JP3533938B2 - Method for producing nitride crystal, mixture, liquid phase growth method, nitride crystal, nitride crystal powder, and vapor phase growth method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a nitride crystal of a group III element, particularly a nitride crystal such as GaN, AlN, InN, etc., a mixture, a liquid phase growth method, a nitride crystal, a nitride crystal powder, And a vapor phase growth method.

[0002]

2. Description of the Related Art GaN, AlN, InN
There is no method capable of easily producing a large group III nitride crystal such as. If a GaN bulk crystal is created, its impact is immeasurable for realizing a blue laser diode and the like. In addition, bulk crystals of wide-cap semiconductor materials are expected to be in full swing in the 21st century.

As a method of producing a GaN crystal powder, a method of producing an oxide of Ga such as Ga ₂ O ₃ by reacting with ammonia has been put into practical use, and the powder produced by this is used as a reagent. Commercially available.

A method capable of easily producing a bulk crystal of a group III nitride crystal has not been developed yet. Although S. Porowski et al. Published the following document, the size of the obtained crystal was several mm despite the fact that the production of the crystal was dangerous and difficult because it required a very high pressure.
Small and small.

"Prospects for high-pressure crystal
growth of III-V nitrides ”S.porowski, J.Jun, P.Perli
n, I.Grzegory, H.Teisseyre and T.SuskiInst.Phys.Con
f.Ser.No.137: Chapter 4Paper presented at the 5th
SiC and Related Materials Conf., Washington, DC, l99
Group III nitrides typified by 3 GaN have a very high melting point, and sublimation and decomposition occur at a temperature below the melting point, so that a melt cannot be produced and crystal growth from the melt is impossible. Further, since the solubility in the group III melt is very low, it is difficult to grow crystals from the solution. The Group III nitride crystal growth methods that have been put to practical use so far are HVPE (hydride vapor phase epitaxy) and MOVPE (metalorganic vapor phase epitaxy).
Method and MBE (Molecular Beam Epitaxy) method. In addition, the GaN-based LED thus manufactured has been put on the market. MO
The following documents have been published as examples of crystal growth of GaN by the VPE method.

[Novel metalorganic chemical vapor de
position system for GaN growth ”S. Nakamura, Y. Hara
da and M. Seno, Appl.Phys.Lett.58 (18) 6, l991

[0007]

[Problems to be Solved by the Invention] II represented by GaN
In recent years, group I nitride crystals have been attracting attention as a material for blue light emitting devices. In order to create a device, it is necessary to epitaxially grow a GaN crystal or the like on the substrate. In this epitaxial growth, it is imperative that the lattice constant and the coefficient of thermal expansion of the substrate crystal be the same as those of the crystal grown thereon in order to prevent the occurrence of strain in the growing crystal. However, a bulk crystal of nitride that can be used as a substrate has not been obtained so far, and a sapphire substrate or the like having a different lattice constant has been used as a substitute, and epitaxial growth has been performed on it.

The epitaxial growth method is currently MO
Although the VPE method is the mainstream,
It is easy to catch fire, dangerous, and expensive. In addition, it requires large, complex and expensive growth equipment. It is inevitable that hydrogen will enter the grown crystal as an impurity, which causes a problem that it is difficult to increase the carrier of the p-type crystal.

Therefore, in order to make the p-type crystal have a high carrier, it is necessary to bring the p-type dielectric layer to the surface of the device and perform the nitride crystal treatment. Since it was necessary to bring the p-type dielectric layer to the surface of the device, the degree of freedom in designing the device structure was narrow.

As another epitaxial growth method, a group III nitride crystal is dissolved as a solute in a solvent of the group III element, and L
There is a method of PE (liquid phase epitaxial) growth. However, the group III nitride crystals that have hitherto been commercially available are fine powders produced by reacting Ga oxides such as Ga ₂ O ₃ with ammonia in the case of GaN. There is a problem in that the surface of is difficult to get wet with Ga and is therefore difficult to dissolve in Ga.

The powder of the nitride crystal is used as a fluorescent material,
Application is expected as a dopant material in liquid phase epitaxial growth of GaAs, GaP, etc. However, the GaN crystal powder that has hitherto been commercially available has a low purity in spite of its high price, and is not suitable as a starting material for vapor phase growth. Also, due to its shape, it is difficult to dissolve in the semiconductor melt,
There is a problem that it is difficult to use as a raw material for liquid phase growth or a dopant raw material.

The object of the present invention is to solve the above-mentioned problems of the prior art and to provide a novel nitride crystal which can easily and inexpensively obtain a high-purity group III element nitride crystal such as GaN. Manufacturing method, mixture, vapor phase growth method, nitride crystal,
It is to propose a nitride crystal powder and a vapor phase growth method.

