TRANSIENT SIMULATIONS OF CONVECTION AND SOLUTE SEGREGATION OF GAAS GROWTH IN GRADIENT FREEZE FURNACE

Transient numerical simulations are reported for the growth of selenium-doped gallium arsenide in a prototype of the vertical gradient freeze system built by GTE Laboratories. The simulations show that the combined effects of latent heat release and the small axial temperature gradient indicative of gradient freeze systems lead to a continuously varying growth rate and large deflections of the melt/crystal interface. Intense laminar convection in the melt is driven by the resulting radial temperature gradients and causes vigorous mixing of the dopant everywhere except near the interface at the center of the ampoule. This spatial nonuniformity in the flow leads to large radial segregation. Axial segregation of the dopant resembles the prediction of the stagnant film model, but cannot be quantitatively correlated with this expression.