 metal nitride crystal with higher purity can be obtained. Examples of the element that adsorbs oxygen include Al, Ti, Zn, Mg, Si, and B. From the viewpoint of obtaining a highly purified periodic table group 13 metal nitride crystal, the gettering agent is a nitride crystal. It is preferable that it is not dissolved in the process of crystal growth and is difficult to be taken into the grown crystal or that does not deteriorate the crystal quality even if taken into the grown crystal. Considering the above, the gettering agent is preferably Al or an Al alloy.

The gettering agent may be contained in the crystal raw material, but may be placed in another place in the reaction vessel. The gettering agent may be added in the form of aluminum fluoride (AlF ₃ ), aluminum nitride (AlN), or a complex (Al (NH ₄ ) ₃ F ₆ ) or (AlF ₄ NH ₄ ). In either case, after heating and pressurization, it becomes a complex (AlF ₄ NH ₄ ) and dissolves in ammonia.

  The amount of the element used for the gettering agent is preferably 0.05 to 20 mol%, more preferably 0.1 to 10 mol%, based on the solvent. If the amount of the gettering agent added is small, the effect of suppressing the uptake of impurities in the grown crystal may not be sufficiently obtained. If the amount of the gettering agent added is too large, the gettering agent may affect the dissolution of the crystal raw material, and the crystal growth rate may be slow.

(Base substrate)
The base substrate is not particularly limited as long as it is a known substrate used for crystal growth of Group 13 metal nitride crystals of the periodic table. Gallium nitride (GaN), indium gallium nitride (InGaN), aluminum gallium nitride ( The same type of periodic group 13 metal nitride crystals as AlGaN) can be used. In addition, metal oxides such as sapphire (Al ₂ O ₃ ) and zinc oxide (ZnO), silicon-containing materials such as silicon carbide (SiC) and silicon (Si), arsenic gallium (GaAs), and the like are used. be able to. However, it may be a base substrate having a lattice constant, a crystal lattice size parameter that matches or matches the desired group 13 metal nitride crystal of the target periodic table, or heteroepitaxy (ie, the crystallographic position of some atoms). It is preferable to use a base substrate composed of a single crystal material piece or a polycrystalline material piece arranged so as to guarantee (coincidence).

  As the base substrate used for crystal growth of the periodic table group 13 metal nitride crystal of the present invention, single crystals produced by an ammonothermal method and crystals obtained by cutting them can be preferably used. A crystal produced by an ammonothermal method is preferably used as a base substrate because it has little distortion and can grow a good nitride crystal. In addition, by using a crystal produced by an ammonothermal method as a base substrate, the growth crystal can contain hydrogen and oxygen so as to have a desired concentration ratio, and a growth crystal having excellent crystallinity is grown. be able to.

  The surface orientation of the main surface of the base substrate is not particularly limited, but it is preferable to select a base substrate having the M surface as the main surface.

  It is preferable that the surface state of the base substrate is controlled to be smooth. That is, pretreatment is preferably performed on the base substrate. For example, the pretreatment includes subjecting the base substrate to a melt back process, polishing the growth crystal growth surface of the base substrate, and cleaning the base substrate. Thereby, the surface state of the base substrate can be made smooth, and the concentration ratio of hydrogen and oxygen introduced into the crystal can be set to a desired range. Thereby, the crystallinity of the group 13 nitride crystal grown on the base substrate can be improved.

  In the pretreatment, the surface of the base substrate on which crystals can grow can be polished by, for example, chemical mechanical polishing (CMP). As for the surface roughness of the base substrate, for example, the root mean square roughness (Rms) measured by an atomic force microscope is preferably 1.0 nm or less, more preferably 0.5 nm, and particularly preferably 0.3 nm. .

(Mineralizer)
In the present invention, it is preferable to use a mineralizer when growing a periodic table group 13 metal nitride crystal by the ammonothermal method. The mineralizer is used to improve the solubility of the crystal raw material in a solvent containing nitrogen such as ammonia.

In order to obtain the periodic table group 13 metal nitride crystal of the present invention, it is preferable to select a compound containing a fluorine element as a mineralizer, and it is more preferable to select ammonium fluoride.
Conventionally, in order to perform high-speed crystal growth, a mineralizer containing iodine element that tends to increase the solubility difference between the raw material dissolution region and the crystal growth region has been often used. However, as shown in FIGS. 6 and 7, the emission spectrum of the periodic table group 13 metal nitride crystal (Comparative Examples 2 and 3) grown using a mineralizer containing iodine element was measured by a low temperature photoluminescence method. Is observed, only a broad single peak (peak with a wide half-value width) is observed, and the carrier (oxygen) enters an excessive state.
On the other hand, the compound containing elemental fluorine has a function as a mineralizer and elemental fluorine has a strong deoxygenation property, adsorbs oxygen in the reaction vessel, and the oxygen is taken into the grown crystal. It also demonstrates the function of suppressing the Therefore, by using a compound containing elemental fluorine as a mineralizer, the first emission peak and the second emission peak are clearly separated in the observed emission spectrum, and the highly purified periodic table group 13 metal nitride A physical crystal can be obtained.

  The molar concentration of the fluorine element contained in the mineralizer with respect to the solvent is preferably 0.5 mol% or more, more preferably 1.0 mol% or more, and further preferably 2.0 mol% or more. Further, the molar concentration of the fluorine element contained in the mineralizer with respect to the solvent is preferably 75 mol% or less, more preferably 50 mol% or less, and further preferably 20 mol% or less. If the concentration is too low, the solubility tends to decrease and the growth rate tends to decrease. On the other hand, if the concentration is too low, the effect of preventing the incorporation of oxygen in the periodic table group 13 metal nitride crystal cannot be sufficiently obtained, and depending on other crystal growth conditions, the obtained periodic table group 13 metal nitride crystal can be obtained. There is a case where the purity of is low. On the other hand, when the concentration is too high, the solubility tends to be too high and the generation of spontaneous nuclei increases, or the degree of supersaturation becomes too high and control tends to be difficult.