Another object of the present invention is to provide a novel crystal growth method capable of easily growing a bulk crystal of a group III element nitride crystal such as GaN, which has not been obtained so far, and a simple method. Another object of the present invention is to propose a new crystal growth method capable of safely performing group III nitride crystal epitaxial growth.

[0014]

The first essential point of the present invention is as follows.
There are three main types.

A nitrogen-containing gas such as ammonia is injected into a melt of a Group III element such as Ga at a high temperature to cause a reaction. As a result, a large amount of group III nitride fine crystals float in the melt of the group III element.

Liquid-phase epitaxial growth of Group III nitride crystals is performed using the mixture of Group III elements and Group III nitride microcrystals thus obtained as a raw material. The Group III element nitride microcrystals obtained by the above-described method are well compatible with the Group III element melt, and the Group III nitride microcrystals can be easily dissolved in the Group III element melt.

A group III nitride crystallite obtained by removing a group III element from the above mixture by acid cleaning or the like is used as a raw material to produce a group III nitride crystal by vapor phase growth, melting, or sintering. The raw material obtained by this method is characterized by high purity and low cost.

More specifically, a method of injecting a vapor of a group V element into a group III melt to synthesize a group III-V compound is called an injection method and is a known technique. For example, In, which is one of III-V group compound semiconductors,
As an example of synthesizing a polycrystal of P, there are the following academic conference reports.

"Mass synthesis of InP polycrystals by P-injection method", Shibata et al., 34th Joint Lecture on Applied Physics (1987) 28
pZ-1 However, the injection method is used to synthesize Group III melts.
A so-called melt growth method in which a vapor of a group V element is heated to a temperature equal to or higher than the melting point of a group V compound, a melt of the group III-V compound is once prepared, and this is cooled to prepare a crystal. On the other hand, in the method for synthesizing a nitride according to claim 1 of the present invention, a gas containing nitrogen is injected into a Group III melt at a temperature much lower than the melting point of the nitride to be synthesized. , Liquid phase
The conventional injection method in that the III-group element reacts with the vapor-phase V-group element to directly form the solid-phase III-nitride crystal in the III-element melt (it cannot melt the nitride). Is a completely new synthetic method. This is the nitride II
This is a positive use of the characteristics of very low solubility in Group I element melts.

In the method for producing a nitride crystal according to the present invention, by mixing an impurity element with a group III metal element, an impurity-doped group III nitride crystal can be produced. 2). And this claim 1
Alternatively, a mixture of a group III nitride powder and a group III metal raw material can be obtained by the method for producing a nitride crystal described in 2 .

The mixture of the group III nitride crystal and the group III metal raw material according to claim 3 of the present invention is a group III metal raw material whose surface is completely formed even though the group III nitride crystal is a fine crystal. The main feature is that it is wet. When a crystal fine powder is added as a raw material for liquid phase growth or as a dopant, a fine powder having a large surface area compared to its volume has a problem that it is difficult to adapt to the Group III melt and is therefore very difficult to dissolve. Especially in the case of nitride crystals with low saturation solubility,
This difficulty in melting becomes a fatal defect for crystal growth. The group III nitrides that have hitherto been commercially available are almost in a fine powder state, and uniformly have the above-mentioned drawbacks.
The mixture of the group III nitride fine crystal powder and the group III metal raw material according to the present invention has the surface completely covered with the group III metal raw material because the nitride crystal is synthesized in the group III melt. When it is used as a liquid phase growth raw material, it is very easily dissolved, and the saturated solubility can be easily reached as compared with conventional raw materials. As a result, the controllability and reproducibility of epitaxial growth are dramatically improved, and a high-purity group III nitride crystal can be obtained .

Further, in the conventional group III nitride synthesis method, since a group III oxide or chloride is used as a raw material, a step of removing unreacted substances from the synthesized nitride powder is always necessary. In the production method according to claims 1 to 3 of the present invention, since no oxide or chloride is used as a raw material, the unreacted substance does not become an impurity during liquid phase growth, and therefore, when used as a raw material for liquid phase growth. The mixture can be directly used as a raw material for liquid phase growth without extracting the group III nitride alone. The fact that the extraction step can be omitted not only leads to a drastic reduction in the step, but also contamination of the raw material that tends to occur in the extraction step can be eliminated, and high-purity liquid phase growth is possible.

