A study was made of the effect of decreasing the temperature, and/or adding shallow acceptors, upon photo-quenching of the EL2 mid-gap donor in semi-insulating material. Measurements were made of the near-infrared photo-absorption and photocurrent, at 8.6 to 130K, in samples which contained C acceptor concentrations that ranged from 1.8 x 1015 to 1.43 x 1016/cm3. The results revealed a strong effect of the 2 parameters upon the photo-quenching. The latter was enhanced at lower quenching temperatures and higher C concentrations. The results could be consistently explained by assuming that a deep-acceptor level, which was located at Ev+(0.07 to 0.08)eV, triggered the onset of EL2 photo-quenching when it was neutral, but triggered the onset of EL2 photo-recovery when it was negatively ionized.

M.Suemitsu, H.Takahashi, N.Miyamoto: Physical Review B, 1995, 52[3], 1666-73