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 shie lds have been added in order to decrease the thermal gradient in the growin g crystal. The shape of these shields has been optimized with the help of g lobal numerical simulations of heat transfer and thermomechanical stresses in the growing crystal. 50% reduction of the thermal stresses has been obta ined and the dislocation density drastically decreased tin the upper part o f 2-in Fe doped crystal, from 50 000 to 30 000 cm(-2)). The resulting reduc tion of the thermal gradient in the melt (from 12 to 6 K/cm) can lead to th e destabilisation of the interface especially for tin-doped crystals: compu ted thermal gradients are compared with the Mullins/Sekerka theory of inter face stability and show a good agreement with experimental data. (C) 1999 E lsevier Science B.V. All rights reserved.