The invention described in claim 3 relates to a liquid phase growth method, but the present invention can also be applied to a vapor phase growth method. That is , a group III nitride microcrystal obtained by the method for producing a nitride crystal according to claim 1 or 2.
Removing the Group III metal source from the Group III metal source mixture
A group III nitride crystal powder can be obtained. By using this nitride crystal powder as a starting material, a group III nitride crystal can be vapor-grown (claim 4 ), and the group III nitride crystal can be obtained by the vapor phase growth .

The invention according to claim 5 is the above III.
II nitride powder families, melting, a method for producing a re-solidified or sintering Group III nitride crystal, the method of manufacturing the same
A group I nitride crystal can be obtained.

In the method for producing a nitride crystal according to claim 1 or 2, the group III element is Al, Ga or I.
The gas containing any one of n and containing the nitrogen atom may be ammonia gas.
6 ). Further, in the inventions according to claims 3 to 5 ,
The group III element can be any one of Al, Ga and In.

The second important point of the present invention is that III such as gallium is used.
A seed crystal or substrate crystal is dipped in a melt of a group element, and bubbles of a gas containing nitrogen such as ammonia are intermittently brought into contact with the surface of the seed crystal or the substrate crystal. This is a method of growing a nitride crystal of a group III element on the surface by reacting a gas containing a.

Also in this method of growing a nitride crystal, a gas containing nitrogen is injected into a group III melt at a temperature much lower than the melting point of the nitride to be synthesized, so that the group III element in the liquid phase and the gas in the gas phase are separated from each other. V
It is premised that the solid-state group III nitride crystal is directly generated in the melt of the group III element by reacting the group element (a melt of the nitride cannot be formed). This is a positive use of the feature that the solubility of the nitride in the Group III element melt is extremely low, and this premise itself is, as already mentioned, the injection method. It is a crystal growth method based on a new concept that is completely different from the melt growth method.

Gallium, aluminum, indium, etc.
A gas containing a Group III element and nitrogen such as ammonia or hydrazine is used as a melting point of a nitride (for example, GaN is 200
It is said that it is more than 0 ℃)
It is known to react at a temperature of about 1000 ° C. to form a group III nitride. For example, there are the following reports.

[Crystal growth of GaN by reaction be
tween Ga and NH ₃ ”D.E1well et.al., J. Crystal Growth 66 (l984) 45-5
4 However, the generated GaN does not dissolve in the group III melt, but only becomes fine powder and precipitates on the surface of the group III melt.

In the method for producing a nitride crystal according to claim 7 or 8 , a seed crystal or a substrate crystal is dipped in a melt of a Group III element such as gallium, and a gas containing nitrogen such as ammonia on the surface thereof. The air bubbles in are contacted intermittently. By reacting a gas containing nitrogen with a group III element on 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 are nitrided, and a nitride crystal is grown on the underlayer. You can go. By carrying out this reaction continuously, it is possible to grow an epitaxial film and a bulk crystal.

In the method for producing a nitride crystal according to claim 7 or 8 , the group III element is Al, Ga or I.
The gas containing any one of n and containing the nitrogen atom may be ammonia gas.
9 ). Further, the production method for nitride crystals according to claim 7 or 8, the temperature of the Group III element melt is lower than the melting point of the grown nitride crystal (claim 1
0 ).

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below, focusing on examples.

Example 1 As an example of the present invention, a device as shown in FIG. 1 was manufactured. With this device, G
An example in which aN microcrystals are synthesized will be described.

3000 g of Ga was housed in a quartz crucible 1 having an inner diameter of 70 mm and a height of 150 mm, and Ga was heated to 950 ° C. by a heater 2 to form a Ga melt 3. Subsequently, 0.51 of ammonia gas was introduced into the Ga melt 3 using the gas introduction pipe 4.
Blowing was continued for 5 hours at a flow rate of / min. The gas blown into the melt 3 reacts with the melt to generate GaN microcrystals,
The crystallites floated on the surface of the melt. The ammonia gas that did not contribute to the reaction becomes bubbles and passes through the melt 3.
It goes out into the space above the container and is discharged to the outside of the container through the exhaust pipe 5. The discharged ammonia gas was discharged to the atmosphere through a wet type abatement device. After gas was injected for 5 hours, the gas to be injected was switched to nitrogen and the Ga 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. The surface of the GaN microcrystal was completely wet with the Ga melt. The Ga melt had a weight increase of 10.2 g before and after the synthesis work. From this calculation, 61 g of GaN microcrystals could be synthesized.

