JPH04362085A - Method for growing single crystal by zone melting method - Google Patents

Abstract

PURPOSE:To prevent the condensation of high vapor pressure components among spaces on the upper part of an ampul and to grow single crystals having a uniform compsn. from the upper part to the lower part. CONSTITUTION:Tellurium 10 is melted and is entered the space part of an ampul at the upper end part of a raw material, by which the spaces are filled. Next, at the time of exeucting the growing of crystals, the high vapor pressure ccaponents evaporated by heating can not escape to the upper part 9c of the ampul with a low temp., the escape of the high vapor pressure components from the raw material does not occur.

Description

[Detailed description of the invention]

0001

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

0002

[Prior Art] A method for growing single crystals using the zone melting method is shown in FIG.
-xCdxTe (1>x>0) is shown. 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 zone (excess tellurium Hg
1-yCdyTe)3, raw material (polycrystalline Hg1-xC
After evacuating the inside of the ampoule 1, the ampoule 1 is sealed with a stopper 5. The entire ampoule prepared in this way is suspended from above in the center of a fixed annular heater 6 in order to melt the band melting portion 3.
Once the melting zone 3 has melted at a predetermined temperature, it is slowly lowered downward 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.

[0003] This band melting method (THM=Travelin
It is also called g Heater Method. ) Several papers have been published regarding single crystal growth using For example, Journal of Vacuum Science and Technology (1985, 1
(Mon./February, published by the American Vacuum Society) {J. Vac. Sc
i. Technol. A3(1), Jan/Feb
, 1985}, pp. 95-99, R. Triboule
THM, a breakth
rough in HgCdTe bulk meta
llugy” and the same magazine A6 (4), Jul/Au
g, 1988, pp. 2795-2799, L. Col
ombo et al., “Growth of Hg-bas
ed alloys by thetraveling
Heater Method”, etc.

From these articles and FIG. 2, it appears that the inner wall of the ampoule, the stopper, and the raw material are in close contact with each other at the lower part of the stopper for vacuum sealing at the upper end of the ampoule. However, in actual ampoule assembly, in order to seal the ampoule with the stopper, an oxyhydrogen burner is used from outside the ampoule to seal the stopper set inside the ampoule and the inner wall of the ampoule at a temperature of 1,500 mm.
A method of welding at temperatures as high as ℃ is used. Hg1-xCd
xTe has a melting point of about 700° C., and all components have relatively high vapor pressures, especially mercury, which has 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. Therefore, when welding, as shown in Fig. 3, the welding part 8 and the upper end of the raw material 4 are separated by several centimeters.
It is necessary to leave an interval between Furthermore, since the coefficient of thermal expansion of quartz, which is the material of the ampoule, is smaller than that of Hg1-xCdxTe, when the raw material 4 expands during crystal growth, if there is no gap 9a (1 to 2 mm) between it and the stopper 5, the ampoule will be damaged. Due to these circumstances, in the actual assembly, there is always a gap 9a shown with diagonal lines between the three parts as shown in Figure 3.
9c exists. Further, there is also some gap 9b between the inner wall of the ampoule and the raw material 4. This is because the raw materials are synthesized in separate ampoules, so a gap is required to accommodate them in the growth ampule.

[0005]

[Problem to be Solved by the Invention] When monocrystallizing a crystalline material containing a component with high vapor pressure by the zone melting method using an ampoule assembly that inevitably has gaps, the following problems occur. A problem arises. That is, since the band melting zone has the highest temperature in the assembly, it is natural that
The temperature of the raw material located above it is also high. Therefore, components with high vapor pressure, ie, mercury in this case, gradually evaporate from the raw material. Then, it passes through the gap 9b between the inner wall of the ampoule 1 and the raw material 4, and gathers at the upper part where the temperature is lower.
Condense. The final location is the gap 9c between the stopper and the ampoule, which is not welded, among the gaps 9. In one experiment, the amount of mercury that evaporated and condensed in this area was approximately 200 mg;
The value is close to 1% of the amount of mercury in g. As is well known, this material is an infrared detection material. It is known 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 evaporation of mercury gradually increases as the melt zone moves, so the compositional shift is not uniform between the beginning and the end of the grown crystal. Therefore, it is not effective to compensate in advance for the mercury that is expected to evaporate. An object of the present invention is to solve the problems of the prior art as described above and to provide a method for growing a single crystal having a desired composition uniformly from the upper part to the lower part by a zone melting method.

