Positron lifetime measurements were used to study the recovery of point defects in electron-irradiated n-type material which had been completely compensated during irradiation. The irradiation temperature was 20K, and isochronal annealing was carried out at 77 to 650K. After annealing at temperatures below 450K, the positrons detected irradiation-induced Ga vacancies and Ga antisite defects in a negative charge state. The main recovery stage of Ga was found at 200 to 300K. The Ga antisites annealed out at 500K. Because n-type conductivity also reappeared after annealing at 500K, it was concluded that the negative Ga antisites played an important role in the compensation of n-type GaAs during electron irradiation. A removal of compensation at 500K revealed irradiation-induced As vacancies which were converted from positive charge states to neutral or negative states. The As vacancies which were introduced during irradiation had similar ionization levels to those which were found in as-grown material. The As vacancies recovered at 550 to 650K, and their introduction rate was about 0.5/cm after annealing at 550K. It was suggested that the low value of the introduction rate indicated that the recovery of As vacancies began below 550K.

K.Saarinen, A.P.Seitsonen, P.Hautojärvi, C.Corbel: Physical Review B, 1995, 52[15], 10932-46