JP2008143778A - Method for producing nitride single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a massive nitride single crystal of group 13 elements of the periodic table, wherein a large massive single crystal can be prepared in good yield, inexpensively, and stably. <P>SOLUTION: In the method of performing crystal growth by the ammonothermal method using ammonia as a solvent, the crystal growth is performed by using two types of crystals having different average particle sizes to each other as starting raw materials while applying supersonic waves to a growing part in which seed crystals are arranged and/or to a raw material-filling part from which the raw materials are supplied. Further, a precipitate-collecting net is provided near the converging point of convection current of the solvent generated by the temperature difference during the crystal growth in a reaction vessel to catch crystallites or the precipitates in a transportation stream and allow the crystallites to be selectively precipitated on the collecting net. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for growing a bulk single crystal of a group 13 element nitride, particularly a bulk single crystal of GaN.

GaN is useful as a material applied to electronic devices such as light emitting diodes and laser diodes. Currently, the gallium nitride (GaN) crystal size and growth produced by known methods is sufficient for some applications, however, for many other applications, the crystal size and quality of gallium nitride is not sufficient. . For practical GaN crystallization, see S.
Nakamura et al., J. Appl. Phys. 37 (1998) L309, etc. have proposed a method of performing vapor phase epitaxial growth by MOCVD (Metal-Organic Chemical Vapor Deposition) on a substrate such as sapphire or silicon carbide. However, in this method, problems such as GaN lattice defects are pointed out because of heteroepitaxial growth in which the lattice constant and thermal expansion coefficient of the substrate and GaN are different. Specifically, at least one of high-concentration transition, vacancies and impurities can be mentioned. These defects can have undesirable effects and adverse effects on epitaxially grown gallium nitride and can adversely affect the operation of the resulting electronic devices based on gallium nitride. For this reason, GaN obtained by these methods cannot exhibit satisfactory performance for use in application fields such as blue lasers. Currently, heteroepitaxial gallium nitride growth requires complex and long processes to reduce the defect concentration in gallium nitride. For this reason, in recent years, establishment of a manufacturing technique for GaN bulk single crystals has been strongly desired. As for crystallization of GaN by such homoepitaxy growth, three methods are currently largely divided, and three methods are being developed. First, under pressures in the range of about 10 to about 20 kbar and temperatures in the range of about 1200 ° C. to about 1500 ° C., disclosed by S. Porowski et al. In J. Crystal Growth 178 (1997) 174. This is a method of reacting nitrogen and Ga (high pressure method), but this increases the cost of the apparatus and makes the reaction process complicated. Furthermore, the quality of the gallium nitride crystals produced by this method may be sufficient in terms of transition density for some gallium nitride applications. However, the quality of gallium nitride crystals formed by this method exhibits a high concentration of undesirable nitrogen vacancy defects, which adversely affects gallium nitride crystal applications. Secondly, the method of reacting gallium and NaN ₃ under pressure, atmospheric pressure flux growth, and metathesis reaction (GaI ₃ + Li ₃ N) disclosed by Masato Aoki et al. In J. Crystal Growth 218 (2000) 7-12. Gallium nitride grown from other methods such as) has also been proposed. It is difficult to control the growth region, and there is concern about contamination by flux. Furthermore, this growth method is considered to be expensive, and produces a high-quality, defect-free bulk gallium nitride single crystal. Not considered. Although these methods have succeeded in crystallization to some extent, they have not yet obtained a larger single crystal. On the other hand, as a third method, R. Dwilinski et al. Reported a GaN crystal synthesis method by an ammonothermal method in ACTA PHYSICA POLONICA A Vol.88 (1995). Here, a method of obtaining a single crystal of GaN using KNH ₂ as a mineralizer for crystallization at high temperature in supercritical ammonia is disclosed. In addition, JWKOLIS et al. Proposed synthesizing crystals using KNH ₂ and KI as mineralizers by the ammonothermal method in J. Crystal Growth 222 (2001) 431-434. Andrew P. Purdy et al. In Chem. Master 1999, 11, 1648-1651 also proposed using ammonium halide or the like as a mineralizer in the ammonothermal method. And in J. Crystal Growth 209 (2000) 208-212, XLChen et al., By using a platinum liner in the stainless steel autoclave of the reaction vessel also in the ammonothermal method, suppresses the generation of square columnar GaN crystals, Hexagonal GaN can be selectively crystallized. These documents propose crystallization of GaN in the ammonothermal method, but since no seed crystal is used, crystal growth is random, and it is assumed that the crystal growth orientation and size are difficult to control. However, crystals of a size that can be applied to industrial products such as blue lasers have not been obtained. In addition, the ammonothermal method using these supercritical ammonias shows a slow growth rate, and therefore, bulky or large gallium nitride crystals cannot be easily produced. The pressure vessel also limits these gallium nitride growth methods. The pressure vessel limits the supercritical ammonia growth process to a pressure below about 5 kbar, and thus limits the temperature and reaction rate of the supercritical ammonia growth process. Furthermore, since these documents do not describe detailed conditions for crystal growth, it is not clear whether the crystal growth rate is dominated by diffusion in the ammonothermal method or dominated by GaN formation reaction.

On the other hand, French patent publication FR 2796657 A1 proposes that a polycrystal of nitride is first prepared and crystal growth is performed by using this as a raw material by a solvothermal method. This document describes the growth of a GaN single crystal by a solution growth method. According to this growth method, a GaN polycrystalline nitride is formed in the lower part of the crystal growth apparatus, while a GaN seed crystal is formed in the growth apparatus. Each is placed on top and then filled with a nitride solvent. In this state, the inside of the crystal growth apparatus is operated at a growth temperature of 100 to 600 ° C. and a pressure of 5 MPa to 2 GPa. Here, the lower and upper temperatures in the crystal growth apparatus are 10 lower than the upper temperature. A single crystal of GaN is grown by operating so as to be higher by ˜100 ° C.

