JPH09227268A - Method for producing solid solution single crystal - Google Patents

Abstract

(57) [Abstract] [Problem] Even if the convection control in the raw material melt is incomplete,
Provided is a novel method for producing a solid solution single crystal which enables growth of a mixed crystal (solid solution single crystal) having a uniform composition. SOLUTION: A raw material whose composition is changed in advance so as to offset the composition change in the grown crystal due to segregation and convection is prepared, and the crystal is grown by directional solidification using this raw material.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a high quality mixed crystal (solid solution) single crystal having a uniform composition.

[0002]

2. Description of the Related Art Conventionally, many attempts have been made to grow a mixed crystal (solid solution) having a uniform composition, but no good method has been found yet. Some of the conventional methods are Pb _1-x Sn _x T
e (mixed crystal of PbTe and SnTe) will be described as an example. The directional solidification method has been conventionally used for many crystal growths as one of the simplest crystal growth methods.
This unidirectional solidification method is applied to the Pb _1-x Sn _x Te (x = 0.
FIG. 1 shows the axial direction SnTe concentration of the grown crystal when applied to 2). It can be seen that the SnTe concentration along the axial direction gradually increases as the crystal grows, and there is no uniform portion in any part of the crystal. This is P shown in FIG.
As is clear from the bTe-SnTe pseudo-binary phase diagram, this phenomenon is caused by the fact that the liquidus and solidus lines do not match (segregation) and convection in the melt.

Conventionally, as a method for suppressing the convection in the melt, a zone melting method for narrowing the melting zone, a method for applying a magnetic field, or a method for utilizing a microgravity field has been used. However, in the zone melting method, it is difficult to form a sufficiently narrow melting zone sufficient to suppress convection, and the method of using a magnetic field or microgravity only weakens convection to some extent, and it is difficult to completely suppress it. I know there is.

In FIG. 3, a space shuttle is used to
The SnTe concentration distribution in the growth axis direction is shown when a crystal was grown with a microgravity of 0 ^-4 g. Length from 33mm to 43mm
Although a uniform composition region of about 10 mm was realized over the period of time, compared with the composition distribution expected to be realized when convection was completely suppressed (shown by the broken line in the figure), the length of the uniform composition region was It's still short. This is because, as described above, the convection in the melt is not sufficiently suppressed even under the microgravity of 10 ⁻⁴ g.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and grows a mixed crystal (solid solution single crystal) having a uniform composition even if the convection suppression in the raw material melt is incomplete. An object of the present invention is to provide a new method for producing a solid solution single crystal that enables the above.

[0006]

In the conventional method for producing a single crystal, a polycrystalline raw material having a uniform composition was used as a starting raw material for crystal growth. On the other hand, in the method for producing a solid solution single crystal of the present invention, a crystal raw material in which the solute concentration is continuously changed along the axial direction by a unidirectional solidification method or the like is prepared in advance, and a solid solution single crystal is produced using this raw material. Growing crystals is the most important feature.

That is, in the method for producing a solid solution single crystal according to claim 1 of the present invention, the composition as a whole agrees with the composition of the intended solid solution, and the concentration distribution of the constituent mixed substances is along the axial direction. A continuously changing crystal sample is used as a starting material, and a substance having a segregation coefficient smaller than 1 among the constituent mixed substances of the crystal sample has a higher concentration. It is characterized in that the intended solid solution single crystal is obtained by unidirectionally solidifying toward the other end.

In the method for producing a solid solution single crystal according to claim 2 of the present invention, a raw material whose composition as a whole matches the composition of the intended solid solution is filled in an electric furnace in a longitudinal shape, and the length of the raw material is increased. Directional solidification is performed in a first direction along the direction to prepare a crystal sample, the front end and the rear end of the crystal sample are exchanged and reloaded into the electric furnace, and the first unidirectional solidification is performed. It is characterized in that the intended solid solution single crystal is obtained by unidirectionally solidifying in the second direction in which the solidified portion first solidifies.

