It was noted that the mechanism of H migration in amorphous Si remained an unresolved problem. The main problem was the small activation energy (1.5eV), relative to the

strength of Si-H bonds (2 to 3.5eV). First-principles finite-temperature simulations were performed here which demonstrated clearly that H was not released spontaneously, as usually proposed, but awaited the arrival of a floating bond. The so-called migrating species was a floating-bond plus H complex, with H jumping from Si to Si and with the floating bond floating around it. Migration ceased when the floating bond moved away.

Diffusion Mechanism of Hydrogen in Amorphous Silicon - Ab Initio Molecular Dynamics Simulation. Y.S.Su, S.T.Pantelides: Physical Review Letters, 2002, 88[16], 165503 (4pp)