  The fluorine-containing compound may be used alone as a mineralizer or in combination with other mineralizers, but is preferably used alone as a mineralizer. Thereby, a periodic table group 13 metal nitride crystal with higher purity can be obtained. Further, the inner wall surface of the reaction vessel is generally coated with platinum in order to obtain corrosion resistance against a corrosive mineralizer or the like, but a fluorine-containing compound is used alone as a mineralizer. Accordingly, it is possible to use a corrosion-resistant metal such as silver, which is inferior to platinum but relatively inexpensive, for the coating material. As a result, the cost for the apparatus can be greatly reduced.

As the mineralizer, other mineralizers may be used in a small amount in addition to the compound containing fluorine element. The mineralizer used in combination may be a basic mineralizer or an acidic mineralizer, but is preferably an acidic mineralizer. Basic mineralizers include alkali metals, alkaline earth metals, compounds containing rare earth metals and nitrogen atoms, alkaline earth metal amides, rare earth amides, alkali nitride metals, alkaline earth metal nitrides, azide compounds, and other hydrazines. Class of salts. A preferred example is an alkali metal amide, and specific examples include sodium amide (NaNH ₂ ), potassium amide (KNH ₂ ), and lithium amide (LiNH ₂ ). Moreover, as an acidic mineralizer, the compound containing a halogen element is used preferably. Examples of mineralizers containing halogen elements include ammonium halide, hydrogen halide, ammonium hexahalosilicate, and hydrocarbyl ammonium fluoride, tetramethylammonium halide, tetraethylammonium halide, benzyltrimethylammonium halide, halogenated Illustrative examples include alkylammonium salts such as dipropylammonium and isopropylammonium halides, halogenated alkyl metals such as alkyl sodium fluoride, halogenated alkaline earth metals, and metal halides. Of these, an additive (mineralizing agent) containing a halogen element is preferably an alkali halide, an alkaline earth metal halide, a metal halide, an ammonium halide, or a hydrogen halide, more preferably a halogenated. Alkalis, ammonium halides, and halides of group 13 metals of the periodic table are listed, and ammonium halides, gallium halides, and hydrogen halides are particularly preferable. Examples of the ammonium halide include ammonium chloride (NH ₄ Cl), ammonium iodide (NH ₄ I), and ammonium bromide (NH ₄ Br). One mineralizer may be used alone, or a plurality of mineralizers may be appropriately mixed and used.

In the production method of the present invention, it is preferable to use the mineralizer after purification and drying as necessary, in order to prevent impurities from being mixed into the group 13 metal nitride crystal to be grown. The purity of the mineralizer is usually 95% or higher, preferably 99% or higher, more preferably 99.99% or higher.
In order to reduce the supply of oxygen from other than the nitride raw material, it is desirable that the amount of water and oxygen contained in the mineralizer is as small as possible, and the content thereof is preferably 1000 wtppm or less, and preferably 10 wtppm or less. More preferred is 1 wtppm or less.

In order to remove water and oxygen from the atmosphere in the reaction vessel, the inside of the reaction vessel is sealed and heated to 200 ° C. or higher, and the moisture adhering to the surface of the member is vaporized as 1 × 10 ⁻⁷ Pa using a pump or the like. A method of degassing is conceivable. Furthermore, a method of introducing a mineralizer with a high purity gas is also conceivable. There is also a method in which members and raw materials are stored in advance in a dry atmosphere with a dew point of 0 ° C. or less, and the reaction vessels and the members and raw materials to be placed in the reaction vessels are assembled therein.

(solvent)
As the solvent used in the ammonothermal method, a solvent containing nitrogen can be used. As the solvent containing nitrogen, it is preferable to use a solvent that does not impair the stability of the nitride single crystal to be grown. Examples of the solvent include ammonia, hydrazine, urea, amines (for example, primary amines such as methylamine, secondary amines such as dimethylamine, tertiary amines such as trimethylamine, and ethylenediamine. Diamine) and melamine. These solvents may be used alone or in combination.

  In order to reduce supply of unnecessary oxygen to the grown crystal, it is desirable that the amount of water and oxygen contained in the solvent is as small as possible, and the content thereof is preferably 1000 wtppm or less, and preferably 10 wtppm or less. More preferably, it is 0.1 wtppm or less. When ammonia is used as a solvent, the purity is usually 99.9% or more, preferably 99.99% or more, more preferably 99.999% or more, and particularly preferably 99.9999% or more. .

(Reaction vessel and installation member)
A specific example of a crystal manufacturing apparatus that can be used in a method for manufacturing a periodic table group 13 metal nitride crystal is shown in FIG. The crystal production apparatus used in the present invention includes a reaction vessel.
The crystal manufacturing apparatus has an autoclave (pressure-resistant container) 1, and a baffle plate 5 is installed in the autoclave 1. The raw material 4 is installed on the upper part of the baffle plate 5, and the base substrate (seed crystal) 6 is installed on the lower part of the baffle plate 5. That is, in the crystal manufacturing apparatus of FIG. 1, the lower part of the baffle plate 5 is the crystal growth region 2, and the upper part of the baffle plate 5 is the raw material melting region 3.

  The oxygen concentration in the reaction vessel is preferably low. The oxygen concentration in the reaction vessel is preferably 10 wtppm or less, more preferably 5 wtppm or less, and further preferably 1 wtppm or less. By sufficiently reducing the oxygen concentration in the reaction vessel so as to be equal to or lower than the above upper limit value, impurities taken into the crystal are reduced, and a nitride crystal having better crystallinity can be obtained.

The reaction vessel in the present invention means a vessel for producing a nitride crystal in a state in which a nitrogen-containing solvent in a supercritical state and / or a subcritical state can be in direct contact with its inner wall surface. Preferred examples include the structure itself and capsules installed in a pressure-resistant container.
The pressure-resistant container as the reaction container used in the present invention is selected from those capable of withstanding the high-temperature and high-pressure conditions when the nitride crystal is grown by the ammonothermal method. The production method of the present invention is not particularly limited as long as it has pressure resistance and corrosion resistance, but the reaction vessel is preferably a platinum group metal or a metal containing Ni, and contains a Ni-based alloy. Is more preferable. In particular, when a reaction vessel made of such a material is used, it is preferable because it is easy to grow a crystal at a low pressure using a fluorine-containing mineralizer.

