JPH0749101B2 - Growth method of semiconductor cubic boron nitride single crystal. - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for growing a semiconductor cubic boron nitride single crystal.

2. Description of the Related Art Conventionally, silicon, gallium arsenide, and the like have been widely used as semiconductor materials. However, at high temperatures, for example, silicon semiconductors have a drawback that they cannot be used at high temperatures of 150 ° C. or higher and gallium arsenide semiconductors at 250 ° C. or higher. .

On the other hand, cubic boron nitride is expected as a semiconductor that can be used at high temperatures, but since it is a substance synthesized under high pressure and high temperature, its manufacturing method is significantly limited. That is, conventionally
The semiconductor cubic boron nitride has been produced by using hexagonal boron nitride as a raw material together with a solvent containing a substance (referred to as a dopant) that gives semiconductor characteristics at high temperature and high pressure, and using the solubility of both as a driving force. According to this method, crystals are formed by natural nucleation in the immediate vicinity of the raw material, so that the size is limited to the adjacent crystals and is limited to 1 mm at maximum, usually 0.5 mm or less. For this reason, semiconductor cubic boron nitride has not yet been put into practical use, although it is expected to have excellent properties as a high temperature semiconductor.

OBJECT OF THE INVENTION The present invention has been made to eliminate the above-mentioned drawbacks of the conventional method, and an object thereof is to provide a method for growing a good-quality semiconductor cubic boron nitride single crystal having a practical size.

As a result of intensive studies to achieve the above object, the present inventors have found that boron nitride is formed in a high temperature portion which is sealed under high temperature and high pressure and which is formed in the lower part of a growth container in which a seed crystal is not placed. Place the raw material, place the boron nitride solvent containing the dopant on top of the raw material, form a low temperature part by making a temperature difference in the solvent, and place the boron nitride raw material placed in the high temperature part on the temperature difference. A large cubic boron nitride single crystal of good quality with semiconductor characteristics by dissolving in an attached solvent and utilizing the difference in solubility of boron nitride due to the temperature difference to deposit and grow crystals at low temperature in the solvent. The present invention has been completed based on this finding.

That is, the present invention, the boron nitride raw material is placed in a high temperature part which is sealed under high temperature and high pressure and is formed in the lower part of the growth container in which the seed crystal is not placed, and the boron nitride containing the dopant is contained. The solvent is placed on the raw material, a low temperature portion is formed by making a temperature difference in the solvent, and the boron nitride raw material placed at the high temperature portion is dissolved in the solvent having a temperature difference, and the boron nitride is caused by the temperature difference. The gist is a method for growing a semiconductor boron nitride single crystal, which is characterized in that a crystal is deposited and grown at a low temperature portion in a solvent by utilizing the difference in solubility of.

The growth container used in the present invention has a structure that can be sealed under high temperature and high pressure, in which the solvent and boron nitride are separated,
A perforated partition plate is preferably provided in order to control the dissolution rate of boron nitride in the solvent. However, as shown below, it is not always necessary. As the material of the growth container, a metal having a high melting point and not reacting with the BN solvent, such as molybdenum or tantalum, is used.

An example of this growth container is shown in FIG. The growth container is composed of inner and outer cylinders 2 and 3 made of, for example, molybdenum and an upper lid 1 in order to ensure hermeticity, and a partition plate 4 is provided inside. The upper lid 1 serves to prevent the molten solvent 6 from flowing out of the container along the wall surfaces of the inner and outer cylinders 2 and 3. The BN raw material 5 is filled between the lower bottom and the partition plate 4, and the dopant-containing BN solvent 6 is filled between the partition plate 4 and the upper bottom. That is, the BN raw material 5 is placed in the lower part of the growth container, and the BN solvent 6 is placed thereon.
Are placed. An opening is provided in the center of the partition plate 4,
By appropriately changing the opening diameter r, the dissolution rate of the BN raw material 5 is controlled. In this case, the opening diameter r may increase and may coincide with the inner diameter of the container. In this case, the partition plate is unnecessary.

FIG. 2 shows a state in which the growth container 8 is loaded in the pressure medium 10 in the graphite heater 9 in the reaction chamber of the high temperature and high pressure generator.

