The minimisation of thermal stresses during the growth of GaAs crystals

Abstract

Undesirably high dislocation densities in Czochralski grown gallium arsenide crystals are generally accepted to be due to high thermal stresses generated by temperature gradients in the crystal during growth. Detailed numerical calculations are presented, using finite element methods, for partially and fully grown crystal geometries to calculate the resulting stresses. By varying such parameters as the ambient temperature, heat transfer coefficient and crystal geometry the dislocation density can be minimised and hence optimum growth conditions predicted. It is shown that the optimum conditions during the initial stages of crystal growth are radically different to those required for the mature crystal geometry.