Theory of the resonant and non-resonant luminescence changes in amorphous silicon

Abstract

The resonant and non-resonant luminescence changes in a-silicon are considered. It is suggested, that the effect is closely related to the anomalous spin-dependent magnetoresistance and photoconductivity changes observed in evaporated and glow-discharge-deposited silicon. The novel feature here is the existence of stable quenching lines. This considerably reduces the choice of recombination models to either a geminate radiative process with singlet-spin memory or to the usual localized-localized recombination process with a spin-dependent, non-radiative transition. The steady-state and time-dependent features of the latter model are analysed. The results are in good agreement with experiment if the exchange interaction between the spins is assumed to be negligibly small. Some interesting and novel time-dependent effects are found and related to recent observations. In particular, it is found that microwave chopping can turn a quenching line into an enhancing one. The problems associated with exchange-coupled spins are discussed. It is concluded that anomalous spin effects in pair models can only be expected for the recombination of distant electron-hole pairs.