Comparison of calculated and measured dislocation density in LEC-grown GaAs crystals

Abstract

Dislocation densities in melt-grown GaAs crystals, ranging from 3 × 10 3 to 7 × 10 4 cm -2, are compared to values predicted by a micro-mechanical creep model based on the Alexander-Haasen formulation of slip in diamond crystals. The temperature and thermal strain histories of the crystals are obtained from the numerical simulation of the growth and cool-down processes. These histories are used in the creep model, and the associated time-variation of dislocation densities are calculated. The measured and calculated dislocation densities show a remarkably good agreement in the central region of the crystal. Towards the crystal periphery, however, the measured dislocation densities are appreciably larger than the predicted values. The possible reasons for this anomaly are discussed. The reported agreement between model and experimental results indicates that dislocation densities as low as 10 3 cm -2 are related to thermal-stress-induced slip in the matrix. The implications of this finding on various approaches for reduction of the dislocation density in melt-grown crystals to below currently attainable levels of high-10 2 to low-10 3 cm -2 are discussed.