JPH1160394A - Growth of nitride crystal and growth of gallium nitride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily grow a nitride crystal of a group III element such as GaN, especially a large-size bulk crystal which is not conventionally obtd. SOLUTION: The growing method of the nitride crystal includes a process to house a nitride crystal powder (source material 6) and a liquid sealing material 5 in a cylinder 7 and to heat the source material and to pressurize it with a piston 3. The GaN crystal is grown by heating a flux and GaN crystal powder under pressure to melt the GaN in the flux, then cooling to grow the GaN crystal. In this method, the flux is heated to >=800 deg.C and the flux contains at least one or more of Ga, In, Pd, Sn, Bi and Na.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a nitride crystal of a group III element, particularly a crystal of GaN, AlN, InN or the like.

[0002]

2. Description of the Related Art A method for producing a bulk crystal of a nitride crystal has not yet been established. At the research and development level, for example, the following literature has been published by S. Porowski et al. "Prospects for hig-pressure cr
ystal growth of III -V nitrides "S. Porowski, JJ
un, P. Perlin, I. Grzegory, H. Teisseyre and T. Suski In
st.Phys.Conf.Ser.No.137: Chapter4 Paper Presented at the 5th SiC and Related Materia
ls Conf., Washington, DC, 1993 This method dissolves nitrogen gas in metallic Ga under high temperature and pressure and cools it to grow a GaN crystal.
A crystal of about 5 mm has been obtained so far.

On the other hand, a method of dissolving a substance to be crystal-grown in an appropriate flux and reprecipitating the crystal to grow the crystal is applied as a flux method to the growth of an oxide crystal or the like. Recently, the following newspaper has been announced (Nikkan Kogyo Shimbun 1997.1.21). That is, “At Tohoku University, metal Ga and sodium azide powder were placed in a stainless steel tube, sealed, and then placed at 700 ° C. for 3 hours.
By heating for one day, a GaN single crystal was grown by a flux method using sodium produced by decomposition of the raw material as a flux, and the grown crystal was about 1 mm in size. On the other hand, a method of accommodating a material as a raw material in a cylinder and performing heat molding while pressurizing the material with a piston is called a hot press, and is generally used for molding ceramics and the like.

[0004]

SUMMARY OF THE INVENTION A nitride crystal of a group III element represented by GaN has attracted attention as a material for a blue light emitting device. In order to produce an element, it is necessary to epitaxially grow, for example, a GaN crystal or the like on a substrate. In this epitaxial growth, it is ideal that the lattice constant and the coefficient of thermal expansion of the crystal serving as the substrate are the same as those of the crystal grown thereon, in order to prevent the occurrence of strain in the growing crystal. However, since a large GaN crystal could not be manufactured, a sapphire substrate or the like has been used instead.

Although the development of bulk crystal growth of GaN seems to be proceeding, GaN has a very high melting point, and tends to sublimate and decompose before melting, so that semiconductors conventionally used have been used. Crystal growth methods such as
Large crystals cannot be grown, and only very small crystals of a few mm square have been obtained so far.
The situation is far from practical use.

On the other hand, in the above-mentioned hot press method, compaction molding of a nitride such as AlN is possible by using an appropriate binder, but a single crystal has not yet been grown. This is because the melting point of the nitride crystal is very high, and the nitride decomposes before the melting point is reached, and nitrogen comes out of the raw material.

The present invention solves the above-mentioned problems of the prior art and provides a nitride crystal of a group III element such as GaN, in particular,
It is an object of the present invention to propose a new crystal growth method capable of easily growing a large bulk crystal that has not been obtained.

[0008]

According to the present invention, there is provided a method for growing a nitride crystal, comprising the steps of: accommodating a nitride crystal powder and a liquid sealing material in a cylinder; I do.

Further, after a nitride melt is prepared,
The temperature may be returned to room temperature to solidify the nitride melt. Heating may be performed until just before the nitride crystal powder is melted, so that the nitride crystal is solid-phase grown. The nitride crystal powder may be pre-compacted. The starting material of the nitride is preferably a GaN crystal powder synthesized by an injection method. It is preferable that the raw material powder be placed in a vacuum or a nitrogen atmosphere at least until the liquid sealing material is melted. It is preferable to provide a temperature gradient in the nitride raw material in the cylinder. It is preferable to arrange a seed crystal on the low temperature side in the nitride raw material. It is preferable to increase / decrease the pressure and / or increase / decrease the temperature during the crystal growth. B ₂ 0 ₃ in the liquid encapsulant, KCl or NaCl can be used. When compacting nitride crystal powder,
As a binder, a constituent element of a nitride crystal can be used. When compacting the nitride crystal powder, a compound containing an OH group can be used as a binder.