As a metal containing Ni, pure Ni (Ni200, Ni201, etc.) having a carbon content of 0.2% by mass or less; Fe, Co as an impure element with a Ni content of 40% by mass or more and 2.5% by mass % Ni-based alloys (for example, Inconel 625 and the like (Inconel is a registered trademark of Huntington Alloys Canada Limited, the same shall apply hereinafter); Ni—Cu alloys having a Ni content of 40% by mass or more (such as Monel 400). The base alloy may contain Cr, Al, Ti, Nb, and V that form nitrides in a supercritical NH ₃ environment, and may further contain W and Mo as solid solution strengthening elements.
Pure Ni includes “Ni200” having a carbon content of 0.2% by mass or less, “Ni201” having an extremely low carbon content, and the like. The Ni used in the present invention is preferably a very low carbon grade. In the case of Ni with a low carbon content, the phenomenon of aging embrittlement is unlikely to occur, and even at a temperature of about 500 to 600 ° C., carbon does not precipitate at the grain boundaries as graphite, and tends to be brittle as a material. preferable.
Examples of the Ni-based alloy include Ni—Cr, Ni—Cr—Mo, and Ni—Cr—W alloys in which the Fe content is preferably limited to 7% by mass or less, and more preferably 5% by mass or less. Further, the Ni-based alloy is a Ni-based alloy having an Fe content of 5.0% by mass or less and a Co content of 2.0% by mass or less from the viewpoint of suppressing selective elution of Fe and Co in a fluorine environment. preferable.
From the above viewpoint, the Ni-containing metal is preferably a Ni-based alloy with a Ni content exceeding 40% by mass, more preferably a Ni-based alloy with a Ni content exceeding 45% by mass, It is particularly preferable that the Ni-base alloy exceed 50 mass%.

The mode in which the reaction vessel is constituted by these alloys is not particularly limited. The reaction vessel may be formed by directly lining or coating the inner surface of the pressure-resistant vessel, or a capsule made of a material having excellent corrosion resistance may be disposed in the pressure-resistant vessel. Since pure Ni is soft and rich in workability, a reaction vessel can be easily formed by lining the inner surface of the vessel to a thickness of about 0.5 mm. It is also possible to change the lining once every few years.
The shape of the reaction vessel can be any shape including a cylindrical shape. Further, the reaction vessel may be used standing upright, horizontally or diagonally.

Moreover, in order to further improve the corrosion resistance of the reaction vessel and the installation member, the excellent corrosion resistance of the platinum group or platinum group alloy can be used. The reaction vessel and the installation member can be made of a platinum group or a platinum group alloy, and the inner wall of the reaction vessel can be made of a platinum group or a platinum group alloy.
Furthermore, the reaction vessel is preferably a pressure vessel. In particular, when the inner wall of the reaction vessel is a platinum group or a platinum group alloy, or when the reaction vessel and the surface of the installation member are coated or lined with a platinum group or a platinum group alloy, other materials forming the reaction vessel can be pressure resistant. It is preferable to ensure the property.
Ti, W, Mo, Ru, Nb and alloys thereof can be used as materials having pressure resistance and corrosion resistance other than platinum group metals and metals including Ni. Preferably, Mo, W, and Ti can be used.

The constituent material and the coating material forming the reaction vessel and the installation member may include a platinum group or a platinum group alloy.
Examples of the platinum group include Pt, Au, Ir, Ru, Rh, Pd, and Ag. The platinum group alloy refers to an alloy mainly composed of these noble metals. Among platinum group alloys, an alloy containing Pt or Pt and Ir having excellent corrosion resistance can be used.

  As the material for lining, it is preferable to use at least one kind of metal or element of Pt, Ir, Ag, Pd, Rh, Cu, Au and C, or an alloy or compound containing at least one kind of metal. . Among them, it is preferable to use an alloy or a compound containing at least one kind of metal or element among Pt, Ag, Cu and C, or at least one kind of metal for the reason that lining is easy. For example, Pt simple substance, Pt-Ir alloy, Ag simple substance, Cu simple substance, graphite, etc. are mentioned.

  In the present invention, as described above, by using a fluorine-containing compound alone as a mineralizer as a mineralizer, Ag or an alloy containing Ag can be suitably used as a coating material or a lining material. it can. Thereby, the cost concerning a reaction container can be reduced significantly.

(Manufacturing process)
An example of the manufacturing method of the periodic table group 13 metal nitride crystal of this invention is demonstrated. When carrying out the method for producing a periodic table group 13 metal nitride crystal of the present invention, first, a seed crystal, a nitrogen-containing solvent, a raw material, and a mineralizer are put in a reaction vessel and sealed. . Here, as the base substrate, it is preferable to use a base substrate having an M surface as a main surface.

  In the production process of the present invention, it is preferable to provide a step of removing oxygen, oxides or water vapor present in the reaction vessel before introducing the material into the reaction vessel. In order to remove oxygen, oxides or water vapor present in the reaction vessel, the reaction vessel is filled with a nitride crystal raw material, and then the reaction vessel is evacuated, or an inert gas is contained in the reaction vessel. A method that satisfies the above can be adopted. In addition, oxygen, oxides, or water vapor can be removed by drying the reaction vessel and various members included in the reaction vessel. As a drying method, there are a method of heating the reaction vessel using an external heater or the like, a method of combining heating and vacuuming, and the like. Thereby, the oxygen crystal | crystallization introduce | transduced in a crystal | crystallization can be reduced and the nitride crystal | crystallization excellent in crystallinity can be obtained.

  Further, in the manufacturing process, a surface adsorbing substance isolating process may be further provided. The surface adsorbing substance isolating step refers to a step of immobilizing oxygen, oxide or water vapor present in the reaction vessel. Further, the surface adsorbing substance isolation step includes a step of coating or lining the surface of a reaction vessel or a member containing oxygen, oxide, or water vapor among various members installed in the reaction vessel. By coating or lining the surface of the member, it is possible to prevent the surface adsorbing material from being exposed and taken into the periodic table group 13 nitride crystal.

