A COMPARISON OF REDUCING THE DISLOCATION DENSITIES IN GAAS GROWN BY THE VERTICAL GRADIENT FREEZE AND LIQUID-ENCAPSULATED CZOCHRALSKI TECHNIQUES

We have recently applied the quasi-steady state heat transfer/thermal stress model for dislocation generation to the vertical gradient freeze (VGF) process for GaAs, permitting a direct comparison with the original treatment of liquid-encapsulated Czochralski (LEC) growth. Very recent high temperature critical resolved shear stress (CRSS) data on undoped VGF and In-doped LEC specimens were used. We show that the approximately threefold increase in CRSS with In is sufficient to inhibit defect formation in the central approximately 75% of 3 in. diameter LEC wafers grown in a high ambient temperature gradient, duplicating the etch-pit density (EPD) data. Undoped VGF wafers are predicted to be nearly dislocation-free. The theoretical results on 3 in. material track the low EPD counts in both the [100] and [110] directions in a 5 K/cm gradient imposed on the crystals' surface. We also discuss the origin of dislocations in regions free of thermal stresses and propose their suppression by the addition of a small amount of In in VGF experiments.