Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Havin growth from molten state
Patent
1997-04-15
1999-11-23
Hiteshew, Felisa
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Havin growth from molten state
117 83, 117204, 117205, 117206, C30B 1112
Patent
active
059893370
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for growing a single crystal and, in particular, to a useful technique applied to a method for growing a single crystal by precipitating a solute from a solution including a raw material dissolved in a solvent.
BACKGROUND ART
The Bridgman method and the gradient freeze method have been known as methods for growing a single crystal.
The Bridgman method which is one for growing a single crystal, comprises the steps of; putting a crucible filled with a polycrystalline raw material in a crystal growth furnace, heating the crucible by a heater to melt the material, and thereafter moving the crucible toward a lower temperature side in a temperature gradient of 10-50 .degree. C./cm which is formed in the furnace, to precipitate a solute which cannot keep dissolving in the solvent, on a lower temperature portion of the crucible. For example, Japanese Patent Application Publication (Examined) No. Tokuko-hei 7-51471 discloses a technique for obtaining a single crystal having a good stoichiometry and few defects, in which a reaction tube which connects a crystal growth chamber enclosing a container (crucible) containing a raw material therein to a storage chamber enclosing a host atom for controlling the vapor pressure thereof is used, and growth of the single crystal is carried out while controlling the vapor pressure of the host atom by controlling the temperature of the storage chamber enclosing the host atom.
The gradient freeze method which is one for growing a single crystal, comprises the steps of; heating a crucible filled with a polycrystalline raw material by a heater to melt the material in a crystal growth furnace, and thereafter changing the temperature profile in the crystal growth furnace by controlling the power supplied to the heater while retaining the crucible at a predetermined position, to precipitate a solute on a lower temperature portion of the crucible.
The present inventor proposed an improved technique of the Bridgman method or the gradient freeze method, which is one (hereinafter, it may be simply referred to a solvent method) for growing a compound semiconductor single crystal having a higher melting point, e.g., ZnSe, ZnTe or the like, than the softening point of quartz glass, comprises the steps of; putting a raw material and a solvent in a crucible, heating the crucible to make a solution by dissolving the material in the solvent, and moving the crucible toward a lower temperature side in a temperature gradient which is formed in a crystal growth furnace, or changing the temperature profile in the furnace, to precipitate a solute from the solution. This solvent method has the advantage that it is possible to easily obtain a compound semiconductor single crystal having a high melting point and a high dissociation pressure at low cost.
However, even if either of the Bridgman method and the gradient freeze method is adopted for the solvent method, there is a problem of occurrence of cracks or defects in the grown single crystal caused by thermal stress due to the difference between the coefficients of thermal expansion of the remaining solvent in the crucible and of the grown crystal, in a cooling step after the single crystal growth. The coefficient of thermal expansion of Te is 14.times.10.sup.-6 /K, and the coefficient of thermal expansion of ZnTe is about twice that of Te. Therefore, when a ZnTe single crystal is grown in a Te solvent, cracks occur or defects such as dislocation or the like are sometimes introduced into the grown single crystal, by the remaining Te solvent in the crucible even if cooling after the crystal growth was sufficiently gradually carried out.
The Journal of Crystal Growth, 72, p.97-101 (1985); the Journal of Crystal Growth, 59, p.135-142 (1982); and the REVUE DE PHYSIQUE APPLIQUEE, 12, P.151-154 (1977) reported solvent evaporation processes for precipitating CdTe solute by evaporating Cd solvent from a solution which comprises the Cd solvent and the CdTe solute, in order to grow a CdTe single cryst
REFERENCES:
patent: 4190486 (1980-02-01), Kyle
patent: 5471938 (1995-12-01), Uchida et al.
patent: 5685907 (1997-11-01), Fujikawa et al.
B. Lunn and V. Bettridge, Revue De Physique Appliquee, Tome 12, pp. 151-154, (Febrier 1977).
A.W. Vere, V. Steward, C.A. Jones, D.J. Williams and N. Shaw, Journal of Crystal Growth, vol. 72, pp. 97-101 (1985).
J.B. Mullin, C.A. Jones, B.W. Straughan and A. Royle, Journal of Crystal Growth, vol. 59 pp. 135-142 (1982).
Hiteshew Felisa
Japan Energy Corporation
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