Diffusion of Hydrogen in Amorphous Silicon in the Low Concentration Regime

Abstract

We report the first measurements of hydrogen diffusion kinetics in a-Si in the regime of low H concentration (<2×l019 cm−3). The results differ substantially from the diffusion behavior typically observed in hydrogenated a-Si:H at H concentrations >1020 cm−3. The activation energy and pre-exponential factor for low-concentration H diffusion are found to be 2.70 ± 0.02 eV and 2.2 × 104 cm2s−1, respectively, and are shown to be independent of both annealing time and H concentration. It is difficult to reconcile the combination of high activation energy and large pre-exponential factor with a simple deep-trap-limited diffusion model. Consequently, an alternative mechanism for H diffusion involving the migration of dangling bonds coupled with a H bond-switching step is proposed.