Numerical modeling of the semiconductor alloys solidification by using a baffle under microgravity and terrestrial conditions

Some experiments on Te-doped InSb solidification by using a baffle in sealed ampoules performed under microgravity conditions in the Glovebox of the International Space Station (2002) are numerically investigated in order to analyze the baffle effect on the solute distribution. The numerical results, in agreement with previous experimental secondary mass spectroscopy (SIMS) measurements of the longitudinal Te distribution in the crystals, show a diffusive-controlled segregation. The shape of the initial transient in dopant concentration is explained as an effect of the partial chemical mixing between the undoped seed and the liquid feed. Due to low-residual gravitational accelerations on the Space Station, the buoyancy convection is drastically reduced and the use of the baffle has no significant effect on the solute distribution. The numerical analysis of the thermal field shows that the heat conducted towards the graphite baffle has a flattering effect on the solid-liquid interface. This can reduce the radial segregation during the growth of diluted alloys. The thermal effect of the baffle becomes important for the ground-based growth of concentrated semiconductor alloys, which shows large chemical segregations and interface curvatures due to the damping solutal effect on the melt convection. By using a baffle under terrestrial conditions, the interface curvature and the radial segregation can be reduced. Therefore, the chemical homogeneity of the higher doped crystals can be improved, as shown also by comparing the numerical results obtained for the Bridgman solidification of the GaInSb (20% initial InSb concentration) with and without baffle. Finally, the growth parameters are numerically optimized to improve the quality of higher doped semiconductor crystals. (C) 2007 Elsevier B.V. All rights reserved.