JPH107496A - Production of nitride crystal and production unit therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the growth of a large-sized bulk single crystal of a group III element nitride such as GaN which has not been available so far. SOLUTION: A group III element feedstock is charged into a quartz vessel 1, heated by a heater 2 and melted. The resultant melt 3 is then fed with a nitrogen-contg. material such as ammonia gas via a gas charge piping 4 to carry out a reaction and dissolve the resultant nitride in the melt 3. While continuing the feed and reaction, the melt 3 is cooled to effect deposition of the nitride crystal. The above dissolution process and deposition process are then repeated alternately, thus obtaining the objective large-sized nitride crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing a nitride crystal, and more particularly to a nitride crystal of a group III element such as GaN, AlN, InN, etc., in which it was conventionally difficult to obtain a large crystal. And a material suitable for the production of

[0002]

2. Description of the Related Art As a method for producing a GaN crystal powder, CVD, HVPE and MOVPE methods for producing by reacting a Ga oxide such as Ga ₂ O ₃ with ammonia have been put into practical use. Are commercially available for reagents. Other methods for producing GaN crystals are disclosed by S. Porowski (Reference 1), D. Elwell (Reference 2), and others.

[0003] Document 1 describes that under high nitrogen gas pressure, III
A group III material is melted to grow a group III nitride crystal, and a very high pressure is required. Therefore, the production of the crystal is dangerous and difficult, and the size of the obtained crystal is several mm. About small.

[0004] Also, the one disclosed in Reference 2 is based on III such as gallium.
Reacting a nitrogen-containing substance such as ammonia with the melt of the group raw material and dissolving until the group III nitride reaches saturation,
A method of precipitating a nitride crystal of a group III element by cooling the saturated solution, but the size of the obtained crystal is also small.

Reference 1: "Prospects for high-pressure c"
rystal growth of III-V nitrides "S.Porowski, J.Jun,
P.Perlin, I.Grzegory, H.Teisseyre and T.Suski, Inst.P
hys.Conf.Ser.No.137: Chapter 4 Paper presented at t
he 5th SiC and Related Materials Conf., Washington,
DC, 1993 Reference 2: Journal of Crystal Growth 66 (1984) 45-54 "Cr
ystal Growth of GaNby the Reaction Between Ga and
NH ₃ "D. Elwell et.al etc.

[0006]

Generally, since the solubility of nitride is very small, the yields of crystals are too low in the methods of the above-mentioned documents 1 and 2 to obtain crystals of a practical size. could not. Therefore, still large III
There is no method capable of easily producing a group nitride crystal, and as a result, the following problems have occurred.

(1) A nitride crystal of a group III element represented by GaN has attracted attention as a material for a blue light emitting device. To create a device, for example, GaN
It is necessary to epitaxially grow a crystal or the like. In this epitaxial growth, in order to prevent the occurrence of strain in the growing crystal, it is ideal that the lattice constant and the coefficient of thermal expansion of the crystal serving as the substrate are the same as those of the crystal grown thereon. Until now, large GaN crystals could not be produced, so sapphire substrates had to be substituted.

(2) There is a case where it is required to dope nitrogen into a semiconductor crystal such as GaAs or GaP. In the case of doping with nitrogen, if a nitride crystal such as GaN is used as a dopant, the doping efficiency is increased. It is known to improve. However, GaN crystals conventionally available on the market
Powdered materials produced by a method or the like are mainly used, and there are problems in that the purity is low in spite of being expensive, and the shape is difficult to dissolve in a semiconductor melt.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to easily grow a nitride crystal of a group III element such as GaN, particularly a large bulk single crystal which has not been obtained before. It is an object of the present invention to provide a method and an apparatus for producing a nitride crystal which can be used.

Further, the present invention provides a substrate for a blue light emitting device,
It is another object of the present invention to provide a method of manufacturing a nitride crystal and an apparatus therefor, which can realize a dopant which is inexpensive, has high purity and is easily soluble in a semiconductor melt.

[0011]

The present invention pays attention to the method of D. Elwell et al. Shown in Reference 2 and finds that a large crystal can be obtained by repeating cooling and heating of a saturated solution. It was invented.

[0012] The invention according to claim 1 comprises a step of heating and melting a group III raw material, supplying a nitrogen atom-containing substance to the group III material, and dissolving the nitride in the group III raw material melt. And cooling the group III raw material melt to precipitate nitride crystals while continuing the above-mentioned reaction. The method is alternately repeated.

