A BOUNDARY-LAYER MODEL FOR MACROSEGREGATION OF BRIDGMAN GROWN GE1-XSIX MIXED-CRYSTALS

We investigated macrosegregation of Ge1-xSix mixed crystals over a gre at variety of compositions. The axial profiles found experimentally ar e explained by a new one-dimensional boundary layer model, which takes into account the appropriate boundary conditions for Bridgman growth and the non-negligible variation of the segregation coefficient. Compa rison of the experimental data with calculations reveals that, in the setup employed here, the melt is close to the limiting case of complet e mixing. The diffusion boundary layer thickness is only a few tens of microns. This is in contrast to known experiments, where additional s olutal damping of the convection severely affects macrosegregation.