At the time of introducing the material, an inert gas such as nitrogen gas may be circulated. Usually, the seed crystal is placed in the reaction vessel at the same time or after filling the raw material and the mineralizer. After installation of the seed crystal, heat deaeration may be performed as necessary. The degree of vacuum at the time of deaeration is preferably 1 × 10 ⁻² Pa or less, more preferably 5 × 10 ⁻³ Pa or less, and particularly preferably 1 × 10 ⁻³ Pa or less.

  Thereafter, the whole is heated to bring the inside of the reaction vessel into a supercritical state or a subcritical state. In the supercritical state, the viscosity of a substance is generally low and it diffuses more easily than a liquid, but has a solvating power similar to that of a liquid. The subcritical state means a liquid state having a density substantially equal to the critical density near the critical temperature. For example, in the raw material filling part, the raw material is melted as a supercritical state, and in the crystal growth part, the temperature is changed so as to be in the subcritical state, and crystal growth utilizing the difference in solubility between the supercritical state and the subcritical state raw material is also performed. Is possible.

  In the supercritical state, the reaction mixture is generally maintained at a temperature above the critical point of the solvent. When an ammonia solvent is used, the critical point is a critical temperature of 132 ° C. and a critical pressure of 11.35 MPa. However, if the filling rate with respect to the volume of the reaction vessel is high, the pressure far exceeds the critical pressure even at a temperature below the critical temperature. In the present invention, the “supercritical state” includes such a state exceeding the critical pressure. Since the reaction mixture is enclosed in a constant volume reaction vessel, the increase in temperature increases the pressure of the fluid. In general, if T> Tc (critical temperature of one solvent) and P> Pc (critical pressure of one solvent), the fluid is in a supercritical state.

  Under supercritical conditions, a sufficient growth rate of the Group 13 metal nitride crystal of the periodic table can be obtained. The reaction time depends in particular on the reactivity of the mineralizer and the thermodynamic parameters, ie temperature and pressure values. During synthesis or growth of Group 13 metal nitride crystals of the periodic table, the pressure in the reaction vessel is preferably 25 MPa or more, more preferably 30 MPa or more, and more preferably 50 MPa or more from the viewpoint of crystallinity and productivity. It is more preferable to set it to 80 MPa or less. The pressure in the reaction vessel is preferably 125 MPa or less, more preferably 120 MPa or less, and more preferably 100 MPa or less, from the viewpoint of safety while suppressing the incorporation of unnecessary impurities in the grown crystal. preferable.

  In particular, by setting the pressure in the reaction vessel to 125 MPa or less, it is possible to effectively suppress the incorporation of unnecessary impurities in the grown crystal without sacrificing the growth rate of the grown crystal. That is, by setting the pressure in the reaction vessel to 125 MPa or less, it is possible to promote the circulation around the seed crystal and to suppress the incorporation of unnecessary impurities in the grown crystal. On the other hand, it is generally said that when the pressure in the reaction vessel is low, the crystal growth rate tends to be low. However, in reality, when the pressure in the reaction vessel is reduced to 125 MPa or less, the viscosity of the solvent decreases, so the convection rate of the solvent and the circulation rate of the solvent at the crystal growth interface increase, the feed rate of the raw material and the reaction by-product The discharge speed of becomes faster. As a result, a crystal growth rate comparable to that obtained when the pressure in the reaction vessel is increased can be obtained.

  Further, when the pressure in the reaction vessel is lowered, generation of miscellaneous crystals that occur when the fluorine concentration of the mineralizer is high can be suppressed, so that the fluorine concentration of the mineralizer can be set relatively high. As a result, the solubility of the crystal raw material in the solvent can be sufficiently increased, and the effect of effectively suppressing the oxygen uptake of the grown crystal by the deoxygenation property of the fluorine element can be obtained. Furthermore, since the pressure resistance required for the reaction vessel is reduced, a relatively inexpensive reaction vessel can be used, and the manufacturing cost can be greatly reduced.

  The pressure is appropriately determined depending on the filling rate of the solvent volume with respect to the temperature and the volume of the reaction vessel. Originally, the pressure in the reaction vessel is uniquely determined by the temperature and the filling rate, but in practice, the raw materials, additives such as mineralizers, temperature heterogeneity in the reaction vessel, and free volume Depending on the presence of

  From the viewpoint of crystallinity and productivity, the lower limit of the temperature range in the reaction vessel is preferably 320 ° C or higher, more preferably 370 ° C or higher, and further preferably 450 ° C or higher. From the viewpoint of safety, the upper limit value is preferably 700 ° C. or less, more preferably 650 ° C. or less, and further preferably 630 ° C. or less. In the method for producing a periodic table group 13 metal nitride crystal of the present invention, the temperature of the raw material dissolution region in the reaction vessel is preferably higher than the temperature of the crystal growth region. The temperature difference (| ΔT |) is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, preferably 100 ° C. or lower, and 90 ° C. or lower, from the viewpoints of crystallinity and productivity. More preferably, 80 ° C. or lower is particularly preferable. The optimum temperature and pressure in the reaction vessel can be appropriately determined depending on the type and amount of mineralizer and additive used during crystal growth.

  In order to achieve the temperature range and pressure range in the reaction vessel, the injection rate of the solvent into the reaction vessel, that is, the filling rate, is the free volume of the reaction vessel, that is, the crystal raw material and seed crystal (underlying substrate) in the reaction vessel. If used, subtract the volume of the seed crystal and the structure on which it is installed from the volume of the reaction vessel, and if a baffle plate is installed, further add the volume of the baffle plate from the volume of the reaction vessel. The liquid density at the boiling point of the solvent remaining after subtraction is usually 20 to 95%, preferably 30 to 80%, more preferably 40 to 70%.