According to the method of growing a GaN crystal of the present invention, the flux and the GaN crystal powder are heated under pressure to dissolve the GaN in the flux, and then cooled to grow the GaN crystal. In the method, the heating temperature of the flux is 800 ° C. or more, and the flux contains at least Ga, In, Pb, Sn, Bi, and Na.
Or any one or more of the above.

Before heating the raw material to 800 ° C. or higher,
It is preferable that the GaN crystal powder and the melted flux are sufficiently mixed so that the surface of the GaN crystal powder is completely covered with the melted flux. Raw material GaN
The crystal powder is preferably a mixture of GaN and Ga synthesized by the injection method. A temperature gradient is provided in the flux in which the raw material GaN is dissolved, and this is cooled to precipitate GaN crystals on the lower temperature side. A seed crystal is arranged in the flux, and a GaN crystal can be deposited on the seed crystal. It is preferable to float a liquid sealant on the flux. A compressed gas such as nitrogen can be used as the pressurizing means. A cylinder and a piston can be used as the pressurizing means.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for growing a nitride crystal and a method for growing a GaN crystal according to an embodiment of the present invention will be described below.

(1) The gist of one embodiment of the present invention is as follows.
When heating and pressurizing the nitride of the raw material, a liquid sealing material is used in order to prevent decomposition and sublimation of the nitride.

As a modification of the hot pressing method, HIP
(Hot isostatic pressing) method is known. This is a method in which hot pressing is performed using an appropriate pressure medium in order to uniformly apply pressure to a sample. For the pressure medium in the HIP, in order to emphasize the releasability from the sample, it is common to use another powder that does not react with the gas or the sample, and there is no effect of suppressing the decomposition and sublimation of the raw material. . This is a point different from the present invention using a liquid sealant. On the other hand, since the liquid sealant in the present embodiment also functions as a pressure medium, it is possible to pressurize the nitride raw material isotropically and grow a uniform crystal.

As a starting material of the nitride, a GaN crystal powder produced by an injection method can be used. This is because the powder produced by this method has a uniform particle size and high purity, so that when pressure is applied, the pressure is easily applied isotropically, and a uniform and high-purity crystal can be grown. . In addition, in the injection method, a large amount of GaN powder can be obtained easily and inexpensively, which is effective in reducing the production cost of GaN single crystals.

As a binder, a constituent element of a nitride crystal can be used. For example, in the case of crystal growth of GaN, it is preferable to add a small amount of metal Ga to GaN powder and mix well, and then use this as a starting material for crystal growth. This is a means for maintaining the purity of the grown crystal. In this sense, it is desirable not to use a binder containing a component that becomes an impurity.
As a binder other than the above, a binder containing an OH group can be used. A binder containing an OH group (for example, polyvinyl alcohol) is used as a liquid sealing material at a high temperature.
₂ 0 ₃ and easily absorbed in KCl, it is not easily become a source of contamination of impurities.

[0017] Liquid encapsulant, B ₂ 0 ₃ and KCl, N
The reason for using aCl is that it is stable even at high temperatures and does not react with the raw materials, cylinders and pistons.

Preferably, the raw powder is placed in a vacuum until the liquid encapsulant melts. This is because the gas existing between the powder particles of the raw material is vented and bubbles are not formed in the grown crystal or the liquid sealant. It is also preferable to place the same in nitrogen. This is because a nitrogen gas is put into the raw material powder, and this is dissolved in the raw material melt to synthesize a nitride as much as possible.

It is preferable to provide a temperature gradient in the raw material. This is because the crystal growth direction is limited to one direction from the low temperature side to the high temperature side, and a large and uniform single crystal is grown. The same purpose is applied to the case where a seed crystal is arranged on the low temperature side.

It is preferable that the height of the raw material is larger than the diameter. This is because the temperature gradient in the raw material during the crystal growth is made larger in the longitudinal direction than in the radial direction, whereby the crystal growth in the above-described one direction is more likely to occur.

It is also possible to repeatedly raise and lower the pressure and raise and lower the temperature. This precipitates nitride crystal nuclei,
This is because re-melting is caused, and large nitride single crystal grains are grown while leaving selectively dominant growth nuclei.

