JPH0321511B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention relates to the structure of a crystal growth ampoule for growing single crystals or enlarged crystal grains of metals, compound semiconductors, etc., particularly the structure of crystal growth ampoules used in the vertical Bridgeman method and the vertical gradient-ent freezing method. It is related to. The ampoule of the present invention can be made of not only metals but also CdTe, HgCdTe,
High-quality single crystals or inorganic materials, including - group compound semiconductors such as GaAs, InP, halides, ferroelectric materials, ferrites, etc. used in the creation of piezoelectric elements and electro-optic crystals. Useful for producing enlarged grains. BACKGROUND TECHNOLOGY As a method for growing crystals of inorganic materials as described above, the vertical Bridgeman method and the vertical gradient freezing method are often used.
In these methods, raw materials are stored in a container, heated in an electric furnace with an appropriate temperature gradient to melt the raw materials, and the container is moved relatively vertically within the furnace to gradually increase the temperature. Solidification and single crystallization of the raw material melt are performed while lowering the temperature. As a container, an ampoule made of quartz or the like is often used to vacuum-seal the raw material in order to prevent contamination due to oxidation of the raw material and volatilization loss of easily evaporable components. As for the form of the ampoule, a cylindrical ampoule with an inverted conical bottom is commonly used. For example, Japanese Utility Model Application Publication No. 1983-7596 discloses a crucible for growing a single crystal, which has a conical portion at the bottom of the container. JP-A No. 58-135195 describes the fact that in the prior art, in semiconductor crystal growth ampoules with a pointed bottom, a large number of small-angle grain boundaries were generated within a single crystal. When using this ampoule, the occurrence of small angle grain boundaries within one single crystal was reduced, but we realized that many single crystals were formed at the same time, making it impossible to obtain a single crystal with a large cross-sectional area. proposed a structure with multiple branches at the tip. Jitsukai Showa 49-119445
No. 1, No. 1, discloses a crucible for crystal growth, also with a conical bottom, showing a dual structure of a thinner inner crucible for elasticity and a thicker outer crucible to withstand high vapor pressures. The outer crucible functions as a protector to prevent the contents from being oxidized even if the inner crucible is destroyed. However, in reality, such ampoules are not necessarily effective, and there is a desire for ampoules of even better quality and a higher effect on crystal growth. Problems with the Prior Art As mentioned above, in the vertical Bridgeman method and the vertical gradient freezing method, single-walled ampoules with an inverted conical bottom have been the mainstream. However, such ampoules often have poor crystallinity due to the formation of subgrain boundaries during crystal growth. Furthermore, if the difference in thermal expansion coefficient of the crystal is large compared to the material of the ampoule, there is a problem that the ampoule may break or burst during cooling after crystal growth. If the bottom of the ampoule has an inverted conical shape, the inclined surface of the cone becomes the place where crystal nuclei are generated, and many crystals with different growth directions are likely to be formed.Also, the probability of occurrence of sub-grain boundaries is high, and the crystallinity of the product is likely to be very poor. It was also recognized that Means for Solving the Problems As a result of conducting research on crystal growth using ampules of various shapes, the present inventors found that in order to promote the growth of large single crystals and reduce the occurrence of subgrain boundaries, It was concluded that it is fundamentally important to prevent the internal melt from being affected by temperature fluctuations on the outer wall of the ampoule as much as possible, and more preferably to eliminate the presence of inclined walls. For this purpose, it has been found that it is effective to make the ampoule a double structure consisting of an inner tube and an outer tube with a vacuum gap formed therebetween, and to make the ampoule bottom a flat bottom structure. The double-tube structure is also advantageous in that it avoids problems such as oxidation of crystals due to ampoule breakage, because even if the ampoule inner tube breaks during cooling, the outer tube remains undamaged. It has been found that it is also effective to provide a means for promoting heat flow at the center of the ampoule bottom in order to facilitate the generation of crystal nuclei at the center of the ampoule bottom. In the case of a single-tube structure, for example, in direct synthesis, there was a concern that the molten metal would leak from the inner tube into the inner tube-outer tube gap due to bumping due to reaction heat, but it is possible to weld the upper end of the inner tube to the inner surface of the outer tube or By keeping them in contact, penetration of molten metal into the gap can be effectively prevented. SUMMARY OF THE INVENTION Thus, the present invention provides a crystal growth ampoule used for producing single crystals or enlarged crystal grains by the vertical Bridgeman method or the vertical gradient freezing method, which comprises