The diffusion mechanisms in amorphous material were investigated within the context of first-principles results for Si-H interactions. Specific definitions were provided for the various quantities which entered into the description of H diffusion in amorphous Si, and values which were deduced from first-principles theory were linked to these quantities. The H chemical potential, H, was associated with the formation energy of Si-H bonds with respect to bulk Si. The Si-H bond energy level, ESi-H, was located at a distance, below H, which corresponded to the formation energy of a dangling bond. It was argued that H atoms could move readily between the H and ESi-H levels in amorphous Si; thus maintaining the equilibrium picture that underpinned the description of diffusion. The resultant framework was consistent with experimental observations, and avoided the need for more convoluted explanations: such as diffusion along interconnected void surfaces. It was concluded that, although explicit first-principles calculations of amorphous networks were still required in order to obtain the specific energy distributions, the basic correlation between observed quantities and calculated values had now been accomplished.

C.G.Van de Walle, R.A.Street: Physical Review B, 1995, 51[16], 10615-8