The growth of the periodic table group 13 metal nitride crystals in the reaction vessel is carried out by heating and heating the reaction vessel using an electric furnace having a thermocouple, etc., so that the reaction vessel is subcritical in a solvent such as ammonia. Alternatively, it is carried out by maintaining a supercritical state. The heating method and the rate of temperature increase to a predetermined reaction temperature are not particularly limited, but are usually performed over several hours to several days. If necessary, the temperature can be raised in multiple stages, or the temperature raising speed can be changed in the temperature range. It can also be heated while being partially cooled.
The above-mentioned “reaction temperature” is measured by a thermocouple provided so as to be in contact with the outer surface of the reaction vessel and / or a thermocouple inserted into a hole having a certain depth from the outer surface, and It can be estimated in terms of internal temperature. The average value of the temperatures measured with these thermocouples is taken as the average temperature. Usually, an average value of the temperature of the raw material melting region and the temperature of the crystal growth region is defined as the average temperature.

  In the method for producing a periodic table group 13 metal nitride crystal of the present invention, a pretreatment can be added to the seed crystal. Examples of the pretreatment include subjecting the seed crystal to a meltback process, polishing the growth surface of the seed crystal, and washing the seed crystal.

  In the pretreatment, in order to polish the surface of the seed crystal capable of crystal growth, for example, chemical mechanical polishing (CMP) can be performed. The surface roughness of the seed crystal should be, for example, 1.0 nm or less from the viewpoint that the root mean square roughness (Rms) measured by an atomic force microscope performs meltback and subsequent crystal growth evenly. Is preferable, 0.5 nm is more preferable, and 0.3 nm is particularly preferable.

  The reaction time after reaching a predetermined temperature varies depending on the type of Group 13 metal nitride crystal of the periodic table, the raw material used, the type of mineralizer, and the size and amount of the crystal to be produced, but usually several hours. From a few hundred days. During the reaction, the reaction temperature may be constant, or the temperature may be gradually raised or lowered. After a reaction time for forming the desired crystal, the reaction temperature is lowered. The temperature lowering method is not particularly limited, but the heating may be stopped while the heating of the heater is stopped and the reaction vessel is installed in the furnace as it is, or the reaction vessel may be removed from the electric furnace and air cooled. If necessary, quenching with a refrigerant is also preferably used.

  After the temperature of the outer surface of the reaction vessel or the estimated temperature inside the reaction vessel is below a predetermined temperature, the reaction vessel is opened. The predetermined temperature at this time is not particularly limited, and is usually −80 ° C. to 200 ° C., preferably −33 ° C. to 100 ° C. Here, the valve may be opened by pipe connection to a valve connection port of the valve attached to the reaction vessel, passing through a vessel filled with water or the like. Further, if necessary, the ammonia solvent in the reaction vessel is sufficiently removed by making a vacuum or the like, and then dried, and the periodic table group 13 metal nitride crystal formed by opening the reaction vessel lid and the like and Additives such as reaction raw materials and mineralizers can be taken out.

  In the manufacturing method of the periodic table group 13 metal nitride crystal of the present invention, after the periodic table group 13 metal nitride crystal is grown on the seed crystal, a post-treatment may be added. The type and purpose of post-processing are not particularly limited. For example, the crystal surface may be melted back in the cooling process after growth so that crystal defects such as pits and dislocations can be easily observed.

(Wafer)
A group 13 nitride substrate can be formed by subjecting the periodic table group 13 metal nitride crystal grown on the base substrate to processing such as slicing, grinding, and polishing. By cutting out in a desired direction, a wafer (semiconductor substrate) having an arbitrary crystal orientation can be obtained. When a periodic table group 13 metal nitride crystal having a large and large-diameter M-plane is manufactured by the manufacturing method of the present invention, a large-diameter M-plane wafer is obtained by cutting in a direction perpendicular to the m-axis. Can do. In addition, when a periodic table Group 13 metal nitride crystal having a large-diameter semipolar surface is manufactured by the manufacturing method of the present invention, a large-diameter semipolar surface wafer is obtained by cutting out parallel to the semipolar surface. be able to. These wafers are also characterized by being uniform and of high quality.

(device)
The periodic table group 13 nitride substrate obtained by the above manufacturing method is suitably used for devices such as light emitting elements, electronic devices, and power devices. Examples of the light-emitting element in which the periodic table group 13 nitride crystal or wafer of the present invention is used include a light-emitting diode, a laser diode, and a light-emitting element obtained by combining these with a phosphor. Moreover, examples of the electronic device using the periodic table group 13 nitride crystal or wafer of the present invention include a high-frequency element, a high withstand voltage high-power element, and the like. Examples of high-frequency elements include transistors (HEMT, HBT), and examples of high voltage and high-power elements include thyristors (SCR, GTO), insulated gate bipolar transistors (IGBT), and Schottky barrier diodes (SBD). . Since the epitaxial wafer of the present invention has a feature of excellent pressure resistance, it is suitable for any of the above applications.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

<Example 1>
In this example, a periodic table group 13 metal nitride crystal was grown using the crystal manufacturing apparatus shown in FIG.
A seed crystal (thickness: about 330 μm) 6 was placed in the lower region (crystal growth region 2) of an autoclave lined with platinum (inner dimensions: diameter 22 mm, length 293 mm, volume: about 119 ml). The seed crystal 6 is obtained by slicing a crystal produced by an ammonothermal method so that the M-plane (10-10) is a main surface and polishing both surfaces, and then chemically polishing the main surface [CMP (chemical mechanical polishing)]. Finished. The surface roughness Rms of the main surface measured by an atomic force microscope was 0.5 nm or less.
Next, a baffle plate 5 was installed in the inner space of the autoclave 1. Then, 60.2 g of the GaN polycrystal produced by the HVPE method as the raw material 4 was weighed and put into a region above the baffle plate 5 in the autoclave 1 (raw material dissolution region 3).

