Tight-binding molecular dynamics calculations indicated a mechanism, for H diffusion in hydrogenated amorphous material, which involved a family of low-energy configurations where H atoms could bond to Si atoms. The H was suggested to move through the amorphous network by successively breaking existing nearby Si-Si bonds and simultaneously forming an intermediate Si-H bond with one of the Si atoms; thus creating a new dangling bond in the vicinity. The broken bonds could reform when the H had moved away. Therefore, the diffusing H atoms always carried with them a newly created dangling bond, and the motion of H was closely related to the motion of transient dangling bonds in amorphous hydrogenated material. The tight-binding calculations predicted that the formation energies for these processes would range from 1.3 to 2.3eV.

Mechanism for Hydrogen Diffusion in Amorphous Silicon. R.Biswas, Q.Li, B.C.Pan, Y.Yoon: Physical Review B, 1998, 57[4], 2253-6