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 degrees C have been performed. Samples were subjected to either isochronal anneals to temperatures in the range 300 to 600 degrees C or rapid thermal anneals to 700, 800, and 900 degrees C. A significant increase in the S-parameter was observed for all samples annealed to temperatures greater than 400 degrees 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.