JPH08217589A - Production of single crystal - Google Patents

Abstract

PURPOSE: To produce a compd. semiconductor single crystal having a high m.p. and high dissociation pressure with good reproducibility at a low cost by dissolving the crystal to be grown into a solvent to form a satd. soln. and growing the crystal from the soln. by a horizontal temp. gradient method and horizontal Bridgeman method. CONSTITUTION: Single crystal raw material and its solvent are put into an ampoule and a board arranged with a seed crystal is installed at its one end. After the ampoule is vacuum sealed, the ampoule is heated in a heating furnace to dissolve the raw material into the solvent to prepare a raw material soln. The single crystal is grown by gradually lowering the temp. of the heating furnace while the temp. distribution in the horizontal direction of the heating furnace is so controlled that the temp. on the seed crystal side falls below the temp on the raw material soln. side. Fig. illustrates a single crystal growth method by the horizontal temp. gradient method. The raw material and the solvent are put into the boat 3 and the seed crystal 6 is placed in the prescribed position of the boat 3. The boat is then vacuum sealed into the ampoule 2. The ampoule is heated by a heater 1 and the raw material soln. 5 made into a satd. concn. is brought into contact with the seed crystal 6. The single crystal 4 is then grown by gradually lowering the temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a single crystal, particularly a horizontal temperature gradient method (HGF method) and a horizontal Bridgman method.
The present invention relates to a method for producing a single crystal by (HB method).

[0002]

2. Description of the Related Art Since II-VI group and III-V group compound semiconductors have a high vapor pressure at the melting point, various measures have been taken to grow single crystals. The III-V compound semiconductor is a liquid-encapsulated Czochralski (LEC) method in which a crystal is pulled by using a sealing agent such as B ₂ O ₃ and is industrially used for the production of a III-V compound semiconductor single crystal. Has been. On the other hand, II-VI group compound semiconductors have significantly lower thermal conductivity than III-V group compound semiconductors, and are also lower than B ₂ O _{3 in} liquid-encapsulated Czochralski (LEC) method. Group VI compound semiconductor single crystals cannot be grown. Therefore, for CdTe and the like, a quartz ampoule is generally grown by the vertical temperature gradient method (VGF method) or the vertical Bridgman method (VB method).

However, since the melting points of ZnTe and ZnSe which are the same II-VI group compound semiconductors are remarkably higher than the softening point of quartz glass and the vapor pressure is as high as -10 atm, the method of encapsulating in a quartz ampoule cannot be used. Therefore, a growth method in which a compound semiconductor raw material is sealed in a high melting point metal container such as Mo has been developed (JP-A-63-310786). However, this method is disadvantageous in cost because Mo and the like are expensive. Therefore, by the vertical temperature gradient method (VGF method) and the vertical Bridgman method (VB method), a method of growing a single crystal by dissolving a compound semiconductor raw material in a solvent to form a saturated solution and gradually cooling it was developed. . With this method, it is possible to grow crystals at a temperature lower than the softening point of the silica glass because it is not necessary to melt the raw material, and there is no need for a high-pressure container because the vapor pressure can be 1 atm or less. However, in this method, since a vertical furnace is used, gas convection easily occurs, and since the raw material container is also vertical, thermal convection is large and the temperature fluctuates, so that it is difficult to obtain a single crystal. Regarding seeding as well, a special method must be taken to set the seed on the bottom of the raw material (Ishikawa, "High-Purity Compound Semiconductor Crystals Project Research Summary" ((Fund))
There were drawbacks such as Kanagawa Academy of Science and Technology), P19-P33).

[0004]

SUMMARY OF THE INVENTION The present invention solves the above problems, and an object thereof is to produce a compound semiconductor single crystal having a high melting point and a high dissociation pressure at low cost and with good reproducibility. .

[0005]

[Means for Solving the Problems] As a means for solving the above problems, the raw material is dissolved in a solvent and the horizontal temperature gradient method (HGF
Method) and a horizontal Bridgman method (HB method) were devised. That is, the present invention, in the ampoule, a single crystal raw material and its solvent is placed and a boat in which a seed crystal is placed at one end thereof is installed, the ampoule is vacuum-sealed, and then the ampoule is heated in a heating furnace. The raw material is dissolved in a solvent to form a raw material solution, and the temperature of the heating furnace is gradually controlled while controlling the temperature distribution in the horizontal direction of the heating furnace so that the temperature on the seed crystal side is lower than the temperature on the raw material solution side. The method for producing a single crystal, which is characterized by growing a single crystal while lowering, and a boat containing the single crystal raw material and its solvent is installed in the ampoule, and the ampoule is vacuum-sealed. While heating in a heating furnace to dissolve the raw material in a solvent to form a raw material solution, while controlling the temperature distribution in the horizontal direction of the heating furnace so that the temperature on one side of the boat is higher than the temperature on the other side, Gradually lower the temperature of the heating furnace While producing a single crystal characterized by growing a single crystal, and in the ampoule, put a single crystal raw material and solvent put a boat with a seed crystal placed at one end thereof, after vacuum sealing the ampoule , Heating the ampoule in a heating furnace to melt the raw material in a solvent to form a raw material solution, so that the temperature distribution in the horizontal direction of the heating furnace is such that the temperature on the seed crystal side is lower than the temperature on the raw material solution side. A method for producing a single crystal, which is characterized in that the ampoule and the heating furnace are relatively moved while being controlled to grow the single crystal.

