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

The role of convection in heat and mass transfer processes under terrestria l and space conditions is investigated on the basis of the assessment of di mensionless parameters. It has been shown that convection near the crystall ization front will be of nonstationary character due to reconstruction of v ortex regions with the decrease of the melt height. Numerical calculations of Oberbeck-Boussinesq equations have shown that nongravitational motion so urces (Marangoni convection) generate under space conditions a basic flow w hich is of higher intensity than under earth conditions. The total time of flow evolution increases essentially. This nonlinear effect of space condit ions on hydrodynamics will bring about qualitative changes in heat and dopa nt transfer processes. The experiments were performed on crystallization of germanium doped with gallium at reduced natural convection. It has been sh own that inhomogeneities appear in the crystal in the form of dopant striat ions at achieving a certain level of convection. Theoretical predictions ar e in agreement with experimental data obtained. (C) 1999 Elsevier Science B .V. All rights reserved.