KR100419285B1 - Method of fabricating nitride crystal - Google Patents

Abstract

PURPOSE: A method for fabricating a nitride crystal is provided to enable high-purity group III nitride crystal such as of GaN to be produced easily at low cost in view of having been difficult to obtain large-sized crystal of such nitrides so far. CONSTITUTION: A group III metallic element is heated and melted. The resulting melt(3) is injected with a nitrogen atom-containing gas such as NH3 at a temperature not higher than the melting point of the aimed nitride to produce group III nitride crystallites with high wettability to the melt. The resultant mixture of the above crystallites and the melt is used as a starting material for the liquid growth process. Group III nitride powder afforded by eliminating the group III metallic element from the above mixture is used as starting material for the vapor growth process. Alternatively, a seed crystal or substrate crystal is immersed in a group III element melt such as of Ga. Bubbles of a nitrogen-containing gas such as NH3 are intermittently contacted with the surface of the above crystal to react the gas with the group III element on the surface to effect the growth of the aimed group III nitride crystal on the surface.

Description

METHODS OF FABRICATING NITRIDE CRYSTAL

The present invention relates to a method for producing nitride crystals of group III metal elements, in particular, nitride crystals such as GaN, AlN and InN, mixtures, liquid phase growth methods, nitride crystals, nitride crystal powders and vapor phase growth methods.

There is no method for producing large Group III nitride crystals such as GaN, AlN, InN, etc. easily. If a GaN bulk crystal can be produced, the effect in realizing a blue laser diode or the like is beyond imagination. In addition, bulk crystals of wide band gap semiconductor materials are expected to become full-scale in the 21st century.

As a method for producing GaN crystal powder, a method of producing GaN by reacting an oxide of Ga such as Ga ₂ O ₃ with ammonia has been put into practical use. Powders prepared by this method are commercially available for reagents.

A method for easily producing bulk crystals of group III nitride crystals has not been developed yet. See 'Prospects for high-pressure crystal growth of III-V nitrides' S. Porowski, J. Jun, P. Perlin, I. Grzygoy, H. Teisseyre and T. Suski Inst. Phys. Conf. Ser. No. 137 Chapter 4 Paper presented at the 5th SiC and Related Materials Conf., Washington, DC, 1993), but because it requires very high pressure, it is dangerous and difficult to manufacture crystals. However, the size of the obtained crystal is as small as a few mm.

The group III nitride represented by GaN has a very high melting point and sublimation and decomposition at a temperature below the melting point, so that the melt cannot be formed and crystals cannot grow from the melt. In addition, the Group III nitride has a very low solubility in the Group III melt, so that crystal growth from the solution is difficult. The crystal growth methods of Group III nitrides that have been put to practical use so far are three types of vapor epitaxial growth: HVPE (hydrogen vapor phase epitaxial growth) method, MOVPE (organic metal vapor phase epitaxial growth) method, and MBE (molecular beam epitaxial) method. Only law. In addition, GaN-based LEDs manufactured thereby are commercially available. Examples of crystal growth of GaN by the MOVPE method are described in 'Nove1 metal organic chemica1 vapor deposition system for GaN growth' S. Nakamura, Y. Harada and M. Seno, Appl. Phys. Lett. 58 (18) 6,1991) It is announced in.

Nitride crystals of group III metal elements represented by GaN have recently attracted attention as materials for blue light emitting devices. In order to manufacture a device, it is necessary to epitaxially grow a GaN crystal etc., for example on a board | substrate. In this epitaxial growth, the lattice constant and the coefficient of thermal expansion of the crystal serving as the substrate are ideal to be the same as the crystal growing on the substrate in order to prevent the occurrence of distortion in the growing crystal. However, so far no bulk crystals of nitride have been obtained which can be used as substrates. The lattice constant was substituted with another sapphire substrate or the like and epitaxially grown on the sapphire substrate.

As epitaxial growth method, MOVPE method is mainly used, but organic metal, which is a raw material, is easy to ignite, which is dangerous, expensive, and requires a large, complex and expensive growth device. Hydrogen as an impurity can not be avoided during growth crystallization, which causes this, making it difficult to increase the carrier concentration of the p-type crystal.

Therefore, in order to increase the p-type crystal carrier concentration, it is necessary to arrange the p-type dielectric layer on the surface of the device to perform nitride crystallization. Because of the need to arrange the p-type dielectric layer on the device surface, the degree of freedom in designing the device structure is low.

Another epitaxial growth method is the LPE (liquid epitaxial growth) method in which a group III nitride crystal is dissolved as a solute in a melt of a group III metal element, thereby growing a liquid epitaxial layer in a solution. However, conventionally, Group III nitride crystals, which are commercially available, are fine powders prepared by reacting Ga oxides such as Ga ₂ O ₃ with ammonia in the case of GaN, and due to their shape, the surface of the GaN crystals does not easily get wet. Therefore, there is a problem that the powder does not melt well in Ga.

The nitride crystal powder is expected to be applied as a fluorescent material or as a dopant material in liquid epitaxial growth such as GaAs and GaP. However, conventionally commercially available GaN crystal powders are expensive and low in purity, making them unsuitable as starting materials for vapor phase growth. In addition, due to its shape, it is difficult to be used as a raw material for liquid growth or a dopant raw material because it is hardly soluble in a semiconductor melt.

On the other hand, a method called hot pressing in which a raw material is put into a cylinder and pressurized with a piston while heating and molding is generally used for molding of ceramics and the like.

According to hot pressing, nitrides such as AlN can be molded under pressure using a suitable binder, but no single crystal has grown. This is because the melting point of the nitride crystal is very high, and the nitride is decomposed and nitrogen is released from the raw material before the temperature of the raw material reaches the melting point.

It is an object of the present invention to solve the problems of the prior art as described above, and to produce a nitride crystal of a high purity Group III metal element such as GaN, which can be obtained easily and at low cost, a mixture, a vapor phase growth method, To provide a nitride crystal, nitride crystal powder and vapor phase growth method.

Another object of the present invention is a novel crystal growth method capable of easily and safely growing bulk crystals of nitride crystals of group III metal elements such as GaN, which have not been obtained so far, and group III nitrides simply and safely. An object of the present invention is to provide a novel crystal growth method capable of epitaxial growth of crystals.

1 is a schematic cross-sectional view of a GaN crystal synthesis apparatus according to the first to seventh embodiments of the present invention,

2 is a schematic cross-sectional view of a GaN crystal liquid phase growth apparatus according to a second embodiment of the present invention,

3 is a graph showing a temperature program when growing a GaN crystal liquid phase according to a second embodiment of the present invention,

4 is a diagram showing the results of photoluminescence measurement of a liquid epitaxially grown undoped GaN crystal film according to a second embodiment of the present invention at room temperature,

5 is a diagram showing the results of photoluminescence measurement of a liquid epitaxially grown Si-doped GaN crystal film according to a third embodiment of the present invention at room temperature,

6 is a diagram showing the results of photoluminescence measurement of a liquid epitaxially grown Mg-doped GaN crystal film according to a fourth embodiment of the present invention at room temperature,

7 is a diagram showing the results of photoluminescence measurement of undoped GaN microcrystalline powders according to a fifth embodiment of the present invention at room temperature,

8 is a schematic cross-sectional view of a GaN crystal vapor deposition apparatus according to a sixth embodiment of the present invention.

9 is a schematic cross-sectional view of a GaN crystal growth apparatus according to an eighth embodiment of the present invention,

10 is a diagram showing the results of photoluminescence measurement of GaN crystals prepared according to the eighth embodiment of the present invention at room temperature,

11 is a schematic cross-sectional view of a GaN crystal epitaxial growth apparatus according to a ninth embodiment of the present invention,

12 is a diagram showing the results of photoluminescence measurement of GaN epitaxial growth crystals prepared according to the ninth embodiment of the present invention at room temperature,

13 is a cross-sectional view showing a crystal growth apparatus used in another embodiment of the present invention,

14 is a cross-sectional view showing a crystal growth apparatus used in another embodiment of the present invention,

15 is a cross-sectional view showing a GaN crystal growth apparatus used in still another embodiment of the present invention.