When the temperature of the melt is repeatedly raised and lowered as in the production method of the present invention, the size of the precipitated crystal can be increased. Therefore, even if the solubility of the nitride is small, the yield of the crystal can be increased. And a practical crystal can be obtained.
In this case, the crystal precipitated by cooling the saturated solution of the nitride may be dissolved again when the temperature of the group III raw material melt as the solvent is raised again. During this time, a substance such as ammonia is continuously reacted with the group III raw material melt, thereby preventing the crystal once deposited from being redissolved. This is possible because the rate at which the crystal dissolves in the melt is sufficiently slower than the rate at which gas such as ammonia reacts with the melt to dissolve the nitride, so the amount of crystal re-dissolution is ignored. Because it is as small as possible.

According to a second aspect of the present invention, there is provided a method for producing a nitride crystal according to the first aspect, wherein a temperature gradient is provided in the group III raw material melt. When a temperature gradient is provided in the group III raw material melt, nitride crystals can be preferentially grown in a low temperature portion of the group III raw material melt.

According to a third aspect of the present invention, in the second aspect, a temperature gradient is provided in the group III raw material melt,
A method for producing a nitride crystal, characterized in that a seed crystal is arranged in a low-temperature portion of a group III raw material melt provided with a temperature gradient.
When a temperature gradient is provided in the group III raw material melt and a seed crystal is arranged in the low temperature part, nitride crystals precipitate on the seed crystal,
Since the nitride crystal grows easily using the nucleus as a nucleus, the nitride crystal can be grown larger.

According to a fourth aspect of the present invention, in the first to third aspects, the group III raw material is Al, Ga, I
n is a method for producing a nitride crystal in which the substance containing a nitrogen atom is ammonia gas (NH ₃ ) or hydrazine gas (N ₂ H ₄ ). When the substance containing a nitrogen atom is ammonia gas or hydrazine gas, it is safe because there is no need to use dangerous raw materials.

According to a fifth aspect of the present invention, there is provided a container for accommodating a group III raw material, and heating means for heating and melting the group III raw material in the container and forming a temperature gradient in the group III raw material melt. A crystal supporting rod for supporting a seed crystal in a low temperature part of the group III raw material melt having a temperature gradient, a supply means for supplying a nitrogen atom-containing substance to the group III raw material melt in the container,
Of the nitrogen-containing substances supplied into the container, II
An exhaust device for exhausting a surplus that has not reacted with the group I raw material melt.

The operation of the manufacturing apparatus of the present invention will be described. First, a group III raw material is housed in a container, and the group III raw material in the container is heated and melted by a heating means. At this time, the heating amount of the heating means is made non-uniform to form a temperature gradient in the group III raw material melt. The seed crystal is placed in a low temperature part of the group III raw material melt in which a temperature gradient is formed by supporting the seed crystal on the crystal support rod. Next, a substance containing nitrogen atoms is supplied from the supply means to the raw material melt in the container. When a substance containing a nitrogen atom is supplied, the raw material melt reacts with the nitrogen atom to dissolve the nitride in the group III raw material melt. While continuing this supply reaction, the heating of the heating means is stopped, and the group III raw material melt is cooled to precipitate nitride crystals. By alternately repeating the dissolution of the nitride and the precipitation of the nitride by heating and cooling as described above, the nitride crystal is deposited on the seed crystal. In this process, of the nitrogen-containing material supplied into the container, an excess that has not reacted with the raw material melt is exhausted from the exhaust means.

According to a sixth aspect of the present invention, there is provided the apparatus for producing a nitride crystal according to the fifth aspect of the invention, further comprising a cooling means for cooling the crystal supporting rod. When a cooling means for cooling the crystal support rod is added, the seed crystal supported by the crystal support rod is more effectively cooled, so that the yield of the crystal can be significantly increased.

[0020]

Embodiments of the present invention will be described below.

Example 1 As an example of the present invention, an apparatus for manufacturing a nitride crystal as shown in FIG. 1 was manufactured. The quartz container 1 contains a group III raw material, a heater 2 provided on the outer periphery including the bottom of the quartz container 1 for heating and melting the group III raw material in the quartz container 1, and a III container in the quartz container 1.
A gas introduction pipe 4 for supplying a substance containing nitrogen atoms to the group 3 raw material melt 3, and a surplus of the nitrogen containing substances supplied to the quartz container 1 which did not react with the group III raw material melt 3. And an exhaust pipe 5 for exhausting air.

