JPS62223088A - Method for growing compound single crystal - Google Patents

Abstract

PURPOSE:To produce compound single crystal having low dislocation density and a little grain boundary in good yield, by making a specific temperature gradient in the vicinity of a solid-liquid interface of a compound melted in a crucible. CONSTITUTION:A compound is put in a crucible having a conic bottom part and sealed. Then, the crucible is attached to a drive shaft of Bridgman furnace, fed to Bridgman furnace and the compound is melted by setting temperatures of a high-temperature zone and a low-temperature zone in such a way that the temperature gradient in the vicinity of a solid-liquid interface is 1-10 deg.C/cm. The whole crucible is moved to the low-temperature zone and gradually cooled to grow compound single crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for growing a compound single crystal with a low dislocation density (and few grain boundaries) by the Bridgman method.

[Conventional technology]

Cadmium telluride (CdTe) single crystals are used as substrates for epitaxial growth of mercury cadmium telluride, which is a material for infrared detectors, and as materials for radiation detectors that can operate at room temperature. To obtain a CdTe single crystal, the compound is usually synthesized by vacuum sealing Cd and Te in a crucible with sharp protrusions and then melting, or by vacuum sealing a separately synthesized compound polycrystal in a crucible and melting it. This is gradually cooled and solidified to grow a single crystal. The reason why a crucible having a sharp protrusion is used in this growth method is to use a minute single crystal that is first precipitated within the tip of the protrusion as a seed crystal to turn the whole into a single crystal. Various methods for growing single crystals based on this principle are known, but the representative one is the Bridgman method, in which a crucible is moved from a high temperature zone to a low temperature zone in an electric furnace with an appropriate temperature gradient. It is used for crystallization. The Bridgman method is further divided into a vertical type and a horizontal type, and the vertical Bridgman method will be explained below as an example.

The vertical Bridgman method uses a crucible with a conical bottom and an electric furnace whose upper part is kept at a temperature higher than the melting point of CdTe (1092 °C) and whose lower part is kept at a temperature lower than the melting point of CdTe. The conventional method for growing CdTe single crystals is to set the temperature of the high temperature zone to 1100 to 1200 °C, the temperature of the low temperature zone to about 800 to 1000 °C, and the temperature gradient of the solidification zone that transitions from the high temperature zone to the low temperature zone to be 20 to 120 °C. . Since the crucible descends at a very slow rate of several nanometers per hour and is considered to be in a thermal equilibrium state, it is almost safe to assume that this temperature gradient is equal to the temperature gradient near the solid-liquid interface inside the crucible. However, according to the conventional growth conditions as described above, the size of the single crystal in the resulting CdTe crystal is small, that is, there are many grain boundaries, and it takes time and effort to cut out a crystal plate (wafer) in the desired orientation. However, it had the disadvantage of low wafer yield. Another disadvantage is that the dislocation density, which is an important quality of a single crystal, is extremely high at approximately 106c+n-''.As shown in Figure 2, these dislocations are mainly arranged in a network structure. is called a cell structure, but if there is a cell structure like this, each cell (
This may cause slight differences in crystal orientation between the diameters of about 100 to 300 μm and non-uniformity in electrical characteristics.

When mercury cadmium telluride is epitaxially grown on such a CdTe single crystal substrate, dislocations and cell structures of dislocations propagate to the epitaxial layer, making it impossible to obtain a high-quality epitaxial layer.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for growing compound single crystals that eliminates the drawbacks of the above-mentioned conventional methods and allows high-quality compound single crystal wafers with low dislocation density to be obtained with good yield.

[Means for solving problems]

To achieve this objective, the present inventors focused on the temperature gradient of the solidification zone, that is, the temperature gradient near the solid-liquid interface, as a control factor for grain boundaries and dislocation density, and conducted growth experiments with various temperature gradients. As a result, the temperature gradient was reduced by 1 to b, and most of the melt became single crystal. Moreover, the resulting single crystal had no dislocations in the cell structure, and the dislocation density was reduced to about one-tenth. The present invention was achieved by discovering that this can be reduced.