  Furthermore, in the international patent application publication WO 01/24921 A1, a GaN seed crystal is used, the reaction vessel is sealed, the inside of the reaction vessel is heated to a high temperature and high pressure, and the HPHT method is used. There has been proposed a method for growing a single crystal of GaN using a reaction between a nitrile solvent and a nitride solvent. This document also proposes the use of copper or platinum as a material for the reaction vessel that has low permeability to hydrogen harmful to the HPHT reactor and exhibits desirable cold welding characteristics that are not easily corroded by the HPHT reaction. Has been. In addition, the same document discloses that a raw material with relatively low crystallinity, a raw material with high crystallinity, an amorphous raw material, or the like is used as a raw material GaN crystal. It is described that it is supplied to the crystal growth process as it is.

  In such a GaN growth method, an ammonothermal method or an HPHT method using a seed crystal is used. Therefore, although crystal growth is improved, a crystal having a sufficient crystal size cannot be obtained. In the ammonothermal method, the solubility of the nitride raw material in the nitriding solvent, the ion portability during solvent convection, the control of the recrystallization factor to the seed crystal, etc. are important factors, and these should be controlled comprehensively. However, in the method described in the above-mentioned document, only basic crystal growth conditions are studied, and it is the actual situation that improvement is still desired. For example, when a seed crystal is used, the seed crystal falls due to elution of the seed crystal, the problem of adhesion or precipitation of the microcrystal on the seed crystal, the adhesion and crystal growth of the microcrystal contained in the raw material at the reaction vessel terminal, No effective countermeasures have been taken for various obstruction factors related to the growth of large block crystals such as the lack of supply of the raw material to the seed crystal and the deflection of crystal growth. In addition, in an environment where crystal growth is performed by the ammonothermal method using ammonia in a supercritical state as a solvent, the reaction vessel and the container can be used in a combination of conditions such as oxidizing power, reducing power, acidity, and alkalinity in the system. It is extremely important to provide each member such as a baffle plate with sufficient corrosion resistance from the viewpoint of industrial stable production and the influence on the purity and characteristics of crystals. Therefore, establishment of a method for obtaining a larger and higher performance massive single crystal with good yield, inexpensively and stably is strongly desired industrially.

In view of the above-mentioned problems, the present inventors have intensively studied a method capable of producing a single crystal having a size in the range of 10 to 100 mm by an industrially available and economical method, and as a result, have reached the present invention. . That is, the gist of the present invention is as follows.
(1) In a method for producing a bulk single crystal of a nitride of a group 13 element of a periodic table, a polycrystalline nitride of a group 13 element of a periodic table is used as a raw material in a reaction vessel composed of an alloy containing nickel and chromium. A process for producing a bulk single crystal of a group 13 element nitride nitride, characterized in that it is supplied to a raw material filling part of the reaction vessel, a seed crystal is placed in a growing part, and crystal growth is carried out in an ammonothermal manner. (2) The production method according to 1 above, wherein the group 13 element of the periodic table is gallium (Ga) or aluminum (Al).
(3) The manufacturing method according to (1) or (2) above, wherein the alloy containing nickel and chromium is a nickel / chromium alloy or a nickel / chromium / molybdenum alloy.
(4) The production method according to (1), (2) or (3) above, wherein a mineralizer having a nitrogen atom is contained in the reaction vessel.
(5) The above (4), wherein the mineralizer having a nitrogen atom is at least one compound selected from the group consisting of alkali metal amides, ammonium halides, alkali metal nitrides or alkaline earth metal nitrides. The manufacturing method as described.

(6) The alkali metal amide is potassium amide (KNH ₂ ) (5
) Described production method.
(7) The production method according to the above (6), wherein the ammonium halide is ammonium bromide (NH ₄ Br) or the like.
(8) The reaction vessel contains at least one compound selected from the group consisting of ammonia (NH ₃ ), hydrazine (NH ₂ NH ₂ ), urea and the like, amines, and melamine as a solvent. The manufacturing method of said (1) thru | or (7) description.
(9) The method according to (8), wherein the solvent is used in a supercritical state.
(10) The production method according to (1) to (9) above, wherein the reaction vessel is sealed and the reaction vessel is reacted at a high temperature and pressure.
(11) The production method as described in (1) to (10) above, wherein a baffle plate is provided between the raw material filling part and the growing part in the reaction vessel.
(12) The method according to (11) above, wherein the material of the surface of the baffle plate is an alloy containing nickel and chromium.
(13) The method according to (12) above, wherein the alloy containing nickel and chromium is a nickel / chromium alloy or a nickel / chromium / molybdenum alloy.

According to the method for producing a bulk single crystal of a nitride of a group 13 element of the periodic table of the present invention, contamination of impurities is prevented by a simple and economical process, and a large bulk single crystal is obtained in a high yield and at a low cost. Obtained stably.
Further, according to the present invention, even in a reaction system under a severe condition for a reaction vessel such as an ammonothermal method using ammonia in a supercritical state as a solvent, it exhibits sufficient corrosion resistance for a long period of time and is not suitable for bulk crystals. Impurity contamination is prevented, and high-performance bulk crystals are industrially stable. An inexpensive and simple process for producing nitride bulk crystals is provided.

  Hereinafter, the present invention will be described with reference to the synthesis of a GaN single crystal. However, the present invention is not, of course, limited to the synthesis of the above-described substances, and includes a group 13 element of the periodic table and its alloys (for example, GaInN, It can also be applied to the synthesis of GaAlN) nitrides. Thus, whenever there is doubt about gallium, one of these elements or an alloy of these elements can be used in place of gallium, considering its appropriate characteristics (especially when it is solid or liquid) .

