QUENCHING AND RECOVERY SPECTRA OF MIDGAP LEVELS (EL2) IN SEMIINSULATING GAAS MEASURED BY DOUBLE-BEAM PHOTOCONDUCTIVITY

Optical cross sections for transition of midgap donor levels (EL2) from normal states to metastable states and vice versa, were determined in semi-insulating GaAs by double-beam photoconductivity technique. The photoconductivity response to secondary light is quenched with one or two time constants depending upon the occupancy of normal states at thermal equilibrium, and optical quenching spectra are obtained from the larger time constant. Optical recovery measurement indicated that only a certain fraction of total quenching is recovered optically and that this fraction depends upon wafers. A new model of EL2, AsGa in association with any acceptor, is proposed based upon the observed results on different liquid-encapsulated Czochralski and metalorganic chemical vapor deposition semi-insulating wafers and other results reported so far.