FLOATING-ZONE AND FLOATING-SOLUTION-ZONE GROWTH OF GASB UNDER MICROGRAVITY

Three GaSb single crystals have been successfully grown under microgra vity on SPACEHAB-4 during the STS-77 Space Shuttle flight. Two Te-dope d crystals with 16 mm diameter and lengths of 31.5 and 18 mm, respecti vely, were grown by the floating-zone method. From the transition of s triated to striation-free material it was possible to determine the cr itical Marangoni number for the onset of time-dependent thermocapillar y convection for the FZ growth: Ma(c2) = 375 +/- 125. This is in good agreement with 3-D numerical simulations resulting in Ma(c2) = 355 +/- 90. The simulations showed that the 3D flow pattern with an azimuthal instability varies from SI-FZ configurations; the reason is most prob ably the more barrel-shaped zone caused by the large growth angle of 3 0.7 degrees. In addition to the FZ crystals, one undoped crystal with 15 mm diameter and 1 mm crystallized length was grown from a free Bi z one, the first time a crystal was grown from a free solution zone in s pace. On earth, a free Bi solution zone is not only limited to small d iameters as in the FZ method, but cannot be used at all due to fluid c reep. Under mu g, the Bi zone was stable and the grown crystal is free of cracks. (C) 1998 Elsevier Science B.V. All rights reserved.