MODELING OF THE DYNAMICS OF HGCDTE GROWTH BY THE VERTICAL BRIDGMAN METHOD

Abstract

The transients in vertical Bridgman growth of nondilute alloys of HgCdTe are studied by numerical integration of the time-dependent equations for momentum, solute and energy transport and the conditions for the evolution of the melt/crystal interface according to the pseudo-binary phase diagram. The stabilizing axial density gradient caused by the rejection of heavier HgTe at the interface damps convection driven by the radial temperature gradients and by the density inversion at low CdTe concentrations. For typical conditions of crystal growth in small ampoules, the temperature and solute fields are controlled by conduction and diffusion, respectively. The major effects of the nondilute alloy are to increase the deflection of the solidification interface caused by the differences in thermal conductivities in the system and to couple the evolution of the crystal growth rate with the composition field to the long time scale for equilibration of the solute field at the start of growth. The evolution in time of the flow field from the structure driven entirely by the temperature field to the weaker thermosolutal flow is demonstrated for terrestrial growth and lower gravity conditions. The importance of the ampoule translation rate and ampoule size on the predictions for solute segregation is emphasized.