Temperature field simulation and correlation to the structural quality of semi-insulating GaAs crystals grown by the vapour pressure controlled Czochralski method (VCz)

Recent results of global thermal field modelling using the software program s CrysVUN++ and STHAMAS are presented for 3- and 4-inch VCz SI GaAs growth assemblies. For the first time global simulations including the gas and mel t convection in a VCz arrangement are shown. In contrast to conventional LE C the impact Of gas convection on the temperature distribution in the growi ng crystal is not dominant in the VCz case. Contrary to that melt convectio n cannot be neglected and needs to be controlled by crucible and crystal ro tation rates. Simulations were used to optimise the temperature fields in t he VCz arrangements and thus, to reduce the von Mises stress within the gro wing crystal. Doing this, the EPD could be reduced by approximately one ord er of magnitude compared to conventional LEC Minimum EPD's were found to be in the range of some 10(3) cm(-2) for 4 " crystals. The observed nearly fl at (slightly convex) interfaces are in agreement with the simulations. The achieved good radial uniformity of the carbon incorporation and electrical parameters is due to the improved thermal boundary conditions. (C) 2000 Els evier Science B.V. All rights reserved.