DEEP-ACCEPTOR-MEDIATED PHOTOQUENCHING OF THE MIDGAP DONOR EL2 IN SEMIINSULATING GAAS

The effects of lowering the temperature and/or adding shallow accepters in semi-insulating GaAs on the photoquenching effect of the midgap donor EL2 have been extensively studied. Measurements were made on the near-infrared photoabsorption and the photocurrent at T = 8.6-130 K for various samples containing different concentrations of carbon accepters ranging from 1.8 X 10(15) to 14.3 X 10(15) cm(-3). The results indicate a strong influence of the two parameters on the photoquenching; the photoquenching was more enhanced both at lower quenching temperatures and at higher carbon concentrations. The results were consistently explained by assuming a deep-acceptor level located at E(v) + (70-80) meV, which triggers the onset of EL2 photoquenching when it is neutral, while it triggers the onset of EL2 photorecovery when it is negatively ionized.