First-principles ab initio density functional calculations of H dynamics in hydrogenated amorphous Si were reported. Thermal motion of the host Si atoms drove H diffusion, as was demonstrated by direct simulation and explained using simple models. The Si-Si bond centres and Si ring centres were local energy minima, as expected. A new mechanism was also described for the breaking of Si-H bonds to release free atomic H into the network. This was fluctuating bond centre detachment-assisted diffusion, in which a bond centre H could be liberated by intercession of a third nearby Si. The H dynamics in a-Si:H was dominated by structural fluctuations intrinsic to the amorphous phase not present in the crystal.

Thermally Stimulated H Emission and Diffusion in Hydrogenated Amorphous Silicon. T.A.Abtew, F.Inam, D.A.Drabold: Europhysics Letters, 2007, 79[3], 36001 (5pp)