(2) The essential point of another embodiment of the present invention is that a powder of GaN itself is used as a raw material to be a solute in a flux method, and the surface of the raw material powder is previously fluxed so as not to be sublimated or decomposed. I covered it.

The use of crystal powder to be grown as a raw material for the flux method is apparent at first glance, and it is also a commonly used method for crystal growth of oxide crystals by the flux method. However, in the crystal growth of GaN, there has been no report that a flux method using GaN itself as a raw material has been performed so far. The reasons are as follows: first, it was difficult to prepare the GaN crystal powder itself, and it was difficult to obtain the raw material. Second, the powder raw material had low density and was easily floated on the flux, and the surface was hardly wet by the flux. As a result, it is difficult to dissolve in the flux. It is believed that increasing the particle size of the raw material powder makes it easier to dissolve it. However, at present, there is no report on how to easily obtain a GaN crystal having a large particle size.

However, recently, a powder synthesis method of GaN called an injection method has been developed. As a result of intensive studies by the present inventor on the GaN powder synthesis method, according to the present method, the GaN powder can be easily produced, and the first problem described above has been solved. In addition, in the injection method, GaN powder dispersed in metallic Ga was obtained. It was found that using this as a raw material and using Ga as a flux could solve the second problem of powder wettability. did.
Furthermore, as a result of repeated studies, methods other than the injection method,
For example, GaN powder produced by a method of reacting gallium chloride and ammonia gas at a high temperature can be suppressed to such an extent that sublimation and decomposition do not become a problem if they are mixed well with molten Ga in advance and the surface is covered with flux. all right. This effect can be obtained not only when Ga is used for the flux but also for In, Pb, Sn, Bi,
It was also observed when a flux containing at least one of Na was used.

In this embodiment, the growth of GaN at a temperature of 800 ° C. or more is performed at a temperature of 800 ° C.
This is because the mode of GaN crystal growth changes.

In other words, the amount of GaN dissolved in the flux increases as the flux temperature increases. Therefore, in order to perform crystal growth efficiently, the higher the growth temperature, the better. Since the solubility of GaN in the flux changes continuously with respect to temperature, the amount of dissolution does not change at a temperature of 800 ° C., but if the GaN crystal grows at a temperature of 800 ° C. or less, the dissolution rate becomes higher. GaN is undissolved GaN
It was found that it re-precipitated only on the powder surface and that large crystals could not be grown irrespective of the pressure and cooling time.

On the other hand, at a temperature of 800 ° C. or higher, although precipitation is observed on the undissolved powder, new crystal nuclei also grow in the low temperature portion of the flux, and consequently a clue for growing GaN single crystals greatly is obtained. I knew it could be done.

At a low temperature near 800 ° C., it is difficult to grow a large crystal, but it is not impossible if a temperature gradient is provided in the flux and the crystal is grown by the temperature difference method over a long time. .

The work of adjusting the flux to the surface of the GaN raw material powder needs to be performed at a temperature lower than 800 ° C. This is because when the temperature exceeds 800 ° C., sublimation or decomposition of GaN starts. Therefore, the material used as the flux needs to have a melting point of 800 ° C. or less.

The material used as the flux has a melting point of 8
In addition to the condition that the temperature is not higher than 00 ° C., it is necessary to select a material that can dissolve GaN and that does not react with GaN to generate another compound. For example, although aluminum or the like satisfies the former condition, it reacts with GaN to generate AlN and cannot be used as a flux. Further, the flux for growing the GaN crystal needs to be stable without being decomposed even at a high temperature enough to dissolve GaN.

As a flux, a mixture of Ga and Bi can be used. By doing so, there is an advantage that the generation density of precipitation nuclei is suppressed during the crystal growth of GaN, and the yield of single crystals is improved.

The pressurization of the flux can be performed with a compressed gas such as nitrogen. In particular, when the pressurized gas is nitrogen, decomposition and desorption of GaN dissolved in the flux can be suppressed.

In order to suppress desorption of GaN from the flux and evaporation of the flux itself, it is preferable to apply pressure after covering the surface of the flux with a liquid sealant. The type of the pressurized gas in this case is not limited as long as it reacts with the liquid sealant or the constituent materials of the device and does not cause a problem. Of course, it is also possible to pressurize mechanically with a piston or the like.

[0034]

Embodiments of the present invention will be described below.

(Example 1) As an example of the present invention, an example in which a GaN crystal was grown using an apparatus having a configuration as shown in FIG. 1 will be described. This embodiment uses a liquid sealant.

