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，进行了一项实验，使用模拟Czochralski壳体的玻璃容器来观察过程中的热量和流体流动。容器内的流动和温度分布是悬浮在液体中的微胶囊液晶的可视化。结果表明，当晶体和容器的转速、容器壁面与液固界面的温差以及熔体的热物性等参数在一定范围内时，液体的流动和温度都会发生周期性的振荡。由超级计算机进行的数值模拟表明，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，用提拉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。第二年，我们研究了外加磁场对提拉法生长的熔体中振荡流动的抑制作用。通过分析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降低。数值分析揭示了磁场对砷化镓(GaAs)生长过程的影响。研究发现，在磁场强度足够大的情况下，磁场完全抑制了水流的脉动。

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.