Next, 9 ₄ % purity NH ₄ F sufficiently dried as a mineralizer was weighed so that the F concentration was 2.5 mol% with respect to the amount of NH ₃ used as a solvent. The raw material 4 was charged above. Next, the lid of the autoclave 1 equipped with the valve was immediately closed, and the autoclave 1 was weighed.
Next, an operation was performed so that the conduit connected to the autoclave 1 and the conduit connected to the vacuum pump communicated, and the valve was opened to evacuate the interior of the autoclave 1. Thereafter, while maintaining the inside of the autoclave 1 in a vacuum state, the autoclave 1 was cooled with a dry ice methanol solvent, and the valve was once closed. Then, after operating so as to communicate and a conduit connected to the conduit and NH ₃ bomb connected to the autoclave 1, again opening the valve, and the NH ₃ without touching the outside air are continuously charged into the autoclave 1. After controlling the flow rate and filling NH ₃ as a liquid in the autoclave 1, the valve was closed again. After the temperature of the autoclave 1 was returned to room temperature and the outer surface was sufficiently dried, the increment by NH ₃ filled was measured.

Subsequently, the autoclave 1 was housed in an electric furnace composed of a heater divided into two parts in the vertical direction. The temperature was raised while controlling the outer surface temperature of the autoclave so that the temperature of the lower crystal growth region 2 in the autoclave 1 was 625 ° C. and the temperature of the upper raw material dissolution region 3 was 575 ° C. After reaching the set temperature, the temperature was maintained for 96 hours. The pressure in the autoclave 1 was 100 MPa. Further, the variation of the outer surface control temperature of the autoclave being held was ± 5 ° C. or less.
Thereafter, the temperature was lowered over about 9 hours until the temperature of the lower outer surface of the autoclave 1 reached 50 ° C., then the heating by the heater was stopped, and the autoclave 1 was naturally cooled in an electric furnace. After confirming that the temperature of the lower outer surface of the autoclave 1 dropped to almost room temperature, the valve attached to the autoclave 1 was opened, and NH ₃ in the autoclave 1 was removed. Thereafter, the autoclave 1 was weighed to confirm that NH ₃ in the autoclave 1 was discharged. After that, the valve was once closed and operated so that the conduit connected to the autoclave 1 and the conduit connected to the vacuum pump could communicate with each other, and then the valve was opened again to remove NH ₃ in the autoclave 1 almost completely. Thereafter, the lid of the autoclave 1 was opened, and the grown crystal (gallium nitride crystal) was taken out.

When the thickness of the grown gallium nitride crystal was measured, it was 2.15 mm. The crystal growth rate was 455 μm / day, which was 227.5 μm / day when converted to the growth rate in the M-axis (10-10) direction.
Further, the rocking curve of the obtained gallium nitride crystal was observed by an X-ray diffraction method. As a result, the half width of (100) diffraction was 142 arcsec in the c-axis parallel direction and 26 arcsec in the c-axis vertical direction, which was a favorable value. Further, when the oxygen concentration and silicon concentration in the crystal were measured by SIMS analysis, the oxygen concentration was 5.0 × 10 ¹⁸ atms / cm ³ and the silicon concentration was below the detection limit.

<Examples 2 and 3>
Crystal growth was carried out in the same manner as in Example 1 except that the concentration of the mineralizer and the pressure in the autoclave 1 were changed as shown in Table 1, and that aluminum (gettering agent) was added to the raw material dissolution region. .
When the rocking curve was observed by the X-ray diffraction method for the gallium nitride crystal obtained in Example 2, the (100) diffraction half-width was 20 to 23 arcse in the c-axis parallel direction and 19 to 25 arcsec in the c-axis vertical direction. Very good results were obtained.
Furthermore, for the gallium nitride crystals obtained in Examples 2 and 3, when the oxygen concentration and silicon concentration in the crystals were measured by SIMS analysis, the oxygen concentration was 8.0 × 10 ¹⁸ atms / cm ³ . The silicon concentration was below the detection limit.

<Comparative Example 1>
With respect to Example 1, the mineralizer concentration, the upper temperature, and the lower temperature were changed to the conditions described in Table 1, and the pressure was increased by about twice.
In this comparative example, crystal growth was performed using a RENE41 autoclave (inner volume of about 345 cm ³ ) having an inner dimension of 30 mm in diameter and 450 mm in length as a pressure-resistant container and a Pt—Ir capsule as a reaction container. Capsule filling was performed in a sufficiently dry nitrogen atmosphere glove box. As a raw material, 50.98 g of polycrystalline GaN particles were weighed and placed in the capsule upper region (raw material dissolution region). Next, GaF ₃ having a purity of 99.999% which was sufficiently dried as a mineralizer was charged, weighed so that the F concentration was 1 mol% with respect to the amount of NH _3, and charged into the capsule.

  Furthermore, a platinum baffle plate was installed between the upper raw material melting region and the lower crystal growth region. As a seed crystal, one hexagonal GaN single crystal wafer grown by HVPE and having a C-plane as the principal plane and a wafer having the m-plane as the principal plane and particulate crystals spontaneously nucleated by HVPE were used. The main surface of the seed crystal was subjected to chemical mechanical polishing (CMP) finish excluding particulate crystals, and the surface roughness was confirmed to be Rms of 0.5 nm or less by measurement with an atomic force microscope. These seed crystals were hung on a platinum seed crystal support frame by a platinum wire having a diameter of 0.2 mm, and placed in a crystal growth region above the capsule.

Next, a cap made of Pt—Ir was connected to the upper part of the capsule by welding, and the weight was measured. A valve was connected to the tube attached to the upper part of the cap, and vacuum deaeration was performed with a vacuum pump. Thereafter, the capsule was cooled with a dry ice ethanol solvent while maintaining the vacuum state. Subsequently, NH ₃ was filled without touching the outside air. Based on the flow rate control, NH ₃ was filled as a liquid corresponding to about 57% of the effective volume of the capsule (converted to an NH ₃ density of −33 ° C.), and then the valve was closed again. The filling amount was confirmed from the difference in weight before and after NH ₃ filling.

Next, the capsule was inserted into an autoclave equipped with a valve, the lid was closed, and the weight of the autoclave was measured. Next, the valve attached to the autoclave was opened and vacuum deaeration was performed. Thereafter, the autoclave 1 was cooled with a dry ice ethanol solvent while maintaining a vacuum state. Subsequently, NH ₃ was filled in the autoclave without touching the outside air. Based on the flow rate control, NH ₃ was charged as a liquid corresponding to about 59% of the effective volume of the autoclave (autoclave volume−filled volume) (converted to an NH ₃ density of −33 ° C.), and then the valve was closed again. The temperature of the autoclave 1 was returned to room temperature, the outer surface was sufficiently dried, and the weight of the autoclave was measured. The weight of NH ₃ was calculated from the difference from the weight before filling with NH ₃ to confirm the filling amount.