The method for producing a solid solution single crystal according to claim 3 of the present invention is the method for producing a solid solution single crystal according to claim 2, wherein a magnetic field is applied in the electric furnace when the second unidirectional solidification is carried out. It is characterized by

A method for producing a solid solution single crystal according to a fourth aspect of the present invention is the method for producing a solid solution single crystal according to the second aspect, in which a unidirectional sweep zone melting method is used as the second unidirectional solidification method. Is used.

Further, in the method for producing a solid solution single crystal according to claim 5 of the present invention, the seed crystal and the composition as a whole coincide with the intended composition of the solid solution, and the concentration distribution of the constituent mixed substances is along the axial direction. And a continuously changing crystal sample are used as raw materials, and among the mixed substances in the crystal sample, a substance having a segregation coefficient smaller than 1 has a higher concentration, and the seed is provided on the end face side of the crystal sample. After arranging a crystal and melting a part of the seed crystal, unidirectional solidification is performed from the high-concentration side end face of the crystal sample including the melted part toward the other end, thereby obtaining a target solid solution. A feature is that a single crystal is obtained.

The method for producing a solid solution single crystal according to claim 6 of the present invention is characterized in that, in the method for producing a solid solution single crystal according to claim 5, a magnetic field is applied in an electric furnace when unidirectional solidification is carried out. And

In the method for producing a solid solution single crystal according to claim 7 of the present invention, in the method for producing a solid solution single crystal according to claim 5, a unidirectional sweep zone melting method is used as the method for unidirectional solidification. Is characterized by.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention.

(First Embodiment) Purity of 99.
Using 9999% Pb, Sn, Te, Pb _0.8 S
After weighing so as to have a composition of n _0.2 Te, it was vacuum-sealed in a quartz tube. After heating the quartz tube to about 1000 ° C. in an electric furnace to prepare a melt having a Pb _0.8 Sn _0.2 Te composition, the quartz tube was taken out of the electric furnace, immersed in water and rapidly cooled to obtain Pb _0.2 Sn _0.2. A polycrystal having a Te composition was synthesized. Then, the polycrystalline body was vacuum-sealed in another quartz container again, and a high temperature part was heated to about 1000 ° C. and a low temperature part was heated to about 600 ° C. in a temperature gradient furnace to form a temperature gradient region of about 60 ° C./cm. Was used to unidirectionally solidify at a solidification rate of about 5 mm / h. The SnTe concentration distribution in the obtained crystal was as shown in FIG. That is, the SnTe concentration gradually increases in the crystal growth axis direction, and no uniform composition region is found anywhere.

Next, the crystal sample prepared as described above was vacuum-sealed in another quartz container for crystal growth,
The final stage of crystal growth was performed. FIG. 4 is a cross-sectional view of the crystal growth container at this stage.

The quartz container 1 has its tip processed into a conical shape, and the conical portion 2 is a means for producing only one crystal nucleus to form a single crystal. The crystal sample 3 preliminarily unidirectionally solidified has a SnTe concentration of one end face 4
From the other end face 5, the SnTe
The quartz container 1 is vacuum-sealed so that the end surface 4 having the higher concentration faces the direction of the conical portion 2.

FIG. 5 is a graph showing the outline of the crystal growth at this stage, and also shows the curve 6 showing the temperature distribution in the furnace and the arrangement relationship of the quartz container 1. That is,
The electric furnace is a vertical furnace and is heated so that the lower part has a low temperature region and the upper part has a high temperature region. In this temperature distribution, the low-temperature melt having a high specific gravity comes to the lower part, and the thermal convection is suppressed.
However, this is only an ideal theory, and it is difficult to make the radial temperature distribution of the melt in the quartz container completely axisymmetric in reality. Therefore, generation of local thermal convection to some extent is inevitable.

FIG. 6 shows SnTe in a crystal sample before heating.
A curve 7 showing the concentration distribution and a curve 8 showing the SnTe concentration distribution after 1 hour when melted at 1000 ° C. are shown. The SnTe concentration distribution is blunted due to the uniform concentration distribution due to diffusion and the stirring effect due to local thermal convection.
Also shown in FIG. 6 is a curve 9 showing the SnTe concentration distribution when crystallization is started from such a state and unidirectionally solidified at 5 mm / h. Since solidification starts from the higher SnTe concentration, the ratio of SnTe incorporated into the crystal is 1
It can be seen that the smaller segregation effect is canceled out and that a crystal having a relatively uniform composition is growing.

