Boron‐ and stoichiometry‐related defect engineering during B2O3‐free GaAs crystal growth

Abstract

AbstractGaAs crystals have been grown without B2O3 encapsulation by the vapour‐pressure controlled Czochralski (VCz) method to reduce undesired boron incorporation and to enable in situ control of the Ga/As ratio in the melt. With increasing Ga content of the melt the omnipresent As precipitate concentration decreases in as‐grown GaAs crystals. Semiinsulating (SI) GaAs crystals could been obtained even from melts with a composition of 46 at.% As. Comparative cathodoluminescence (CL) measurements on those crystals and on boron‐contaminated GaAs show that the luminescence bands at 1.316 eV and at 1.441 eV are related to BAs. Reduced concentrations of boron and EL2 result in significant lower near‐band edge absorption, mainly caused by the photoionization cross section of As antisites in SI GaAs. These VCz GaAs crystals possess improved optical properties. Semi‐conducting (SC) GaAs:Si crystals were grown from near‐stoichiometric melts. Positron annihilation lifetime spectroscopy measurements show that the low boron concentration in our SC VCz GaAs results always in 3 times higher Ga vacancy concentrations compared to standard SC GaAs. CL bands due to optical transitions at 0.95 eV and 1.15 eV are related to auto‐compensating (VGaSiGa)2‐ and (SiGaVGaSiGa)– complexes, respectively, and depend on the doping level. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)