[0006]

[Means for Solving the Problems] The present invention provides a method for growing a single crystal by a vertical zone melting method in which a raw material containing a component with a high vapor pressure is inserted into an ampoule. This is a method for growing a single crystal using a zone melting method, which is characterized in that the single crystal is grown after the gaps between the two are filled with molten tellurium.

[0007]

[Effect] High vapor pressure components (for example, mercury) that evaporate in the ampoule condense in the gap between the quartz at the top of the ampoule, where the temperature is lowest. If the area is sealed, high vapor pressure components can be blocked. In order to achieve this, in the present invention, a small amount of tellurium is placed between the upper end of the raw material and the stopper, and after the ampoule is vacuum sealed as usual, this tellurium is melted by heating from the outside. Then, by letting it flow into the gap, it closes the gap. As a result, the evaporated high vapor pressure components will condense near the upper end of the raw material, but the temperature at the upper end of the raw material has risen to some extent due to heat conduction from the melting zone at the bottom, so the high vapor pressure components will vaporize. Since the pressure is also high and close to saturation, the components do not condense in the same amount as in conventional methods. Furthermore, unlike conventional methods, the components condensed at the top of the raw material will eventually be incorporated into the crystal growth process. Therefore, no significant errors or deviations occur in the composition of the grown crystals.

[0008]

[Example] Next, an example of the present invention will be described. As for assembling the ampoule, first, as previously described, the seed crystal, the melted zone, and the raw material were stacked in this order from below in a quartz ampoule. Next, as shown in FIG. 1(a), unlike the conventional method, a small amount of tellurium 10 was placed on top of the raw material 4, and a stopper 5 was placed on top of it. After this, the inside of the ampoule is evacuated again using the conventional vacuum evacuation device, and when the predetermined degree of vacuum is reached, the upper part of the stopper 5 is heated from the outside of the ampoule with an oxyhydrogen burner flame, and the stopper 5 and ampoule 1 are separated. The ampoule was vacuum sealed by welding. The sealing part of the stopper (
After cutting off the ampoule material above the welding part 8), a hanging ring 11 was welded and the ampoule material was suspended from a lowering device. Next, Figure 1(b)
), the height of the heater 6 was adjusted so that it was located at the position of the tellurium 10, and the minimum power needed to melt the tellurium was supplied to the heater 6. Then, as shown in the figure, the melted tellurium 10a that became liquid was made to just close the upper part of the gap 9b. This is because the tellurium 10 melts and spreads laterally, and when it comes into contact with the inner wall of the ampoule 1, the gap is naturally closed, so no special operation is required. After this, as usual 1
A single crystal was grown at a rate of dropping a length of 150 μm per hour. During the growth, a small amount of mercury condensation was observed in the upper part of raw material 4, that is, below the part where the gap was filled with tellurium, but no condensation was observed in the gap above the tellurium. Next, the grown single crystal is cut into plate shapes in the vertical direction.
As a result of examining the composition distribution using conventional means, it was found that there was no significant difference in the composition between the upper and lower parts of the crystal, indicating that no shift in crystal composition occurred due to excessive evaporation of mercury.

[0009]

[Effects of the Invention] As detailed above, if the method of the present invention is used, even if a single crystal is grown using a material containing a high vapor pressure component by the zone melting method, compositional deviation due to evaporation of the component will not occur. , it is possible to grow a good single crystal with a uniform composition as a whole.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram for explaining the method of the present invention.

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

FIG. 3 is an explanatory diagram showing the relationship between the sealing part of the ampoule and the gap.

[Explanation of symbols]

1 Ampoule 2 Seed crystal 3 Melting zone 4 Raw material 5 Stopper 6
Heater 7 Single crystal 8
Welded parts 9a, 9b, 9c between ampoule and plug
10,10a Tellurium 11 Hanging ring

Claims (1)

[Claims] Claim 1: In a method of inserting a raw material containing a component with high vapor pressure into an ampoule and growing a single crystal by a vertical zone melting method, the gap between the raw material and the ampoule at the upper end of the raw material is filled with molten tellurium. A method for growing a single crystal using a zone melting method, which is characterized in that single crystal growth is performed after sealing.