Growth of GaAS crystals from Ga-rich melts by the VCz method without liquid encapsulation

The growth experiments and properties of undoped GaAs crystals grown by the vapour pressure controlled Czochralski (VCz) method without boric oxide encapsulant from Ga-rich melts are presented. Morphological and structural features were investigated by sensitive etching procedures. The precipitate content was analysed by laser scattering tomography. The mean scattering intensity of As precipitates decreases with increasing Ga excess in the melt. An enhanced probability of Ga-rich inclusion incorporation has been observed. In 3-in crystals, the mean etch pit density was decreased down to 5 x 103 cm(-2) with improved radial homogeneity. The etch pits did not show cell patterning. Markedly reduced contents of boron and hydrogen have been detected. No oxygen defects and related complexes independently on the carbon concentration were ascertained by local vibrational mode. For the first time, the carbon concentration in the grown crystals was reduced by carefully controlling the CO content of the growth atmosphere in a VCz arrangement without boric oxide encapsulant. Such experiments without B2O3 encapsulant are of fundamental character and offer numerous information about the point defect situation in as-grown crystals. (C) 2004 Elsevier B.V. All rights reserved.