16 is a cross-sectional view showing a GaN crystal growth apparatus used in still another embodiment of the present invention,

17 is a cross-sectional view showing a GaN crystal growth apparatus used in still another embodiment of the present invention.

The first point of the present invention is broadly divided into three types.

(1) A gas containing nitrogen such as ammonia is injected into a melt of a group III metal element such as Ga and reacted. As a result, a large amount of group III nitride microcrystals appears on the surface of the melt of the group III metal element.

(2) Liquid phase epitaxial growth of group III nitride crystals is performed using a mixture of the group III metal element and the group III nitride microcrystals thus obtained as raw materials. The Group III metal element nitride microcrystals obtained by the above-described method are easily wetted by the Group III metal element melt so that the Group III metal element microcrystals can be easily dissolved in the Group III metal element melt.

(3) A gaseous growth, melting and sintered crystals of group III nitride crystals are prepared by using the group III nitride microcrystals obtained by removing the group III metal element by pickling and the like from the above mixture. The raw material obtained by this method is high purity and inexpensive.

The method of synthesizing the Group III-V compound by injecting the vapor of the Group V element into the Group III melt is a known technique called an injection method. For example, an example of synthesizing polycrystals of InP, one of group III-V compound semiconductors, is reported to the society ('mass synthesis of InP polycrystals by P-injection'), Shibata et al. 28p-Z-1).

However, the injection method heats the Group III melt above the melting point of the synthesized Group III-V compound, injects the vapor of the Group V element into a melt of the Group III-V compound, and cools the melt to produce crystals. The so-called melt growth method. In contrast, the first production method of the nitride crystal of the present invention injects a gas containing nitrogen in the Group III melt at a temperature much lower than the melting point of the nitride to be synthesized, and the liquid Group III metal element and the gaseous Group V element. Is reacted directly with the conventional implantation method in that it directly produces solid Group III nitride microcrystals in the Group III metal element solution (it cannot be formed in the melt of nitride). This advantageously takes advantage of the fact that the solubility of nitrides in Group III metal element melts is very low.

In the first manufacturing method, a nitride crystal of group III doped with an impurity can be prepared by mixing an impurity element with a group III metal element (a second production method of nitride crystal). A mixture of a group III nitride powder and a group III metal element is obtained by the first and second production methods of nitride crystals.

The mixture of group III nitride crystals and group III metal elements obtained by the first and second manufacturing methods of the nitride crystals of the present invention and the group III metal elements has a surface of which the group III metal is completely formed even though the group III nitride crystals are fine crystals. There is a big characteristic in the point wetted by an element. When crystalline fine powder is added to a raw material or a dopant for liquid phase growth, the fine powder having a large surface area relative to its volume does not wet well with the Group III melt, and thus the fine powder is not easily dissolved. In particular, in nitride crystals with low saturated solubility, low solubility is a fatal defect in crystal growth. Group III nitrides such as those conventionally marketed are mostly fine powders, and have consistently had the above-mentioned drawbacks.

In the conventional group III nitride synthesis method, an oxide or chloride of group III is used as a raw material, and thus a step of removing unreacted material from the synthesized nitride powder is necessary. The first and second manufacturing methods of the nitride crystals of the present invention, and methods for producing these and using a mixture of the group III nitride microcrystals and the group III metal elements obtained by the group III metal elements are used as starting materials. In the liquid phase growth method of group III nitride crystals, since no oxide or chloride is used as a raw material, the unreacted material does not become an impurity during liquid phase growth. Therefore, when the oxide or chloride is not used as a raw material for liquid phase growth, the mixture can be used directly as a raw material for liquid phase growth without extracting only group III nitride. If this extraction step can be omitted, not only can the process be greatly shortened, but also the contamination of the raw materials that are likely to occur in the extraction step can be eliminated, and high-purity liquid growth can be achieved.

The present invention provides a first or second method for producing nitride crystals, a mixture of group III nitride microcrystals obtained from group III metal elements, and a group III metal element, and a mixture of the group III as a starting material. Although a liquid phase growth method of nitride crystals is disclosed, the present invention can also be applied to a vapor phase growth method. That is, the invention also relates to a nitride crystal powder of Group III obtained by removing the Group III metal element from the mixture obtained by the first or second production method of the nitride crystal and the Group III metal element.

There is also provided a method for producing a group III nitride crystal by melting, resolidifying or sintering the group III nitride crystal powder and resolidifying or sintering the melt.

The second point of the present invention is to immerse the seed crystal or substrate crystal in a melt of a group III metal element such as gallium, and to contact the crystal surface intermittently with a bubble of a gas containing nitrogen such as ammonia, so that the seed crystal or substrate crystal A method of growing a nitride crystal of a group III metal element on a crystal surface by reacting a group III metal element with a gas containing nitrogen on the surface thereof.

The growth method of the nitride crystal is also injected into the Group III metal element melt at a temperature far lower than the melting point of the nitride to be synthesized, and the Group III metal element melts by reacting the liquid Group III metal element with the gaseous Group V element. It is assumed that direct generation of a solid group III-nitride crystal is impossible (a nitride melt cannot be produced from the melt of nitride). This advantageously takes advantage of the fact that the solubility of nitrides in Group III metal element melts is very low. This premise itself is a crystal growth method based on a new concept completely different from the growth method using a melt such as the above injection method.

Gases containing group III metal elements such as gallium, aluminum, and indium and nitrogen such as ammonia and hydrazine are considerably lower than the melting point of nitride (for example, GaN is said to be 2000 ° C. or higher). It is known to produce group III nitrides by reaction at a temperature of. For example, the following report ('Crystal growth of GaN by reaction between Ga and NH ₃ ' D.E1well et.al., J.Crysta1 Growth 66 (1984) 45-54).

However, the produced GaN does not dissolve in the Group III melt but only precipitates on the surface of the Group III melt.

In the third manufacturing method of nitride crystals, the seed crystals are immersed in a melt of a group III metal element such as gallium, and the bubbles of gas containing nitrogen such as ammonia are intermittently brought into contact with the crystal surface. Substrate crystals are immersed in the melt of the Group III metal element, and bubbles of gas containing nitrogen such as ammonia are intermittently brought into contact with the crystal surface. By reacting a Group III metal element with a gas containing nitrogen at the surface of the seed crystal or the substrate crystal, the Group III atoms bonded to the surface of the seed crystal or the substrate crystal can be nitrided, and the nitride crystal can be epitaxially grown on the substrate. By carrying out this reaction continuously, an epitaxial film or a bulk crystal can be grown.

In the third or fourth manufacturing method of the nitride crystal, the Group III metal element is any one of Al, Ga, and In, and the gas containing the nitrogen atom may be ammonia gas.

A method for growing nitride crystals, which is the third point of the present invention, is characterized by including a step of receiving a nitride crystal powder and a liquid sealant in a cylinder and heating the same with a piston.

After heating under pressure to form a melt of nitride, the temperature and pressure can be returned to normal pressure and room temperature to solidify the melt of nitride. In addition, the nitride crystal can be heated to the solid phase just before the melting point of the nitride crystal powder. The nitride crystal powder may be preformed under pressure. The starting material of the nitride is preferably a GaN crystal powder synthesized by the injection method. It is preferable to keep the raw material powder in a vacuum or nitrogen atmosphere until at least the liquid sealant melts. The nitride raw material in the cylinder preferably has a temperature gradient. It is preferable to arrange the seed crystal at the low temperature side of the nitride raw material. It is desirable to repeat the temperature increase and decrease and / or the pressure increase and decrease during crystal growth. When forming the nitride crystal powder under pressure, a component element of the nitride crystal can be used as the binder.

