Abstract
Buoyancy driven convection in closed vertical cylinders heated from below and crystal growth in corresponding configurations (vertical Bridgman technique with top seeding) have been studied experimentally and theoretically. The hydrodynamic state in such configurations is described by three dimensionless numbers, the Rayleigh number Ra, the aspect ratio (height h/diameter d) and the Prandtl number Pr. Two different types of melts have been investigated, H 2O (Pr = 6.7), and Ga and GaSb melts (Pr ≈ 2 × 10 -2) for various aspect ratios (0.5 ⩽ h/ d ⩽ 5) and Rayleigh numbers up to 10 8. Both experimental results and numerical analysis for the onset of convection (critical Rayleigh number Ra c1) and the state of convective flow are presented. The values of Ra c1 for 0.5 ⩽ h/ d ⩽ 5 and the symmetries of the basic flow (axial symmetry for h/ d = 0.5 and non-axial symmetry for 1 ⩽ h/ d ⩽ 5) are in good agreement with the theoretical predictions of Charlson and Sani [1]. Te-doped GaSb crystals have been grown by using the vertical Bridgman technique with top seeding. Temperatures have been measured in the GaSb melt during growth and compared with the results of our flow investigations in Ga melts. It shows clearly, that the occurrence of doping striations in the GaSb crystals can be very well correlated to the unsteady flow regimes.
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