In accordance with the present invention, this type of nitride synthesis includes two steps: In the first step, a fine polycrystalline nitride, such as gallium nitride (hereinafter referred to as “microcrystalline raw material”) is prepared. In the second step, single crystal growth is realized from the microcrystalline material. This raw material is often polycrystalline GaN, and the average grain size of the microcrystalline raw material is preferably 5 μm or less.
When such an average particle diameter is in a small range, the specific surface area is increased and the reactivity with the solvent is improved. The grain size of the fine crystal raw material of a better mode is to use a GaN microcrystalline raw material having a small average particle diameter, that is, a high dissolution rate. In this case, the desirable average particle diameter of the GaN microcrystal raw material is 1 μm or more. When a microcrystalline raw material having an average particle size of 1 μm or less is used, it is transported to the crystal growing part by thermal convection and may adhere to the seed crystal, so it is necessary to take a workaround.

  By using two kinds of microcrystal raw materials having different average particle diameters, Ga (containing) can be obtained by mixing a fast dissolution rate with a small crystallite raw material and a slow dissolution speed with a large particle diameter in the system. It is possible to suppress the supply of ions to the crystal growth section, and as a result, it is possible to suppress the disadvantage of growing the bulk single crystal, which is elution of the seed crystals. Moreover, the shape of the GaN microcrystal is not particularly limited, but a spherical shape is preferable in consideration of the uniformity of dissolution in a solvent.

  Since the method of the invention applies to other nitrides (eg, nitrides of other elements such as AlN, InN or Group III), the first step of the method may be developed in different ways. The conditions for preparing the microcrystalline raw material are common. In the case of gallium, for example, the first step is performed as follows. At a temperature slightly higher than the transition temperature to the liquid state, gallium is mixed with one or more fine materials to prepare an easy-to-operate powder, thus gallium with one or more of the above materials (minerals). Wrapping agent). Such mineralizers (or solubilizers) are well known in the art to increase the solubility of the solute in the reaction medium and to transfer the solute to the nucleation site. A mineralizer is interpreted as a "catalyst" because it is consumed when the solute dissolves in the reaction medium and regenerates when crystals form. Examples of suitable mineralizers are mineralizers having fluoride or nitrogen atoms. Examples of fluorides include ammonium fluoride, hydrogen fluoride, sodium difluoride, ammonium hexafluorosilicate, and hydrocarbyl ammonium fluoride such as tetramethyl ammonium fluoride, tetraethyl ammonium fluoride, benzyltrimethyl ammonium fluoride, dipropyl fluoride. Ammonium fluoride, and ammonium isopropyl fluoride. In addition, a fluorinated alkyl metal salt such as sodium fluoride may be used as long as it is reactive in the reaction mixture. Preferably, the fluoride source is ammonium fluoride, hydrogen fluoride, sodium fluoride, sodium difluoride, or ammonium hexafluorosilicate. More preferably, the fluoride source is ammonium fluoride.

Mineralizers having nitrogen atoms are all fine compounds that can have nitriding ability during decomposition or can increase the nitriding ability of the solvent. For example, alkali metal amides such as sodium amide (NaNH ₂ ), potassium amide (KNH ₂ ), lithium amide (LiNH ₂ ), lithium diethylamide ((C ₂ H ₅ ) ₂ NLi)), ammonium chloride (NH ₄ Cl) Ammonium halides such as ammonium fluoride (NH ₄ F) and ammonium bromide (NH ₄ Br), alkali metal nitrides or alkaline earth nitrides such as Li ₃ N, Mg ₃ N ₂ , Ca ₃ N ₂ , and Na ₃ N Metals, NH ₂ NH ₃ Cl or NH ₃ NH ₃ Cl ₂ , NHI, chromium nitride (CrN
), Niobium nitride (NbN), silicon nitride (Si ₃ N ₄ ), zinc nitride (Zn ₃ N ₂ ), ammonium carbonate ((NH ₄ ) ₂ CO ₃ ). Other mineralizers include NaCl, KI
Alkali metal halides such as Li ₂ S, KNO ₃ , phosphorus nitride (PN, P = N) and the like. In addition, when various nitrogen compounds exemplified as the following solvents are used in a small amount, they may serve as a mineralizer.

If an appropriate mineralizer is selected among these, the nitriding rate in the presence of NH _{3 in} the supercritical state is much higher than in the case of using only the solvent NH ₃ . When the mineralizer or co-mineralizer used further forms a hydrogen atmosphere during decomposition, the nitriding rate can be improved. In general, it is preferable to select a mineralizer from a material that can activate gallium and promote nitridation of gallium. In particular, it is important to select a mineralizer that separates Ga contained in the raw material of the present invention from GaN. Gallium has, for example, can be divided by NH ₂ NH ₃ Cl, when Ga content of polycrystalline nitrides is large, it is preferred to use NH ₂ NH ₃ Cl as Kyoko agent.

In order to reliably perform the first step, in the case of gallium, the amount of gallium and the amount of mineralizer are optimized. For example, a ratio in the range of 1-10 can be selected as the NH ₂ NH ₃ Cl / Ga molar ratio. The reaction is carried out in a container into which a solvent and a reagent are introduced. Solvents include, for example, ammonia (NH ₃ ), hydrazine (NH ₂ NH ₂ ), urea, and amines such as primary amines such as methylamine, secondary amines such as dimethylamine, and trimethylamine. Tertiary amines, diamines such as ethylenediamine, or any other solvent that does not impair the stability of nitride III-V such as melamine can be used. These solvents can be used alone or in combination.

