JPH11246297A - Method for growing nitride-based compound semiconductor crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce the bulk crystal having high quality by growing the bulk crystal to hardly cause decomposition of a powdery or polycrystalline raw material, at the time of performing the growth of a bulk crystal of a nitride-based compound semiconductor such as GaN. SOLUTION: This method comprises: a stage A for once synthesizing a nitride-based compound semiconductor from a raw material system contg. at least a group III metal element and the nitrogen element; a stage C for growing a single crystal of this nitride-based compound semiconductor with the resulting synthesized nitride-based compound semiconductor as the raw material; and further, prior to the stage C, a stage B for removing hydrogen from the synthesized nitride-based compound semiconductor to be used in the stage C as the raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a nitride crystal of a group III element, in particular, a nitride compound semiconductor crystal such as GaN, AlN and InN.

[0002]

2. Description of the Related Art A nitride compound crystal of a group III element represented by GaN has recently attracted attention as a material for a blue light emitting device. However, a bulk crystal of a nitride that can be used as a substrate has not been obtained, and a crystal grown epitaxially on a sapphire substrate or the like having a different lattice constant is used.

As a method for producing a GaN crystal powder, which is a starting material for growing a GaN bulk crystal, Ga
A method of producing a Ga oxide such as ₂ O ₃ by reacting it with ammonia has been put to practical use, and a powder produced by this method is commercially available for a reagent. In addition, V
A method of synthesizing a group III-V compound by injecting a vapor of a group III element is called an injection method and is a known technique. As one type of this injection method, the present inventors have also developed a method of synthesizing GaN by injecting ammonia gas into molten metal Ga, and have applied for a patent (Japanese Patent Application No. 9-153755).

On the other hand, a method capable of easily producing a bulk crystal of a group III nitride compound has not been developed yet. For example, the following document has been published by S. Porowski et al., Because the production of crystals is dangerous and difficult because of the extremely high pressure required, the size of the obtained crystals is about several mm. small.

[0005] "Prospects for high-pressure crystal g
rowth of III-V nitrides "S.Porowski, J.Jun, P.Perlin,
I. Grzegory, H. Teisseyre and T. Suski, Inst. Phys. Conf.
Ser.No.137: Chapter 4Paper presented at the 5th SiC
and Related Materials Conf., Washington, DC, 1993 Therefore, there is a desire for a new crystal growth method that can easily grow a bulk crystal of a nitride compound semiconductor of a group III element such as GaN, which has not been obtained until now. Have been.

[0006]

However, it is difficult to grow a nitride compound semiconductor bulk crystal. The reason for this is that, despite the high melting points of these compounds, they decompose at temperatures much lower than their melting points. For example, according to the example of GaN, GaN has a melting point of 1800 ° C. or 2700 ° C. However, actually, when a conventionally obtained GaN crystal is heated, it is decomposed into metallic Ga and nitrogen gas at about 1100 ° C., and a melt of GaN cannot be obtained. This is why the melting point of GaN is not clearly known. Also, Ga
N has low solubility in various solvents, and if the solvent temperature is raised to increase the amount of dissolution, the above-described decomposition occurs, so that it is difficult to prepare a solution. Therefore, in any of the crystal growth methods such as the melt growth method, the solution growth method, and the sublimation growth method, there is no report that a practical bulk crystal has been obtained due to the problem of the decomposition.

Accordingly, an object of the present invention is to solve the above-mentioned problems, and when performing bulk crystal growth of a nitride-based compound such as GaN, the above-mentioned raw material powder or polycrystal is unlikely to be decomposed, so that high quality and high quality can be obtained. An object of the present invention is to provide a method for growing a nitride-based compound semiconductor crystal from which a bulk crystal can be obtained.

[0008]

The synthesis of a nitride compound is usually carried out in a hydrogen atmosphere for the purpose of reducing and removing an oxide in a raw material. In addition, hydrogen compounds such as ammonia, hydrazine, and monomethylhydrazine are used as a source of the group V element. Therefore, the resulting nitride-based compound powder or polycrystal contains a large amount of hydrogen atoms. On the other hand, the present inventors have found that the hydrogen atoms in the crystal have an effect of promoting the decomposition of the nitride compound.

For example, hydrogen atoms in GaN can be removed by subjecting a GaN crystal to a heat treatment in an atmosphere gas containing no hydrogen. Examination of the decomposition onset temperature of GaN synthesized by the injection method revealed that there was a difference of 300 ° C. or more between the case where hydrogen removal treatment was performed and the case where hydrogen removal treatment was not performed.