In the vertical temperature gradient method (VGF method) and the vertical Bridgman method (VB method), a circular wafer can be obtained with a high yield, and the thermal stress is evenly applied, so that a crystal with a low dislocation density is easily obtained. There is an advantage called. As a disadvantage, since the furnace is vertical and gas convection is intense, convection of the melt of the raw material is likely to occur, and twin crystals and polycrystals are generated in the crystal. In the method using a solvent, compositional supercooling is more likely to occur than in the case of a melt, so it is necessary to increase the temperature gradient, but the vertical temperature gradient method (VGF method) or the vertical Bridgman method
In the (VB method) and the like, the temperature gradient tends to be small due to the influence of gas convection, and in order to prevent this, it is necessary to divide the heater into fine pieces. Such a defect is caused by using the vertical furnace, and the horizontal furnace may be used.

A method for growing a single crystal by the horizontal temperature gradient method (HGF method) will be described with reference to FIG. The raw material and the solvent are put in a boat, the seed crystal 6 is set at a predetermined position of the boat, and the ampoule 2, for example, a quartz ampoule is vacuum-sealed. The ampoule 2 is heated by the heater 1 to melt the solvent and dissolve the raw material therein. The melt is brought into contact with the seed crystal 6 while maintaining the temperature so as to have a saturated concentration, and then the temperature is gradually lowered to grow the single crystal 4. The seed crystal 6 is used if necessary.

According to this method, it is possible to grow single crystals of ZnTe, ZnSe, GaAs, GaP, etc. even at a temperature below 800 ° C. However, considering the solubility of raw materials and the growth rate, 800 ° C. to 1 ° C.
Growth at 200 ° C is preferred. In addition, since the temperature gradient can be made large by this method, the growth rate can be made quite fast, but if it is too fast, twins and polycrystals will be generated, and the dislocation density will become high, so the growth rate of 5 mm / hr or less. Is preferred.

The same applies to the horizontal Bridgman method (HB method)
(Figure 2). The raw material and the solvent are put in a boat, the seed crystal 6 is set at a predetermined position of the boat 3, and the ampoule 2 is vacuum-sealed. The heaters 1a and 1b are adjusted so that the temperature and the temperature gradient are appropriate, and the ampoule 2 is placed so that the seed crystal 6 is located on the low temperature side.
After the installation, the ampoule 2 and the heating furnace are relatively moved to grow the single crystal 3.

In these methods, since the depth of the boat is shallow, thermal convection of the solution is unlikely to occur due to the temperature difference between the upper and lower sides, and the temperature fluctuation is small, so twins and polycrystals are less likely to occur. Further, since gas convection is unlikely to occur, the temperature gradient in the growth direction can be increased and compositional supercooling is unlikely to occur. The yield of raw materials decreases when a circular wafer is obtained because the cross section of the boat is D-shaped, but the probability of polycrystal formation depends on the vertical temperature gradient method (VGF).
Method) or the vertical Bridgman method (VB method), which is low enough to make up for it. The dislocation density is similar to the vertical temperature gradient method (VGF method) and the vertical Bridgman method (VB method),
Compared to the liquid-encapsulated Czochralski method (LEC method) and other methods, extremely low values can be obtained.

[0011]

【Example】

(Example 1) The growth of a ZnTe single crystal will be described as an example.
ZnTe has a melting point of 1295 ° C and a vapor pressure at the melting point of about 4 atm, and it causes softening and rupture when a quartz glass ampoule is used. Therefore, using Te as a solvent, Te: Zn = 7:
Mixed at a ratio of 3 (molar ratio). The saturation temperature of ZnTe at this time is 1
080 ℃, vapor pressure is about 0.7atm.

First, ZnTe; 500 g and Te; 440 g are put into a boat, and a ZnTe seed crystal is set at a predetermined position of the boat. After setting this boat in a quartz ampoule, the interior of the quartz ampoule is evacuated and vacuum sealed with an oxyhydrogen burner. This is set in the furnace and the temperature of the boat is raised to 1085 ° C with a heater to dissolve ZnTe in the Te solvent. After that, the temperature on the seed crystal side of the boat is set to 1080 ° C. and the other end is set to 1100 ° C. to make a temperature gradient in the boat (solid line in FIG. 3) to bring the melt into contact with the seed crystal. After allowing the seed crystal to sufficiently adjust, the temperature inside the furnace was gradually lowered as shown in FIG. 3 to grow a ZnTe single crystal. About half of the seed crystal of the obtained crystal was ZnTe single crystal, and the other was Te. Similarly, the experiment was repeated 5 times, but no trouble such as bursting of the quartz ampoule occurred.
A single crystal could be grown over and over. The single crystal could be grown with a high probability because, in addition to the small temperature fluctuations mentioned above, the growth of the crystal proceeds from the solution surface toward the bottom of the boat, so the polycrystal from the contact point between the boat and the melt. This is because growth does not occur.

