Hydrogen Diffusion Mechanism in Amorphous Silicon from D Tracer Diffusion: Theory and Experiment

We compare experimental diffusion studies to the results of a theoretical study of diffusion controlled by a single deep trap level. Analytic solutions for the D profiles after annealing depend on the characteristic H release time, τ, from the deep trap. At times much shorter than τ, the D profile develops exponential wings whose decay length is the mean D displacement between trapping events. The long-time D profile is a solution to the ideal diffusion equation, but with an effective diffusion coefficient that can be calculated from features of the early-time profiles. New experimental data establish the validity of the model at a range of anneal times and temperatures. We also find that the mean displacement of free H before retrapping decreases with both increased illumination and increasing anneal temperature.