an inner tube with a bottom end and Provided is an ampoule for crystal growth which has a double tube structure consisting of an outer tube and is characterized in that the bottom end surfaces of the inner tube and the outer tube are flat. This ampoule can be used in a form in which a heat flow promoting means is attached to the center of the bottom of the outer tube, and further in a form in which the periphery of the upper part of the inner tube is welded or in contact with the inner wall surface of the outer tube. DETAILED DESCRIPTION OF THE INVENTION In the vertical Bridgeman method or the vertical gradient freezing method, as shown in FIG. This solidifies the melt and results in single crystallization. In the vertical Bridziman method, the ampoule is lowered, while in the vertical gradient freezing method, the ampoule is fixed and the furnace is cooled. FIG. 1 shows a specific example of a sample of the present invention. 1st
Figure a shows an ampoule having a double tube structure consisting of an inner tube 1 and an outer tube 3 with a bottom end and a flat bottom end surface 5. In these ampoules, the inner tube is inserted into the outer tube, the substance to be crystal grown is weighed to match the target composition, and then charged into the inner tube.The ampoule is then evacuated and the upper end of the outer tube is melt-sealed. It is formed by A vacuum gap exists between the inner and outer tubes. In this case, even if the bottom temperature is low, crystal nuclei will be generated in the lower part, and even if multiple nuclei are generated, crystal growth will occur in the same direction due to the flat bottom structure, so the crystals obtained will eventually coalesce. large crystals can be obtained. Subgrain boundaries are also less likely to occur. The double tube structure minimizes the influence of temperature fluctuations on the outside of the ampoule to the inside of the ampoule inner tube, improving the single crystallization rate and producing high-quality crystals without sub-grain boundaries. The double tube structure, together with the flat bottom structure, greatly increases the single crystallization rate and makes it possible to produce high quality crystals. Furthermore, since the ampoule is double layered, due to the difference in thermal expansion coefficient of the crystal ampoule materials, even if the inner tube is damaged during cooling after crystal growth, the crystal will not come into contact with the outside air, and the crystal will not be oxidized. It can be prevented. FIG. 1b shows a structure in which a rod 7 is attached to the center of the bottom of the outer tube of the ampoule shown in FIG. 1a as a means for promoting heat flow. As a result, crystal nuclei are generated at the center of the ampoule bottom, and the crystal grains become larger. Since the outflow effect of latent heat during crystal growth is enhanced, the single crystallization rate and quality of the crystal are improved more effectively than in case a. In addition to rods, it is also possible to use heat pipes, cooling gas blowing pipes, etc. as means for promoting heat flow.Also, by installing a cooling pipe at the end of the rod and flowing cooling water, the heat flow effect can be further enhanced. It can be increased. FIG. 1c shows a specific example in which the periphery of the upper part of the inner tube of the ampoule of FIG. 1b is welded or abutted to the outer tube at W (of course, it is also applicable to the ampoule of FIG. 1a). In direct synthesis before crystal growth, molten metal may overflow from the inside due to bumping due to reaction heat and leak into the gap between the inner and outer tubes. In such a case, normal crystal growth cannot occur, so it is necessary to weld the upper part of the inner tube to the outer tube to prevent leakage. To make it, the peripheral part of the inner tube is first welded to the outer tube, and at this time several small holes are formed in the wall of the inner tube so that the gap can be evacuated. Thereafter, raw materials are charged and the outer tube is melt-sealed after evacuation. Alternatively, the inner tube may be inserted into the outer tube with its upper end periphery in close contact with the outer tube. Transparent quartz, opaque quartz, pyrex glass, glass, etc. are used as the material for the ampoule. The outer tube may be made from these materials and the inner tube may be made from carbon, PBN, alumina, magnesia, etc. In addition, the inner tube contains carbon,
A material coated with PBN, alumina, SiC, etc. may also be used. The rod is preferably made of the same material as the ampoule from the viewpoint of weldability, but various materials can be used by employing an appropriate joining method. The size of the ampoule varies depending on the target material, but it is generally 40 to 75 mm in diameter and 13 to 15 cm in height. Example Regarding the growth of CdTe crystal, the effect of the ampoule according to the present invention was confirmed. A two-stage furnace as shown in Figure 2 is used for crystal growth, with the upper stage heated at 1150°C.
The temperature of the lower furnace was set at 800°C, and crystal growth was carried out using the ampoule shape shown in Fig. 1c. As crystal growth methods, we investigated the Bridgeman method and the gradient freezing method. The crystal growth conditions are as follows. Γ Bridziman method Ampoule lowering rate 1 nm/hr Temperature gradient 3℃/cm Ampoule inner diameter 1φ Γ Gradient freezing method Cooling rate 1℃/hr Temperature gradient 4℃/cm Ampoule inner diameter 3/φ The quality was as follows.

