The effect of secondary illuminations (0.9, 1.45eV) upon photo-quenched and photo-enhanced states in semi-insulating material was investigated by using piezoelectric photoacoustic measurements at 80K. It was found that secondary illumination of 0.9 and 1.45eV caused optical recovery of the piezoelectric photoacoustic signal from EL2* to EL20. The appearance of a broad band, at 0.8 to 1.0eV, in the piezoelectric photoacoustic spectrum was observed after secondary illumination of 0.9eV. The most important result was that the piezoelectric photoacoustic spectra after secondary illumination of 0.9eV, of both the photo-quenched and photo-enhanced states, were the same for the entire photon-energy region. It was concluded that secondary light of 0.9eV induced both optical recovery and the generation of a metastable state of the EL6 level. The differing rates of transformation of these 2 processes explained well the complex nature of the piezoelectric photoacoustic signal under secondary illumination.

Piezoelectric photoacoustic studies of optical recovery of metastable states related to EL2 and EL6 levels in semi-insulating GaAs A.Fukuyama, Y.Akashi, K.Yoshino, K.Maeda, T.Ikari: Physical Review B, 1998, 58[19], 12868-75