NMR probe of band tail states in a-Si:H

Abstract We measured the dipolar spin–lattice relaxation time (T1d) of the bonded hydrogen in hydrogenated amorphous silicon at low temperature. At 15 K, after the sample is irradiated by λ=6500 A light for 2 s, T1d is reduced by about one order of magnitude. The reduction of T1d is attributed to the cross-relaxation between the hydrogen and localized paramagnetic band tail states that are induced by the light. Within experimental error, T1d is proportional to the inverse of the square of the density of the paramagnetic states, consistent with a previously proposed model.