This device is assembled inside a water-cooled casing 2 made of stainless steel. A receiving stand 9 is provided on the bottom surface of the water-cooled casing 2, and a cylinder 7 is mounted on the receiving stand 9. A heater 4 and a heat insulating material 8 are provided on the outer periphery of the cylinder 7. The piston 3 is slidably fitted to the upper end of the cylinder 7. The piston 3 is moved up and down by a push rod 1 connected to a hydraulic cylinder (not shown) so as to pressurize a raw material 6 disposed in a cylinder 7. The cylinder 7, the piston 3, the pedestal 9, the heater 4, and the heat insulating material 8 are made of high-purity graphite.

The cylinder 7 has an inner diameter of 10 mm and a height of 60 m.
m as a cylindrical material, in which injection 6
10 g of the GaN crystal powder produced by the method and 2 g of B ₂ O ₃ as the liquid sealant 5 were added. GaN crystal powder and B ₂ 0
No. ₃ was sufficiently ground in a mortar to reduce the particle size, and when placed in the cylinder 7, B ₂ O ₃ was arranged so as to cover the periphery of the GaN crystal powder. Since the volume of the powdered raw material 6 is increased, it is difficult to put the whole amount in the cylinder 7 at one time. During the charging of the raw material 6, the raw material 6 is compressed by using the piston 3 and divided into several degrees. Charged.

The inside of the housing 2 of the device charged with the raw material 6 is
1 × 10 ^-2 torr via atmosphere gas replacement valve 10
Then, the pressure in the powder of the raw material 6 was released. In this state, a pressure of 4 ton / cm ² was applied to the raw material using the piston 3 and the raw material was heated to 2200 ° C. using the heater 4. After pressurizing and heating the raw material 6 for 3 hours, the heater temperature was lowered to 600 ° C. at a rate of 2 ° C./min, the pressurization at the piston 3 was released, and the sample was taken out after cooling to room temperature.

In the cylinder 7 taken out, there is a GaN single crystal having a large particle diameter, which is considered to be formed by slowly solidifying the melted GaN.
aN polycrystalline layer, and furthermore, a thin B
₂ 0 ₃ of the coating was covered. The size of the GaN single crystal grain was a hexagonal prism having a diameter of 7 mm and a height of 16 mm.

(Embodiment 2) As another embodiment of the present invention,
Using the same apparatus as in Example 1, the following GaN crystal growth was performed. This embodiment also uses a liquid sealant.

A thin coating of melted B ₂ O ₃ was prepared on the inner wall of the cylinder 7 and the end faces of the piston 3 and the pedestal 9. Next, 10 g of the GaN powder produced by the injection method and 0.5 g of metallic Ga were mixed well while heating to 30 ° C. to melt the Ga, and the mixture was compressed by a press to form a disk having a diameter of 9 mm and a height of 22 mm. Preformed into a shape. The preformed raw material 6 is set in a cylinder 7 and heated to 650 ° C. in a nitrogen atmosphere to form a liquid sealant 5.
In a state where B ₂ O ₃ was softened, a pressure of 4 ton / cm ² was applied to the raw material 6 using the piston 3. further,
In this state, the raw material was heated to 2200 ° C. and left for 3 hours. Thereafter, the raw material is cooled in the same manner as in Example 1,
A GaN single crystal having a particle size similar to that of Example 1 was obtained.

(Embodiment 3) As another embodiment of the present invention,
Using the same apparatus as in Example 1, the following GaN crystal growth was performed. This embodiment also uses a liquid sealant.

In the cylinder 7, as raw material 6, inje
10 g of the GaN crystal powder produced by the ction method and 2 g of B ₂ O ₃ as the liquid sealant 5 were added. When the GaN powder was put into the cylinder, B ₂ O ₃ was arranged so as to cover the periphery of the GaN powder.

The inside of the water-cooled casing 2 of the apparatus charged with the raw material is passed through the atmosphere gas replacement valve 10 to 1 × 10 ^-2 t.
The pressure in the powder of the raw material 6 was released by reducing the pressure to orr. In this state, using the piston 3 for the raw material, 100 ton / c
m ² , and 1900 ° C. using heater 4
Until heated. After the raw material was left for 48 hours while being pressurized and heated, the heater temperature was lowered to 600 ° C. at a rate of 20 ° C./min, the pressurization by the piston was released, and the sample was taken out after cooling to room temperature.