The method for growing a Group III nitride crystal of the present invention in which the flux and the Group III nitride crystal powder are heated under pressure to dissolve the Group III nitride crystal powder in the flux, and then the solution is cooled to grow the Group III nitride crystal, The heating temperature is 800 ° C. or higher, and the flux contains at least one of Ga, In, Pb, Sn, Bi, and Na.

It is preferable that the raw material of the group III nitride crystal powder and the flux is a mixture of the group III metal element and the group III nitride crystal powder synthesized by the injection method. The flux in which the raw material Group III nitride is dissolved has a temperature gradient. The solution can be cooled to precipitate group III nitride crystals on the low temperature side. The seed crystals may be disposed in the flux, and group III nitride crystals may be precipitated on the seed crystals. It is desirable to float a liquid sealant on the flux. Cylinders and pistons can be used as the pressing means.

Hereinafter, a method for growing group III nitride crystals according to another embodiment of the present invention will be described.

(1) The point of embodiment of this invention is the use of the liquid sealing agent in order to prevent decomposition | disassembly and sublimation of the said nitride when heating and pressurizing nitride which is a raw material.

As a modification of the hot press method, the HIP (high temperature isotropic press) method is known. HIP is a method of hot pressing using a suitable medium to uniformly apply pressure to a sample. Since the medium of HIP regards the releasability with the sample, it is common to use gas or other powder that does not react with the sample. The medium has no effect of suppressing decomposition or sublimation of the raw material. This point is different from the present invention using a liquid sealant. On the other hand, since the liquid sealant in the present embodiment also acts as a medium, it is possible to pressurize the nitride raw material isotropically to grow homogeneous crystals.

As a starting material of the nitride, a GaN crystal powder produced by the injection method may be used. The powder produced by this method is of high purity, fine in particle size, and uniform in size. Therefore, pressure is easily isotropically applied during pressurization, and homogeneous and high purity crystals can be grown. In addition, since the GaN powder can be obtained in large quantities easily and inexpensively in the implantation method, it is effective to reduce the manufacturing cost of the GaN single crystal.

As a binder, a member of nitride crystals 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 the GaN powder and mix well, and to grow the crystal as a starting material. This is a means to maintain the purity of the grown crystals. In this sense, it is preferable not to use a substance containing a component likely to be an impurity in the binder.

It is preferable that the raw material powder is placed under vacuum until the liquid sealant melts to remove gas existing between the powder particles of the raw material so that no bubbles are formed during growth crystallization or the liquid sealant. In order to inject nitrogen gas into the powder of a raw material, it is preferable to place a raw material powder in nitrogen. Nitrogen gas is dissolved in the raw material solution to synthesize as much nitride as possible.

The raw material preferably has a temperature gradient to grow a large, homogeneous single crystal by limiting the growth direction of the crystal in one direction from the low temperature side to the high temperature side. The same purpose is also provided when seed crystals are placed on the lower side.

It is preferable to make the height of the raw material larger than the diameter so that the temperature gradient in the raw material becomes larger in the longitudinal direction than the radial direction during the crystal growth. As a result, crystal growth in one direction is easy.

The pressure and temperature may rise and fall repeatedly to precipitate and re-melt the nuclei of nitride crystals, and optionally to grow large nitride single crystal grains, leaving a predominant growth nucleus.

(2) The point of another embodiment of the present invention is to cover each surface of the raw material powder with flux in advance so that the powder does not sublimate or decompose using the group III nitride crystal powder itself as a raw material that is a solute in the flux method.

The method of using the powder of the crystal to be grown as the raw material of the flux method seems obvious, and the flux method is generally used in oxide crystal growth. However, in the crystal growth of group III nitride, the flux method using the group III nitride crystal itself as a raw material has not been reported until now. For this reason, first, it is difficult to produce crystal powder of group III nitride, which makes it difficult to obtain raw materials. Second, powder raw materials have low density, which is easy to float on the flux, and the surface of raw materials is difficult to get wet with flux. The point which is hard to melt | dissolve in is mentioned. It is thought that the powder is easy to dissolve when the particle size of the raw material powder is large. However, no method for obtaining a Group III nitride crystal having a large particle size is reported.

However, according to the first and second production methods of the nitride crystals of the present invention, the powder of the group III nitride crystals can be easily produced, which solves the first problem described above. The second problem can also be solved by using a mixture of the group III nitride microcrystals obtained by the first or second production method of the nitride crystal and the group III metal element.

Further, as a result of repeated studies, even if a GaN powder produced by a method other than the injection method, for example, a method of reacting gallium chloride and ammonia gas at a high temperature, the GaN powder was mixed well with Ga which was previously melted, It was found that when each surface of the GaN powder was covered with flux, the sublimation or decomposition was suppressed to the extent that it was not a problem. This effect was also recognized even when Ga was used as the flux, even when a flux containing at least one of In, Pb, Sn, Bi, and Na was used.

The reason why GaN is grown at a temperature of 800 ° C. or higher in the present embodiment is that the mode of crystal growth of GaN changes at 800 ° C. as a boundary.

That is, the amount of GaN dissolved in the flux increases as the flux temperature increases. Therefore, the higher the growth temperature is, the more preferable the crystal growth is. Since the solubility of GaN in the flux varies continuously with temperature, the amount of dissolution does not change around 800 ° C. However, it was found that when GaN crystals were grown at a temperature of 800 ° C. or lower, dissolved GaN was reprecipitated only on each surface of undissolved GaN powder, and large crystals could not be grown even if the pressure or cooling time changed.

On the other hand, if the temperature is 800 ° C or higher, it is precipitated on the undissolved powder, but new crystal nuclei are also grown at the low temperature part of the flux, and as a result, GaN single crystals can be largely grown.

It is difficult to grow large crystals at low temperatures near 800 ° C, but it is not impossible if the flux has a temperature gradient and grows the crystals by the temperature difference method.

The work of wetting the surface of the GaN raw material powder with flux needs to be performed at a temperature lower than 800 占 폚. This is because the sublimation or decomposition of GaN starts when it exceeds 800 degreeC. Therefore, the material used as a flux needs to have melting | fusing point 800 degrees C or less.

For the material used as the flux, it is necessary to select a material that can dissolve GaN and not react with GaN to produce other compounds, in addition to the condition that the melting point is 800 ° C or lower. For example, when growing a GaN crystal, aluminum or the like satisfies the former condition but generates AlN by reacting with GaN, and thus cannot be used as a flux. In addition, the flux for GaN crystal growth needs to be stabilized without decomposition even at a high temperature sufficient to dissolve GaN.

As the flux, a raw material obtained by mixing Bi with Ga can be used. The raw material has the advantage that the frequency of precipitation nuclei is suppressed during the crystal growth of GaN, so that the yield of a single crystal is improved.

In order to suppress the removal of GaN from the flux and the evaporation of the flux itself, it is preferable to cover the surface of the flux with a liquid sealant and pressurize it. As the pressurized gas in this case, any kind of gas can be used as long as it has a property that does not cause a problem by reacting with the liquid sealing agent or the constituent material of the apparatus. It is apparent that the raw material can also be mechanically pressurized with a piston or the like.

<Detailed Description of the Preferred Embodiments>

Examples of the present invention are described below.

(Example 1)

As an embodiment of the present invention, the apparatus shown in Fig. 1 was fabricated. An example of synthesizing GaN microcrystals using this apparatus will be described.

