Positron lifetime measurements were performed on Au/GaAs samples at room temperature. A square-wave alternating-current bias revealed a frequency-dependent interface-related lifetime intensity that peaked at about 0.4Hz. These observations were explained in terms of ionization of the deep-donor level, EL2, to EL2+ in GaAs which was adjacent to the Au/GaAs interface. This caused a transient electric field to be experienced by positrons which drifted towards the interface. The EL2 donor level was found to be located at 0.80eV below the conduction band minimum. The results suggested that positron annihilation could, in some cases, act as an alternative to capacitance transient spectroscopy for characterizing deep levels in semiconductors and semi-insulators.

Y.Y.Shan, C.C.Ling, A.H.Deng, B.K.Panda, C.D.Beling, S.Fung: Physical Review B, 1997, 55[12], 7624-8