Hydrogen Diffusion Mechanism in Amorphous Silicon From Deuterium Tracer Studies

We study D tracer diffusion in hydrogenated amorphous silicon (a-Si:H) by annealing sandwich structures of a-Si:H/a-Si:H:D/a-Si:H. Our experimental D profiles are fit well by the analytic solutions that we derive for a trap-controlled diffusion model. For anneals shorter than the deep H release time, the D profiles follow the asgrown profiles except for exponential wings at low concentration. The wing amplitude increases nearly linearly with time. In the long-time limit, the solutions are identical to the trap-free case, but with an effective diffusion coefficient that can be calculated from features of the early-time tracer profiles. We measure parameters of H diffusion including the H release time from deep traps and the mean displacement of free H before retrapping. We discuss implications of these results for models of H trapping in a-Si:H.