  Subsequently, the autoclave was accommodated in an electric furnace composed of a heater divided into two parts in the vertical direction. The temperature was raised over 9 hours so that the temperature of the crystal growth region on the outer surface of the autoclave was 625 ° C. and the temperature of the raw material dissolution region was 595 ° C. (average temperature 610 ° C.). Hold for 7 days. The pressure in the autoclave was 250 MPa. Further, the variation in the control temperature of the outer surface of the autoclave during holding was ± 0.3 ° C. or less.

Thereafter, the temperature of the outer surface of the autoclave was naturally cooled to return to room temperature, to open the valve comes to the autoclave to remove NH ₃ in the autoclave. Thereafter, the autoclave was weighed to confirm the discharge of NH ₃ , and then the lid of the autoclave was opened and the capsule was taken out. A hole was made in the tube attached to the upper part of the capsule to remove NH ₃ from the inside of the capsule. When the inside of the capsule was confirmed, gallium nitride crystals were deposited on the entire surface of the seed crystal on either the C-plane or the M-plane. The growth rates differed depending on the plane orientations, and were Ga plane: 100 μm / day, N plane: 140 μm / day, M plane: 150 μm / day, and A plane: 330 μm / day.
In the crystal grown on the N-plane, crepes-like defects could be visually confirmed. Moreover, when it checked with the optical microscope about the M surface, it confirmed that many cracks were contained.
When the M-plane growth part was observed at low temperature PL, a single broad peak (wide half width) was observed, and it was found that the impurity concentration was high.

<Comparative example 2>
Compared to Example 1, the upper temperature and lower temperature were changed to the conditions described in Table 1, the pressure was about doubled, and fluorine and iodine were mixed and used as a mineralizer.
The apparatus and procedure used for the growth are the same as in Comparative Example 1, but the iodine input is larger than that of fluorine, and the dissolution and transport of GaN occurs from the high temperature region to the low temperature region. The raw crystal was placed in a high temperature range.
When the M-plane growth part is measured at low temperature PL, a single broad (wide half-value width) peak is observed, and it can be seen that the impurity concentration is high.

<Comparative Example 3>
For Example 1, the upper temperature, lower temperature and pressure were changed to the conditions described in Table 1, and fluorine and iodine were mixed and used as the mineralizer.
The apparatus and procedure used for growth are the same as those in Example 1. Since the amount of fluorine input was larger than that of iodine and dissolution and transport of GaN occurred from the low temperature region to the high temperature region, the seed crystal was installed in the high temperature region and the raw material crystal was installed in the low temperature region as in Example 1.
When the M-plane growth part is measured at low temperature PL, a single broad (wide half-value width) peak is observed, and it can be seen that the impurity concentration is high.

<Comparative Example 4>
Using the same seed crystal as in Example 1, crystal growth was performed by the HVPE method. The measured value of low temperature PL at the time of making it grow in the same <10-10> direction as Examples 1-3 and Comparative Examples 1-3 is shown. It is a broad peak similar to Comparative Examples 1 to 3, and it can be seen that excessive impurities are introduced.
In general, crystal orientation of GaN is highly dependent on the plane orientation, and O is less likely to be taken in when grown in the Ga plane <0001> direction, but O is likely to be taken in when grown in the M plane <10-10> direction. Has been pointed out.
In order to obtain a crystal having a low oxygen concentration in the M-plane growth, it is necessary to lower the oxygen concentration in the growth atmosphere, and it is possible to grow at a low pressure using fluorine and a gettering agent by the ammonothermal method. It can be seen that this is an effective technique for obtaining high-purity crystals.

<Comparative Example 5>
As compared with Comparative Example 1, as shown in Table 1, the mineralizer concentration was lowered, and the growth was performed by changing the upper temperature, the lower temperature, and the pressure. When the M-plane growth part was observed at low temperature PL, a single broad peak (wide half width) was observed, and it was found that the impurity concentration was high.

<Comparative Example 6>
As compared with Comparative Example 1, as shown in Table 1, the mineralizer concentration was lowered, and the growth was performed by changing the upper temperature, the lower temperature, and the pressure. When the M-plane growth part was observed at low temperature PL, a single broad peak (wide half width) was observed, and it was found that the impurity concentration was high.
In addition, the crystal obtained by performing growth in the same manner as in Comparative Example 6 except that the pressure was changed to 64 MPa, the oxygen concentration and silicon concentration in the crystal were measured by SIMS analysis. As a result, the oxygen concentration was 2.5 × 10 ²⁰ atms / cm ³ , the silicon concentration was 4 × 10 ²⁰ atms / cm ³ , and the appearance of the crystal was slightly deeply colored. A single broad peak (wide half-value width) is observed in this crystal as in Comparative Example 6.

(Observation of emission spectrum by low temperature electroluminescence (PL) method)
For low-temperature PL measurement, a He-Cd laser (wavelength: 325 nm) is used as a light source to irradiate the sample with a beam intensity of 38 W / cm ² , and a spectroscope manufactured by Hamamatsu Photonics (model number: C5094) and a detector manufactured by Hamamatsu Photonics (model number) : BT-CCD PMA-50) by measuring the emission spectrum at a temperature of 10K.
In general, when PL measurement is performed on GaN at a low temperature of 10K, a peak near 3.472 eV is called I _{2, A} (Donor Bound Exciton), and a sub-peak at 3.476 eV is called I _{2, B.} Separately from this, the peak existing at 3.435 to 3.460 eV is referred to as Two Electron Satellites. The total of 3.430 to 3.480 eV including these DBE and TES is referred to as Near Band Edge light emission.
In the present specification, DBE is observed when DBE is observed, and NBE is expressed when the peak is broad and TES is not observed.
The emission peak existing in the range of 3.435 to 3.460 eV as the first emission peak (TES), the emission peak existing in the range of 3.465 to 3.480 eV as the second emission peak (DBE or NBE), The presence or absence of each emission peak was determined as follows.
○: With emission peak ×: Without emission peak

The emission spectrum of the GaN crystal of Example 1 is shown in FIG. In the GaN crystal of Example 1, the first emission peak and the second emission peak were observed, and as the first emission peak, a total of two emission peaks were observed near 3.446 eV and 3.456 eV. Further, the half width (FWHM) of the second emission peak was 6.0 meV.
The emission spectrum of the GaN crystal of Example 2 is shown in FIG. A total of three emission peaks were observed around 3.441 eV, around 3.446 eV, and around 3.456 eV, and the half-value width of the second emission peak was 6.3 meV.
The emission spectrum of the GaN crystal of Example 3 is shown in FIG. As in Example 1, a total of two emission peaks were observed around 3.446 eV and around 3.456 eV, and the half width of the second emission peak was 7.1 meV.