(Second Embodiment) FIG. 7 shows the SnTe concentration distribution in the axial direction of the Pb _{1 -x} Sn _x Te single crystal grown in the second embodiment of the present invention. In the present embodiment, the crystal growth was performed by the same method as in the first embodiment, but the crystal was grown at the time of unidirectional solidification again in the subsequent step.
The difference is that a magnetic field of 00 Gauss was applied to further suppress convection in the melt. As is clear from the figure, the uniformity of SnTe concentration distribution in the grown crystal is further improved. This is because the convection was suppressed and the stirring of the melt was further reduced.

(Third Embodiment) FIG. 8 is a diagram showing an outline of a crystal growth method at the final stage in the third embodiment of the present invention. The electric furnace heating section has three zones, and as shown in the furnace temperature distribution curve 10, the temperature of the central heating section is raised to perform zone melting. By this method Pb
_When crystal growth of _1-x Sn _x Te was performed, a single crystal having a composition distribution very similar to that of FIG. 7 could be obtained. Also in this embodiment, the effect of the present invention of crystallizing from the higher solute concentration and the effect of suppressing convection in the melt by narrowing the width of the melting zone are well meshed, and Pb _1-x excellent in composition uniformity is obtained. A Sn _x Te single crystal was obtained.

(Fourth Embodiment) FIG. 9 is a sectional view of a crystal growth container 12 according to a fourth embodiment of the present invention. The end face 14 having a high SnTe concentration of the polycrystalline raw material 13 produced by unidirectionally solidifying in advance is arranged on the seed crystal 16 side in the container 12 so as to be in contact therewith. For the seed crystal 16, a single crystal having a Pb _0.8 Sn _0.2 Te composition close to that produced by another method is used. In such a configuration,
When the seed crystal 16 was heated in a temperature gradient furnace so that the central portion of the seed crystal was at about 890 ° C., the seed crystal 16 melted leaving about half of it.
The crystal raw material 13 is in a molten state in which the whole is melted. When the crystal growth container 12 was moved from this state to the low temperature side at a speed of 5 mm / h, solidification started from the undissolved seed crystal toward the melt side, and eventually the whole grew into a large single crystal.

FIG. 10 shows the axial direction SnTe concentration distribution of the crystal after the crystal growth in the present embodiment. From this figure, the obtained crystals show almost uniform SnTe.
It can be seen that there is a concentration distribution.

As described above, in the above embodiment, IV-VI
Although a homogeneous mixed crystal (solid solution) of the group compound semiconductors PbTe and SnTe has been described as an example, the principle of the present invention is not limited to the above substances, but a solid solution single crystal of elements such as Si and Ge, or III InA of group V compound semiconductor
It is obvious that the present invention can be applied to the production of a solid solution single crystal of s and GaAs or a CdTe-HgTe solid solution single crystal of a II-VI group compound semiconductor.

[0025]

As described above, according to the method of the present invention, since the raw material whose composition is varied so as to cancel the composition variation in the grown crystal due to the segregation and the convection in advance is used, the convection in the melt is prevented. If it is suppressed to some extent, there is an advantage that a single crystal of a solid solution (mixed crystal excellent in uniformity) can be obtained.

The method of the present invention is not limited to a particular material and can be widely applied to general solid solution crystals. In particular, PbTe-SnTe and InAs-GaA are applicable.
A solid solution semiconductor of a compound such as s is a promising application field of the present invention because high quality and uniform composition are required for producing a laser diode or the like.

[Brief description of drawings]

FIG. 1 is a graph showing the concentration distribution of SnTe in the growth axis direction in the case of unidirectionally solidifying a polycrystalline raw material having a uniform composition of Pb _0.8 Sn _0.2 Te as a starting material.

FIG. 2 is a state diagram of a PbTe-SnTe pseudo binary system.

