JPS6321278A - Ampule for growing single crystal - Google Patents

Abstract

PURPOSE:To obtain an ampule for growing single crystal wherein the growth of a high-quality compound semiconductor is easy by constituting the titled ampule of a double structure of an outer tube and an inner tube and making the inner tube to a crucible shape made of pBN. CONSTITUTION:The titled ampule is constituted of a double structure of an outer tube and an inner tube and this inner tube is made to a crucible shape made of pBN. The above-mentioned pBN in boron nitride produced by a chemical vapor growing method and for example, it is a high-purity material synthesized by allowing gaseous boron chloride to chemically react with gaseous ammonia at high temp. pBN is not rigid like high-purity quartz and shows proper flexibility. Further it is not closely stuck or fused for a compound semiconductor material especially for CdTe from a point of wettability. Therefore at a time for growing single crystal or cooling it, oppressing force is not applied by the crucible made of pBN for the single crystal material incorporated therein.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ampoule for growing compound semiconductor single crystals, and in particular, in order to manufacture high-quality compound semiconductor single crystals with a low density of dislocation etch pits, studies have been made in terms of structure and material. Regarding added ampoules. The ampoule of the invention is particularly made of CdTe.

■-■ group compound semiconductors such as HgCdTe and Q a A
Suitable for single crystal growth of ■-■ group compound semiconductors such as 85InP, but also includes gold clay, halides, ferroelectric substances used for making piezoelectric crystals and electro-optic crystals, ferrites, etc. It can also be used to produce single crystals or enlarged grains of inorganic materials.

BACKGROUND OF THE INVENTION As described above, the vertical Bridgman method is known as a method for growing single crystals of compound semiconductors.

In this method, raw materials are stored in a container, melted in an electric furnace with an appropriate temperature gradient, and the temperature of the raw materials is gradually lowered by moving the container and furnace in a relative vertical direction. Assimilation and single crystallization of the melt takes place. As a container, it is round! In order to prevent contamination due to acetylation of the raw material and volatilization loss of easily evaporable components, ampules in which the raw material is sealed with true nitrogen are often used.

Prior Art and its Problems Conventionally, high purity quartz has generally been used as an ampoule material for crystal growth. However, it has been recognized that quartz angles tend to produce corner dislocation densities in single crystal materials, especially in CdTe, which tends to lead to a decline in the quality of the produced single crystals. . In connection with this, the ease with which the produced single crystal can be extracted from the ampoule is poor, and a situation has often arisen in which the produced single crystal cannot be extracted without breaking the ampoule. Quartz ampules have not been found to be able to replace them from the viewpoint of their sealing properties, and are currently used despite these drawbacks.

Methods such as applying a carbon coating to the inner surface of the quartz ampoule have been used to avoid adhesion between the single crystal produced and the quartz, or to avoid contamination from the quartz.
It was highly effective.

SUMMARY OF THE INVENTION The fundamental cause of the above drawbacks is thought to be that stress is applied to the single crystal during growth or cooling due to the quartz material, which induces the generation of dislocations.

In addition, quartz has good wettability with many materials, especially CdTe, and therefore tends to cause sagging as described above. Therefore, the present inventors have repeatedly investigated the structure and material of the ampule to eliminate these drawbacks.

As a result, it was discovered that the above drawbacks could be fundamentally solved by (1) making the ampoule a double structure consisting of an outer tube and an inner tube, and (2) making the inner tube a crucible made of PBN. I got it. Since the pBN rutsuho is more flexible than quartz, that is, it is not as rigid as quartz, it easily deforms and exerts a compressive force on the single crystal grown inside it. Furthermore, especially with respect to CdTe, it does not adhere closely to CdTe from the viewpoint of wettability, and the single crystal can be extracted easily.

In this way, by making the ampoule a double structure and making it possible to select the structure and/or material of the outer tube and inner tube separately, the inner tube can be used to relax stress and improve adhesion to the growing single crystal. The material and structure of the outer tube can be selected from the viewpoints of mitigation of pollution, non-contamination, etc., and the material and structure of the outer tube can be selected from the viewpoint of sealability and other general considerations.

Thus, the present invention provides an ampoule for single crystal growth, which has a dual structure of an outer tube and an inner tube, and the inner tube is in the form of a pBN crucible.

In the vertical Bridgman method, as shown in Figure 2,
In an electric furnace having a predetermined temperature gradient, the ampoule containing the raw material melt and the furnace are given relative vertical movement to solidify the melt, resulting in single crystallization. In the vertical Bridgman method, the ampoule is lowered.