[Table] Represent.
From the table, it can be seen that the shape of the ampoule has a significant effect on the single crystallization rate and its crystallinity. The improved ampoule of the present invention achieves improved crystallinity and single crystallinity. Effects of the Invention (1) By forming the ampoule into a double structure, the outer wall of the ampoule is less susceptible to temperature fluctuations during crystal growth, and the generation of crystal nuclei on the outer wall is suppressed. Therefore, large single crystal parts are easily formed, the occurrence of sub-grain boundaries is reduced, and high quality crystals are formed. Furthermore, even if the ampoule breaks during cooling after crystal growth, it does not come into contact with the atmosphere, so oxidation of the crystal does not occur during cooling. (2) The flat bottom of the ampoule prevents the growth of crystals with different growth directions, and together with the above-mentioned double structure, larger crystal grains are obtained, and the generation of subgrain boundaries is further suppressed. (3) When a heat flow promoting means such as a rod is attached to the center of the bottom of the ampoule outer tube, the generation of crystal nuclei that become seeds is likely to occur at the center of the ampoule bottom, and as the crystal grains become larger, subgrain boundaries also occur. It becomes hard and produces high quality crystals. (4) Measures are taken to prevent damage to the ampoule due to the difference in thermal expansion coefficient between the crystal and the material of the ampoule, and also problems caused by bumping due to reaction heat when directly synthesizing the crystal before crystal growth are also solved.

[Brief explanation of the drawing]

Figures 1a, 1b and 1c are cross-sectional views of specific examples of ampules according to the invention. FIG. 2 is a drawing together with a cross section of the crystal growth apparatus used in the examples and a graph showing its temperature distribution. 1: Inner tube, 3: Outer tube, 5: Bottom end surface, 7: Rod, W: Welded part.

Claims (1)

[Scope of Claims] 1. A crystal growth ampoule used for producing single crystals or enlarged crystal grains by the vertical Bridgeman method or the vertical gradient freezing method, comprising an inner tube and an outer tube with a bottom end; 2.
An ampoule for crystal growth, which has a double tube structure and has flat bottom end surfaces of the inner tube and the outer tube. 2. The ampoule according to claim 1, wherein a heat flow promoting means is attached to the center of the bottom of the outer tube. 3. The ampoule according to claim 1 or 2, wherein the upper periphery of the inner tube is welded to or in contact with the inner wall surface of the outer tube.