Numerical and experimental investigations of convection and heat/mass transfer effect in melts on inhomogeneity formation during Ge crystal growth by the Bridgman method

The role of convection in heat and mass transfer processes under terrestrial and space conditions is investigated on the basis of the assessment of dimensionless parameters. It has been shown that convection near the crystallization front will be of nonstationary character due to reconstruction of vortex regions with the decrease of the melt height. Numerical calculations of Oberbeck-Boussinesq equations have shown that nongravitational motion sources (Marangoni convection) generate under space conditions a basic flow which is of higher intensity than under earth conditions. The total time of flow evolution increases essentially. This nonlinear effect of space conditions on hydrodynamics will bring about qualitative changes in heat and dopant transfer processes. The experiments were performed on crystallization of germanium doped with gallium at reduced natural convection. It has been shown that inhomogeneities appear in the crystal in the form of dopant striations at achieving a certain level of convection. Theoretical predictions are in agreement with experimental data obtained. (C) 1999 Elsevier Science B.V. All rights reserved.