Therefore, the present invention provides a step of desorbing a hydrogen atom contained in a crystal from a nitride synthetic powder or polycrystal as a raw material prior to a bulk crystal growth step. Is difficult to decompose.

(1) A method for growing a nitride-based compound semiconductor crystal according to claim 1, wherein the nitride-based compound semiconductor is once synthesized from a system containing at least a group III metal element and a nitrogen element as raw materials. (FIG. 1A) and a step of removing hydrogen from the synthesized nitride-based compound semiconductor (FIG. 1B)
And a step of growing a single crystal of the nitride-based compound semiconductor using the nitride-based compound semiconductor obtained by removing the hydrogen as a raw material (FIG. 1C).

In this method, a nitride-based compound semiconductor is first synthesized from a system containing at least a group III metal element and a nitrogen element as raw materials, and the obtained nitride-based compound semiconductor is used as a raw material. The method for growing a single crystal of a compound-based compound semiconductor includes a step of removing hydrogen from a nitride-based compound semiconductor as a raw material prior to the single-crystal growth step. When performing bulk crystal growth, decomposition of the synthesized raw material powder or polycrystal hardly occurs, and a high-quality bulk crystal can be obtained efficiently.

(2) The essential point of the present invention is to include a step of removing hydrogen from a nitride-based compound semiconductor as a raw material prior to a single crystal growth step. It does not matter whether or not is contained in the crystal.

Therefore, a step of once synthesizing a nitride-based compound semiconductor from a raw material containing at least a group III metal element and a compound raw material containing at least a nitrogen element and a hydrogen element; The method may include a step of removing hydrogen and a step of growing a single crystal of the nitride-based compound semiconductor using the nitride-based compound semiconductor obtained by removing the hydrogen as a raw material. ). This specifies a case where the form of claim 1 is a form containing a nitrogen element and a hydrogen element in a compound raw material.

Similarly, a step of once synthesizing a nitride-based compound semiconductor from a system containing at least a group III metal element, a nitrogen element and a hydrogen element in a raw material or an atmosphere gas; The method may include a step of removing hydrogen from a semiconductor, and a step of growing a single crystal of a nitride-based compound semiconductor using a nitride-based compound semiconductor obtained by removing the hydrogen as a raw material (claim) Item 3). This is because the form of claim 1 contains II
It specifies a case where the hydrogen element is contained together with the group I metal element and the nitrogen element.

Further, the present invention relates to a method for preparing a powder or a polycrystalline nitride based on a mixture containing at least a group III metal element, a nitrogen element and a hydrogen element in a raw material or an atmosphere gas. A step of synthesizing a compound semiconductor; a step of separating a nitride-based compound semiconductor powder or polycrystal from the mixture; a step of removing hydrogen from the obtained nitride-based compound semiconductor powder or polycrystal; Growing a single crystal of the nitride-based compound semiconductor using a powder or a polycrystal of the nitride-based compound semiconductor obtained by removing the compound as a raw material. 4).

According to a third aspect of the present invention, in the first aspect, a raw material or an atmosphere gas contains a hydrogen element together with a group III metal element and a nitrogen element. Or, a case is specified in which the nitride gas is obtained in the form of powder or polycrystal of a nitride-based compound semiconductor in an atmosphere gas.

(3) In the method for growing a nitride-based compound semiconductor crystal according to claim 1, wherein the step of synthesizing the nitride-based compound semiconductor comprises heating and melting a group III metal element. Then, a gas containing a nitrogen atom is injected into the melt of the group III metal element at a temperature equal to or lower than the melting point of the nitride to be obtained, and the group III nitride microcrystals are melted in the melt of the group III metal element. (Claim 5).

In a usual injection method, a group III melt is heated to a temperature higher than the melting point of a group III-V compound, and a vapor of a group V element is injected into the group III melt. And cooling it to produce a crystal, which is one of the so-called melt growth methods, whereas the method for synthesizing nitride according to claim 5 is much lower than the melting point of the nitride to be synthesized. A nitrogen-containing gas is injected into the group III melt at a temperature, and the group III element in the liquid phase reacts with the group V element in the gas phase to form a solid group III nitride crystal in the group III melt. Is a new synthesis method that is completely different in that it directly produces (but cannot melt the nitride). This takes advantage of the fact that the solubility of the nitride in the group III element melt is extremely low, and actively utilizes it.

