Computer-assisted growth of low-EPD GaAs with 3" diameter by the vertical gradient-freeze technique

We have grown 3", silicon-doped GaAs crystals with low dislocation density by the vertical gradient freeze (VGF) method. The thermal conditions in a newly designed, multi-zone VGF-furnace were optimized by the aid of numerical simulation. A computer controlled temperature-time program of the 9 heaters was acquired which allows to keep the axial temperature gradient in the solid (liquid) GaAs at the optimized constant values of 7(2) K/cm during the whole growth process. By using these calculated heater temperatures in real growth experiments, we succeeded in growing 3" single crystals with EPD < 500 cm(-2). (C) 1999 Elsevier Science B.V. All rights reserved.