It was recalled that relaxation phenomena which involved the motion of H in hydrogenated amorphous material, that had traditionally been described in terms of a distribution of relaxation times and a stretched-exponential functional, had been re-analyzed in terms of re-trapping in a 3-level energy diagram. It was shown that the latter expression could also be obtained on the basis of H transport via interstitial positions which were in thermal equilibrium with a set of H traps that were located at about 1eV below the H chemical potential. However, models which were based upon H re-trapping gave a good account of the relaxations only for temperatures above room temperature. A dispersive behavior was assumed to be responsible for the discrepancy at lower temperatures.

Hydrogen motion and stretched-exponential relaxation in a-Si:H Q.Zhang, G.J.Adriaenssens: Journal of Physics - Condensed Matter, 1998, 10[26], 5897-904