In hydrogenated amorphous material, values as low as zero were found for the exponent which characterized the light-intensity dependence of the minority carrier concentration. Model simulations of the temperature dependence of this exponent, and of the phototransport properties of the majority carriers, showed that the low values were associated with the presence of an acceptor-like center whose energy level lay 0.3 to 0.5eV above the valence-band edge. The results showed that the usual analysis of the photo-electronic properties in terms of dangling bonds and band-tail states alone was unjustified, and that the so-called safe hole traps that were supposed to exist in this material could now be identified as being O-induced acceptor-like centres.

Sensitization of the Electron Lifetime in a-Si:H: the Story of Oxygen. I.Balberg, R.Naidis, L.F.Fonseca, S.Z.Weisz, J.P.Conde, P.Alpuim, V.Chu: Physical Review B, 2001, 63[11], 113201 (4pp)