AbstractThe experimental conception of the floating zone (FZ) technique for the growth of GaAs crystals with larger diameters under microgravity, including the use of a stoichiometry control by a controlled As-vapor source, is explained in this paper. Also first results of preparatory experiments are given, which are obtained from ballistic rocket flights in the frame of the German TEXUS program and from terrestrial crystal growth.In the second part of the paper we discuss the very important problem of the thermocapillary convection (Marangoni effect) occurring in a GaAs melt zone. The results of a three-dimensional time-dependent numerical simulation of the thermocapillary convection show a very good agreement to existing experimental results in the literature and of our group. It follows from these calculations for liquid GaAs and from the experimental results of the terrestrial FZ growth of GaAs single crystals (6 mm diameter), that the limit for the transition from steady to unsteady thermocapillary convection, i.e. the formation of doping striations, is relatively low. Therefore, means and methods to stabilize this type of convection, i. e. to increase the critical Marangoni number for the transition to unsteady convection were studied. It is especially discussed to what extent static magnetic fields can be used to solve this problem for the case of the FZ method for GaAs. A value of the induction B0 = 0.08 T was calculated which is necessary to avoid striations in the GaAs crystals (20 mm diameter) to be grown during the German D2-mission by the FZ technique.
Growth of GaAs single crystals by the floating zone technique under microgravity
Advances in Space Research ; 11 , 7 ; 297-304
1991-01-01
8 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
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