Modeling of thermosolutal convection during Bridgman solidification of semiconductor alloys in relation with experiments

Thermosolutal convection during vertical Bridgman directional solidification of Ga1-xInxSb alloys has been studied by numerical simulation. The transient analysis of heat, momentum and species transport has been performed by using the finite element code FIDAP((R)). In the case of vertical Bridgman configuration, the thermal convection is driven by the radial temperature gradients. The solute (InSb) rejected at the solid-liquid interface, which is heavier than the GaSb component, damps the thermally driven convection. The solutal effect on the melt convection has been analyzed for low (x = 0.01) and high (x = 0.1) doped Ga1-xInxSb alloys. It is found that the damping effect is negligible for Ga0.99In0.01Sb alloy grown at low pulling rates (V = 1 mum/s), but cannot be neglected if the pulling rate is increased. In the case of concentrated alloys, the low level of convection intensity leads to an increase of radial segregation and interface curvature during the whole growth process as also shown by experiments. The effect of solutal buoyancy force on the melt convection is analyzed for the horizontal Bridgman configuration under microgravity conditions. An inverse but lower solutal effect on the melt convection, as compared with vertical Bridgman arrangement, is observed. The results are in good agreement with the experimental data, and show that convective transport can be observed even for low (2 x 10(-6) g(0)) residual gravity levels. (C) 2004 Elsevier B.V. All rights reserved.