  These solvents are preferably used in a supercritical state. A supercritical fluid means a concentrated gas that is maintained above its critical temperature, and the critical temperature is a temperature at which the gas cannot be liquefied by pressure. Supercritical fluids generally have lower viscosities and are more easily diffused than liquids, but have solvating power similar to liquids. The reaction mixture is maintained at a temperature above the critical temperature of the solvent (400 <T <800 ° C.). Since the reaction mixture is enclosed within a constant volume (container volume), an increase in temperature increases the pressure of the fluid. In general, the pressure is in the range of 40-400 MPa. Since T> Tc (critical temperature of one solvent) and P> Pc (critical pressure of one solvent), the fluid is in supercritical conditions. Under the above conditions, formation of GaN microcrystals is observed. In fact, the solubility of the reagents introduced in the solvent is very different between subcritical and supercritical conditions, so that supercritical conditions induce sufficient seed formation of GaN, thus forming microcrystals. Is done. On the other hand, in the subcritical state, it may be disadvantageous compared to the supercritical state in terms of corrosion of the reaction vessel. Although the reaction vessel in the present invention is an alloy containing nickel and chromium, which will be described later in detail, the corrosion resistance of these materials shows different characteristics depending on the supercritical state oxidizing power, reducing power, and pH. The reaction time depends in particular on the reactivity of the mineralizer or co-mineralizer and on the thermodynamic parameters, ie temperature and pressure values. The GaN (or one of its alloys) microcrystals thus obtained is suitable for single crystal growth by the ammonothermal method in the second step.

  In addition, the polycrystalline raw material of the present invention can also be prepared by heat-treating a gallium compound in an ammonia gas stream in a temperature range of 600 ° C. or higher to cause a nitriding reaction. In such a nitriding reaction, the gallium compound is preferably reacted in a solid phase, and when it is necessary to increase the surface area of the gallium compound in the solid phase and increase the reaction rate, the gallium compound in the solid phase is removed with a mortar or a pulverizer. It is desirable to pulverize sufficiently to make fine powder. Such a finely powdered gallium compound may be formed into a pellet by pressurization for the purpose of facilitating its handling, etc., and a liquid having a certain degree of hydrophilicity with a high viscosity such as glycerin or ethylene glycol is used as a binder. You can knead together. The heat treatment temperature range of the gallium compound in the above-mentioned ammonia gas stream is adjusted by the thermal decomposition temperature of the gallium compound to be used, but the particle size controllability and crystallinity of the product, or heating required for production is economically performed. In this respect, the temperature is usually 600 ° C to 1200 ° C, preferably 700 ° C to 1100 ° C, and more preferably about 750 ° C to 1050 ° C. If this temperature is too low, the progress of the nitriding reaction and the crystallinity of gallium nitride may be extremely hindered. Such heating is performed by putting a gallium compound to be used as a raw material in a reactor and raising the temperature to a predetermined temperature through an ammonia gas stream. The rate of temperature rise is not particularly limited, but is preferably 1 to 50 ° C./min, preferably 3 to 30 ° C./min, more preferably about 5 to 20 ° C./min in terms of productivity and temperature rise controllability. It is. The ammonia gas stream means a gas stream containing ammonia. The ammonia content in the gas is usually 10 to 100 mol%, preferably 30 to 100 mol%, more preferably about 50 to 100 mol% in terms of reaction rate, and the gas mixed with ammonia is the production of the present invention. It is preferable to use an inert gas such as nitrogen gas or argon gas that does not cause a chemical reaction that adversely affects the nitriding reaction of the method.

  In order to suppress the formation of oxides as impurities, it is desirable to make the oxygen gas concentration in the ammonia gas stream as small as possible. This concentration is, for example, 10 ppm or less, preferably 1 ppm or less, more preferably 0. It is about 1 ppm or less. Typical examples of the gallium compound include anionic gallium salts and gallium chalcogenides containing elements belonging to Group 15 or Group 16 of the periodic table, and these may contain crystal water. Of course, an anhydride is desirable. Specific examples include gallium salts of strong acid anions such as gallium sulfate and gallium nitrate, gallium salts of low oxidation anions such as gallium sulfite and gallium nitrite, and gallium chalcogenides such as gallium oxide. Gallium and gallium oxide are preferably used in terms of crystallinity of the product, and gallium sulfate is more preferably used in terms of a suitable thermal decomposition temperature. The thermal decomposition temperature of such a gallium compound is preferably within the above heat treatment temperature range. For example, a gallium compound having a thermal decomposition temperature within a temperature range of about 600 ° C. to 1000 ° C. such as gallium sulfate is preferable in the present invention. Used. A more preferable range of the thermal decomposition temperature is about 650 ° C to 900 ° C, and more preferably about 700 ° C to 850 ° C. Here, the thermal decomposition temperature is defined as a temperature at which 50% of the total weight in a state where low-molecular-weight substances such as crystal water and adsorbed water are removed is lost by heating in air. The gallium compound having a low water content is preferably used in the present invention. For example, it is desirable to use as a raw material a water molecule that does not contain water as much as possible, such as crystal water or adsorbed water. When the water content is high, the crystallinity and purity of the product may be extremely lowered. Therefore, the water content in the gallium compound is usually about 3 times or less, preferably about 2 times or less, more preferably about 1.6 times or less as the weight of water relative to the weight of the gallium element contained. The supply amount and speed of the ammonia gas stream are not limited and are adjusted by the amount of the gallium compound used as a raw material, the cross-sectional area of the reaction vessel, etc., but usually an excess equivalent amount of ammonia molecules relative to the gallium atoms of the gallium compound Is preferable from the viewpoint of reaction rate and completion of the reaction. The progress of the nitriding reaction is confirmed by, for example, analyzing the crystal structure of the product by the X-ray diffraction method using copper Kα rays as the X-ray source. This is possible by comparing known diffraction patterns derived from.