Ga 3000g was filled into a quartz crucible 1 having an internal diameter of 70 mm and a height of 150 mm, and Ga was heated to 950 ° C. with a heater 2 to obtain a Ga melt 3. Ammonia gas was injected into the Ga melt 3 for 5 hours at a flow rate of 0.51 / min via the gas introduction tube 4. The gas injected into the melt 3 reacted with the melt to form GaN microcrystals. GaN microcrystals floated on the surface of the Ga melt. The ammonia gas, which did not contribute to the reaction, became a bubble, passed through the melt 3 to the upper space of the vessel, and was discharged out of the vessel through the exhaust pipe 5. The ammonia gas discharged was discharged into the atmosphere through a wet exhaust gas treatment device. After 5 hours of gas injection, the gas injected was converted to nitrogen and the Ga melt was cooled to room temperature.

The cooled Ga melt was removed from the vessel and observed. Large amounts of GaN microcrystals floated on the Ga melt. The surface of the GaN microcrystals was completely wet with Ga melt. As compared with the Ga melt before synthesis, it was found that the weight of the Ga melt increased by 10.2 g after the synthesis operation. According to the calculation based on the weight gain, 61 g of GaN microcrystals were synthesized.

(Example 2)

In a similar manner to Example 1, GaN microcrystals were synthesized. A liquid epitaxial growth of GaN was performed by a slide boat method using a mixture of Ga microcrystals floating on the surface of the Ga melt and a GaN melt as a raw material. 2 is a schematic cross-sectional view of a device used for growth. 3 shows the temperature program during liquid phase epitaxial growth. As a raw material 12, 20 g of a mixture of a Ga melt and GaN microcrystals was placed in a graphite boat 11. On the slide boat 17, a (25 × 25 mm) c-plane sapphire substrate 16 was placed. The quartz reaction tube 14 had a nitrogen gas flow atmosphere therein, and the raw material was heated by the heater 13 until the output of the thermocouple 15 became 1150 ° C. After keeping the raw material in this state for 4 hours, the temperature was lowered to 1100 ° C., the slide rod 17 was moved by pulling the operating rod 18, and the sapphire substrate 16 was brought into contact with the raw material 12. Then, the temperature of the raw material was lowered to 600 ° C. at a rate of 1 ° C. per minute, and the operating rod 18 was pushed to return the slide boat 17 to its original position to separate the substrate 16 and the raw material 12. . The heater was turned off and the raw material 12 was cooled to room temperature.

The grown substrate was taken out and the surface and the cross section were observed. A transparent film was grown on the surface of the sapphire substrate. As a result of SEM observation of the cross section, the film thickness was 4.2 탆. The photoluminescence measurement result of the growth film at room temperature is shown in FIG. 4. As shown in Fig. 4, a sharp emission peak appeared at 360 nm corresponding to GaN band edge emission, and the growth film was found to be a high quality GaN film. The electrical properties of the growth film were measured by Van der Pauw method. Desirable properties such as carrier concentration of 1 × 10 ¹⁷ cm ⁻³ and mobility of 520 cm ² / V · sec were shown.

(Example 3)

A slide boat method similar to Example 2 was carried out in a similar manner to Example 1, except that 20 mg of Si was previously added to the raw material Ga to synthesize GaN microcrystals, and a mixture of the obtained Ga melt and GaN microcrystals was used as the raw material. The liquid phase epitaxial growth of GaN was performed.

The result of having measured photoluminescence of the obtained GaN film at room temperature is shown in FIG. A sharp emission peak appeared at 369 nm corresponding to light emission of Si-doped GaN, and it was confirmed that Si was doped into the growth film. The carrier concentration of the growth film measured by Van der Pauw method was n-type 6 × 10 ¹⁸ cm ⁻³ .

(Example 4)

A slide boat method similar to Example 2 was carried out in a similar manner to Example 1, except that 7 mg of Mg was added to the raw material Ga in advance to synthesize GaN microcrystals, and a mixture of the obtained Ga melt and GaN microcrystals was used as the raw material. The liquid phase epitaxial growth of GaN was performed.

The result of photoluminescence measurement of the obtained GaN film at room temperature is shown in FIG. An emission peak appeared at 445 nm corresponding to emission of Mg-doped GaN, and it was confirmed that Mg was doped into the growth film. The carrier concentration of the growth film measured by Van der Pauw method was p-type 5 × 10 ¹⁷ cm ⁻³ . The film obtained by MOVPE growth does not activate Mg in the crystal and does not exhibit p-type electrical properties unless heat-treated, whereas the Mg-doped GaN film obtained in this manner is as-grown. Preferred p-type electrical properties have been shown in. Therefore, it can be considered that the hydrogen atom which prevents the activation of Mg is not doped.

(Example 5)

A mixture of undoped GaN microcrystals and metal Ga synthesized in a similar manner to Example 1 was taken, hydrochloric acid and hydrogen peroxide solution were added to the mixture to dissolve only Ga, and then only GaN microcrystals were filtered through a filter paper. The filtered powder was washed thoroughly with pure water and dried in a vacuum high temperature vessel. As a result, 61 g of an off-white powder was obtained. When the powder was observed under a microscope, the powder was composed of fine crystals based on hexagonal column shapes each having a grain size of about 10 μm. The result of photoluminescence measurement of this powder at room temperature is shown in FIG. A sharp emission peak appeared at 360 nm corresponding to the band edge emission of GaN, and the obtained fine crystal was found to be high quality GaN. The concentration of impurities that could be contaminated in the powder obtained was measured by secondary ion mass spectrometry (SIMS). About 5 × 10 ¹⁵ cm ⁻³ of Si, which appears to be doped from the quartz vessel, was detected, but others were below the detection limit.

(Example 6)

Using GaN microcrystalline powder obtained in Example 5 as a raw material, vapor phase epitaxial growth of GaN was performed by an apparatus as shown in FIG. As a raw material, 25 g of GaN fine crystal powder 26 was filled in a quartz crucible 23 having a diameter of 50 mm. The quartz crucible 23 was supported by a graphite susceptor 25 and placed in the quartz vessel 21. On the other hand, the c-plane sapphire substrate 28 of (25 mm × 25 mm) was fixed with the substrate holder 22 made of graphite, and suspended in the quartz crucible 23 so that the substrate surface faced the raw material 26. In this state, the inside of the quartz container 21 was replaced with ammonia gas atmosphere. The raw material was heated with heater 24 while flowing ammonia gas at 0.5 l / min. Heating was controlled so that it might become 1100 degreeC by the output of the thermocouple 27 arrange | positioned under the crucible. At this time, the surface temperature of the board | substrate 28 was about 850 degreeC. The raw material was kept in a heated state for 24 hours, and crystals were grown by sublimation.

A transparent GaN film was grown on the surface of the sapphire substrate taken out. When the surface of the GaN film was observed under a microscope, the shape of triangle to hexagon was observed. The average thickness of the growth film was about 400 μm. As a result of measuring the electrical properties of the growth film by the van der Pau method, the carrier concentration was 2 X 10 ¹⁷ cm ^-3 and the mobility was 490 cm ² / V · sec.

(Example 7)

InN was synthesized in the same manner as in Example 1 using In instead of Ga. The same conditions as in Example 1 were used except that the synthesis temperature was set at 600 ° C. The synthesized InN was cooled to 180 ° C. and a mixture of InN microcrystals and metal In floating on the In melt surface was taken out before In solidified.

Hydrochloric acid and hydrogen peroxide solution were added to dissolve only In, and then the solution was filtered through filter paper to obtain only InN microcrystals. The powder obtained by filtration was thoroughly washed with pure water and then dried in a vacuum hot container. As a result, about 200 g of pale gray-white powder was obtained. When the powder was observed under a microscope, the powder was composed of fine crystals based on hexagonal pillar shapes each having a grain size of about 8 µm. As a result of photoluminescence measurement of this powder at room temperature, an emission peak of 650 nm corresponding to the band edge emission of InN was observed.

