MELT GROWTH OF SEMICONDUCTORS IN WEIGHTLESS ENVIRONMENT

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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.