(4) The nitride-based compound semiconductor includes any one of AlN, GaN, and InN or a mixed crystal thereof. Ammonia or hydrazine can be used as a raw material for synthesizing the nitride-based compound semiconductor (claim 7).

(5) Claims 1, 2, 3, 4, 5, and 6
Or in the method for growing a nitride-based compound semiconductor crystal according to 7, wherein the step of removing hydrogen includes the step of heat-treating the nitride-based compound semiconductor as a raw material at a temperature of 400 ° C. or more and in an atmosphere containing no hydrogen. There is a step of applying (claim 8).

However, in the step of removing hydrogen, the step of subjecting the nitride-based compound semiconductor as a raw material to a heat treatment at a temperature of 400 ° C. or higher in a nitrogen gas stream (claim 9) A step of subjecting the nitride-based compound semiconductor to a heat treatment at a temperature of 400 ° C. or more in a vacuum.
0) a step of subjecting a nitride-based compound semiconductor as a raw material to a heat treatment at a temperature of 400 ° C. or more in an oxygen stream.
1) Or a step of irradiating a nitride-based compound semiconductor as a raw material with an electron beam in a vacuum (Claim 12).

The dehydrogenation of these nitrides can be carried out using the equipment required in the conventional crystal growth method as it is, and the desired treatment can be performed without newly adding a large-scale equipment. The effect of can be obtained. Therefore,
There is little danger of new raw material contamination. Regarding safety,
In particular, it is an excellent method that does not involve the occurrence of new dangerous work.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will now be described with reference to Ga.
An example in which an N single crystal is grown will be mainly described.

The method of growing a nitride-based compound semiconductor crystal used in this embodiment is based on a method of temporarily removing a group III metal element, a nitrogen element, and a hydrogen element from a system containing a raw material or an atmosphere gas.
Synthesizing a powdery or polycrystalline nitride-based compound semiconductor as a mixture with a group I metal raw material (raw material synthesis step);
A step of separating the nitride-based compound semiconductor powder or polycrystal from the mixture (separation step), a step of removing hydrogen from the obtained nitride-based compound semiconductor powder or polycrystal (dehydrogenation step), Growing a single crystal of the nitride-based compound semiconductor using a powder or polycrystal of the nitride-based compound semiconductor obtained by removing hydrogen as a raw material (single-crystal growth step).

(Raw Material Synthesizing Step A) Using the apparatus shown in FIG. 2, GaN microcrystals were synthesized by an injection method. Ga in a quartz crucible 1 with an inner diameter of 70 mm and a height of 150 mm
2,000 g, and Ga was heated to 950 ° C. by the heater 2 to form a Ga melt 3. Subsequently, ammonia gas was continuously blown into the Ga melt 3 at a flow rate of 0.5 l / min for 5 hours using the gas introduction pipe 4. The gas blown into the melt 3 reacted with the melt to generate GaN microcrystals, and the microcrystals floated on the melt surface. The ammonia gas that has not contributed to the reaction passes through the melt 3 as bubbles, exits into the space above the container, and is discharged out of the container through the exhaust pipe 5. The discharged ammonia gas was released to the atmosphere through a wet abatement system. After gas injection for 5 hours, the gas to be injected was switched to nitrogen, and the Ca melt was cooled to room temperature.

When the cooled Ga melt was taken out of the container and observed, a large amount of GaN microcrystals floated above the Ga melt.

(Separation step A) This GaN microcrystal and metal G
A mixture of (a) was collected, and hydrochloric acid and hydrogen peroxide solution were added thereto to dissolve only Ga, and then filtered with a piece of paper to extract only GaN microcrystals. The filtered powder was sufficiently washed with pure water, and then dried in a vacuum high-temperature bath. As a result, 61 g of an off-white GaN microcrystalline powder was obtained.

(Dehydrogenation Step B) Using the apparatus shown in FIG. 3, dehydrogenation treatment was performed on the GaN fine powder crystals obtained in the above step. A GaN microcrystalline powder 6 is placed in a quartz boat 7.
0 g was inserted, and this was inserted into the furnace tube 9. Thereafter, while flowing nitrogen gas into the furnace at a rate of 2 liters per minute through the nitrogen gas introduction pipe 11, 750
Heated to ° C. After reaching 750 ° C., it was kept in that state for 2 hours, cooled to room temperature and taken out.

