Introduction and recovery of point defects in electron-irradiated Te- and Si-doped GaAs studied by positron lifetime spectroscopy.

Abstract

Positron lifetime experiments have been performed to study the recovery of point defects in electron-irradiated n-type GaAs, which has been completely compensated in the irradiation. Irradiation temperature was 20 K and isochronal annealings were performed from 77 to 650 K. After all annealings below 450 K positrons detect irradiation-induced Ga vacancies and Ga antisite defects in a negative charge state. The main recovery stage of Ga is at 200--300 K. The Ga antisites anneal out at 500 K. Since the n-type conductivity reappears also after annealing at 500 K, we conclude that the negative Ga antisites have an important role in the compensation of n-type GaAs in the electron irradiation. Removal of compensation at 500 K reveals irradiation-induced As vacancies, which are converted from positive charge state to neutral or negative. The As vacancies introduced in the irradiation have similar ionization levels to those found in as-grown GaAs. The As vacancies recover at 550--650 K and their introduction rate is about 0.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ after annealing at 550 K. The low value of the introduction rate may indicate that the recovery of the As vacancies starts already before 550 K.