Example 2 GaN as in Example 1
Microcrystals are synthesized, and Ga melt and G float on the top of Ga melt.
Liquid phase epitaxial growth of GaN was performed by a slide boat method using a mixture of aN microcrystals as a raw material. A schematic sectional view of the apparatus used for growth is shown in FIG. Into the graphite boat 11, 20 g of a mixture of Ga melt and GaN fine crystals was placed as the raw material 12. 25 mm for slide boat 17
A square c-plane sapphire substrate 16 was set. The inside of the quartz reaction tube 14 was set to a nitrogen gas flow atmosphere, and the raw material was heated by the heater 13 until the output of the thermocouple 15 reached 1150 ° C. After leaving for 4 hours in this state, lower the temperature to 1100 ° C,
The operation rod 18 was pulled and the slide boat 17 was moved to bring the sapphire substrate 16 into contact with the raw material 12. After this,
Lower the raw material temperature to 600 ℃ at a rate of 1 ℃ per minute,
The slide boat 17 was returned to its original position by pressing 8, and the substrate 16 and the raw material 12 were separated. After that, the heater power was turned off and the temperature was cooled to room temperature. A temperature program during liquid phase epitaxial growth is shown in FIG.

The substrate after the growth was taken out and the surface and cross section were observed. A transparent film had grown on the surface of the sapphire substrate. The film thickness obtained from SEM observation of the cross section is 4.
It was 2 μm. The photoluminescence measurement result of the grown film at room temperature is shown in FIG. A sharp emission peak of 360 nm corresponding to the band edge emission of GaN was observed, and it was confirmed that the grown film was a good quality GaN film. When the electrical characteristics of the grown film were measured by the Van der Pauw method, the carrier concentration was 1 × 10 ¹⁷ cm ⁻³ and the mobility was 520 cm ² / V · sec, which showed favorable characteristics.

Example 3 In the same manner as in Example 1, 20 mg of Si was added to Ga as a raw material in advance to synthesize GaN microcrystals, and the obtained mixture of Ga melt and GaN microcrystals was used as a raw material. Then, by the same slide boat method as in Example 2,
Liquid phase epitaxial growth of aN was performed.

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

Example 4 In the same manner as in Example 1, 7 mg of Mg was added to Ga as a raw material in advance to synthesize GaN microcrystals, and the obtained mixture of Ga melt and GaN microcrystals was used as a raw material. By the same slide boat method as in Example 2.
Liquid phase epitaxial growth of N was performed.

The photoluminescence measurement result of the obtained GaN film at room temperature is shown in FIG. An emission peak at 445 nm corresponding to the emission of Mg-doped GaN was observed, and it was confirmed that the grown film was doped with Mg. When the carrier concentration of the grown film was measured by the Van der Pauw method, it was p-type 5 × 10 ¹⁷ cm ⁻³ . In the Mg-doped GaN film obtained by this method, the Mg obtained in the MOVPE growth does not activate the Mg in the crystal and does not exhibit p-type electric characteristics unless heat treatment is applied, whereas in the as-grown state. It showed good p-type electrical characteristics. It is considered that this is because there was no mixing of hydrogen atoms which hinders activation of Mg.

Example 5 A mixture of undoped GaN microcrystals and metallic Ga synthesized by the same method as in Example 1 was sampled, and hydrochloric acid and hydrogen peroxide solution were added thereto to dissolve only Ga. Only GaN fine crystals were taken out by filtering with filter paper. The filtered powder was thoroughly washed with pure water and then dried in a vacuum high temperature tank. As a result, 61 g of off-white powder
Was obtained. When this powder was observed with a microscope, the particle size
It was composed of fine crystals based on hexagonal prisms of about 10 μm. FIG. 7 shows the room temperature photoluminescence measurement result of this powder.
Shown in. A sharp emission peak at 360 nm corresponding to the band-edge emission of GaN was observed, and the obtained fine crystals were of high quality Ga.
It was confirmed to be N. The concentration of impurities that may be mixed in the obtained powder was measured by secondary ion mass spectrometry (SI
MS), but it seems that Si from the quartz container
Was detected at about 5 × 10 ¹⁵ cm ⁻³ , but all were below the detection limit.

(Example 6) Using the GaN microcrystalline powder obtained in Example 5 as a raw material, a Ga apparatus was used to produce Ga.
Vapor phase epitaxial growth of N was performed. Into a quartz crucible 23 having a diameter of 50 mm, 2 pieces of GaN fine crystal powder 26 as a raw material
5 g was put, and this was supported by the graphite susceptor 25 and set in the quartz container 21. On the other hand, a 25 mm square c-plane sapphire substrate 28 is attached to the graphite substrate holder 22.
The substrate was suspended in the quartz crucible 23 so that the surface of the substrate faced the raw material 26. In this state, the inside of the quartz container 21 was replaced with an ammonia gas atmosphere, and then the heater 24 was supplied while flowing 0.5 liters of ammonia gas per minute.
The raw material was heated at. For heating, thermocouple 2 placed under the crucible
The output of 7 was controlled so as to be 1100 ° C. At this time, the surface temperature of the substrate 28 was about 850 ° C. Crystal growth was carried out by holding the raw material for 24 hours while heating the material to sublimate it.