(Single Crystal Growth Step C) Using the apparatus shown in FIG. 4, a single crystal of GaN was grown by sublimation using the GaN fine powder crystal subjected to the dehydrogenation treatment in the above step as a raw material. 25 g of a dehydrogenated GaN microcrystalline powder 18 as a raw material was placed in a pBN crucible 15 having a diameter of 50 mm, and this was supported in a septa 17 made of graphite and set in a stainless steel container 13. On the other hand, a 25 mm square c-plane sapphire substrate 20 is fixed to a graphite substrate holder 14, and the substrate is pB-sized so that the substrate surface faces the raw material 18.
It was suspended in the N crucible 15. In this state, the inside of the container 13 is replaced with a nitrogen gas atmosphere, and the heater 1 around the susceptor 17 is replaced.
In 6 the material was heated. Heating is done by thermocouple 1 under crucible
With the output of 9, the temperature was controlled to be 1500 ° C. At this time, the surface temperature of the substrate was about 1050 ° C. The crystal growth was performed by holding the raw materials in a heated state for 24 hours.

On the surface of the sapphire substrate taken out, several transparent hexagonal columnar single crystals of GaN were grown.
The grown crystal has a diameter of 0.5 to 12 mm and a thickness of 0.6
１．０1.0 mm. When the electrical characteristics of the grown crystal were measured by a Van der Pauw method, the carrier concentration was 2 × 10 ¹⁷ cm ⁻³ and the mobility was 490 cm ² / V · sec.
And good characteristics.

According to the above-described embodiment, the decomposition of the nitride crystal can be suppressed by a simple method. As a result, the crystal growth of the nitride-based semiconductor, which has been conventionally difficult, can be easily performed. It can be performed easily and inexpensively by a simple method.

(Comparative Example) As a comparative example, an experiment was conducted in which the GaN fine powder crystal obtained in the above-mentioned raw material synthesizing step was directly put into the crucible 15 without performing the dehydrogenation treatment, and the above-mentioned single crystal growing step was performed. As a result, the GaN microcrystalline powder entered as a raw material was completely decomposed, and only the metallic Ga remained in the crucible 15, and nothing grew on the sapphire substrate 20.

The GaN crystal, which depends on the concentration of hydrogen contained therein, starts to decompose at a temperature of 1000 ° C. or higher in the case of a crystal produced using a normal hydride of a group V element as a raw material. If there is hydrogen gas in the heating atmosphere, the decomposition start temperature will be further lowered. On the other hand, the GaN crystal subjected to the dehydrogenation treatment according to the present invention does not decompose even when heated to at least 1200 ° C., although it depends on the degree of dehydrogenation. As described in the embodiment, if dehydrogenation is sufficiently performed, it can withstand a high temperature of 1500 ° C. or more. Ga by sublimation method
In the case of crystal growth of N, sublimation of GaN starts at around 900 ° C., and the higher the temperature, the higher the vapor pressure, so that crystal growth can be performed efficiently.
Therefore, it is important how high the temperature can be heated without causing decomposition.

The above-mentioned theory can be said to be the same in liquid phase growth in which GaN is dissolved in a solvent. For example,
When GaN is dissolved in metallic Ga and GaN is grown in a liquid phase, the higher the temperature of the Ga solvent, the higher the solubility of GaN. However, conventionally, GaN was decomposed in the solvent, and the solvent could not be heated to a temperature at which practical solubility was obtained. According to the growth method of the present invention, prior to the single crystal growth step, GaN is decomposed by performing a step of desorbing hydrogen atoms contained in the crystal from a nitride synthetic powder or polycrystal as a raw material. The GaN can be heated to a temperature at which high solubility can be obtained without causing the GaN liquid phase growth.

(Other Embodiments) In the above embodiment, the case where GaN crystals are grown by sublimation has been described.
However, prior to the GaN crystal growth of the present invention, the raw material G
The method of dehydrogenating an aN powder or polycrystal to make it difficult to decompose can be applied to a liquid phase growth method or a melt growth method other than the sublimation method in the above-described embodiment.

In the case of liquid phase growth, Ga to be dissolved in a solvent is used.
If the N raw material is subjected to a dehydrogenation treatment, the solubility of GaN can be increased by heating to a high temperature without causing decomposition of GaN, and as a result, the crystal growth rate can be increased.