(Variation)

In the previous examples, GaN crystal growth was mainly observed, and InN crystal growth was mentioned, but the present invention can also be applied to AlN crystals and mixed crystals of AlN or InN such as AlGaN and GaInN.

As a gas containing nitrogen, in addition to ammonia, it is possible to use hydrazine, mono methyl hydrazine, or the like.

While embodiments of liquid crystal growth under atmospheric pressure have been described, the crystal growth rate can be further increased when the crystal is grown under a high pressure atmosphere of nitrogen or ammonia.

While embodiments of liquid phase growth and vapor phase growth relating to epitaxial growth on sapphire substrates have been described, the present invention can also be applied to epitaxial growth or nitride bulk crystal growth using other substrates.

The yield and grain size of the nitride microcrystals obtained by the synthesis can be controlled by the residence time of a gas such as ammonia injected into the Group III melt. Modifications such as changing the end shape of the gas inlet tube or providing a path through which gas bubbles escape from the solution by quartz pores may be considered.

(Other embodiment)

The nitride microcrystals obtained in the present invention can be widely applied as semiconductor materials or luminescent materials. In particular, the liquid phase growth method according to the present invention is effective to apply to the production of ultraviolet-yellow light emitting device.

For example, when the raw material housing part is provided in two positions in the liquid growth apparatus described in Example 2, the Mg-doped GaN raw material is filled in one of the parts, and the Si-doped GaN is filled in the remaining parts, thereby forming a p-type. And an n-type GaN film can be continuously grown on the substrate. When the epitaxial growth substrate obtained by this method is used in the LED manufacturing process, a p-n junction type blue LED can be easily produced. According to this method, LEDs can be manufactured easier, safer, and at a lower cost than conventional MOVPE. In normal GaN growth by MOVPE, it is necessary to further heat-treat the formation of p-type crystals. Therefore, there is a limitation to design the structure of the device so that the surface of the crystal is always p-type. Using the liquid epitaxial growth method according to the present invention, since p-type conductivity is obtained without heat treatment, the tolerance in the structural design of the device can be significantly increased.

Since the nitride synthesis temperature, the atmospheric pressure, the raw material input amount, etc. depend on the type of nitride to be synthesized and the type of raw material to be used, it is difficult to determine the optimum condition unconditionally.

(Example 8)

As Example 8 of the present invention, the apparatus shown in Fig. 9 was manufactured. An example of growing a GaN crystal using this apparatus will be described.

A quartz vessel 31 having an inner diameter of 70 mm and a height of 200 mm was filled with 3000 g of molten Ga 33, and a SiC single crystal piece (6 mm X 6 mm) was attached to the end of the seed crystal support jig 34 with the seed crystal 35. It fixed in the molten Ga 33. In this state, the molten Ga 33 was heated by the heater 32 and controlled to be 1000 ° C by the output of the thermocouple 37.

Subsequently, ammonia gas was introduced from the bottom of the quartz vessel 31 for 76 hours at a rate of 0.2 l / min through the ammonia introduction tube 36 made of quartz having an internal diameter of 6 mm.

The ammonia gas introduced into the molten Ga 33 was bubbled in the melt. The number of bubbles generated was about 350 per minute. Ammonia gas bubbles generated in the melt collided with the surface of the seed crystal 35 to form GaN crystals on the seed crystal surface one after another. Unreacted ammonia gas reached the surface of molten Ga while being bubbled, and was discharged out of the container. The exhaust gas was treated with a wet scrubber and released into the atmosphere. GaN microcrystals having a diameter of several micrometers formed by reacting bubbles of ammonia gas and Ga outside the surface of the seed crystals floated on the surface of molten Ga, and did not contribute to the growth of the seed crystals.

The grown crystals were cooled and taken out of molten Ga. Metal Ga attached to the surface was washed with hydrochloric acid. As a result, a hexagonal columnar GaN crystal having a diameter of about 10 mm and a height of about 6 mm was obtained. The obtained crystals were transparent yellowish brown. The obtained crystals were confirmed to be GaN crystals by X-ray diffraction analysis. The full width at half maximum (FWHM) of the X-ray diffraction peaks was about 2 minutes. This indicates that the crystal obtained has desirable crystallinity.

10 shows the result of photoluminescence measurement of the obtained crystal at room temperature. A sharp emission peak appeared at 360 nm, corresponding to band edge emission of undoped GaN. In addition, it was confirmed by photoluminescence measurement that the obtained crystal was a high quality GaN crystal.

(Example 9)

As Example 9 of the present invention, the apparatus shown in Fig. 11 was manufactured. An example of epitaxially growing GaN crystals using this apparatus will be described.

A quartz crucible 45 having an inner diameter of 70 mm and a height of 150 mm was placed in a graphite slab 44 and installed in a stainless container 43. 3000 g of molten Ga 48 is charged into a quartz crucible 45, and a (25 mm × 25 mm) c-plane sapphire single crystal substrate (hereinafter referred to as a sapphire substrate) is attached to the end of the substrate supporting jig 47 and melted. It was immersed in Ga (48). The sapphire substrate 49 was fixed in molten Ga 48 by tilting it several degrees from the horizontal. A quartz ammonia gas inlet tube 41 bent in a J-shape was installed in the molten Ga 48. The end of the gas introduction pipe 41 was fixed to be located directly below the bottom end of the sapphire substrate 49. In this state, the molten Ga 48 was heated by the heater 42 and controlled to be 950 ° C by the output of the thermocouple 46. Then, ammonia gas was introduced into the molten Ga 48 for 1 hour at a rate of 0.1 l / min through the ammonia introduction tube 41. The introduced ammonia gas was bubbled in the melt. The number of bubbles was about 200 per minute. Bubbles of ammonia gas generated in the solution hit the lower end of the sapphire substrate 49 and were generated along the substrate surface. Then, bubbles reaching the surface of the molten Ga 48 were discharged out of the container. The exhaust gas was treated with a wet scrubber and released into the atmosphere.

The grown crystals were cooled, taken out of the molten Ga 48, and the metal Ga attached to the surface was washed with hydrochloric acid. As a result, a transparent crystalline thin film having a thickness of 4 μm was obtained on the sapphire substrate. The obtained crystals were confirmed to be GaN crystals by X-ray diffraction analysis. The full width at half maximum (FWHM) of the X-ray diffraction peaks was about 5 minutes.

Fig. 12 shows the results of photoluminescence measurement of the obtained crystals at room temperature. A sharp emission peak appeared at 360 nm corresponding to the band edge emission of undoped GaN, and it was confirmed that the obtained crystal was a high quality GaN crystal. .

Nitride crystal growth temperature, atmospheric pressure during growth, raw material input amount, etc. depend on the type of nitride to be grown and the type of raw material to be used, and thus it is difficult to determine unconditionally.

The reason for selecting ammonia as a gas containing nitrogen is a result of considering a certain degree of chemical activity, stability and economy. In theory, hydrazine gas, monomethyl hydrazine and the like can also be used. However, these gases have a greater risk of explosion than ammonia.

During crystal growth, the temperature of the group III raw material is set below the melting point of the growing nitride to prevent decomposition or remelting of the grown crystals.

(Variation)

Although the GaN crystal growth was observed in the above embodiments, the present invention can also be applied to the crystal growth of AlGaN or GaInN, which is InN, AlN or a mixed crystal of InN and AlN. Further, by doping an impurity element into a Group III melt or a gas containing nitrogen, a nitride crystal doped with impurities can be grown.

As a gas containing nitrogen, it is possible to use hydrazine, mono methyl hydrazine and the like in addition to ammonia.

In order to control the size and number of gas bubbles generated in the melt, the terminal shape of the gas inlet tube such as introducing ammonia into the Group III melt can be variously modified. For example, a plurality of bubble nozzles may be provided at the end of the gas introduction pipe, or a net may be provided at the end of the gas introduction pipe.

