A boundary layer model for macrosegregation of Bridgman grown Ge1-xSix mixed crystals

We investigated macrosegregation of Ge1-xSix mixed crystals over a great variety of compositions. The axial profiles found experimentally are 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. Comparison of the experimental data with calculations reveals that, in the setup employed here, the melt is close to the limiting case of complete mixing. The diffusion boundary layer thickness is only a few tens of microns. This is in contrast to known experiments, where additional solutal damping of the convection severely affects macrosegregation.