Variable energy positron beam characterization of defects in as-grown and annealed low temperature grown GaAs

Variable energy positron annihilation measurements on as-grown and annealed GaAs grown by molecular beam epitaxy at temperatures between 230 and 350°C have been performed. Samples were subjected to either isochronal anneals to temperatures in the range 300 to 600°C or rapid thermal anneals to 700, 800, and 900°C. A significant increase in the S-parameter was observed for all samples annealed to temperatures greater than 400°C. The positron annihilation characteristics of the defect produced upon annealing are consistent with divacancies or larger vacancy clusters. The concentration of as-grown and anneal generated defects is found to decrease with increasing growth temperature.