Thermal stress simulation and interface destabilisation in indium phosphide grown by LEC process

A multi-step procedure to decrease the dislocation density in InP wafers is described. The crystal growth process is conventional LEC but thermal shields have been added in order to decrease the thermal gradient in the growing crystal. The shape of these shields has been optimized with the help of global numerical simulations of heat transfer and thermomechanical stresses in the growing crystal. 50% reduction of the thermal stresses has been obtained and the dislocation density drastically decreased tin the upper part of 2-in Fe doped crystal, from 50 000 to 30 000 cm(-2)). The resulting reduction of the thermal gradient in the melt (from 12 to 6 K/cm) can lead to the destabilisation of the interface especially for tin-doped crystals: computed thermal gradients are compared with the Mullins/Sekerka theory of interface stability and show a good agreement with experimental data. (C) 1999 Elsevier Science B.V. All rights reserved