The present invention provides an ampoule most suitable for such a single crystal growth method. FIG. 1(a) shows a specific example of the ampoule of the present invention. The ampoule has a double structure consisting of an outer tube 1 and an inner tube 2, and the inner tube 2 has a pBN crucible shape. A single crystal material to be grown is weighed and stored in the inner tube 2 to match the target composition, and the upper end of the outer tube 1 is sealed by appropriate means after the inside of the ampoule is evacuated.

pBN is boron nitride produced by chemical vapor deposition, and is a high-purity material synthesized by, for example, chemically reacting boron chloride gas and ammonia gas at high temperatures.

pBN is not rigid like high-purity quartz, which is a conventional common ampoule material, and exhibits appropriate flexibility. Furthermore, it does not adhere or adhere to compound semiconductor materials, particularly CdTe, from the viewpoint of wettability. Therefore, no compressive force is applied to the single crystal material inside the pBN crucible during single crystal growth or cooling. In the case of conventional quartz materials,
Because of its rigidity, it caused pressure on the internal single crystal from the surroundings, thus inducing many dislocations, whereas p
Due to the moderate flexibility of the BN crucible, it is deformable and depending on the state of the single crystal material it can be slightly deformed outwards so as not to compress it. This relieves the stress in the single crystal.

Figures 1(b)-(d) illustrate modifications to the barrel that further promote stress relief and ease of extraction.

In Figure 1(b), the pBNu crucible in the inner tube is
1. A radius is formed at the joint between the wall and the bottom. This may improve the flexibility of the pBN crucible.

In FIG. 1(c), the entire pBN crucible portion of the inner tube is rounded. This structure is also effective in improving the flexibility of the pBN crucible.

FIG. 1(d) shows an example of a structure in which a taper T is provided that widens from the pBN crucible toward the opening.

This is applicable to the first (b) and (c) drawings. This further enhances stress relaxation and extraction of the single crystal.

Preferably, the wall thickness of the pBNvV crucible is about 1 inch or less.

The outer tube is made of quartz, Pyrex glass, glass, etc. with sealing properties.
It can be made from any material based on general ampoule considerations such as strength, cost, etc.

In this way, by making the ampoule a 2"M' structure, there is a great degree of freedom in selecting the structure and material of the outer tube and inner tube. The structure and material can be freely selected depending on the purpose of each function. It is a feature of the present invention that the vacuum gap existing between the outer tube and the inner tube minimizes the influence of temperature fluctuations on the outside of the ampoule into the inside of the inner tube of the ampoule. However, it is also effective in promoting the growth of high-quality single crystals with close subgrain boundaries.Also, even if the inner tube ruptures due to the difference in thermal expansion, the outer tube will prevent the single crystal from coming into contact with the outside air. However, such rupture accidents can be drastically reduced according to the present invention.

Effects of the Invention 1 The ampoule has a double structure and the use of a pBN crucible inner tube prevents the induction of dislocation in the produced single crystal and facilitates extraction.

2. Contamination of the single crystal can be prevented.

& Since the structure of the inner tube and outer tube can be freely designed, it is possible to create the optimal ampoule from the viewpoint of single crystal quality and workability.

4. Due to the existence of a vacuum gap between the inner tube and the outer tube,
During crystal growth, variations in the temperature and thickness of the outer wall of the ampoule have minimal influence on the produced single crystal, and the generation of crystal nuclei on the outer wall is suppressed, making it possible to produce high-quality single crystals with few sub-grain boundaries.

5. From the above points, it is particularly easy to grow compound semiconductors of extremely madder quality.

Example The effect of the ampoule of the present invention was confirmed using a CdTe crystal. For crystal growth, a two-stage furnace as shown in Figure 2 was used, with the upper stage set at 1150°C and the lower stage set at 800°C7, and an ampoule with the structure shown in Figure 1(d) was used. I used something. Bridgman was considered as a crystal growth method. The crystal growth conditions were as follows: Ampoule lowering speed: 1 mm/hr Temperature gradient: 3°C/Ampoule inner diameter: 2wσ For comparison purposes, crystal growth was performed under the same conditions using a conventional quartz ampoule.

The etch bit density and its distribution were investigated for the produced single crystal using Nakagawa etchant. As a result, the etch bits of the CdTe single crystal produced in the quartz ampoule were distributed in a cell-like manner7, and the etch pit density was lX10' to 3X10@[:crrL-''). With this, the etch pits are uniformly distributed and the bit constant is 1X10.
'~5X10'(CIrL-'') and potash, high quality Cd
A Te single crystal was obtained.

Figures 1(a), 1(b), 1(c) and 1(d) show specific examples of ampules according to the invention, and Figure 2 shows the cross section of the crystal growth apparatus used in the examples and its temperature. Show the distribution.

1: Outer tube 2: Inner tube R: Earl T: Taper Figure 1 (q)

Claims (1)

[Claims] 1) It has a double structure of an outer tube and an inner tube, and the inner tube has a pB
An ampoule for single crystal growth characterized by being in the form of a crucible made of N. 2) Claim 1, in which the pBN crucible of the inner tube is rounded at the joint between its side wall and bottom.
Ampoule as described in section. 3) The ampoule according to claim 1, wherein the entire bottom of the inner tube of the pBN crucible is rounded. 4) Claims 1 to 3 in which the pBN crucible of the inner tube is tapered to expand from the bottom toward the opening.
An ampoule as described in any one of the following paragraphs. 5) The ampoule according to any one of claims 1 to 4, wherein the outer tube is made of quartz, Pyrex glass, glass, or the like. 6) An ampoule according to any one of claims 1 to 5 for growing II-VI group and III-V compound semiconductor single crystals. 7) An ampoule according to claim 6 for growing a CdTe single crystal.