JPH04224188A - Method for growing single crystal by zone melting method - Google Patents

Abstract

PURPOSE:To grow a single crystal uniform in composition from the upper part to the lower part by continuously heating a part of the ampule adjacent to the terminal part not contg. a polycrystal material throughout the crystal growth. CONSTITUTION:A heater 10 is wound around the gap 9' between an ummelted ampule 1 and a plug 5 in the length equivalent to that of the gap to cover the gap. The temp. of the heater 10 is set at the same temp. as a single crystal growth heater, and the heater is energized at the same time that a power is supplied to the growth heater. The entire ampule is then lowered with respect to the growth heater, and the molten part is moved from the front end of the rod-shaped polycrystal material sealed into the ampule to the terminal end to grow a single crystal. As a result, a high-vapor-pressure component is not condensed on the upper part of the ampule at low temp., the high-vapor-pressure component is not escaped from the polycrystal material, and a single crystal uniform in composition from the lower part to the upper part is grown.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of growing a single crystal by sealing a crystalline ionic material containing a component with a high vapor pressure in an ampoule and using the so-called zone melting method.

0002

2. Description of the Related Art The outline of the zone melting method is as shown in FIG. 2, which shows, as an example, HgCdTe, which is a multi-component semiconductor material containing Hg as one component, which has a high vapor pressure. This figure shows an intermediate stage of single crystal growth by the zone melting method, but at the initial stage of growth, in the ampoule 1, from the bottom, there is a seed crystal (CdTe) 2, a zone melting part (HgCdTe with excess Te), 3. After the polycrystalline material (HgCdTe) 4 is placed and the inside of the ampoule 1 is evacuated, the stopper 5 is removed.
is sealed by. The entire ampoule prepared in this way is suspended from above in the center of a fixed annular growth heater 6 for melting the band melting part 3, and the band melting part 3 is melted at a predetermined temperature. Once you do that, it will slowly descend downwards as shown by the arrow in the figure. At the initial stage, the seed crystal 2 and the melted zone 3 are in contact with each other, but as the ampoule gradually descends and the melted zone 3 gradually separates from the seed crystal 2, the single crystal 7 is placed on top of the seed crystal 2. is growing. FIG. 2 shows this intermediate stage. This zone melting method (THM=Traveling・Heater・M
Several papers have been published regarding single crystal growth using the method. For example, Journal of Science and Technology (January/February 1985, published by the Vacuum Society of America) = J. V
ac, Sci. Technol. A3(1), Jan/
Feb 1985, pp. 95-99, R. Tribou
THM, a break, written by let (Trible)
long・in・HgCdTe・bulk・met
allugy'', as well as the same magazine A6 (4), Jul/A
ug. 1988, pp. 2795-2799, L. Co
“Growth of Hg-base” by Lombo et al.
d・alloys・by・the・traveling
・heater・method”, etc.

As can be seen from the drawings in these papers and FIG. 2 of this specification, at the bottom of the stopper for vacuum sealing at the upper end of the ampoule, the inner wall of the ampoule, the stopper, and the polycrystalline material touch each other. It looks like they are in close contact.

However, in actual ampoule assembly, in order to seal the ampoule with a stopper, an oxyhydrogen burner is used from outside the ampoule to heat the stopper set inside the ampoule and the inner wall of the ampoule at a high temperature of 1500°C. A method of welding is used. HgCdTe has a melting point of about 700° C., and all components have relatively high vapor pressures, with Hg in particular having such a high vapor pressure that it evaporates even at room temperature. Therefore, bringing a high-temperature flame such as an oxyhydrogen burner close to a material made of these components may cause decomposition or evaporation of the material. For this reason, it is necessary to leave a gap of several cm between the welded portion 8 and the polycrystalline material. Furthermore, the coefficient of thermal expansion of quartz, which is the material of the ampoule, is
When the polycrystalline material 4 expands during crystal growth, the ampoule will be damaged unless there is a gap (1 to 2 mm) between it and the plug 5. Due to these circumstances, in an actual assembly, there is always a gap 9 shown with diagonal lines between the three parts, as shown in FIG. Further, there is also some gap between the ampoule inner wall 1' and the polycrystalline material 4. Because,
This is because the polycrystalline material is synthesized in a separate ampoule, so a gap is required to insert it into the growth ampoule.

[0005]

[Problem to be solved by the invention] When a crystalline material containing a component with a high vapor pressure is single-crystallized by the band melting method using an ampoule assembly that inevitably has gaps as described above, the following occurs. A problem arises. Naturally, the temperature of the melt zone is the highest in the assembly, but the temperature of the polycrystalline material located above it is also high, so the components with high vapor pressure, in this case Hg, gradually It evaporates. Then, it passes through the gap between the inner wall 1 of the ampoule and the polycrystalline material 4 and gathers at the upper part where the temperature is lower.
Condense. The final location is the gap 9' between the stopper and the ampoule, which is not welded, among the gaps 9. In one experiment, the amount of Hg that evaporates and condenses in this area is
The amount was about 200 mg, which is close to 1% of the amount of Hg in the 50 g total weight of the polycrystalline material.