  The crystallite raw material of GaN (or one of its alloys) thus obtained is usually present in a mixture of unreacted Ga and by-products because it is difficult to make the reaction efficiency 100%. is there. In this case, unreacted Ga and by-product components must be removed after the first step, and when the particle size of the microcrystalline raw material is small, removal thereof is difficult. In order to remove unreacted Ga and by-products remaining on the surface of the microcrystal raw material, a treatment of several hours to several tens of hours is required in the acid solution. In order to increase the removal rate, it is effective to perform heat treatment, for example, use in a state where hydrochloric acid is boiled is effective. On the other hand, if this removal treatment is excessive, attention should be paid because there is a possibility that a surface with excessive N is formed on the particle surface. Performing such a treatment is disadvantageous in terms of production efficiency, and the present inventors have added Ga without removing unreacted Ga and by-products remaining on the surface of the microcrystalline raw material. Thus, it is effective to use as a starting material (hereinafter referred to as “starting material”) used for the bulk GaN single crystal growth in the second step including the microcrystalline raw material obtained in the first step. I discovered that. The hybrid ratio of the starting material is preferably up to about 50%. If residual oxide remains and there is a concern about single crystal growth by the ammonothermal method, deaeration heating is effective.

  In the second step, a massive GaN single crystal is grown. This step is performed in a closed reaction vessel, and is a so-called ammonothermal method. In the drawing, a schematic representation of an apparatus comprising a reaction vessel in the form of a long cylindrical vessel arranged vertically is shown. The upper part of the container is closed by a nozzle connected to a pressure control device (not shown). The vessel is provided in a furnace that encloses the vessel over its entire height and can apply a temperature gradient to the vessel along the vessel axis.

The container is divided into two overlapping zones, that is, a lower raw material filling part and an upper growing part separated by a baffle plate. The temperature gradient ΔT between these two zones is 10-100 ° C. The direction of the gradient depends in particular on the solubility of the raw material as a function of temperature. The raw material filling part is charged with the raw material prepared in the first step, and a seed crystal is placed in the growing part. The seed crystal has a size parameter that matches the size parameter of the GaN crystal lattice (single crystal) or is coordinated to ensure heteroepitaxy (ie, coincidence of the crystallographic position of some atoms) It consists of a piece or a piece of polycrystalline material. The seed crystal can be composed of any material having a crystal structure very close to that of GaN, InN, AIN, or GaN. For example, in the case of GaN, a single crystal of GaN, a single crystal of zinc oxide (ZnO) can be used. Examples thereof include crystals, single crystals of silicon carbide (SiC), lithium gallate (LiGaO ₂ ), and single crystals of zirconium diboride (ZrB ₂ ).

  The seed crystal is held by a noble metal wire, and can be fixed by fastening the noble metal wire to a frame. The noble metal wire is preferably a group 13 element of the periodic table, such as nickel (Ni), tantalum (Ta), titanium (Ti), palladium (Pd), platinum (Pt), or niobium (Nb). As the installation direction of the seed crystal, an arbitrary one is used, but the angle formed between the c-axis of the seed crystal and the convection direction of the nitride solvent is 0 to 180 ° (excluding 0 ° and 180 °), More preferably, the angle is 60 ° to 120 °. By using the seed crystal thus arranged, the obtained GaN single crystal is grown eccentrically with respect to the seed crystal, and a large single crystal can be obtained.

  Although it is not clear why it grows eccentrically in this way, among the side surfaces of the seed crystal whose height direction is the c-axis direction, the portion where the convection is in direct contact and the portion where the convection is in direct contact are caused by convection. The supply rate of the transported Ga (containing) ions is different. On the other hand, the GaN single crystal is hexagonal (wurtzite) and has a 6-fold symmetry axis. For this reason, when growing a GaN single crystal by the ammonothermal method, if the c-axis direction of the GaN (or other) seed crystal is arranged parallel to the convection direction of the nitride solvent, the seed crystal is the center. Although it is thought that it grows almost evenly, according to this method, a surface where the crystal growth is slower than other surfaces is intentionally created by providing a portion where the supply rate of Ga (containing) ions is small and large. However, it is inferred that this slow surface has better growth efficiency than the other fast surfaces, and it is considered that a profit that a large crystal can be obtained is generated.

  The seed crystal can also be used by joining the seed crystals. In this case, the c-axis polarities are matched and brought into contact with each other by bonding using the homoepitaxy action by the ammonothermal method of the present invention or by using a gas phase method such as MOCVD method. It is possible to reduce the dislocation of the part. By joining the seed crystals in this way, a large seed crystal in the c-axis direction can be obtained even when selective growth in the a-axis direction occurs. In this case, it is preferable to join so that not only the c-axis polarity is matched but also the a-axis polarity is matched, and therefore it is preferable to join seed crystals of the same shape.

Further, when the seed crystals are bonded to each other, it is preferable to polish the bonding surface to a smooth surface at a mirror surface level. It is more preferable to polish smoothly at the atomic level. The polishing method is not particularly limited, and can be performed by EEM processing (Elastic Emission Manching), for example. The abrasive used for this is not particularly limited, and examples thereof include SiO ₂ , Al ₂ O ₃ , ZrO ₂ , and colloidal silica is preferable. As described above, the reason for smoothing the c-plane is that if the c-plane is rough, the crystal growth rate is increased, and the consistency between the c-planes serving as joints is likely to be impaired.