In the taken-out cylinder, a Ga particle having a large particle diameter, which is considered to have been formed by solid phase growth of GaN crystal grains, was used.
N single crystal are several, at its periphery there is a relatively grain size fine GaN polycrystal layer, further, the outer periphery entire thin B ₂ 0 ₃ coatings were covered. The shape of the GaN single crystal is not particularly defined, and has the largest size, about 6 mm in diameter and about 10 mm in height.

(Embodiment 4) As another embodiment of the present invention,
Using the same apparatus as in Example 1, the following GaN crystal growth was performed. This embodiment also uses a liquid sealant.

In the cylinder 7, as raw material 6, inje
10 g of the GaN crystal powder produced by the ction method and 2 g of B ₂ O ₃ as the liquid sealant 5 were added. When loading GaN powder the cylinder 7, B ₂ 0 ₃ is arranged so as to cover the periphery of the GaN powder.

The inside of the water-cooled casing 2 of the apparatus charged with the raw material is passed through the atmosphere gas replacement valve 10 to 1 × 10 ^-2 t.
The pressure in the powder of the raw material 6 was released by reducing the pressure to orr. In this state, 10 ton / cm
² and a heater 4 was used to heat to 2200 ° C. After pressurizing and heating the raw materials for 3 hours, lower the heater temperature to 2000 ° C. and leave it for 30 minutes, further reduce the pressing load to 9.5 ton / cm ² , and raise the heater temperature to 2100 ° C. for 30 minutes. After that, the heater temperature was lowered to 2000 ° C., and the pressure load was reduced to 10 ton / cm ^2.
Was repeated 5 times. Finally, the heater temperature was lowered to 600 ° C. at a rate of 2 ° C./min, the pressurization by the piston was released, and the sample was taken out after cooling to room temperature.

In the removed cylinder, the melted G
There is a GaN single crystal having a large particle diameter, which is thought to be formed by slow solidification of aN, and Ga surrounding metal Ga
Polycrystalline layer is a few of N, the outer peripheral entire thin B ₂ 0 ₃ coating had covered further. The size of the GaN single crystal grain was a hexagonal prism having a diameter of 8 mm and a height of 18 mm.

(Embodiment 5) As another embodiment of the present invention,
An example in which GaN crystal growth is performed using an apparatus having a configuration as shown in FIG. 2 will be described. This embodiment also uses a liquid sealant.

This apparatus has substantially the same configuration as the apparatus shown in FIG. 1, except that the heater for heating the raw material is divided into an upper heater 13 and a lower heater 14, and a vertical temperature gradient is provided in the raw material 6 in the figure. There is a difference in what we can do.
The pedestal 9 had a water-cooled structure in order to facilitate the temperature gradient in the raw material.

A GaN single crystal produced by the same method as in the above embodiment was shaped at the bottom of a cylinder 7 made of high-purity graphite and placed as a seed crystal 11. in addition,
As a raw material 6, 10 g of a GaN crystal powder produced by an injection method was placed. The B ₂ 0 ₃ as a liquid sealant 5 2
g, a GaN seed crystal and a powder material were arranged so as to cover the periphery thereof.

The inside of the housing 2 of the apparatus charged with the raw material is passed through the atmosphere gas replacement valve 10 to 1 × 10 ⁻² torr.
The pressure in the powder of the raw material 6 was released. In this state, a pressure of 10 ton / cm ² is applied to the raw material using the piston 3, and the upper part of the raw material is
2000 ° C. below the raw material using a heater 13
Heated. After being left in this state for 3 hours until the raw material powder is completely melted, the heater temperature was set to 1800
C. to 1600 ° C. at a rate of 0.5 ° C./min.
, The pressure with the piston was released, and the sample was taken out after cooling to room temperature.

In the removed cylinder, the melted G
There was a GaN single crystal which seems to be formed by growing aN on the seed crystal, and the entire outer periphery was covered with a thin B ₂ O ₃ film. The GaN single crystal was cylindrical with a diameter of 10 mm and a height of 20 mm.

[0055] In Examples 1-5, the liquid encapsulant, B ₂ 0 ₃ and KCl, other NaCl, Ba
Cl ₂ or CaCl ₂ can also be used.

In the above-described embodiment, the directions in which the load is applied are all vertical, but there may be variations in which the load is applied in the horizontal direction.
In addition, a modification example is considered in which the heating means is changed to induction heating instead of resistance heating, and furthermore, a plurality of heating means are used so that temperature distribution setting and temperature control during crystal growth can be finely performed. Can be The direction of the temperature gradient may be upside down or horizontal. In addition, the direction of the temperature gradient and the direction in which the load is applied do not necessarily need to match.

