Microscale phenomena in bulk GaAs crystals: The effect of thermal gradients.

Undoped bulk crystals of gallium arsenide were grown in a unique Bridgman apparatus. The effect of the temperature gradient impressed over the melt, in conjunction with the role of the melt composition (arsenic source temperature), was investigated. Crystals were photo-etched to produce the interface striation patterns and the defect structures characteristic of the growth conditions. At low gradients the interface was found to be sharply curved, but uniform electron-beam induced current and cathodoluminescence intensities were observed. As the temperature gradient over the melt was increased the interface became flatter, and the uniformity of the EBIC and CL signals deteriorated. Growth of crystals from non-stoichiometric melts resulted in increased dislocation densities, with EBIC and CL yields unique to the Ga:As ratio in the melt. Deep level populations were also observed to respond to variations in the melt composition.