  In the present invention, ultrasonic waves may be further applied to the growing part where the seed crystal is arranged. The seed crystal is subjected to vibration by applied ultrasonic waves in addition to normal thermal vibration according to the temperature of the growing part. For this reason, the seed crystal vibrates at a frequency determined in proportion to the frequency of the applied ultrasonic wave. This vibration has a shape that relatively widens the space in which the atoms of the crystal lattice are located, so that the probability that a raw material compound or the like that contacts the surface of the seed crystal enters the crystal lattice is relatively large compared to the conventional state. Become. Also, even if crystal nuclei and other particles that cause polycrystals are generated, the lattice matching with the crystal interface that has been grown in single crystals until now is poor, so the bonding force is weak and incorporated into the crystal I can't. That is, only crystal nuclei with strong bonding strength and lattice-matched are taken into the crystal to grow a single crystal. That is, generation of polycrystals can be suppressed by ultrasonic vibration. As a result, atoms accurately located at appropriate sites in the crystal lattice achieve a relatively good crystalline quality, thereby improving the electrical and optical properties of the material formed.

  The reason for this is not clear, but can be considered as follows. That is, an ultrasonic wave is a sound wave having a frequency of sound of 20 kHz or more, and when an ultrasonic wave is applied to a substance, changes in pressure, temperature, density, etc. occur in the substance. Such ultrasonic waves have a feature that enables bonding by transmitting ultrasonic waves to atoms constituting the substance, promoting vibrations of the atoms, and dissolving the two substances. Therefore, by using such performance of ultrasonic waves, when ultrasonic waves are applied to the surface of the seed crystal during the growth of the gallium nitride single crystal, the material constituting the seed crystal and the incident material are easily welded to each other. As a result, a high-quality massive single crystal can be grown even at a lower crystal growth temperature compared to the conventional method.

Furthermore, as described later, since the activation rate can be increased by simultaneously applying ultrasonic waves to the raw material compound, the crystal growth efficiency of the growth system can be increased. The vessel is filled with a nitride solvent (eg, hydrazine N ₂ H ₄ or ammonia NH ₃ ) or any solvent that is miscible with nitride III-V. The container is held at a pressure in the range of about 5 MPa-2 GPa. The ratio of the injection of the nitride solvent should be about 60 to 85% of the free volume of the container, that is, the volume remaining when the raw material containing GaN polycrystalline nitride and the baffle plate are installed in the container. preferable. The blending ratio with the nitrogen source is adjusted according to the residual Ga weight mixed with the microcrystals.

In order to ensure the transport of gallium and nitrogen from the raw material to the seed crystal, an intermediate compound capable of supplying anions (eg all other compounds containing N ^3- or nitrogen or all compounds containing halogen anions) is filled in the raw material filling section Is advantageous. The compound results in a chemical reaction between the raw GaN and at least one other compound called “precursor”. In the present invention, as a precursor, in addition to the polycrystalline raw material and the Ga metal contained in the polycrystalline, GaX (X = Cl, Br, I), GaX ₂ (X = Cl, Br, I), GaX ₃ (X = Cl, Br, I), Ga ₂ S, Ga ₂ O, and other compounds may be supplied to the reaction system.

This type of compound improves the solubility of GaN (very little, even in the form of very fine particles), based on the generation of ionic species that promote the transport of gallium and nitrogen. For example, a halide first attacks GaN to form a halogen complex, which is replaced with an amide, forming a complex Ga (NH ₃ ) _x ³⁺ , Ga amide, Ga imide, GaN amine, etc. It may be converted into a possible substance.

In all cases, the intermediate complex compound is decomposed into GaN and N ³⁻ (or NH ₃ ), and the nitride is deposited on the seed crystal. It is necessary to maintain a temperature gradient between them. Complex Ga (NH ₃ ) (with relatively limited stability) by controlling the temperature and pressure conditions of the vessel, taking into account the special properties of the solvent placed in the supercritical state (temperature and pressure) _It is preferable to avoid the _x ³⁺ generation region.

If the crystal growth conditions are satisfied, the intermediate species M _x GaN _y (soluble in the nitride solvent) between the raw material GaN and the additive is produced in an advantageous manner depending on the temperature gradient. Can generate chemical ionic species that can transport gallium and nitrogen. Good solubility of the intermediate compound M _x GaN _y , ie, the production of the ionic species GaN _{2 + δ} (1 + δ) 3−, which is useful for chemical transport of GaN constituents (ie Ga ³⁺ and N ³⁻ ) In order to ensure the essential solubility, the object M can be selected from all elements that increase the ionization degree of the Ga—N bond. It is advantageous if M is an alkali element, in particular lithium), in which case the precursor is Li ₃ N. Parameters affecting the transport of the chemical species of the raw material to the seed crystal are in particular the properties of the intermediate compound M _x GaN _y , the properties of the solvent, the properties of the seed crystal, the temperature gradient ΔT between the raw material and the seed crystal, These are the temperature of the raw material and the pressure value in the container 2. Intermediate compound (in this case, M is an alkali element or earth alkali element), liquid NH ₃ as a solvent, raw material temperature in the range of 100-600 ° C., pressure in the range of 5 MPa-2 GPa, and range of 10-100 ° C. If the temperature gradient is used, it is possible to synthesize a GaN single crystal having a size in the range of 10 to 100 mm (but not limited to this size). The time of the crystal growth process depends on material throughput, chemical parameters that can control material transport (solvent properties, additive or co-additive properties and amounts, temperature gradient), thermodynamic parameters (temperature and pressure) Furthermore, it depends on the size of the desired single crystal. In particular, depending on the latter parameter, a period of 1-10 weeks is required.