(Embodiment 6) As still another embodiment of the present invention, an example in which a GaN crystal is grown using an apparatus having the structure shown in FIG. 3 will be described. This embodiment uses a flux.

The present apparatus is configured such that a heat insulating material 22, a heater 23, and a susceptor 24 made of high-purity graphite are housed in a high-pressure chamber 21 made of water-cooled stainless steel.

On the bottom of a cylindrical pBN crucible 25 having an inner diameter of 50 mm and a height of 150 mm, a sapphire substrate on which GaN was epitaxially grown in advance by MOCVD as a seed crystal 28 was placed. The sapphire substrate was fixed to the bottom of the crucible so as not to float when the flux was put.

In this crucible, injcct
15 g of GaN powder synthesized by the ion method and 100 g of metal Ga as a flux were put. GaN powder and metallic Ga
Was heated to 50 ° C. to melt the metal Ga and mixed well so that the surface of the GaN powder was covered with the metal Ga.

Next, the inside of the furnace was operated to increase the pressure to 20 MPa with nitrogen gas by operating the valve 26, and the raw material 27 was heated to 1600 ° C. while maintaining this pressure. Raw material 27 is 1600
C. for 3 hours to dissolve the GaN powder in the Ga flux, then cooled the raw material temperature to 800.degree. C. at a rate of 1.degree. C./min, and then cooled rapidly to return the pressure to atmospheric pressure.

The seed crystal 28 made of the sapphire substrate having undergone the above growth step was taken out of the furnace, and the adhered Ga was washed away with hydrochloric acid. As a result, a GaN single crystal having a thickness of about 1.3 mm grew on the sapphire substrate. I was

(Embodiment 7) As another embodiment of the present invention,
An example in which GaN crystal growth was performed using an apparatus having a configuration as shown in FIG. 4 will be described. This embodiment also uses a flux.

The configuration of this apparatus is almost the same as that of the apparatus described in the sixth embodiment, except that the heater is divided into three parts, an upper heater 31, a middle heater 32 and a lower heater 33. By independently controlling the temperature, a temperature gradient can be provided in the vertical direction of the raw material 27.

At the bottom of the crucible 25, as a seed crystal 28,
A GaN single crystal produced by the method of Example 6 was placed. The seed crystal 28 was fixed to the bottom of the crucible 25 so as not to float when the flux was put. In the crucible 25, 50 g of GaN powder as a raw material 37 and 100 g of Ga and 20 g of Bi as flux were put. The GaN powder used was obtained by heating metallic Ga to 900 ° C. in an ammonia gas stream to react Ga and N, and then removing unreacted Ga with aqua regia.

The GaN powder and the flux were heated to 250 ° C. in an Ar gas atmosphere and mixed well in a state where the flux was melted, so that the surface of the GaN powder was covered with the flux.

Next, B ₂ O ₃ as a liquid sealant 29 is placed on a raw material 27 obtained by mixing a GaN powder and a flux.
Was put on 15 g. Thus, seed crystal 28, raw material 2
7. The crucible 25 charged with the liquid sealant 29 was set in the growth furnace. Then, by operating the valve 26, Ar
Heated once 700 ° C. In this a gas atmosphere B ₂
0 ₃ melted was then furnace holds a certain time in the vacuum. This is an operation for removing bubbles taken in the flux when the GaN powder and the flux are mixed. Then, around the time has passed about 45 minutes, because the foam from the B ₂ 0 ₃ is no longer come out, the inside of the furnace in Ar gas 20MPa
The heating of the raw material 27 was started while maintaining this pressure.

The temperature of the upper heater 31 was controlled at 1600.degree. C., the temperature of the middle heater 32 was controlled at 1400.degree. C., and the temperature of the lower heater 33 was controlled at 1200.degree.

In this growth, GaN dissolved in the high-temperature part becomes
It diffuses into a low-temperature part and becomes supersaturated, and GaN precipitates on a seed crystal provided in the lowest-temperature part. The reason why the growth time is longer than that in Example 6 is that it takes time to diffuse the solute in the flux. The entire amount of the charged GaN powder does not dissolve in the flux at once, and undissolved GaN is present in the flux during the growth, but since the GaN powder has a smaller density than the flux, the GaN powder has a higher density than the flux. It floats and does not adversely affect the crystal growth on the seed crystal.

After leaving for 96 hours, the temperature of each heater was set to 5 ° C.
The mixture was gradually cooled at a rate of / min for 3 hours, and then rapidly cooled to return the pressure to the atmospheric pressure.

