The mechanism of H transport in amorphous hydrogenated material was considered. It was recalled that the standard model for H migration was that a H atom left a trap site, to reach a higher-energy transport site, migrated among the transport sites and eventually fell back into a trap site. It was presumed that the transport sites were bond-centered sites, and that the trap sites were H-pacifying dangling bonds. It was suggested that there were many published calculations, of the activation energy for H diffusion, that were misleading or incorrectly interpreted. Calculations were presented here which applied to particles hopping in complex media, and these were applied to amorphous hydrogenated material. These calculations, when combined with existing estimates of the energy of various H configurations in amorphous hydrogenated material, showed that the standard model was likely to be incorrect. Some preliminary calculations, presented here, indicated that the mobile H species in amorphous hydrogenated material could be molecular.

Some Theoretical Aspects of Hydrogen Motion in a-Si:H. P.A.Fedders: Physical Review B, 2000, 61[23], 15797-803