A transparent GaN film was grown on the surface of the sapphire substrate taken out. When the surface of the GaN film was observed with a microscope, triangular to hexagonal morphology was observed. The average thickness of the grown film was about 400 μm. When the electrical characteristics of the grown film were measured by the Van der Pauw method, the carrier concentration was 2 × 10 ¹⁷ cm ⁻³ and the mobility was 490 cm ² / V · sec, which showed favorable characteristics.

(Embodiment 7) In the same manner as in Embodiment 1, G
In was used instead of a to synthesize InN. The conditions are the same as in Example 1 except that the synthesis temperature was 600 ° C. The synthesized In was cooled to 180 ° C., and a mixture of InN microcrystals and metallic In floating above the In melt was taken out before In solidified.

Hydrochloric acid and aqueous hydrogen peroxide were added to this mixture to dissolve only In, and the mixture was filtered with a filter paper to take out only InN microcrystals. The filtered powder was thoroughly washed with pure water and then dried in a vacuum high temperature tank. As a result, about 200 g of a pale grayish white powder was obtained. When this powder was observed with a microscope, it was found to consist of hexagonal prism-based microcrystals with a grain size of approximately 8 μm. When the photolumi spectrum of the obtained powder was measured, emission at 650 nm corresponding to the band edge emission of InN was observed.

(Modification) Although the crystal growth of GaN has been mainly described in the above-mentioned embodiment, the crystal growth of InN has been described. In addition, crystal growth of AlN, AlGaN or GaInN which is a mixed crystal of AlN or InN is also described. Can also be applied.

As the gas containing nitrogen, use of hydrazine, monomethylhydrazine, etc. in addition to ammonia can be considered.

Although the example of the liquid phase growth has been described with respect to the crystal growth under the atmospheric pressure, the crystal growth rate can be further increased by performing the growth under the high pressure in the nitrogen or ammonia atmosphere.

In the examples of liquid phase growth and vapor phase growth, the epitaxial growth on the sapphire substrate was described, but the application development to the epitaxial growth using other substrates and the bulk crystal growth of nitride is also possible. .

The yield and grain size of the nitride fine crystals obtained by the synthesis can be controlled by the residence time of the gas such as ammonia injected into the Group III melt. Therefore, modifications such as changing the shape of the tip of the gas injection tube or providing a passage for gas bubbles in the melt by quartz work or the like are conceivable.

(Other Embodiments) The nitride microcrystals obtained by the present invention can be widely applied as semiconductor materials and phosphor materials. In particular, the liquid phase growth method according to one of the present invention is effective when applied to the production of ultraviolet to yellow light emitting devices.

For example, if the liquid phase growth apparatus described in the second embodiment is provided with two raw material storage portions, and the Mg-doped GaN raw material is stored in one side and the Si-doped GaN raw material is stored in the other side, the substrate becomes p-type. The n-type GaN film can be continuously grown. L is added to the epitaxial growth substrate thus obtained.
A pn junction type blue L can be easily obtained by applying the ED manufacturing process.
EDs can be manufactured. According to this method, an LED can be manufactured more easily, safely, and cheaper than the conventional MOVPE method. Also, conventional MOVPE growth G
In the case of aN, it is necessary to perform heat treatment afterwards in order to produce a p-type crystal, and therefore there is a constraint that the device structure must be designed so that the crystal surface is always p-type. When the liquid phase epitaxial growth method according to the present invention is used, p-type conductivity can be obtained without heat treatment, so that the structural design margin of the device becomes extremely large.

Since the synthesizing temperature of nitride, the atmospheric pressure, the amount of raw material used, etc. differ depending on the type of nitride to be synthesized and the type of raw material used, it is difficult to uniquely determine the optimum conditions. .

(Embodiment 8) As an eighth embodiment of the present invention, an apparatus as shown in FIG. 9 was manufactured. An example in which a GaN crystal is grown using this apparatus will be described.

3000 g of melted Ga33 was stored in a quartz container 31 having an inner diameter of 70 mm and a height of 200 mm, and a piece of a SiC single crystal having a side of 6 mm as a seed crystal 35 was attached to the tip of a seed crystal supporting jig 34 in the molten Ga33. , Fixed.
In this state, the molten Ga33 is heated by the heater 32,
The output of the thermocouple 37 was controlled to 1000 ° C.