In the case of melt growth, by heating the dehydrogenated raw material as it is or under pressure, a GaN melt can be produced more easily than in the past. By solidifying the liquid, a bulk crystal of GaN can be obtained.

In the above, the embodiment in which a GaN single crystal was grown was described. However, the growth method according to the present invention is not limited to this, and in addition to GaN crystal growth, InN, AlN, AlGa which is a mixed crystal of these
The present invention can be applied to crystal growth of N, GaInN, and the like.

The nitride crystal obtained by the present invention can be widely applied as a semiconductor material for a light-receiving / emitting element having a short wavelength or a heat-resistant element. In particular, according to the present invention, bulk crystal growth of a nitride crystal is facilitated, and a GaN substrate, which has not been practically used, can be manufactured. as a result,
The crystallinity of the epitaxial growth layer grown on the substrate can be improved, and the device characteristics can be greatly improved. For example, an effect of greatly improving the life of a GaN-based short-wavelength laser diode can be expected.

[0041]

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

(1) The invention according to claims 1 to 4 is characterized in that, prior to the single crystal growth step of growing a single crystal using the powder or polycrystalline nitride compound semiconductor obtained in the synthesis step as a raw material, Since the method includes the step of removing hydrogen from the nitride-based compound semiconductor to become, when performing bulk crystal growth of a nitride-based compound such as GaN, decomposition of the synthesized raw material powder or polycrystal hardly occurs, High quality bulk crystals can be obtained efficiently.

(2) According to the fifth aspect of the invention, the step of synthesizing the nitride-based compound semiconductor includes heating and melting the group III metal element at a temperature lower than the melting point of the nitride to be obtained. The process consists of injecting a nitrogen-containing gas into the melt of the Group III metal element and producing Group III nitride microcrystals in the melt of the Group III metal element. In a short time, a large amount of nitride microcrystal powder can be produced (claim 5).

(3) According to the invention as set forth in claims 8 to 11, the step of removing hydrogen includes the step of removing the nitride-based compound semiconductor as a raw material at a temperature of 400 ° C. or more and in an atmosphere containing no hydrogen. Since the heat treatment is performed in a nitrogen gas stream, in a vacuum, or in an oxygen stream, hydrogen can be reliably removed. Also in the invention of claim 12, since the step of removing hydrogen is a step of irradiating the nitride-based compound semiconductor as a raw material with an electron beam in a vacuum, the hydrogen can be surely removed. .

The dehydrogenation of the nitride can be carried out by using the equipment required by the conventional crystal growth method as it is, and without using a large-scale equipment. Period effect can be obtained. Therefore, there is little danger of new raw material contamination. In terms of safety, it can be said that this is an excellent method that does not involve any new dangerous work.

(4) The growth method of the present invention (claims 1 to 1)
According to 2), the decomposition of the nitride crystal can be suppressed by a simple method. As a result, the crystal growth of the nitride-based semiconductor, which has been conventionally difficult, can be easily and easily performed by the simple method. It can be manufactured at low cost.

In particular, when the method of the present invention is applied to sublimation growth of nitride crystals, the decomposition of nitrides is suppressed, and the raw material is heated to a temperature at which a high vapor pressure can be easily obtained as compared with the conventional method. Will be able to As a result, the growth speed, controllability, reproducibility, and quality of crystal growth are dramatically improved.

When the method of the present invention is applied to the liquid crystal growth of nitride crystals, the decomposition of nitrides is suppressed, and the solution can be heated to a temperature at which high solubility can be easily obtained as compared with the prior art. become able to. As a result, the growth efficiency, controllability, reproducibility, and crystal quality are dramatically improved.

Further, when the method of the present invention is applied to the growth of a melt of nitride crystals, the decomposition of nitrides is suppressed, and a nitride melt can be easily obtained even under a lower pressure than in the prior art. . As a result, an ultrahigh-pressure crystal growth apparatus, which has been conventionally required, becomes unnecessary, and the size and cost of the crystal can be reduced.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a method for growing a nitride-based compound semiconductor crystal of the present invention.

FIG. 2 is a schematic sectional view of a GaN crystal synthesizing apparatus according to one embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a GaN crystal dehydrogenation furnace according to one embodiment of the present invention.

