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

我利用微重力条件研究了一种新的生长方法的有效性，该方法用于生产成分均匀的二元半导体晶体。首先，从热力学的角度提出了一种从宏观角度计算二元半导体晶体生长的方法。可以有效地估计溶液-晶体界面的形状和运动以及流动、温度和浓度场。研究了Bridgman法和区域法生长InAs-GaAs二元晶体的过程，得到了以下结果：(A)Bridgman法：(1)由于熔融化合物半导体的Prandtl数很小，温度场不会因对流而严重变形.(2)当晶体生长方向垂直于剩余重力时，即使在微重力下，浓度场和溶液-晶体界面也会因浮力对流而变形，因为Schmidt数很大.(3)随着晶体尺寸和热流密度的增加，(2)分区法：(1)采用分区法降低了对流速度；(2)减小了区宽，显著减小了温度场、浓度场和溶液-晶界面上的速度和变形，抑制了过冷；(3)通过减小区宽到15 mm，并将区内温度梯度设置为10K/cm，可以生长出均匀的In0.3Ga0.7As单晶。

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.