It is also conceivable to provide a plurality of seed crystals or a plurality of substrate crystals in the Group III melt.

1, 2, 8, 9 and 11 described only the crystal growth vessel showing the main part of the present invention, the mass flow controller and the program for controlling the flow of gas to automatically control the temperature of the heater By constructing a combined system of thermostats, it is easier to control crystal growth.

The nitride crystals obtained in the present invention can be widely applied as semiconductor materials or luminescent materials. In particular, bulk single crystals of nitride are optimal as substrate materials in the manufacture of blue laser diodes.

(Example 10)

As another embodiment of the present invention, an example of growing a GaN crystal using an apparatus configured as shown in Fig. 13 will be described. In this embodiment, a liquid sealant is used.

The apparatus is constructed in a water-cooling chamber 102 made of stainless steel. A pedestal 109 is installed on the bottom surface of the water-cooling chamber 102, and a cylinder 107 is placed on the pedestal 109. Heater 104 and heat insulator 108 are installed around cylinder 107. The piston 103 slides freely into the upper end of the cylinder 107. Since this piston 103 is moved vertically by the push rod 101 connected to the hydraulic cylinder (not shown), the raw material 106 in the cylinder 107 can be pressurized. The cylinder 107, the piston 103, the pedestal 109, the heater 104, and the heat insulator 108 are made of high purity graphite.

The cylinder 107 has an inner diameter of 10 mm and a height of 60 mm. 10 g of GaN crystal powder produced by the injection method as the raw material 106 and ₂ g of B ₂ O ₃ as the liquid sealant 105 were filled in the cylinder 107. GaN crystal powder and B ₂ O ₃ were each sufficiently ground in mortar to reduce grain size. When GaN crystal powder and B ₂ O ₃ were charged to the cylinder 107, B ₂ O ₃ was disposed so as to surround the GaN crystal powder. Since the volume of the powder raw material 106 increased, it was difficult to fill the cylinder 107 all at once. Therefore, while filling the raw material, the piston 106 was used to compress the raw material 106 while being divided into several times.

The pressure in the chamber 102 of the apparatus filled with the raw material 106 was reduced to 1 × 10 ⁻² torr through the atmospheric gas displacement valve 110, and the gas was removed from the raw powder 106. In this state, a pressure of 4 ton / cm ² was applied to the raw material using the piston 103, and the raw material was heated to 2200 ° C. using the heater 104. After pressurizing and heating the raw material 106 for 3 hours, the heater temperature was lowered to 600 ° C at a rate of 2 ° C / min, the pressurization by the piston 103 was released, the temperature was cooled to room temperature again, and the sample was taken. It was.

In the taken out cylinder 107, a large grain size GaN single crystal, which is believed to be obtained by this method of slowly solidifying molten GaN, was formed, and a GaN polycrystalline layer containing metal Ga was formed around the GaN single crystal, and B _The thin film of ₂ O ₃ covered the entire surface. GaN single grains were hexagonal columns 7 mm in diameter and 16 mm in height.

(Example 11)

As another embodiment of the present invention, the following GaN crystals were grown using the same apparatus as in Example 10. The liquid sealant was also used in this example.

The inner wall, the molten end faces of the piston 103 and the pedestal (109), B ₂ O ₃ of the cylinder 107 was prepared a thin coating device. 10 g of the GaN powder produced by the injection method and 0.5 g of the metal Ga were heated to 30 ° C., and the mixture was well mixed with Ga melted. The mixture was pressed with a press and preformed into a disk of 9 mm in diameter and 22 mm in height. The preformed raw material 106 was placed in a cylinder 107 and heated to 650 ° C. in a nitrogen atmosphere to soften B ₂ O ₃ , the liquid sealant 105. In this state, the piston 103 was used to apply pressure of 4 ton / cm ² to the raw material 106. In this state, the raw material was heated to 2200 ° C. and maintained for 3 hours. The raw material was then cooled in the same manner as in Example 10 to obtain a GaN single crystal having a grain size similar to that in Example 10.

(Example 12)

As another embodiment of the present invention, the following GaN crystals were grown using the same apparatus as in Example 10. The liquid sealant is also used in this embodiment.

As the raw material 106, 10 g of GaN crystal powder produced by the injection method and ₂ g of B ₂ O ₃ were charged into the cylinder 107 with the liquid sealant 105. When the GaN crystal powder and the B ₂ O ₃ were filled in the cylinder 107, the B ₂ O ₃ was disposed so as to surround the GaN crystal powder.

The pressure in the chamber 102 of the apparatus filled with the raw material 106 was reduced to 1 × 10 ⁻² torr through the atmospheric gas displacement valve 110, and the gas was removed from the raw material powder 106. In this state, a pressure of 100 ton / cm ² was applied to the raw material using the piston 103, and the raw material was heated to 1900 ° C. using the heater 104. After the raw material was kept in a pressurized and heated state for 48 hours, the heater temperature was lowered to 600 ° C. at a rate of 20 ° C./min, the pressurization by the piston 103 was released, and the temperature was cooled to room temperature again to take a sample. It was.

There were a few large grain size GaN single crystals that are believed to be obtained by this method of solid growth of GaN crystal grains. A relatively small grain size of GaN polycrystalline layer was around the GaN single crystal. In addition, the B ₂ O ₃ thin film covered the entire outer surface. GaN single crystals varied in shape. The largest crystals were 6 mm in diameter and about 10 mm in height.

(Example 13)

As another embodiment of the present invention, the following GaN crystal growth was carried out using the same apparatus as in Example 10. In this embodiment, a liquid sealant is also used.

As the raw material 106, 10 g of GaN crystal powder produced by the injection method and ₂ g of B ₂ O ₃ were charged into the cylinder 107 with the liquid sealant 105. When the GaN crystal powder and the B ₂ O ₃ were filled in the cylinder 107, the B ₂ O ₃ was disposed so as to surround the GaN crystal powder.

The pressure in the water-cooling chamber 102 of the apparatus filled with the raw material 106 was reduced to 1 × 10 ⁻² torr through the valve 110 for replacing the atmospheric gas, and the gas was removed from the raw powder 106. . In this state, a pressure of 10 ton / cm ² was applied to the raw material using the piston 103, and the raw material was heated to 2200 ° C. using the heater 104. After pressurizing and heating the raw material for 3 hours, the heater temperature was lowered to 2000 ° C. and left for 30 minutes. Then, the pressure load was lowered to 9.5 tons / cm ² , the heater temperature was increased to 2100 ° C., and the raw material was left for 30 minutes. The heater temperature was then reduced to 2000 ° C. and the pressurized load was increased to 10 tons / cm ² . After repeating the above cycle five times, the heater temperature was finally reduced to 600 ° C at a rate of 2 ° C / min, the pressurization by the piston was released, and the temperature was cooled to room temperature again to take a sample.

A large grain size GaN single crystal believed to be obtained by slowly solidifying molten GaN was formed in the taken out cylinder 107, and a small amount of GaN polycrystalline layer containing metal Ga was formed around the GaN single crystal, and B ₂ O ₃ The thin film covered the entire surface. GaN single grains were hexagonal columns 8 mm in diameter and 18 mm in height.

(Example 14)

As another embodiment of the present invention, the following GaN crystal growth was carried out using the apparatus shown in FIG. The liquid sealant was also used in this example.

The apparatus is similar to the apparatus shown in FIG. 13 except that the heater for heating the raw material is separated into the upper heater 113 and the lower heater 114 so that the raw material 106 has a temperature gradient in the vertical direction of the drawing. Have substantially the same configuration. Pedestal 109 has a water-cooled structure so that the raw material can easily have a temperature gradient.

