Junction capacitance study of an oxygen impurity defect exhibiting configuration relaxation in amorphous silicon–germanium alloys deposited by hot-wire CVD

We report the observation of light induced electron capture in oxygen contaminated (∼5 × 1020 cm−3) hydrogenated amorphous silicon–germanium alloys grown by hot-wire chemical vapor deposition (HWCVD). By examining the time evolution of dark capacitance after 1.2 eV photoexcitation, we are able to estimate the free energy barrier (⩾0.8 eV) for the release of electrons into the conduction band. Such a large thermal barrier, for a defect whose optical threshold is centered (∼1.35 eV) so close to the band-gap (1.5 eV), indicates significant configurational relaxation once the oxygen impurity state is occupied with photoexcited electrons.