Subsequently, ammonia gas was continuously introduced from the bottom of the quartz container at a rate of 0.2 liters per minute for 76 hours through a quartz ammonia introduction pipe 36 having an inner diameter of 6 mm. The ammonia gas introduced into the molten Ga33 stood up as bubbles in the melt. The number of bubbles was about 350 per minute. Ammonia gas bubbles rising in the melt
It collides with the surface of the seed crystal 35, and Ga is spun on the seed crystal surface one after another.
N crystals are generated. The unreacted ammonia gas reaches the surface of the molten Ga as bubbles as it is and is discharged to the outside of the container. The discharged gas was removed by a wet scrubber and released into the atmosphere. The bubbles of ammonia gas also reacted with Ga to form GaN on the surface other than the surface of the seed crystal. This GaN is a microcrystal with a diameter of about several μm, which floated up on the surface of molten Ga and did not contribute to the growth on the seed crystal.

The grown crystal was cooled, taken out from the molten Ga, and the metallic Ga adhering to the surface was washed off 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 on the SiC seed crystal.
The obtained crystals had a transparent yellowish brown color. The obtained crystal was confirmed to be a GaN crystal by an X-ray diffraction method. The full width at half maximum (FWHM) of the X-ray diffraction peak is about 2 mi.
Therefore, it can be said that the obtained crystal has good crystallinity.

FIG. 10 shows the photoluminescence measurement result of the obtained crystal at room temperature. At 360 nm, a sharp emission peak corresponding to the band-edge emission of undoped GaN was observed, and it was confirmed by photoluminescence measurement that the GaN crystal had good quality.

(Embodiment 9) As a ninth embodiment of the present invention, an apparatus as shown in FIG. 11 was manufactured. An example in which a GaN crystal is epitaxially grown using this apparatus will be described.

Quartz crucible 45 having an inner diameter of 70 mm and a height of 150 mm
Put in the graphite susceptor 44,
Installed inside 3. 3000 g of melted Ga48 is housed inside the quartz crucible 45, and a c-plane sapphire single crystal substrate (hereinafter referred to as sapphire substrate) 49 having a side of 25 mm is attached to the tip of the substrate support jig 47 and immersed in the melted Ga48. did. The sapphire substrate 49 was fixed in molten Ga by inclining from the horizontal by several degrees. In addition, molten Ga
A quartz ammonia gas introduction tube 41 having a J-shaped tip was installed in the tube 48. The tip of the gas introduction pipe 41 is
The sapphire substrate 49 was fixed immediately below the lower end. In this state, the molten Ga 48 was heated by the heater 42, and the output of the thermocouple 46 was controlled to 950 ° C. Then, the ammonia gas is introduced into the ammonia introducing pipe 41.
Was introduced into molten Ga 48 at a rate of 0.1 liter / min for 1 hour. The introduced ammonia gas stood up as bubbles in the melt. The number of bubbles is about 20 per minute
It was 0. The ammonia gas bubbles rising in the melt hit the lower end of the sapphire substrate 49 and ascended along the substrate surface, then reached the surface of the molten Ga 48 and were discharged to the outside of the container. The discharged gas was removed by a wet scrubber and released into the atmosphere.

The grown crystal is cooled and molten Ga4
The metal Ga adhering to the surface was washed out with hydrochloric acid. As a result, a transparent crystal thin film having a thickness of about 4 μm was obtained on the surface of the sapphire substrate 49. The obtained crystal was confirmed to be a GaN crystal by an X-ray diffraction method. The full width at half maximum (FWHM) of the X-ray diffraction peak is about 5 mi.
It was n.

FIG. 12 shows the photoluminescence measurement result of the obtained crystal at room temperature. At 360 nm, a sharp emission peak corresponding to the band edge emission of undoped GaN was observed, and it was confirmed that the GaN crystal was a good quality.

The growth temperature of the nitride crystal, the atmospheric pressure during the growth, the amount of the raw material used, and the like differ depending on the type of the nitride to be grown and the type of the raw material used, and therefore cannot be uniquely determined.

Ammonia is selected as the nitrogen-containing gas because it is chemically active to some extent and is a result of considering safety and economy. In principle, a gas such as hydrazine or monomethylhydrazine is used. Can also be used. However, these gases have a much greater risk of explosion than ammonia.

The temperature of the group III source material during the crystal growth is set to be equal to or lower than the melting point of the growing nitride in order to prevent the grown crystal from being decomposed or remelted.

(Modification) Although the crystal growth of GaN has been described in the embodiment, the present invention can be applied to the crystal growth of InN, AlN, and mixed crystals of these, such as AlGaN and GaInN. Furthermore, by mixing an impurity element into a Group III melt or a gas containing nitrogen, a nitride crystal doped with impurities can be grown.