A GaN single crystal provided by a method similar to that in the previous embodiment was formed and placed into the seed crystal 111 at the bottom of the cylinder 107 made of high purity graphite. On the seed crystals, 10 g of the GaN crystal powder produced by the injection method was placed as the raw material 106. B ₂ O ₃ was disposed as the liquid sealant 105 so as to surround the GaN seed crystal and the powder raw material.

The pressure in the chamber 102 of the apparatus filled with the raw material 106 was reduced to 1 × 10 ⁻² torr through the valve 110 for replacing the atmospheric gas, and the gas was removed from the raw material powder 106. In this state, the piston 103 is used to apply a pressure of 10 ton / cm ² to the raw material, the upper part of the raw material is heated to 2200 ° C. using the heater 114, and the lower part of the raw material using the heater 113. Heated to 2000 ° C. The raw material is held in this state for 3 hours until the raw material powder is completely melted, and then the upper and lower heater temperatures are lowered to 1800 ° C and 1600 ° C at a rate of 0.5 ° C / min, respectively, and then at a rate of 10 ° C / min. Furnaces were reduced to 800 ° C. and 600 ° C., respectively. The pressurization by the piston 103 was released, and the raw material was cooled to room temperature again, and the sample was taken.

A large grain size GaN single crystal believed to be obtained by slowly solidifying molten GaN was formed in the taken out cylinder 107, and a small amount of GaN polycrystalline layer containing metal Ga was formed around the GaN single crystal, and B ₂ O _Three thin films covered the entire surface. GaN single grains were 10 mm in diameter and 20 mm in height.

In each of Examples 10 to 14, in addition to B ₂ O ₃ , KCl and NaCl, BaCl ₂ , CaCl _2, and the like may also be used as the liquid sealing material.

In the previous embodiment, the direction of applying the load was in the vertical direction, but a modification of applying the load in the horizontal direction is also possible. Modifications such as changing resistance heating as heating means into induction heating, setting a fine temperature distribution, and using a plurality of heating means to control the temperature at the time of crystal growth can also be considered. The direction of the temperature gradient may be a vertical direction or a horizontal direction. The direction of the temperature gradient and the direction of application of the load do not always have to coincide.

(Example 15)

As another embodiment of the present invention, an example of growing a GaN crystal using a system having the configuration shown in FIG. 15 will be described. In this embodiment, flux is used.

In the present system, high purity graphite insulation 122, heater 123 and receptor 124 are housed in a stainless steel water-cooled high pressure chamber 121.

At the bottom of the cylindrical pBN crucible 125 having an inner diameter of 50 mm and a height of 150 mm, a sapphire substrate having GaN previously epitaxially grown by MOCVD was disposed as the seed crystal 128. A sapphire substrate was placed so as not to float when the flux was charged. Fixed to the crucible bottom.

As the raw material 127, 15 g of the GaN powder synthesized by the injection method and 100 g of the metal Ga as the flux were filled in the crucible. The GaN powder and the metal Ga were heated to 50 ° C. to mix well in the state where the metal Ga was melted, so that the metal Ga covered the surface of each GaN powder.

The valve 126 was operated to increase the pressure of the furnace to 20 Mpa with nitrogen gas. While maintaining the pressure, the temperature of the raw material 127 was increased to 1600 ° C. The raw material 127 was kept at 1600 ° C. for 3 hours, the GaN powder was dissolved in Ga flux, the raw material temperature was reduced to 800 ° C. at a rate of 1 ° C./min, the material was quenched, and the pressure was returned to atmospheric pressure. Turned.

In the growth process, a sapphire substrate provided as seed crystals 128 was taken out of the furnace and the attached Ga was washed with hydrochloric acid. GaN single crystals with a thickness of about 1.3 mm were grown on the sapphire substrate.

(Example 16)

As another embodiment of the present invention, an example in which GaN crystals are grown using the system having the configuration shown in FIG. 16 will be described. Flux is also used in this embodiment.

The configuration of the system is substantially the same as that of the system described in Example 15, except that three heaters, the upper heater 131, the central heater 132, and the lower heater 133, are used instead of only one heater. same. The heaters independently control the temperature so that the raw material 127 can have a temperature gradient in the vertical direction.

The GaN single crystal produced by the method of Example 15 was placed as seed crystal 128 at the bottom of the crucible 125. The seed crystal 128 is fixed to the bottom of the crucible 125 so that it does not rise when the flux is charged. 50 g of GaN powder as the raw material 137 and 20 g of Ga and 20 g of Bi as the flux were charged into the crucible 125. A GaN powder obtained by heating metal Ga to 900 ° C. in an ammonia gas stream to react Ga with N and removing unreacted Ga with aqua regia was used.

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

Subsequently, 15 g of B ₂ O ₃ was placed as a liquid sealing agent 129 on the raw material 127 obtained by mixing GaN powder and flux. Thus, the crucible 125 filled with the seed crystal 128, the raw material 127, and the liquid sealing agent 129 was arrange | positioned in the growth furnace. Then, the valve 126 was operated to supply the Ar gas atmosphere. The raw material was once heated to 700 ° C. to melt B ₂ O ₃ , and then the inside of the furnace was kept in vacuum for a certain time. This is an operation for removing the air bubbles entering the flux when the GaN powder and the flux are mixed. After about 45 minutes had elapsed, bubbles no longer emerged from B ₂ O ₃ , and the furnace was elevated to 20 MPa with Ar gas. The raw material 137 was heated while maintaining this pressure.

The temperature of the upper heater 131 was 1600 degreeC, the temperature of the middle heater 132 was 1400 degreeC, and the temperature of the lower heater 133 was controlled to 1200 degreeC, and it was left to stand for 96 hours.

In the main growth, GaN melted in the hot portion diffused in the low temperature portion and became supersaturated, and GaN precipitated on the seed crystal disposed at the lowest temperature portion. The growth time is longer than that of Example 15 because the solute diffusion in the flux takes time. The filled GaN powder did not dissolve in the flux all at once. GaN decomposed during growth is present in the flux, but because the GaN powder is less dense than the flux, it floats above the flux and does not adversely affect the crystal growth on the seed crystals.

After maintaining this state for 96 hours, each heater temperature was reduced for 3 hours at a rate of 5 DEG C / min, and then the raw materials were quenched. The pressure returned to atmospheric pressure.

The seed crystals 128 subjected to the growth process were removed from the furnace, and the attached flux was washed with aqua regia. GaN single crystals having a thickness of about 4 mm were grown on the seed crystals.

(Example 17)

As another embodiment of the present invention, an example in which GaN crystals are grown using a system having a configuration as shown in FIG. 17 will be described. Flux is also used in this embodiment.

The system is constructed inside a stainless steel water-cooling chamber 141. A pedestal 145 is installed on the bottom surface of the water-cooling chamber 141, and a cylinder 151 is placed on the pedestal 145. An upper heater 144, a lower heater 143, and a heat insulating material 142 are provided on the outer circumference of the cylinder 151. On the upper end of the cylinder 151, the piston 150 is fitted with sliding freely. The piston 150 moves vertically by the push rod 149 connected to the hydraulic cylinder (not shown), and can pressurize the raw material 147 disposed in the cylinder 151. In addition, the cylinder 151, the piston 150, the upper heater 144, the lower heater 143, and the heat insulating material 142 are made of high purity graphite. The pedestal 145 on which the cylinder 151 is placed is made of water-. The cooling tube 152 allows water-cooling, thereby changing the set temperatures of the heaters 143 and 144 and setting the temperature gradient in the vertical direction of the raw material 147.