The temperature difference in the growth container is controlled by the degree to which the center position a-a 'of the growth container is displaced upward from the center b-b' of the heater.
That is, the temperature in the heater is highest at b-b 'and a-
Assuming that the difference from a ′ is h, the greater the h, the greater the temperature difference, that is, the difference in the concentration of BN in the solvent, and the growth rate increases.

In this way, the high temperature part is formed in the lower part of the growth container 8. The BN raw material 5 will be arranged in this high temperature part.
Also, as is clear from FIG. 2, the BN containing the doping agent
A temperature difference is formed in the solvent 6, and the center of the heater b-b '
A low temperature part is formed in the BN solvent 6 placed on the upper part of the growth container 8 away from the. A semiconductor cubic boron nitride single crystal is grown at a low temperature in the BN solvent 6. In order to obtain a good quality single crystal, it is essential to arrange the low temperature portion above the high temperature portion in this manner.

The filling amount of the solvent in the growth container 8 depends on conditions such as temperature, temperature difference, and internal volume of the container, but is preferably about 2/3 of the internal volume. If the amount is too large, the temperature difference becomes too large, and the solvent becomes transparent in appearance after being rapidly cooled and recovered in the low temperature part, and it becomes difficult to grow crystals there. Therefore, the filling amount of BN raw material becomes the remaining 1/3.

The BN raw material has only to have a chemical composition of BN and to be dissolved in a solvent to supply boron nitride, for example, cubic boron nitride or hexagonal boron nitride powder, particles or a sintered body. To be However, the dissolution rate of the powder is higher than that of the sintered body, and that of hexagonal boron nitride is higher than that of cubic boron nitride. The optimum raw material may be selected depending on the solvent.

As the solvent, an alkali metal, an alkaline earth metal, or a nitride or boronitride having a eutectic relationship with boron nitride is used. Of these, boron nitrides of lithium, magnesium and calcium, for example, compounds such as LiCaBN ₂ , Ca ₃ B ₂ N ₄ and Mg ₃ B ₂ N ₄ are particularly effective.

As the doping agent, beryllium is used when depositing and growing a p-type cubic boron nitride semiconductor, and silicon is used when depositing and growing an n-type cubic boron nitride semiconductor. However, although not limited thereto, carbon and sulfur, which give semiconductor characteristics, react with a metal growth container to form a carbide,
It is not preferable because it easily forms sulfides.

Beryllium and silicon melt at high temperatures and mix with the solvent, so its form, place in the container, and method of putting them do not matter. As a standard, the amount of beryllium is about 1% by weight and the amount of silicon is about 5% by weight.

No seed crystal of boron nitride is placed in the growth container.

A growth container filled with such a boron nitride raw material and a boron nitride solvent containing a dopant is placed in a device that generates high temperature and high pressure, and, for example, high pressure of 4 to 7 GPa and high temperature of 1300 to 2400 ° C. The single crystal is grown by holding at. As a general rule, the pressure and temperature ranges are in the stable region of cubic boron nitride,
Moreover, it is sufficient if it is at least the eutectic point with the boron nitride solvent. If the temperature is too low, the solvent after recovery becomes transparent in the low temperature part, where it is difficult to grow crystals, and therefore, preferably the temperature at which the transparent solvent disappears from the low temperature part of the growth container, more preferably more than that temperature. A temperature as high as 100 ° C is good. The growth temperature cannot be generally stated depending on the type of boron nitride solvent and the temperature difference in the growth container, but for example, in the case of LiCaBN ₂ solvent, it is about 1700 ° C. at the high temperature part of the growth container.

The temperature difference between the high temperature side and the low temperature side in the boron nitride solvent is 0.
If it is close to, crystal growth does not occur, and if it is large, the growth progresses rapidly and becomes a defective crystal. Specifically, the optimum temperature difference can be determined as follows. As shown in FIG.
By changing the position of the growth container, a small polyhedral crystal is obtained when the displacement h is small, that is, the temperature difference is small, and a large polycrystal is obtained when h is large, that is, the temperature difference is large. And large quality crystals can be obtained. Generally, as the amount of the dopant increases, precipitation and growth of semiconductor crystals become less likely to occur. In this case, the deviation h is increased to increase the temperature difference, or the hole diameter r of the partition plate is increased to increase the dissolution rate.