  Furthermore, in the present invention, a chemical reaction between GaN and at least one other compound called “precursor” can be promoted by application of ultrasonic waves. This type of compound improves the solubility of GaN based on the generation of ionic species that facilitate the transport of gallium and nitrogen from the source material to the seed crystal, but the diffusion of ionic species generated by the application of ultrasound is promoted. It is considered that the reactivity of the grain boundaries of the polycrystalline raw material is enhanced by the effect of transmitting ultrasonic waves to the atoms constituting the substance and promoting the vibration of the atoms. It is also possible to reduce the amount of the curing agent added by applying ultrasonic waves.

The GaN single crystal is a hexagonal crystal, but may have a quadrangular prism shape depending on the growth conditions. When growing as hexagonal crystals, it is necessary to select conditions for growing in the c-axis direction. Growth in the c-axis direction is achieved by doping with potassium (K) or a group 2 element. As a Group 2 element, it is achieved by doping magnesium (Mg), beryllium (Be), calcium (Ca) or the like. Doping K can be achieved by using KNH ₂ as a mineralizer. In order to dope Mg and Ca, it can be achieved by using the above Mg ₃ N ₂ , Ca ₃ N _2, etc. as mineralizers.

Further, when it is necessary to promote the growth in the a-axis direction, it is preferable to dope lithium (Li). In order to dope Li, in addition to using LiNH ₂ as a mineralizer, an embodiment using Li ₃ N as a precursor is also included. A major feature of the present invention is that the inner surface of the GaN polycrystalline nitride reaction vessel is made of an alloy containing nickel and chromium. The alloy is a nickel-chromium alloy such as MC alloy (45% by weight of chromium and 1% by weight of molybdenum) manufactured by Mitsubishi Materials, or a nickel / chromium-molybdenum alloy such as MAT21 manufactured by Mitsubishi Materials. (Chromium content is 19% by weight, molybdenum content is 19% by weight) and alloys described in JP-A-1-50936. The lower limit of the chromium content in the alloy containing nickel and chromium used in the present invention is preferably 10% by weight, more preferably 20% by weight, particularly preferably 30% by weight, and most preferably 40% by weight. The upper limit is preferably 55% by weight or less, more preferably 50% by weight or less, and particularly preferably 45% by weight or less. If the chromium content is too small, the corrosiveness tends to increase as the conditions for strong oxidizing power are reached. If the chromium content is too high, the workability tends to be inferior. Further, the chromium content in the case of the nickel-chromium-molybdenum alloy is the same as that in the case of the nickel-chromium alloy in the ratio to nickel, but the lower limit is preferable for the molybdenum content with respect to the whole alloy. Is 1% by weight or more, more preferably 5% by weight, further preferably 10% by weight, particularly preferably 15% by weight or more, and the upper limit is preferably 35% by weight or less, more preferably 30% by weight or less, and still more preferably Is 25% by weight or less, particularly preferably 20% by weight or less. If the molybdenum content is too low, the corrosivity tends to increase as the reducing power becomes stronger.If the molybdenum content is too high, not only does it exceed the solid solution limit for nickel, but also the workability tends to be poor. is there. The composition ratio of these alloys depends on the temperature / pressure conditions of the solvent in the system, the reactivity with the various mineralizers contained in the system and their reactants, and / or the oxidizing power / reducing power, pH. What is necessary is just to select suitably according to conditions. As a method of using these as a material constituting the inner surface of the reaction vessel, the reaction vessel itself may be produced using these alloys, or a method of forming a thin film as an inner cylinder and installing it in the reaction vessel, Any plating method may be applied to the inner surface of the material of the reaction vessel. The preferred composition range of the alloy containing nickel and chromium of the present invention is as described above, but the more detailed composition of the material is not limited to this, and the alloy containing nickel and chromium of the present invention has It does not prevent other metal components such as manganese, silicon, titanium, tantalum, carbon, aluminum, magnesium, calcium and the like from being included within a range that does not impair the characteristics. In the present invention, by using an alloy containing nickel and chromium as the material for the inner surface of the reaction vessel, in a reaction system using an ammonia solvent in a supercritical state, for example, NH ₄ X (X is Cl , even when using a) a halogen Br, etc., Cl ^-. it is possible to reduce the influence regarding corrosion of the neutral region by a halogen ion or the like. The use of the alloy containing nickel and chromium used in the present invention has high weldability and enables industrial production of the reactor at a lower cost than other metals having corrosion resistance, which is industrially advantageous. In this invention, the method of sealing the said reaction container inner cylinder and installing in a reaction container can also be used as needed. As described above, contamination of impurities from the reaction vessel can be suppressed. Then, if necessary, a baffle plate is installed in the container and divided into a raw material filling part filled with a raw material made of GaN polycrystalline nitride and a crystal growth part in which a GaN seed crystal is arranged. The baffle plate preferably has a porosity of 2 to 5% (excluding 5%), and the material of the surface of the baffle plate is the same as the material of the reaction vessel. preferable. Thus, by controlling the aperture ratio of the baffle plate, it becomes easy to appropriately control the degree of supersaturation of GaN in the crystal growth portion under the solution growth conditions.

  In the present invention, the raw material can be further supplied onto the baffle plate. Thus, by further interposing the raw material on the baffle plate, that is, between the raw material filling part and the seed crystal placement part, the transition speed of the crystal growth part to the supersaturated state can be increased, and the seed crystal is eluted. Various disadvantages can be prevented. In this case, the supply amount of the raw material onto the baffle plate is preferably 0.3 to 3 times the dissolution amount of GaN in the crystal growth portion.