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

The tip shape of the tube for introducing a gas such as ammonia into the Group III melt can be modified in various ways for the purpose of controlling the size and number of gas bubbles in the melt. For example, a plurality of air bubble outlets may be provided at the tip of the gas introduction pipe, or a net may be provided at the tip of the gas introduction pipe.

A modification in which a plurality of seed crystals or substrate crystals are placed in the Group III melt is also conceivable.

In the embodiments shown in FIGS. 1, 2, 8, 9 and 11 described above, only the crystal growth container showing the essential part of the present invention has been described.
By constructing a system that combines a mass flow controller that adjusts the gas flow rate and a temperature controller that can automatically control the temperature of the heater, it becomes easier to control the crystal growth.

The nitride crystal obtained by the present invention can be widely applied as a semiconductor material or a phosphor material. In particular, a nitride bulk single crystal substrate is optimal as a substrate material when manufacturing a blue laser diode.

[0073]

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

(1) According to the manufacturing method of claims 1 and 2, the gas containing nitrogen 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 is added. Phase III group element and vapor phase V group element are reacted to directly generate a solid phase group III nitride crystal in the group III element melt, which is easier than the case of forming a nitride melt. Can be mass-produced easily and inexpensively in a short period of time with various devices.

(2) According to claim 1 or 2 of the present invention
The mixture of Group III nitride microcrystals and Group III metal raw materials obtained by the method for producing nitride crystals is completely composed of Group III metal raw materials because the surface of the nitride microcrystals is synthesized in the Group III melt. It is covered, and when this mixture is used as a liquid phase growth raw material, it is very easily dissolved, and it becomes possible to easily obtain a solution having a saturated solubility as compared with a conventional raw material. As a result, the controllability and reproducibility of epitaxial growth are dramatically improved.

(3) According to the growth methods of claims 3 to 5 of the present invention, it is possible to mass-produce a group III high-purity nitride semiconductor crystal easily and inexpensively in a large amount in a short time with a simple apparatus. You can Further, it is safe because it is not necessary to use a gas such as chlorine which has been conventionally used in the HVPE method and a dangerous raw material such as an organic metal which is used in the MOVPE method.
Further, according to the growth method of the present invention, it becomes possible to easily perform liquid phase growth or vapor phase growth of a nitride crystal, which has been particularly difficult in the past. As a result, a device having a high-carrier p-type crystal can be easily manufactured without special treatment of a nitride crystal, and it is not necessary to bring a p-type conductive layer to the element surface. Greater freedom of design.

(4) Further, in the method for growing a nitride according to claims 3 to 5 of the present invention, since no conventional oxide or chloride is used as a raw material, an unreacted material is generated during liquid phase growth. Therefore, when used as a raw material for liquid phase growth,
The mixture can be directly used as a raw material for liquid phase growth without extracting the group III nitride alone. The fact that the extraction step can be omitted not only leads to a drastic reduction in the step, but also contamination of the raw material that tends to occur in the extraction step can be eliminated, and high-purity liquid phase growth is possible.

[0078] (5) Further, according to the manufacturing method according to claim 7, 8 of the present invention, a nitride semiconductor crystal of Group III, it is possible to grow bulk single crystal can not be grown in particular conventional . If this crystal is used as a substrate, blue LE
Not only is it effective in increasing the efficiency and extending the life of D, it also contributes greatly to promoting the practical application of the blue LD, which has not yet been commercialized. Further, such a group III nitride semiconductor crystal can be grown easily and inexpensively with a simple device. In addition, it is safe because it is not necessary to use a gas such as chlorine that has been conventionally used in the HVPE method, or a dangerous raw material such as an organic metal used in the MOVPE method.

[Brief description of drawings]

FIG. 1 is a GaN structure according to first and seventh embodiments of the present invention.
It is a cross-sectional schematic diagram of a crystal synthesizer.

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

FIG. 3 is a graph showing a temperature program during liquid phase growth of a GaN crystal according to a second example of the present invention.

FIG. 4 is a diagram showing a photoluminescence measurement result at room temperature of a liquid phase epitaxial growth undoped GaN junction film according to a second example of the present invention.

FIG. 5 is a diagram showing a photoluminescence measurement result at room temperature of a liquid phase epitaxial growth Si-doped GaN crystal film according to a third example of the present invention.

FIG. 6 is a diagram showing a photoluminescence measurement result at room temperature of a liquid phase epitaxial growth Mg-doped GaN crystal film according to a fourth example of the present invention.

FIG. 7 is an undoped Ga according to a fifth embodiment of the present invention.
It is a figure which shows the photoluminescence measurement result at room temperature of N microcrystal powder.