At the bottom of the cylinder 151 having an inner diameter of 10 mm and a height of 60 mm, a GaN single crystal having a diameter of 10 mm and a thickness of 0.5 mm was placed as the seed crystal 148. In this cylinder 151, 15 g of a mixture of GaN powder and metal Ga synthesized by the injection method and 10 g of metal Ga as flux were placed. Since the mixture of the GaN powder and metal Ga synthesize | combined by the injection method is obtained as a mixture from the beginning, the effort which mixes GaN powder with Ga can be saved. It is difficult to accurately determine the amount of GaN powder contained in the mixture. The amount of GaN powder contained in the mixture thus filled was estimated to be about 5 g when the sampled mixture was analyzed.

The pressure in the water-cooling chamber 141 of the apparatus filled with the raw material was reduced to 1 × 10 ⁻² torr via the atmospheric gas replacement valve 146 to remove bubbles of gas mixed in the raw material 147. In this state, a pressure of 10 ton / cm ² was applied to the raw materials using the piston 150, and the upper heater 144 was heated to 2200 ° C., and the lower heater 143 was heated to 1800 ° C. In this state, the temperature above the raw material 147 was calculated to be about 2100 ° C., and the temperature below it was 1900 ° C. After pressurizing and heating the raw material 147 for 3 hours, the upper heater temperature was lowered to 800 ° C. and the lower heater temperature to 600 ° C. at a rate of 2 ° C./min, respectively, and the pressure was released by the piston 150, and then cooled to room temperature. The sample was taken out.

Inside the removed cylinder there was a large grain size GaN single crystal believed to be obtained by the method of slowly solidifying molten GaN, and around the crystal was a layer of metallic Ga containing a small amount of GaN powder. The GaN single crystal grain was 10 mm in diameter with a maximum height of 11 mm in the form of a columnar bulge.

In addition, the crystal growth method of the present embodiment can be applied not only to GaN but also to growth of nitride crystals other than GaN, for example, AIN, InN, or a mixed crystal thereof. In this case, the kind of flux that can be used and the growth temperature may be different, but are substantially the same as in the case of GaN.

As the liquid sealing agent 129, in addition to B ₂ O ₃ , NaCl, KCl, BaCl ₂ , CaCl ₂ , or the like may be used.

The heaters 131, 132, 133, 143, and 144, which are heating means for the raw material 147, may use resistance heating, induction heating, radiant heating, or the like.

As described above, according to the present invention, the following excellent effects can be obtained.

(1) According to the first and second production methods of nitride crystals, a nitrogen-containing gas is injected into the Group III melt at a temperature much lower than the melting point of the nitride to be synthesized, and the liquid Group III metal element and the gas phase V Group elements are reacted with each other to directly generate solid group III nitride crystals in the group III metal element melt. Therefore, a large amount of crystals can be produced in a short time easily and inexpensively with a simple apparatus as compared with the case of making a melt of nitride.

(2) Nitride crystals of the Group III nitride microcrystals and Group III metal elements obtained by the first or second production method of the nitride crystals of the present invention and the Group III metal elements are formed because the nitride microcrystals are synthesized in the Group III melt. The microcrystalline surface is completely covered with group III metal elements. When the mixture is used for the liquid growth raw material, the mixture is very easily dissolved and a saturated solution can be easily obtained as compared with the conventional raw materials. As a result, the controllability and reproducibility of epitaxial growth are greatly improved.

(3) The first or second manufacturing method of the nitride crystals of the present invention and a mixture of group III nitride microcrystals obtained by group III metal elements and group III metal elements are used as starting materials, or the first or second Group III nitride characterized in that the Group III nitride crystal powder obtained by removing the Group III metal element from the mixture obtained by the second production method is used as a starting material, or the Group III nitride crystal powder is dissolved, resolidified or sintered. According to the crystal growth method, a high purity nitride semiconductor crystal of group III can be easily and inexpensively produced in large quantities in a short time. In addition, this method is safe because there is no need to use dangerous raw materials such as gas such as hydrochloric acid, which has been conventionally used by the HVPE method, and organic metals used by the MOVPE method. According to the growth method of the present invention, liquid phase growth and vapor phase growth of nitride crystals, which are particularly difficult in the past, can be easily performed. As a result, it is easy to manufacture an element having a p-type crystal having a high carrier concentration even without performing special treatment on the nitride crystal. Since there is no need to arrange the p-type conductive layer on the device surface, the degree of freedom in designing the device structure is increased.

(4) In addition, in the nitride growth method of the above (3), since the oxides and chlorides as in the prior art are not used as raw materials, the unreacted material does not become impurities during liquid phase growth. Thus, the mixture can be used directly as a raw material for liquid growth without the need to extract only group III nitrides. Since this extraction step can be omitted, not only can the process be significantly shortened, but also contamination of the raw materials that are likely to occur in the extraction step can be eliminated, and high-purity liquid phase growth is possible.

(5) further, immersing the seed crystals in the Group III metal element melt heated to a temperature below the melting point of the nitride to be obtained of the present invention; Contacting the seed crystal surface intermittently with a bubble of a gas containing a nitrogen atom in a Group III metal element; A method for producing a nitride crystal comprising the step of growing a nitride crystal of a group III metal element on the seed crystal surface, or a substrate crystal in a group III metal element heated and melted at a temperature below the melting point of the nitride to be obtained. Immersing and intermittently contacting the substrate crystal surface with a bubble of a gas containing a nitrogen atom in the Group III metal element to epitaxially grow a nitride single crystal of Group III metal element on the substrate crystal surface. According to the method for producing a nitride crystal, a group III nitride semiconductor crystal, particularly a bulk single crystal that cannot be grown conventionally, can be grown. When this crystal is used as a substrate, it is not only effective for increasing the efficiency and long life of the blue LED, but also greatly contributing to the commercialization of the blue LD, which has not yet been put to practical use. Such group III nitride semiconductor crystals can be easily and inexpensively grown in a simple apparatus. In addition, there is no need to use dangerous raw materials such as gas such as chlorine, which is conventionally used by the HVPE method, and organic metals, which are used by the MOVPE method.

A nitride crystal growth method comprising the step of filling a nitride crystal powder and a liquid sealant into a cylinder of the present invention and heating the raw material with a piston, or heating the flux and the nitride crystal powder under pressure, and According to a method of growing a nitride crystal, such as a nitride crystal growing method, the method of dissolving in flux and cooling the mixture to grow nitride crystals, wherein the heating temperature of the flux is 800 ° C or higher. Bulk crystals of nearby group III nitride compounds (eg GaN) can be produced by a simple method.

The apparatus used in the present invention can use a commercially available hot press apparatus which is widely used for molding ceramics or LEC which is generally used for crystal growth of semiconductors. Therefore, a special apparatus is unnecessary and there is little risk.

It is also economical because only a small amount of liquid sealant or flux is required in addition to the raw material. In particular, the flux method 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 can the efficiency of the nitride-based LED be increased and the lifespan can be extended, but also the effect of promoting the practical use of the nitride LD which has not been put to practical use can also be expected.

Claims (4)

Immersing the seed crystals in the Group III metal element melt heated to a temperature below the melting point of the nitride to be obtained; Intermittently contacting the seed crystal surface with bubbles of a gas containing a nitrogen atom in a Group III metal element; And Thereby continuously growing nitride crystals of the Group III metal element on the seed crystal surface. The method of producing a nitride crystal according to claim 1, wherein the Group III metal element is Al, Ga, or In, and the gas raw material containing the nitrogen atom is ammonia gas. Immersing the substrate crystal in a Group III metal element heated and melted to a temperature below the melting point of the nitride to be obtained; Intermittently contacting the substrate crystal surface with a bubble of a gas containing a nitrogen atom in a Group III metal element; And Thereby epitaxially growing a nitride single crystal of a Group III metal element on the substrate crystal surface. The method for producing nitride crystals according to claim 3, wherein the Group III metal element is Al, Ga or In, and the gas raw material containing the nitrogen atom is ammonia gas.