MELT GROWTH OF SEMICONDUCTORS IN WEIGHTLESS ENVIRONMENT

本项目于1995年4月至1998年3月期间进行。在此期间，我们主要做了两项工作：1)中国14号返回式卫星空间生长掺Te GaSb的表征。1992年，中国科学院物理研究所与东京大学工程研究生院合作，在空间生长了GASB。用化学腐蚀和空间分辨光致发光对生长的晶体进行了表征。化学刻蚀结果表明，生长刚开始时位错就增加了，但随后又减少到零。这意味着晶体是在生长过程中和生长后的非常小的应力条件下生长的。这是因为熔体和生长的晶体都漂浮在石英瓶中。Te的浓度是通过空间分辨光致发光来确定的。结果表明，由于偏析效应，未熔件与再生件交界处的浓度急剧下降。然而，它恢复得非常快，这表明杂质在熔体中的传输是由纯扩散控制的。这意味着，尽管在太空生长过程中存在自由表面，但没有诱导出Marangoni流。观察到这一现象的原因尚不清楚，但可能是熔体上有很薄的氧化层，这可能阻止了Marangoni流的开始。2)美国宇航局GAS计划为GaSb在太空中熔体生长做准备工作在这次合作中，中国小组设计并制造了用于GaSb熔体生长的电炉。该炉由绕组组成，实现了恒定梯度的温度分布。日方制造真空石英安瓶，内置直径10 mm、长10 cm的GaSb单晶。这项实验终于在1998年1月底由STS89号航天飞机进行。飞行结束后，储气罐被送到中国手中，目前正在进行飞行实验评估。

The present project has been conducted from April 1995 to March of 1998. During this period, two major works have been carried out.1) Characterization of Te-doped GaSb grown in space by Chinese recoverable satellite No.14By the joint work between Institute of Physics, Chinese Academy of Sciences and The Graduate School of Engineering, The University of Tokyo, GaSb was grown in space in 1992. The grown crystal was characterized by chemical etching and by spatially resolved photoluminescence. The chemical etching showed that dislocation increase just after the growth starts but then decreases finally to zero. This means the crystal was grown under the condition of very small stress during and after the growth. This is because both the melt and the grown crystal was floating in the quartz ampoule.Te concentration was determined by spatially resolved photoluminescence. It was shown that the concentration drops sharply at the interface between unmelted and regrown parts due to the segregation effect. However, it recovers very quickly suggesting the impurity transport in the melt is governed by pure diffusion. This means that although free surface was present during the growth in space, no Marangoni flow was induced. The reason for this observation is not clear but probably there was very thin oxide layr on the melt which might prevent the onset of Marangoni flow.2) Preparatory works for the melt growth of GaSb in space by NASA GAS programIn this joint work, China group designed and fabricated electric furnace for the melt growth of GaSb. The furnace was consisted of windings and a temperature profile of a constant gradient was realized. Japanese side made evacuated quartz ampoules in which GaSb single crystal of 10 mm in diameter and 10 cm in length was put. The experiment was finally conducted in the end of January 1998 by Space Shuttle STS 89. After the flight, the GAS container was sent to China and now under the evaluation of the flight experiment.