Sensitization of the electron lifetime in a-Si:H: The story of oxygen

We have found, in hydrogenated-amorphous silicon (a-Si:H), values as low as 0 for the exponent γ_h that characterizes the light-intensity dependence of the minority-carrier concentration. The model simulation analyses of the temperature dependence of γ_h and the phototransport properties of the majority carriers show that these unprecedented low values in general, and in a-Si:H in particular, are associated with the presence of an acceptorlike center, the energy level of which lies 0.3-0.5 eV above the valence-band edge. Our results show then that the common analyses of the photoelectronic properties of a-Si:H only in terms of dangling bonds and band-tail states are not justified, and that the “safe hole traps” that were proposed to exist in a-Si:H can be identified now as oxygen-induced acceptorlike centers.