Studies on correlation between the quality of GaAs LEC crystals and the inert gas pressure

Abstract

The surface state, structural perfection, concentration of important residual impurities (C, B, O, H), electrical parameters and EL2 concentration of LEC GaAs single crystals and their dependence on the argon pressure between 0.1 and 4.0 MPa have been investigated systematically. Whereas at pressures > 1.0 MPa the gallium droplets at the crystal periphery disappear completely, the etch pit density and dislocation cell boundaries increase with pressure. The incorporated carbon content and, therefore, the electrical resistivity decrease with increasing argon pressure, especially, in the region between 0.2 and 1.0 MPa very sensitively. A parallel behaviour has been found for boron. As expected, the oxygen concentration behaves oppositely to that of carbon and increases with the pressure. No evident correlations for hydrogen or free electron concentration on the argon pressure have been found. A slight increase of the EL2 concentration was detected. Probable explanations of the observed effects will be given.