Example 2 As in Example 1, ZnTe; 500
After placing g and Te; 440 g in a boat and setting the boat in a quartz ampoule, the interior of the quartz ampoule is vacuum-exhausted and vacuum sealed with an oxyhydrogen burner. Set this in the furnace and raise the boat temperature to 1085 ℃ with a heater
Dissolve Te in Te solvent. After that, the temperature on the low temperature side of the boat is set to 1080 ° C. and the other end is set to 1100 ° C., so that a temperature gradient is formed in the boat. Then, the heater is controlled so as to gradually move the low temperature zone to the high temperature side so that the growth nuclei are generated on the low temperature side of the temperature gradient. Since this growth method is performed by solution growth, the growth rate was set to 0.36 mm / hr in consideration of the diffusion rate of Zn. About half of the grown crystals are the ones set at low temperature
ZnTe single crystal, other was Te. Similarly, the experiment was conducted 5 times, but no trouble such as bursting of the quartz ampoule occurred, and ZnTe single crystals could be grown and reproducibility could be confirmed 5 times. In addition, in order to investigate the quality of the grown crystal, as a result of examining the light emission by the photoluminescence method at a liquid nitrogen temperature of 77 K, a pure green single peak having a sharp peak near 530 nm was observed, and with high purity. It was found to be a single crystal with low dislocation.

(Example 3) Ga: GaAs = 75: 25 (a) in a pBN boat
(t%) put 1500 g of raw material in which polycrystal is dissolved in Ga solvent in advance,
The quartz ampoule was evacuated to 2 × 10 ^-6 torr and then sealed. The heater 1a was set to high temperature soaking 1100 ° C, and the heater 1b was set to low temperature soaking 1000 ° C. Place the quartz ampoule so that the seed crystal is positioned on the heater 1b, and set the quartz ampoule to 0.1 m.
It was moved at m / hr to grow a GaAs single crystal. The <100> surface of the obtained GaAs single crystal was exposed, and the dislocation density was measured by etching with molten KOH and found to be 100 dislocations / cm ³ or less. As described above, the present invention can be applied to III-V group compound semiconductors other than II-VI group compound semiconductors.

[0015]

As described above, in the present invention, when growing a compound semiconductor single crystal having a high melting point and a high dissociation pressure, the growing crystal is dissolved in a solvent to obtain a saturated solution, which is then subjected to the horizontal temperature gradient method (HGF method). ), Since it was grown by the horizontal Bridgman method (HB method), it was found that a single crystal with high purity and low dislocation density can be obtained at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing the growth of a single crystal by a horizontal temperature gradient method (HGF method) (seed crystal; present).

FIG. 2 is a diagram showing growth of a single crystal by a horizontal Bridgman method (HB method).

FIG. 3 is a diagram showing a temperature change during growth of a single crystal by a horizontal temperature gradient method (HGF method) (seed crystal; present) in Example 1. The solid line shows the temperature distribution before growing, and the dotted line shows the temperature distribution during growing.

[Explanation of symbols]

 1 heater 1a heater 1b heater 2 ampoule 3 boat 4 single crystal 5 raw material melt 6 seed crystal

Claims (3)

[Claims] 1. A boat in which a raw material for a single crystal and a solvent for the single crystal are placed in an ampoule and a seed crystal is placed at one end of the ampoule, the ampoule is vacuum-sealed, and then the ampoule is heated in a heating furnace to obtain the aforesaid product. The raw material is dissolved in a solvent to form a raw material solution, and the temperature of the heating furnace is gradually controlled while controlling the temperature distribution in the horizontal direction of the heating furnace so that the temperature on the seed crystal side is lower than the temperature on the raw material solution side. A method for producing a single crystal, which comprises growing the single crystal while lowering it. 2. A boat containing a raw material for a single crystal and a solvent for the single crystal is placed in an ampoule, and the ampoule is vacuum-sealed.
The ampoule is heated in a heating furnace to dissolve the raw material in a solvent to form a raw material solution, and the horizontal temperature distribution of the heating furnace is controlled so that the temperature on one side of the boat is higher than the temperature on the other side. However, the method for producing a single crystal is characterized by growing the single crystal while gradually lowering the temperature of the heating furnace. 3. A raw material for a single crystal and a solvent are placed in an ampoule, and a boat having a seed crystal is placed at one end of the ampoule. The ampoule is vacuum-sealed, and then the ampoule is heated in a heating furnace. Is dissolved in a solvent as a raw material solution, and while controlling the horizontal temperature distribution of the heating furnace so that the temperature on the seed crystal side is lower than the temperature on the raw material solution side, the ampoule and the heating furnace are relatively A method for producing a single crystal, characterized in that the single crystal is grown by moving the single crystal.