FIG. 4 is a schematic sectional view of a GaN single crystal growing apparatus according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Quartz crucible 2 Heater 3 Gallium melt 4 Ammonia gas injection pipe 5 Exhaust pipe 6 Thermocouple 7 Quartz boat 8 GaN microcrystal powder 9 Furnace tube 10 Heater 11 Nitrogen gas introduction pipe 12 Exhaust pipe 13 Stainless steel container 14 Graphite substrate Holder 15 pBN crucible 16 heater 17 susceptor made of graphite 18 GaN microcrystalline powder 19 thermocouple 20 sapphire substrate

Claims (12)

[Claims] A step of temporarily synthesizing a nitride-based compound semiconductor from a system containing at least a group III metal element and a nitrogen element as raw materials; and a step of removing hydrogen from the synthesized nitride-based compound semiconductor. Growing a single crystal of the nitride-based compound semiconductor using the nitride-based compound semiconductor obtained by removing the hydrogen as a raw material. 2. A raw material containing at least a Group III metal element;
From a compound raw material containing at least nitrogen element and hydrogen element,
Once, a step of synthesizing the nitride-based compound semiconductor, a step of removing hydrogen from the synthesized nitride-based compound semiconductor, and a step of nitriding using the nitride-based compound semiconductor obtained by removing the hydrogen as a raw material. Growing a single crystal of a nitride-based compound semiconductor. 3. A step of temporarily synthesizing a nitride-based compound semiconductor from a system containing at least a group III metal element, a nitrogen element, and a hydrogen element in a raw material or an atmospheric gas, and the synthesized nitride-based compound semiconductor. Removing hydrogen from hydrogen, and growing a single crystal of the nitride-based compound semiconductor using the nitride-based compound semiconductor obtained by removing the hydrogen as a raw material. A method for growing a compound semiconductor crystal. 4. A powder or polycrystalline nitride-based compound semiconductor is first synthesized as a mixture with a Group III metal raw material from a system containing at least a Group III metal element, a nitrogen element and a hydrogen element in a raw material or an atmospheric gas. And a step of separating the nitride-based compound semiconductor powder or polycrystal from the mixture, a step of removing hydrogen from the obtained nitride-based compound semiconductor powder or polycrystal, and removing this hydrogen Growing the single crystal of the nitride-based compound semiconductor using the obtained powder or polycrystal of the nitride-based compound semiconductor as a raw material. 5. The method for growing a nitride-based compound semiconductor crystal according to claim 1, wherein the step of synthesizing the nitride-based compound semiconductor comprises heating and melting a group III metal element. At a temperature equal to or lower than the melting point of the nitride to be melted, a gas containing a nitrogen atom is injected into the melt of the group III metal element,
A method for growing a nitride-based compound semiconductor crystal, comprising a step of producing a group III nitride microcrystal in a melt of a group III metal element. 6. The method for growing a nitride-based compound semiconductor crystal according to claim 1, wherein said nitride-based compound semiconductor is any one of AlN, GaN, and InN or a mixed crystal thereof. A method for growing a nitride-based compound semiconductor crystal, the method comprising: 7. The method for growing a nitride-based compound semiconductor crystal according to claim 1, wherein ammonia or hydrazine is used as a raw material for synthesizing the nitride-based compound semiconductor. A method for growing a nitride-based compound semiconductor crystal. 8. The method of growing a nitride-based compound semiconductor crystal according to claim 1, wherein the step of removing hydrogen comprises: A method for growing a nitride-based compound semiconductor crystal, comprising a step of performing a heat treatment at a temperature of not less than ° C. and in an atmosphere containing no hydrogen. 9. The method of growing a nitride-based compound semiconductor crystal according to claim 1, wherein the step of removing hydrogen comprises: A method for growing a nitride-based compound semiconductor crystal, comprising a step of performing a heat treatment at a temperature of not less than ° C. and in a nitrogen gas stream. 10. The method for growing a nitride-based compound semiconductor crystal according to claim 1, wherein the step of removing hydrogen comprises: A method for growing a nitride-based compound semiconductor crystal, comprising a step of performing a heat treatment in a vacuum at a temperature of not less than ° C. 11. The method of growing a nitride-based compound semiconductor crystal according to claim 1, wherein the step of removing hydrogen comprises: A method for growing a nitride-based compound semiconductor crystal, comprising a step of performing a heat treatment in an oxygen stream at a temperature of not less than ° C. 12. The method of growing a nitride-based compound semiconductor crystal according to claim 1, wherein the step of removing hydrogen comprises: A method for growing a nitride-based compound semiconductor crystal, which comprises a step of irradiating an electron beam in a vacuum.