Crystals were grown without B2O3 encapsulation using the vapour-pressure-controlled Czochralski (VCz) method to reduce undesired B incorporation and to permit in situ control of the Ga/As ratio in the melt. Semi-insulating B-reduced 2 and 3in-diameter twin-free GaAs crystals were grown from Ga-rich melts with compositions down to 46at%As. Cathodoluminescence measurements of crystals grown from Ga-rich melts showed that the luminescence bands at 1.316 and 1.441eV were related to BAs. Semiconducting GaAs crystals were grown from stoichiometric melts. The donor was incorporated by Si doping or by using fused silica crucibles. Performing positron annihilation lifetime spectroscopy showed that the low B concentrations in the semi-conducting VCz GaAs always resulted in higher Ga vacancy concentrations when compared with standard GaAs. Cathodoluminescence bands due to optical transitions at 0.95 and 1.15eV were related to auto-compensating (VGaSiGa)2− and (SiGaVGaSiGa)− complexes, respectively, and depended upon the doping level.

Defect Distribution in Boron-Reduced GaAs Crystals Grown by Vapour-Pressure-Controlled Czochralski Technique. F.M.Kiessling, M.Albrecht, K.Irmscher, R.Krause-Rehberg, W.Ulrici, P.Rudolph: Journal of Crystal Growth, 2008, 310[7-9], 1418-23