The mechanism of, and activation barrier to, H diffusion on the surface and in the bulk of plasma-deposited hydrogenated amorphous silicon films during post-deposition exposure of the films to H atoms from a H2 plasma were studied. The work was based upon molecular dynamics simulations of the repeated impingement of H atoms on the surfaces of smooth a-Si:H films at 475 to 800K. The H diffusion mechanism was identical on the a-Si:H surface and in bulk a-Si:H film. The H atom diffused rapidly via a floating-bond mediated migration process. This floating bond accompanied the H atom as it hopped from one Si atom to another. The Si atoms between which the H hopped during diffusion were typically very weakly-bonded or not bonded to each other. The calculated activation barrier to H diffusion was only 0.10eV.

Atomistic Analysis of the Mechanism of Hydrogen Diffusion in Plasma-Deposited Amorphous Silicon Thin Films. Valipa, M.S., Maroudas, D.: Applied Physics Letters, 2005, 87, 261911