[0006] As is well known, this material is an infrared detection material. It has been found that when 1% of Hg is lost, the detectable infrared wavelength shifts considerably to shorter wavelengths. For this reason, if a material with such compositional deviation is used, only a detector with characteristics deviating from the target detection wavelength can be obtained. Furthermore, as mentioned above, the amount of Hg evaporated gradually increases as the melt zone moves, so the composition shift is not uniform between the beginning and end of the grown polycrystal. Therefore, it is not effective to compensate in advance for Hg that is expected to evaporate.

The object of the present invention is to prevent condensation of high vapor pressure components in the gap at the top of the ampoule, and to grow a single crystal using a zone melting method, which makes it possible to grow a single crystal with a uniform composition from the top to the bottom. The purpose is to provide a training method.

[0008]

[Means for Solving the Problems] In order to achieve the above object, in the method of growing a single crystal by the zone melting method according to the present invention, only a part of the rod-shaped polycrystalline material sealed in an ampoule is melted, and this A method for growing a single crystal in which a molten part is moved from the tip of a rod-shaped polycrystalline material to a terminal end to form a single crystal. Heating is continued at the same temperature as the molten part throughout the crystal growth period.

[0009]

[Operation] Evaporated high vapor pressure components (for example, Hg) condense in low-temperature areas, so if that area is heated to a high temperature, no condensation will occur. Therefore, in the present invention, a heater is wound so as to heat the part next to the terminal end of the polycrystalline material, that is, the gap 9' between the unwelded stopper and the ampoule in FIG. 3, so that high vapor pressure components do not condense. That's what I do. If condensation does not occur, the vapor pressure of this component across the gap 9 will increase, and the amount of evaporation will be small and constant. Therefore, no significant errors or deviations occur in the composition of the grown crystal.

0010

[Example] Next, an example of the present invention will be described. To assemble the ampoule, as described above, stack the seed crystal, melted zone, and polycrystalline material in this order from the bottom in the quartz ampoule, and temporarily secure the ampule so that the distance between the top of the polycrystalline material and the stopper is approximately 1 mm. The inside of the ampoule is evacuated using a vacuum evacuation device, and once the specified degree of vacuum is reached, the upper part of the stopper is heated from the outside of the ampoule with an oxyhydrogen burner flame, and the ampoule is vacuum-sealed by welding the stopper and the ampoule. did. After cutting off the ampoule material above the sealing part of the stopper, we welded a hanging ring and hung it from a lowering device, and then adjusted the height of the growth heater so that it was positioned correctly at the melting zone. The process up to this point is completely the same as the conventional process.

Next, as shown in FIG. 1, a heating heater with a length exactly corresponding to the gap 9' between the unwelded ampoule 1 and the stopper 5 is placed so as to cover this area. I wrapped it around 10. The set temperature of this heating heater 10 is the same temperature as that of the single crystal growth heater (approximately 500
℃), and heating was started at the same time as power supply to the growth heater started. After this, 1 hour per hour as usual.
Single crystal growth was performed at a rate of descending the length of 50 μm. When the gap 9' was observed after completion, no condensed Hg was observed. Furthermore, as a result of cutting the grown single crystal into plates in the longitudinal direction and examining the composition distribution using conventional means, we found that there was no significant difference in composition between the upper and lower parts of the crystal. It was found that no deviation occurred.

0012

Effects of the Invention As detailed above, according to the present invention, even if a single crystal is grown using a material containing a high vapor pressure component by the zone melting method, no deviation in composition due to evaporation of the component occurs, and the overall As a result, a good single crystal with a uniform composition can be grown.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the positional relationship between a heated portion and a heater for explaining the present invention.

FIG. 2 is a diagram showing the principle of the zone melting method.

FIG. 3 is a detailed view of the sealing part of the ampoule.

[Explanation of symbols]

1 Ampoule 2 Seed crystal 3 Melting zone 4 Polycrystalline material 5 Plug 6 Growth heater 7 Single crystal 8 Welded part between ampoule and stopper 9 Gap 9' Gap between unwelded stopper and ampoule 10 Heating heater

Claims (1)

[Claims] Claim 1: A single-crystalline method in which only a part of a rod-shaped polycrystalline material sealed in an ampoule is melted, and the melted part is moved from the tip of the rod-shaped polycrystalline material to the end to form a single crystal. A single crystal growth method using a zone melting method, which is characterized in that a part of the ampoule where no polycrystalline material is present next to the terminal end is continuously heated at the same temperature as the melting part throughout the single crystal growth period. How to cultivate.