The seed crystal 28 having undergone the above growth step was taken out of the furnace, and the attached flux was washed away with aqua regia. As a result, a GaN single crystal having a thickness of about 4 mm had grown on the seed crystal.

(Embodiment 8) As another embodiment of the present invention,
An example in which crystal growth of GaN is performed using an apparatus having a configuration as shown in FIG. This embodiment also uses a flux.

This device is assembled inside a water-cooled casing 41 made of stainless steel. At the bottom of the water-cooled housing 42,
5, and a cylinder 51 is mounted on the receiving table 45. The upper heater 4 is provided on the outer periphery of the cylinder 51.
4. A lower heater 43 and a heat insulating material 42 are provided.
A piston 50 is slidably fitted to the upper end of the cylinder 51. The piston 50 is moved up and down by a push rod 49 connected to a hydraulic cylinder (not shown) so that the raw material 47 arranged in the cylinder 51 can be pressurized. The cylinder 11, the piston 10, the upper heater 31, the lower heater 33, and the heat insulating material 2
Made of high purity graphite. Cylinder 11
Is cooled by a water-cooled pipe 52, whereby the heaters 43, 4
In addition to changing the set temperature of 4, the temperature gradient in the up-down direction can be set in the raw material 47.

At the bottom of a cylindrical cylinder 51 having an inner diameter of 10 mm and a height of 60 mm, a seed crystal 48 having a diameter of 10 m
m, a GaN single crystal formed to a thickness of 0.5 mm was placed.
In this cylinder, 15 g of a mixture of GaN powder and metal Ga synthesized by an injection method and 10 g of metal Ga as a flux were put. G synthesized by injection method
Since the mixture of the aN powder and the metal Ga is obtained as a mixture from the beginning, the work of mixing the GaN powder with Ga can be omitted. Although it is difficult to accurately determine the amount of the GaN powder contained in the mixture, the amount of the GaN powder contained in the mixture charged this time was estimated to be about 5 g from the analysis result of the sampled mixture.

The inside of the water-cooled casing 41 of the apparatus charged with the raw material is passed through a valve 46 for replacing atmospheric gas with 1 × 10 ^−2.
The pressure was reduced to torr, and gas bubbles mixed in the raw material 47 were removed. In this state, a pressure of 10 ton / cm ² was applied to the raw material using the piston 50, and the upper heater 44 was heated to 2200 ° C. and the lower heater 43 was heated to 1800 ° C. In this state, the temperature above the raw material 47 is about 210
The lower temperature was calculated to be 0 ° C and 1900 ° C. After pressurizing and heating the raw material 47 for 3 hours, the upper heater temperature is lowered to 800 ° C. and the lower heater temperature is lowered to 600 ° C. at a rate of 2 ° C./min. The sample was taken out after cooling.

In the removed cylinder, the melted G
There was a GaN single crystal having a large particle size, which is considered to be formed by slow solidification of aN, and a metal Ga layer containing a small amount of GaN powder was present around the GaN single crystal. The GaN single crystal grains had a cylindrical shape with a bulging center, a diameter of 10 mm, and a maximum height of 11 mm.

It should be noted that the crystal growth method of the present embodiment uses GaN.
In addition, the present invention can be applied to the growth of a nitride crystal other than GaN, for example, AIN or InN, or a mixed crystal thereof. In that case, the type of available flux,
Although the growth temperature changes, it is essentially the same as in the case of GaN.

[0078] Further, as the liquid sealant 29, B ₂ 0 ₃
Besides, NaCl, KCl, BaCl ₂ , CaCl _{2 and the} like can be used.

The heaters 31 and 3 serving as heating means for the raw material 47
For 2, 33, 43, and 44, a resistance heating type, an induction heating type, a radiation heating type, or the like can be used.

[0080]

As described above, according to the method of growing a nitride crystal of the present invention, it has been almost impossible
Bulk crystals of group nitrogen compounds (eg, GaN) can be manufactured in a simple manner.

As the apparatus used in the present invention, a commercially available hot press apparatus widely used for molding of ceramics and the like and an LEC generally used for crystal growth of semiconductors can be used. No equipment is required and the danger is low.

In addition to the raw materials, only a small amount of liquid sealant and flux are required, which is economical. In particular, the method using a flux is particularly economical because the flux can be repeatedly used.

By using the nitride crystal obtained by the present invention as a substrate crystal, not only high efficiency and long life of a nitride LED can be achieved, but also a nitride LD which has not yet been put to practical use. It can also be expected to promote the practical use of.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a crystal growth apparatus used in an embodiment of the present invention.

