Growth of 20 mm diameter GaAs crystals by the floating zone technique during the D-2 Spacelab Mission

Abstract

Five GaAs single crystals Si-doped and undoped with diameters of 20 mm were grown by the floating-zone-technique (FZ) under microgravity during the second German Spacelab Mission D2. The GaAs rods were sealed in silica ampoules which contained and integrated As-source to provide controlled stoichiometry conditions. The heating system consisted of a specially designed mirror furnace. The results show that stoichiometric material was achieved within the limits of error of a coulometric analysis. The occurrence of dislocation networks could be strongly reduced and nearly avoided. Both oxygen and boron contents of the space-grown crystals are very low. Results of numerical calculations of the curvature of the interface, the distribution of temperature and stress in the crystal are shown to be in good agreement with the experiments.