An example in which a GaN crystal is grown using this apparatus will be described. 3000 g of Ga is stored in a quartz container 1 having an inner diameter of 70 mm and a height of 150 mm.
By heating to 0 ° C., a Ga melt 3 was formed. Then, while blowing ammonia gas at a flow rate of 1.01 / min into the Ga melt 3 using the gas introduction pipe 4, the Ga melt 3
Was raised to 1000 ° C. The gas blown into the melt 3 partially dissolves by reacting with the melt, but surplus ammonia gas 9 that has not contributed to the reaction passes through the melt 3 as bubbles to form the quartz container 1. The gas exits the upper space and is discharged out of the quartz container 1 through the exhaust pipe 5. The discharged ammonia gas is released to the atmosphere through a wet exclusion device.

In the crystal growth, the melt 3 is held at 1000 ° C. for 2 hours, then the temperature of the melt is lowered to 800 ° C. at a rate of −100 ° C./hr, and then 1000 ° C. at a rate of 20 ° C./min. Temperature. The heating and cooling was performed as one cycle, and the heating and cooling by the heater 2 was stopped and the melt 3 was cooled to room temperature. During this time, the ammonia gas was kept flowing at the initial flow rate.

The cooled Ga melt 3 was taken out of the quartz container 1, and Ga was dissolved in hydrochloric acid and filtered with filter paper. As a result, a large amount of GaN single crystal grains having a diameter of 0.5 to 6 mm was obtained. The total weight of the obtained GaN was 61 g.

(Example 2) Crystal growth was performed using the same apparatus as in Example 1 and in the same manner, changing only the rate of temperature rise and fall as follows. The procedure is the same as in Example 1 until heating to 1000 ° C., but after maintaining the melt 3 at 1000 ° C. for 2 hours, the melt temperature is increased at a rate of −20 ° C./hr to 8 ° C.
Cooled to 00 ° C. Thereafter, the temperature was raised to 1000 ° C. at a rate of 20 ° C./min. This heating / cooling was defined as one cycle, and the heating / cooling was performed three consecutive times.
And the melt 3 was cooled to room temperature.

The cooled Ga melt 3 was taken out of the quartz container 1, and Ga was dissolved in hydrochloric acid and filtered with filter paper to obtain a large number of flat GaN single crystals having a diameter of 4 to 20 mm. Among the obtained GaN, the largest one was 19 mm × 22 mm ×
It was a hexagonal flat plate of 2.1 mm.

(Embodiment 3) As Embodiment 3, an example in which an apparatus as shown in FIG. 2 is manufactured and a GaN crystal is grown will be described. The device structure is basically the same as that shown in the first and second embodiments (FIG. 1), but there are two differences. One is to adjust the positional relationship between the quartz container 1 and the heater 2 so that a temperature distribution is provided in the depth direction within the Ga melt 3 so that the temperature decreases as the Ga melt depth decreases. It is a point that was made. The temperature distribution in the depth direction in the melt 3 is as shown in FIG. The second point is that a crystal support rod 6 with a cooler 7 is provided, and a GaN crystal grain that has been grown in advance is held as a seed crystal 8 above the Ga melt 3. Crystal support rod 6
The support rod 6 is cooled by a cooler 7 so that the seed crystal 8 attached to the tip of the support rod 6 is always kept at the lowest temperature in the Ga melt 3.

Using this apparatus, a crystal was grown by giving a temperature cycle to the melt under the conditions shown in Example 2. With this apparatus, the seed crystal 8
Since it grows preferentially on the top, one large single crystal can be grown. In this embodiment, 36 mm × 36 mm × 1
Hexagonal columnar crystals weighing 9 mm and weighing 16.1 g could be grown.

As described above, according to the first to third embodiments, a large-sized GaN crystal with high purity can be obtained. Therefore, if this crystal is used for the substrate, the efficiency and the life of the blue light emitting diode can be increased. Not only is this effective, but it can also contribute significantly to promoting the practical use of blue-emitting laser diodes that have not yet been put to practical use.

The GaN crystal obtained by the embodiment is inexpensive, has high purity, and has a shape easily soluble in a semiconductor melt. Therefore, the GaN crystal is optimal as a dopant for doping nitrogen into a semiconductor crystal such as GaAs or GaP. And the doping efficiency can be improved.