The emission spectra of the GaN crystals of Comparative Examples 1 to 3 are shown in FIGS. Unlike Examples 1 to 4, the first emission peak was not observed, and the half-value widths of the second emission peak were 15.3, 16.2, and 16.4 meV, respectively, which is more than double that of Example 1. Value.
The emission spectrum of the GaN crystal of Comparative Example 4 is shown in FIG. The first emission peak was not observed, and the full width at half maximum (FWHM) of the second emission peak was 14.3 meV.
The emission spectrum of the GaN crystal of Comparative Example 5 is shown in FIG. The first emission peak was not observed, and the full width at half maximum (FWHM) of the second emission peak was 28.0 meV.
The emission spectrum of the GaN crystal of Comparative Example 6 is shown in FIG. The first emission peak was not observed, and the full width at half maximum (FWHM) of the second emission peak was 35.7 meV.

From FIG. 2, in the gallium nitride crystal of Example 1, the second emission peak was observed near 3.472 eV, and the first emission peak was observed near 3.446 eV and 3.456 eV. The half width of the second emission peak was 6.0 meV. Note that the two first emission peaks are derived from oxygen atoms as impurities. Further, as shown in Table 1, the gallium nitride crystal had a low impurity concentration and a high purity.
From FIG. 3, in the gallium nitride crystal of Example 2, the first emission peak is observed at three locations near 3.472 eV, around 3.441 eV, around 3.446 eV, and around 3.456 eV. I was able to. The half width of the second emission peak was 6.3 meV. Further, as shown in Table 1, this gallium nitride crystal had the same purity as the gallium nitride crystal of Example 1.
From FIG. 4, in the gallium nitride crystal of Example 3, as in Example 1, the second emission peak was confirmed near 3.472 eV, and the first emission peak was confirmed at two locations near 3.446 eV and 3.456 eV. We were able to. The half width of the second emission peak was 7.1 meV. Further, as shown in Table 1, the gallium nitride crystal had a low impurity concentration and a high purity.
As shown in FIGS. 5 to 10, in the gallium nitride crystals of Comparative Examples 1 to 6, the separated first emission peak and second emission peak were not observed, but only a broad single peak was observed. The full width at half maximum of this single peak was 14 meV or more, which was more than double the value of the second emission peak of Example 1. The gallium nitride crystal obtained by the method according to Comparative Example 6 had a high impurity concentration and a low purity.

  In Comparative Example 4, the same HPVE method as in the Reference Example was used, but only a broad single peak could be observed. This is because the crystal growth of gallium nitride is highly dependent on the plane orientation, and oxygen is not easily taken in by the growth in the Ga plane (0001) direction performed in Reference Example 1, but the M plane (10− This is probably because oxygen is easily taken in in the growth in the 10) direction.

  From the above results, the periodic table group 13 metal nitride crystal having at least two emission peaks in the range of 3.430 eV to 3.480 eV in the emission spectrum is a periodic table group 13 metal in which only a single broad peak is observed. It was found to be a high quality crystal having a higher purity than a nitride crystal and having few defects such as vacancies and dislocations. The shape of the emission peak depends on the type of mineralizer, the presence or absence of a gettering agent, and the pressure in the autoclave. A compound containing fluorine is used alone as the mineralizer, and aluminum is added as the gettering agent. Further, it has been found that by making the pressure in the autoclave relatively low, the second emission peak has a sharp shape and an extremely high purity gallium nitride crystal can be obtained.

  Since the periodic table group 13 metal nitride crystal of the present invention has a very high purity, it can be used as a material for growth substrates and semiconductor devices on which the periodic table group 13 metal nitride crystal is grown. High nature.

1 Autoclave (pressure-resistant container)
2 Crystal growth region 3 Raw material dissolution region 4 Raw material 5 Baffle plate 6 Underlying substrate (seed crystal)

Claims (7)

  A Group 13 metal nitride crystal of a periodic table obtained by crystal growth in the presence of a nitrogen-containing solvent in a supercritical and / or subcritical state, having an emission spectrum of 3.430 eV observed by a low-temperature photoluminescence method. A periodic table group 13 metal nitride crystal having at least two emission peaks in a range of ˜3.480 eV.   2. The period according to claim 1, wherein the emission spectrum has a first emission peak in a range of 3.435 to 3.460 eV and a second emission peak in a range of 3.465 to 3.480 eV of the emission spectrum. Table Group 13 metal nitride crystals.   The periodic table group 13 metal nitride crystal according to claim 1 or 2, obtained by crystal growth on a base substrate having a nonpolar plane or a semipolar plane as a main surface.   The periodic table group 13 metal nitride crystal according to any one of claims 1 to 3, obtained by crystal growth on a base substrate having a nonpolar plane as a main surface.   The periodic table group 13 metal nitride crystal according to any one of claims 2 to 4, wherein a half-value width of the second emission peak is 12 meV or less.   6. The periodic table group 13 metal nitride crystal according to claim 2, comprising a plurality of the first emission peaks in a range of 3.435 to 3.460 eV of the emission spectrum. 7. .   The periodic table group 13 metal nitride crystal according to any one of claims 1 to 6, wherein the periodic table group 13 metal nitride crystal is a gallium nitride crystal.