Deep-acceptor-mediated photoquenching of the midgap donor EL2 in semi-insulating GaAs

The effects of lowering the temperature and/or adding shallow acceptors 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 acceptors ranging from 1.8×1015 to 14.3×1015 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 Ev+(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.