In the first to third embodiments described above, G
Although the saturated molar concentration of GaN in a is not exactly determined, it is estimated at 3.51 × 10 ⁻³ m at 1000 ° C.
ol / dm ³ , 3.52 × 10 ⁻⁴ mo at 800 ° C.
l / dm ³ , and the Ga melt is heated from 800 ° C. to 100 ° C.
If the temperature is raised between 0 ° C., when 3000 g of Ga melt is used, about 11 g can be theoretically obtained by one temperature rise and fall, and several g of GaN crystal can be obtained even by actual growth.

If the temperature of the Ga melt can be further raised, the saturation concentration of GaN will increase, and a large amount of crystals can be deposited at one time. Since the heater material (or the heating method itself) is restricted, the practical upper limit is about 1200 ° C. at the highest. It is considered that about 800 ° C. is appropriate as to how many times the melt is cooled when the temperature is lowered. If the temperature is further reduced, the amount of precipitated crystals does not increase so much, but rather wastes time and power at the next temperature rise.

Although the temperature rise and fall range is set to 800 ° C. to 1000 ° C. in the embodiment for the above reasons, the optimum value of the temperature cannot be determined in principle. As for the rate of temperature rise and fall, the slower the temperature drop rate, the smaller the number of crystal nuclei that grow and the larger the crystal grain size tends to be.
Since the relationship between the cooling rate and the diameter of the precipitated crystal greatly changes depending on the capacity of the growth apparatus, it is necessary to set the crystal size for each apparatus in accordance with the desired crystal size. The atmosphere pressure in the container is
The higher the solubility of the nitride is, the higher the yield of the crystal becomes. Therefore, the high pressure as in the conventional literature 1 is not required, but the optimum value cannot be determined.

In the first to third embodiments, only the surroundings of the quartz container showing the essential part of the present invention have been described. However, peripheral devices of the quartz container 1 include a mass flow controller for adjusting a gas flow rate and the temperature of the heater 2. By constructing a system in which a temperature controller capable of automatically controlling the crystal growth is constructed, it becomes easier to control the crystal growth.

[0035]

According to the method for manufacturing a nitride crystal of the present invention, a large bulk single crystal, which could not be grown conventionally, can be grown easily and inexpensively. As a result, a substrate for a blue light emitting element and a nitride crystal dopant that is inexpensive, has high purity, and is easily soluble in a semiconductor melt can be realized. In addition, it is safe because it is not necessary to use gases such as chlorine conventionally used in HVPE and dangerous raw materials such as organic metals used in MOVPE.

Further, according to the nitride manufacturing apparatus of the present invention, a group III nitride crystal can be appropriately obtained by a simple apparatus.

[Brief description of the drawings]

FIG. 1 shows Ga according to first and second embodiments of the present invention.
It is a cross section of an apparatus for manufacturing an N crystal.

FIG. 2 is a schematic sectional view of an apparatus for manufacturing a GaN crystal according to a third embodiment of the present invention.

FIG. 3 is a diagram showing a temperature distribution in a melt according to a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Quartz container 2 Heater 3 Group III raw material melt (Ga melt) 4 Gas introduction pipe 5 Exhaust pipe 6 Crystal support rod 7 Cooler 8 GaN seed crystal

Claims (6)

[Claims] A step of heating and melting a group III raw material, supplying a nitrogen atom-containing substance to the group III raw material, and dissolving the nitride in the group III raw material melt; A method for producing a nitride crystal, comprising alternately repeating a step of cooling a group III raw material melt to precipitate a nitride crystal. 2. The method for producing a nitride crystal according to claim 1, wherein a temperature gradient is provided in the group III raw material melt. 3. The method for producing a nitride crystal according to claim 2, wherein a seed crystal is arranged in a low temperature part of the group III raw material melt provided with a temperature gradient. . 4. The nitride according to claim 1, wherein the group III raw material is any one of Al, Ga, and In, and the substance containing a nitrogen atom is ammonia gas or hydrazine gas. Method for producing crystals. 5. A container for accommodating a group III raw material, a group III raw material in the container is heated and melted, and
A heating means for forming a temperature gradient in the group III raw material melt, a crystal support rod for supporting a seed crystal in a low temperature part of the group III raw material melt having the temperature gradient, and a nitrogen support for the group III raw material melt in the container. A nitride comprising: a supply unit that supplies a substance containing atoms; and an exhaust unit that exhausts a surplus of the nitrogen-containing substance supplied into the container that has not reacted with the group III raw material melt. Crystal manufacturing equipment. 6. The apparatus for producing a nitride crystal according to claim 5, further comprising cooling means for cooling said crystal support rod.