The reason why the temperature gradient near the solid-liquid interface is set to 1 to b is that when it exceeds 10° C./cII+, the number of grain boundaries increases and the dislocation density in the single crystal portion increases.

Although it is preferable that this temperature gradient be as small as possible, the lower limit was set at 1°C/c+n in view of the accuracy of temperature control. The reason why such a low temperature gradient reduces grain boundaries and eliminates dislocations in the cell structure is thought to be because the thermal stability of the solid-liquid interface increases. In particular, if there is a slope above and below the crucible, convection of the melt is unavoidable, but it is assumed that by making the temperature gradient gentler, this convection will be suppressed and subtle temperature changes at the solid-liquid interface will be prevented. Ru.

〔Example〕

A quartz ampoule with an inner diameter of 3 cm, a cylindrical part length of 10 cm, and a conical bottom part depth of 4 cm was used as a crucible. A carbon film was attached to the inner surface of the ampoule, 350 g of CdTe polycrystal was charged, and the temperature was set at 10-" Torr. The ampoule was sealed under vacuum.A quartz hanger was welded to the top of the ampoule and attached to the drive shaft of a Bridgman furnace.

The temperature distribution inside the Bridgman furnace is 1100°C in the high temperature zone.
, the low temperature zone was 1060 °C, and the solidification zone distance was 8 cm (therefore, the temperature gradient was 5 °C/am). The drive shaft is lowered to position the entire ampoule in the high temperature zone, and the
．． The rotation speed was maintained at 5 rotations until the CdTe polycrystal was completely melted, and after the melting was completed, the vaginal ampoule was lowered at a rate of 1.5 rotations/hour. After the entire ampoule had moved to the low-temperature zone, the descent was stopped, and while the rotation continued, the temperature inside the furnace was gradually lowered to room temperature. Cultivated Cd
As a result of cutting the Te crystal in the <111> direction, almost no grain boundaries were observed on the cut surface. From this crystal (11
1) A wafer with a flat surface was cut out, polished to a mirror surface, and then etched with an acid-based etching solution. In Figure 1, (111)Cd
A photograph of the surface is shown (62.5x magnification). The spots in the figure are etch pits, which correspond to dislocations, and the dislocation density can be determined from the number of etch pits. In the (111) Cd plane shown in FIG. 1, no cell structure is observed at all, and the dislocation density is 2 X I Q-'cm-''.

For comparison, the high temperature zone is 1130℃, the low temperature zone is 980℃,
The distance of the solidification zone is 5crn (therefore, the temperature gradient is 30℃/c
FIG. 2 shows a photograph of (111)Cd that was similarly etched with respect to the single crystal portion of the CdTe crystal grown as (m). In FIG. 2, a cell structure of dislocations is clearly recognized, and the dislocation density is 5 X I Q -'arm-''.

It can be seen that the method of the present invention reduces the dislocation density to one tenth or less compared to the conventional method.

〔Effect of the invention〕

As described above, according to the present invention, a single crystal with few grain boundaries, which can be formed over the entire wafer, and with extremely few dislocations can be obtained, thereby improving the yield and quality of single crystal wafers at once. was able to achieve this.

Although the present invention has been mainly described with respect to CdTe crystals, the present invention is not limited to CdTe crystals. It goes without saying that the growing method is not limited to the vertical Bridgman method.

[Brief explanation of drawings]

Figure 1 shows the (111) CdTe single crystal grown using the method of the present invention.
) A photograph of the Cd plane after etching. FIG. 2 is a photograph of the (111) Cd plane of a CdTe single crystal grown by the conventional method after etching. Patent applicant Sumitomo Metal Mining Co., Ltd. Procedures Correction Office (spontaneous) May 21, 1986

Claims (1)

[Claims] A method for growing a single crystal of a compound by melting the compound in a crucible and gradually cooling it to grow a single crystal of the compound, characterized in that the temperature gradient near the solid-liquid interface is 1 to 10°C/cm. .