FIG. 2 is a sectional view of a crystal growing apparatus used in another embodiment of the present invention.

FIG. 3 is a sectional view showing a GaN crystal growth apparatus used in still another embodiment of the present invention.

FIG. 4 is a sectional view showing a GaN crystal growth apparatus used in still another embodiment of the present invention.

FIG. 5 is a sectional view showing a GaN crystal growth apparatus used in still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Push rod 2 Water-cooled housing 3 Piston 4 Heater 5 Liquid sealant 6 Raw material 7 Cylinder 8 Insulation material 9 Cradle 10 Atmosphere gas replacement valve 11 Seed crystal 13 Upper heater 14 Lower heater 21 High pressure chamber 22 Heat insulator 23 Heater 24 Susceptor 25 Crucible 26 Valve 27 Raw material 28 Seed crystal 29 Liquid sealant 31 Upper heater 32 Central heater 33 Lower heater 41 Water-cooled housing 42 Insulation material 43 Lower heater 44 Upper heater 45 Receiving stand 46 Valve 47 Raw material 48 Seed crystal 49 Push rod 50 Piston 51 cylinder 52 water cooling pipe

Claims (20)

[Claims] 1. A method for growing a nitride crystal, comprising the steps of: accommodating a nitride crystal powder and a liquid sealing material in a cylinder; and heating while pressurizing with a piston. 2. The method of growing a nitride crystal according to claim 1, wherein after the melt of the nitride is produced, the pressure is returned to normal pressure and room temperature to solidify the melt of the nitride. 3. The method of growing a nitride crystal according to claim 1, wherein heating is performed until immediately before the melting of the nitride crystal powder, and the nitride crystal is grown in a solid phase. 4. The method for growing a nitride crystal according to claim 1, wherein the nitride crystal powder is compacted in advance. 5. The method of growing a GaN crystal according to claim 1, wherein the starting material of the nitride is a GaN crystal powder synthesized by an injection method. 6. The method for growing a nitride crystal according to claim 1, wherein the raw material powder is placed in a vacuum or a nitrogen atmosphere at least until the liquid sealing material is melted. 7. The method for growing a nitride crystal according to claim 1, wherein a temperature gradient is provided in the nitride raw material in the cylinder. 8. The method for growing a nitride crystal according to claim 7, wherein a seed crystal is arranged on a low temperature side in the nitride raw material. 9. The method for growing a nitride crystal according to claim 1, wherein the step of raising and lowering the temperature and / or the step of raising and lowering the temperature are repeated during the crystal growth. 10. In any one of claims 1 to 3, the growth method of the nitride crystal, which is characterized by using a B ₂ 0 _3, KCl or NaCl to the liquid encapsulant. 11. The method for growing a nitride crystal according to claim 4, wherein when compacting the nitride crystal powder, a constituent element of the nitride crystal is used as a binder. 12. The method for growing a nitride crystal according to claim 4, wherein a compound containing an OH group is used as a binder when compacting the nitride crystal powder. 13. A GaN crystal growth method for heating a flux and a GaN crystal powder under pressure to dissolve GaN in a flux and then cooling the GaN to grow a GaN crystal. 800 ° C. or higher, and the flux contains at least Ga, In,
A method for growing a GaN crystal, comprising at least one of Pb, Sn, Bi, and Na. 14. The method according to claim 13, wherein the raw material is 800 ° C.
A GaN crystal growth method characterized in that the GaN crystal powder and the melted flux are sufficiently mixed so that the surface of the GaN crystal powder is completely covered with the melted flux before heating. . 15. The method for growing a GaN crystal according to claim 13, wherein the raw material GaN crystal powder is a mixture of GaN and Ga synthesized by an injection method. 16. The method according to claim 13, wherein a temperature gradient is provided in the flux in which the raw material GaN is dissolved, and the temperature is cooled to precipitate a GaN crystal on a lower temperature side.
aN crystal growth method. 17. The method for growing a GaN crystal according to claim 13, wherein a seed crystal is arranged in the flux, and the GaN crystal is deposited on the seed crystal. 18. The method for growing a GaN crystal according to claim 13, wherein a liquid sealant is floated on the flux. 19. The method of growing a GaN crystal according to claim 13, wherein a compressed gas such as nitrogen is used as the pressurizing means. 20. The method according to claim 13, wherein a cylinder and a piston are used as the pressurizing means.
N crystal growth method.