To make a large crystal, the growth container must be kept at a constant pressure and temperature for a long time. If there are fluctuations in pressure and temperature, good quality crystals cannot be obtained. Crystals grow to the order of 1 mm in about 10 hours.

If the contents of the growth container are removed after quenching and depressurizing the growth container, the grown semiconductor cubic boron nitride single crystal can be easily separated from the solvent.

Advantageous Effects of Invention According to the method of the present invention, 1 mm which cannot be obtained by the conventional technique.
It is possible to make a large-sized and high-quality semiconductor cubic boron nitride single crystal with the above size, and since a sealed growth container is used, the growth environment can be controlled without worrying about impurities outside the container. To be The specific resistance of the obtained single crystal is usually 1 to 10 ³ Ω · cm for the p-type crystal and 10 ³ to 10 ⁵ Ω for the n-type crystal.
-Has excellent effects such as being excellent in cm.

Example 1. A 325-400 mesh cubic boron nitride powder and a LiCaBN ₂ powder are shown in FIG. 1 and are made of a molybdenum container with an upper lid (inner diameter 4 mm,
Inner height 3mm, thickness 1mm) At this time, small particles of about 0.1 mg silicon were put in LiCaBN ₂ , the partition plate was a molybdenum plate having a thickness of 0.2 mm, and the opening diameter of the central portion was 2.0 mm.

This growth container is displaced from the center of the heater shown in FIG.
Was placed in a heater so that the value was 0.5 mm, placed in a high-pressure and high-temperature generation container, and kept at 5.5 GPa and 1800 ° C. for 18 hours. After depressurizing by quenching and collecting, the size of the yellow color is about 1.
Four 2 mm n-type cubic boron nitride single crystals were grown.
The specific resistance was about 5 × 10 ³ Ω · cm.

Example 2. Cubic boron nitride powder of 325 to 400 mesh and LiCaBN ₂ powder are packed in the same growth container as in Example 1. At this time the solvent
About 0.1 mg of metal beryllium powder was placed in LiCaBN ₂ , and the partition plate used was the same as that in Example 1.

The displacement h from the center of the heater shown in Fig. 2 for this container is 1 m.
It was mounted in a heater so that the pressure became m, put in a high-pressure and high-temperature generator, and kept at 5.5 GPa and 1700 ° C. for 24 hours. When recovered after quenching and depressurization, several dark blue p-type cubic boron nitride single crystals having a size of 2.0 to 2.5 mm were grown in the upper low temperature portion of the container.
The specific resistance was about 10 Ω · cm.

[Brief description of drawings]

The drawings show an example for carrying out the method of the present invention. FIG. 1 shows a layout of a growing vessel, and FIG. 1: Upper lid, 2: Inner cylinder, 3: Outer cylinder, 4: Partition plate, 5: BN raw material, 6: BN solvent, 7: Growth crystal, 8: Growth container, 9: Heater, 10: Pressure medium, r: Opening diameter of partition plate, aa ': center line of growth container, bb': heater center line.

Claims (5)

[Claims] 1. A boron nitride raw material is placed in a high temperature portion which is hermetically sealed under high temperature and high pressure and which is formed in a lower portion of a growth container in which a seed crystal is not placed, and a boron nitride solvent containing a dopant. Is placed on the raw material, a low temperature portion is formed by making a temperature difference in the solvent, and the boron nitride raw material placed at the high temperature portion is dissolved in the solvent having a temperature difference, and the boron nitride A method for growing a semiconductor boron nitride single crystal, which comprises depositing and growing a crystal in a solvent at a low temperature by utilizing a difference in solubility. 2. The growing method according to claim 1, wherein the boron nitride raw material is powder, particles or a sintered body of cubic boron nitride or hexagonal boron nitride. 3. The growing method according to claim 1, wherein the boron nitride solvent is selected from alkali metals, alkaline earth metals, and their nitrides or boronitrides. 4. The pressure in the growth container is 4 to 7 GPa and the temperature is 1300.
2. The growing method according to claim 1, wherein the temperature of the low temperature portion in the solvent is in the range from a temperature at which the transparent solvent disappears to a temperature 100 ° C. higher than that temperature. 5. The growing method according to claim 1, wherein the dopant is beryllium when the p-type cubic boron nitride semiconductor is used and silicon when the n-type cubic boron nitride semiconductor is used.