FIG. 3 shows Pb _0.8 Sn _0.2 T under microgravity of 10 ⁻⁴ g.
e is a graph showing SnTe concentration distribution in the growth axis direction of a crystal grown by a unidirectional solidification method from a raw material of uniform composition.

FIG. 4 is a diagram for explaining the first embodiment of the method for producing a solid solution single crystal of the present invention, and is a cross-sectional configuration diagram of the crystal growth container used for the implementation.

FIG. 5 is a diagram for explaining the single crystal manufacturing method according to the first embodiment of the present invention, and is a graph showing a distribution of an applied temperature to a sample.

FIG. 6 is a graph showing a difference in SnTe concentration distribution due to various treatments on raw materials.

FIG. 7 is a graph showing SnTe concentration distribution along the growth axis direction of a single crystal according to the second embodiment of the present invention.

FIG. 8 is a graph showing SnTe concentration distribution along the growth axis direction of a single crystal according to a third embodiment of the present invention.

FIG. 9 is a sectional configuration diagram of a crystal growth container used in a fourth embodiment of the present invention.

FIG. 10 is a graph showing SnTe concentration distribution in the growth axis direction of the single crystal obtained in the fourth embodiment of the present invention.

[Explanation of symbols]

1 Quartz container 2 Tip conical part 3 Crystal sample 4 End face with the highest SnTe concentration 5 End face with the lowest SnTe concentration 6 Curve showing the temperature distribution in the furnace 7 Curve showing the SnTe concentration distribution in the crystal sample before heating 8 At 1000 ° C Curve 9 showing SnTe concentration distribution along the axial direction of the sample melted and rapidly cooled after 1 hour 9 Curve showing SnTe concentration distribution along the growth axis direction of the single crystal obtained in the first embodiment 10 Zone furnace temperature Curve showing distribution 11 Crystal growth sample 12 Crystal growth container 13 Polycrystalline raw material 14 End face with highest SnTe concentration 15 End face with lowest SnTe concentration 16 Seed crystal

Claims (7)

[Claims] 1. A starting material is a crystal sample, the composition of which is the same as that of the target solid solution as a whole, and the concentration distribution of the constituent mixed substances thereof continuously changes along the axial direction. One-way solidification is performed on the crystal sample from the end face side where the substance having a segregation coefficient smaller than 1 is higher in concentration among the constituent mixed substances toward the other end where the substance is lower in concentration. A method for producing a solid solution single crystal, characterized in that the intended solid solution single crystal is obtained by carrying out. 2. A raw material whose composition as a whole matches the composition of a desired solid solution is charged into an electric furnace in a longitudinal shape,
The raw material is unidirectionally solidified in a first direction along the longitudinal direction to produce a crystal sample, and the front end and the rear end of the crystal sample are exchanged and reloaded into the electric furnace, and the first A method for producing a solid solution single crystal, comprising obtaining a desired solid solution single crystal by carrying out unidirectional solidification in a second direction in which a portion solidified last by directional solidification first solidifies. 3. When performing the second unidirectional solidification,
The method for producing a solid solution single crystal according to claim 2, wherein a magnetic field is applied in the electric furnace. 4. The method for producing a solid solution single crystal according to claim 2, wherein a zone melting method of sweeping in one direction is used as the method for performing the second unidirectional solidification. 5. A seed crystal and a crystal sample whose composition as a whole coincides with the composition of a target solid solution and whose concentration distribution of its constituent mixed substances continuously changes along the axial direction are used as raw materials. The seed crystal is placed on the end face side of the crystal sample in which the substance having a segregation coefficient of less than 1 has a higher concentration among the mixed substances in the crystal sample, and a part of the seed crystal is melted. After that, the solid solution single crystal of interest is obtained by unidirectionally solidifying the crystal sample including the melted portion from the end surface on the high concentration side toward the other end. . 6. The method for producing a solid solution single crystal according to claim 5, wherein a magnetic field is applied in an electric furnace when the unidirectional solidification is performed. 7. The method for producing a solid solution single crystal according to claim 5, wherein a zone melting method of sweeping in one direction is used as the method for performing the unidirectional solidification.