  In the reaction vessel of the present invention, a precipitate collection net can be provided above the place where the seed crystal is placed, that is, near the convergence point of the solvent convection. The role of this deposit collection net is as follows. That is, as it goes to the upper part of the reaction vessel, the solvent convection, that is, the solute transport flow, goes to a lower temperature region, but the solute that is supersaturated in such a low temperature part is only on the seed crystal. In addition, there is a problem that the noble metal wire that suspends the seed crystal, the frame that fastens the noble metal wire, and the inner wall of the reaction vessel are deposited as precipitates. In such a case, by providing a precipitate collection net in the vicinity of the convection converging point, the remaining solute that could not be deposited on the seed crystal is inverted downward by the top inner wall, and While capturing the microcrystals or precipitates, the microcrystals can be selectively deposited on the collection net.

  The material of the collection net is preferably the same as that of the reaction vessel. Moreover, in this invention, in order to control supersaturation appropriately in this way, it is preferable to make the ratio of the crystal growth part volume with respect to raw material filling part volume into the range of 1 to 5 times. If the degree of supersaturation exceeds 1.50, the rate of precipitation on the seed crystal is too high, so that the consistency inside the grown crystal is deteriorated and defects are introduced, which is not preferable. Furthermore, since the amount deposited on the inner wall of the growth vessel and the frame increases, it is not preferable because the precipitates are enlarged and come into contact with the GaN single crystal to inhibit the growth of the single crystal.

Here, “supersaturation” refers to a state where the amount of dissolution has increased more than the saturation state, and “supersaturation degree” refers to the ratio between the amount of dissolution in the supersaturated state and the amount of dissolution in the saturated state. In the solution growth method, the ratio of the amount of GaN dissolved in the crystal growth portion that is supersaturated by the transport of GaN by thermal convection from the raw material filling portion and the amount of GaN dissolved in the saturation state of the crystal growth portion is Say.
Supersaturation = (Amount of dissolution in the supersaturated state of the crystal growth part) / (Amount of dissolution in the saturation state of the crystal growth part)
In the present invention, the degree of supersaturation can be controlled by appropriately changing / selecting the density of polycrystalline nitride, the baffle plate opening ratio, the temperature difference between the raw material filling portion and the crystal growth portion, and the like.

In the present invention, the obtained bulk single crystal can be washed with hydrochloric acid (HCl), nitric acid (HNO ₃ ) or the like. Specific embodiments for carrying out the present invention are described below, but the present invention is not limited to these methods. High purity 6N metal gallium and NH ₄ Br are put into a reactor whose inner surface is made of a nickel-chromium-molybdenum alloy, and then N ₄ is used as a solvent.
H ₃ is injected into the reactor at a filling rate of about 60%, and sealed with a cap formed of a nickel / chromium / molybdenum alloy. The reactor is installed in an electric furnace and the temperature is raised to about 500 ° C. The pressure in the reactor at this time is preferably about 350 MPa. After maintaining this state for about 120 hours, it is cooled to room temperature and the polycrystalline GaN is taken out. As a result, a predetermined amount of GaN polycrystal having a grain size of about 0.1 μm to 1.2 μm is obtained. The reactor is filled with the previously obtained GaN polycrystal, and Ga and GaN are further adjusted and added so that the hybridization rate is 10%. Next, a baffle plate made of a nickel-chromium-molybdenum alloy and having an aperture ratio of about 4% is installed, and the inside of the reactor is partitioned into a raw material filling part and a crystal growth part. Then, a plate-like GaN single crystal of about 30 mm × 50 mm cut and mirror-polished as a seed crystal in a plane perpendicular to the C-axis direction is suspended on a Pt frame in about five steps up and down so that the C-axis is directed horizontally. Is placed in the crystal growth section. A solvent composed of about 3 mol / l of KNH ₂ and NH ₃ is injected into the pressure vessel at a filling rate of about 80%, and the autoclave is sealed with a cap that is also made of a nickel / chromium / molybdenum alloy.

  The reactor was installed in an electric furnace composed of a heater divided into about 5 parts vertically, and the raw material filling part was kept at 350 ° C. while keeping the temperature of the crystal growth part always lower than the temperature of the raw material filling part. The crystal growth part is heated to about 300 ° C. The pressure in the reactor at this time is preferably about 800 MPa. After maintaining this state for about 60 days, it is cooled to room temperature and the GaN single crystal is taken out. The extracted GaN single crystal is sliced to a thickness of about 350 μm on a plane perpendicular to the C axis, and then mirror-polished with colloidal silica to obtain 50 rectangular wafers of about 30 mm × 50 mm.

It is a figure which shows the crystal growth container used for the single crystal growth manufacturing method by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 GaN polycrystal raw material 2 GaN seed crystal 3 Baffle plate 4 Frame 5 Crystal growth part 6 Raw material filling part 7 Thermocouple insertion part 7 'Thermocouple insertion part 8 Growth container 9 Noble metal wire

Claims (6)

  In a method for producing a bulk single crystal of a group 13 element nitride, a group 13 element crystal is supplied as a starting material to a raw material filling part of the reaction vessel, a seed crystal is disposed in a growing part, and ammonia Is a method of performing crystal growth by an ammonothermal method using a solvent as a solvent, and includes a step of applying an ultrasonic wave to a growing part in which a seed crystal is arranged, and a group of nitrides of a group 13 element of the periodic table characterized in that Crystal production method.   The manufacturing method according to claim 1, further comprising a step of applying an ultrasonic wave to the raw material filling portion supplied with the starting raw material.   The production method according to claim 1 or 2, wherein the starting material is two kinds of crystals having relatively different average particle diameters.   The manufacturing method according to claim 1, wherein the starting material contains polycrystalline GaN and Ga.   5. The production according to claim 1, wherein a precipitate collection net is provided in the reaction vessel in the vicinity of a converging point of a solvent convection caused by a temperature difference during crystal growth. Method.   6. The method according to claim 1, further comprising the step of producing the starting material by mixing gallium and one or more mineralizers and performing crystal growth by an ammonothermal method. The manufacturing method as described in.

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