FIG. 8 is a schematic sectional view of a GaN crystal vapor phase growth apparatus according to a sixth embodiment of the present invention.

FIG. 9 is a schematic sectional view of a GaN crystal growth apparatus according to an eighth embodiment of the present invention.

FIG. 10 is a diagram showing a photoluminescence measurement result at room temperature of a GaN crystal produced in an eighth example of the present invention.

FIG. 11 is a schematic sectional view of a GaN crystal epitaxial growth apparatus according to a ninth embodiment of the present invention.

FIG. 12 is a diagram showing a photoluminescence measurement result at room temperature of a GaN epitaxially grown crystal produced in a ninth example of the present invention.

[Explanation of symbols]

1 Quartz crucible 2 heater 3 Ga melt 4 Ammonia gas injection pipe 5 exhaust pipe 6 thermocouple 11 graphite boat 12 Mixture of GaN fine powder and Ga 13 heater 14 Quartz reaction tube 15 thermocouple 16 sapphire substrate 17 Graphite Slide Boat 18 Quartz control rod 21 Quartz container 22 Graphite substrate holder 23 Quartz crucible 24 heater 25 Graphite Susceptor 26 GaN microcrystalline powder 27 thermocouple 28 Sapphire substrate 31 Quartz container 32 heater 33 Molten Ga 34 Seed crystal support jig 35 seed crystals 36 Ammonia introduction tube 37 with thermoelectric

Continuation of front page (56) Reference JP-A 64-5902 (JP, A) JP-A 51-151299 (JP, A) JP-A 1-145309 (JP, A) JP-A 4-154607 (JP , A) International Publication 95/004845 (WO, A1) D.M. ELWELL et al. , CRYSTAL GROWTH OF GaN BY THE REACTIO N BETWEEN GALLIUM and AMMONIA, Journal of Crystal Growth, 1984, Vol. 66, pp. 45- 54 (58) Fields surveyed (Int.Cl. ⁷ , DB name) C30B 1/00-35/00 C01B 21/06 C01G 15/00 H01L 21/208 WPI (DIALOG) JSTPlus (JOIS)

Claims (10)

(57) [Claims] 1. A Group III metal is prepared by heating and melting a Group III metal element and injecting a nitrogen atom-containing gas into a melt of the Group III metal element at a temperature below the melting point of the nitride to be obtained. The group III nitride crystallites are completely crystallized on the surface in the melt of the element.
A method for producing a nitride crystal, which is produced by covering with a group III metal raw material. 2. The method for producing a nitride crystal according to claim 1, wherein the group III metal element is mixed with an impurity element to produce a group III nitride crystal doped with the impurity element. A method for producing a nitride crystal. 3. A mixture of a group III nitride microcrystal and a group III metal element, which is obtained by the method for producing a nitride crystal according to claim 1 or 2, is used as a starting material.
Liquid growth method for group III nitride crystals. 4. A group III metal element is removed from a mixture of group III nitride microcrystals and a group III metal element obtained by the method for producing a nitride crystal according to claim 1 or 2.
Vapor growing method of a group III nitride, which comprises using the group III nitride crystal powder that the starting material. 5. A group III metal element is removed from a mixture of group III nitride microcrystals and a group III metal element obtained by the method for producing a nitride crystal according to claim 1 or 2.
Melting III nitride crystal powder that, to re-solidified or sintering
A method for producing a Group III nitride crystal, comprising: 6. Oite the process according to claim 1 or 2 nitride crystal, wherein said group III element is Al, Ga, In
And the gas containing the nitrogen atom is
Production of nitride crystals characterized by being ammonia gas
Build method. 7. A seed crystal is immersed in a heated and melted Group III element.
Soaked in a group III element containing a nitrogen atom on the surface of the seed crystal
The gas bubbles of the
The growth of group III nitride crystals on the crystal surface
A method for manufacturing a nitride crystal. 8. A substrate crystal is placed in a heated and melted Group III element.
Immerse it in a group III element containing nitrogen atoms on the crystal surface of the substrate.
By intermittently contacting gas bubbles of the gas,
Epitaxy of group III nitride single crystal on substrate crystal surface
Method for producing a nitride crystal characterized in that
Law. 9. A method for producing a nitride crystal according to claim 7 or 8.
In the method, the group III element is one of Al, Ga and In
And a gas containing any of the above nitrogen atoms
A method for producing a nitride crystal, the quality of which is ammonia gas . 10. Production of a nitride crystal according to claim 7 or 8.
In the method, the temperature of the Group III element melt is set to grow.
Nitride having a melting point lower than that of the nitride crystal
Crystal manufacturing method.