Photosensitivity of the 714 and 730 cm−1 absorption bands in semi-insulating GaAs: Evidence for a deep donor involving oxygen

The optically induced metastable interconversion processes of the oxygen-related vibrational modes at 730 and 714 cm−1, bands A and B, have been studied and compared with related properties of the EL2 defect. It is shown that the conversion from A to B is due to a charge exchange with the neutral EL2 level. The reverse process, recovery of band A, is observed after quenching of EL2. Conclusive evidence is presented that the two bands are associated with a donor in the upper half of the band gap. From Hall effect measurements, a trap energy of 0.43 eV below the conduction band is expected. A preliminary calibration of the absorption strength yields defect concentrations of ≊1015 cm−3 in some samples.