VARIABLE-ENERGY POSITRON BEAM CHARACTERIZATION OF DEFECTS IN AS-GROWNAND ANNEALED LOW-TEMPERATURE-GROWN GAAS

Variable energy positron annihilation measurements on as-grown and ann ealed GaAs grown by molecular beam epitaxy at temperatures between 230 and 350 degrees C have been performed. Samples were subjected to eith er isochronal anneals to temperatures in the range 300 to 600 degrees C or rapid thermal anneals to 700, 800, and 900 degrees C. A significa nt increase in the S-parameter was observed for all samples annealed t o temperatures greater than 400 degrees C. The positron annihilation c haracteristics of the defect produced upon annealing are consistent wi th divacancies or larger vacancy clusters. The concentration of as-gro wn and anneal generated defects is found to decrease with increasing g rowth temperature.