Growth of Binary Compound Semiconductors of Uniform Compositions By One-Directionnal Growth Method with a Nonuniform Concentration Distribution

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I investigated the validity of a new growth method for producing binary semiconductor crystals, which have uniform compositions, utilizing microgravity conditions. First, I developed a calculation method of growth of binary semiconductor crystals from a macroscopic point of view based on thermofluid dynamics. The shape and movement of the solution-crystal interfaces as well as the flow, temperature and concentration fields can be estimated efficiently. The growth process of an InAs-GaAs binary crystal by the Bridgman and zone methods were investigated and the following results were obtained :(a) Bridgman method :(1) The temperature field is not seriously deformed by convection since the Prandtl number of the molten compound semiconductors is very small.(2) The concentration field and the solution-crystal interface are deformed by buoyancy convection even under microgravity when the crystal growth direction is perpendicular to the residual gravity, since the Schmidt number is large.(3) As the crystal size and the heat flux increase, the deformation of the concentration field and the solution-crystal interface becomes more extensive.(b) Zonemethod :(1) The convective velocity is reduced by employing the zone method.(2) The velocity and the deformation of the temperature and concentration fields and the solution-crystal interfaces are reduced remarkably and, as a result, supercooling is suppressed by reducing the zone width.(3) A uniform In0.3Ga0.7As single crystal may be grown by reducing the zone width to 15 mm and setting the temperature gradient in the zone at 10 K/cm.