INFRARED-ABSORPTION BY DEEP LEVELS IN LOW-TEMPERATURE ELECTRON-IRRADIATED GAAS

Semi-insulating GaAs was irradiated with 3-MeV electrons at 4.5 K and the optical absorption was monitored after irradiation and after annealing up to a temperature of 770 K. The absorption peak at 0.98 eV and the shoulder at 0.8 eV, which are known from room-temperature irradiation experiments, were observed immediately after irradiation at 4.5 K. Hence, the defect connected with these lines is produced directly during irradiation. The well-known recombination stages of Frenkel pairs located around room temperature and at 500 K lead to a reduction of the absorption background but do not affect the intensity of the two lines. This remarkable stability of the defect responsible for the absorption lines is further investigated by high-temperature irradiations and the final annealing between 600 and 650 K is attributed to reactions with mobile Ga vacancies.