A study on heat and fluid flow in melt growth process of single crystal

在这个为期两年的项目的第一年，我们进行了一个实验，使用一个玻璃容器来模拟查克拉尔斯基熔胶，观察过程中的热量和流体流动。将悬浮在液体中的微胶囊液晶显示在容器内的流量和温度分布。结果表明，当晶体和容器的旋转速率、容器壁与液固界面的温差、熔体的热物理性质等参数在一定范围内时，液体的流动和温度出现周期性振荡。超级计算机的数值模拟表明，即使边界条件是轴对称的，也会出现非常相似的现象。这些结果表明，在用切克拉尔斯基法生长的单晶中观察到的生长条纹是由于熔体中的振荡流动所致。第二年研究了外加磁场对佐克拉尔斯基熔体振荡流动的抑制作用。分析了磁场对自然对流的影响，发现当磁场强度超过某一临界值时，熔体的流动速度会迅速下降。通过数值分析揭示了磁场对砷化镓（GaAs）生长过程的影响。结果表明，在磁场强度足够的情况下，磁场可以完全抑制流体的波动。

In the first year of this two-year project, an experiment was conducted, using a.glass container which modeled the Czochralski crusible, to observe the heat and fluid flow during the process. The distribution of flow and temperature in the container was visualized microcapsulated liquid crystal suspended in the liquid. As the result, it was found that the flow and the temperature of the liquid oscillate periodically when the parameters, such as the rotation rates of crystal and container, the temperature difference between the wall of the container and the liquid-solid interface and the thermophysical properties of melt, were within a certain range. Numerical simulation by a super-computer revealed that quite similar phenomena occurred even if the boundary conditions were axisymmetric. These results suggest that the growth striations observed in the single crystal grown by the Czochralski method are due to the oscillatory flow in the melt.In the second year the effect of external magnetic field for damping the oscillatory flow in the Czochralski melt was investigated. As a result of analysis on the effect of magnetic field on natural convection, the flow velocity of the melt is decreased rapidly by magnetic field when its intensity exceeds a certain critical value. Also a numerical analysis was carried out to reveal the effect of magnetic field on the growth process of gallium-arsenide(GaAs). It was found that the magnetic field damped the fluctuation of flow completely if the intensity was sufficient.