Hydrogen motion in hydrogenated amorphous silicon (a-Si:H)

Abstract

Dipolar spin lattice relaxation time, T 1D, measurements of 1H in a-Si:H have been used to probe the local motion of hydrogen in a-Si:H. Variations of T 1D with doping level reveal a trend similar to the changes in hydrogen diffusion constants measured in similar samples using secondary ion mass spectroscopy (SIMS). The temperature variations of T 1D indicate that, if the local motion is thermally activated, the activation energies are at least an order of magnitude smaller than those measured using SIMS. The ‘diffusion constants’ for local hydrogen motion inferred from T 1D measurements are many orders of magnitude faster than the diffusion constants obtained from SIMS. The T 1D measurements are made on the timescale of milliseconds while the SIMS measurements are performed on a scale of several hours to days. A phenomenological model provides a plausible connection between these two measurements, which are made on very different timescales.