Thermally stimulated H emission and diffusion in hydrogenated amorphous silicon

TL;DR

This study uses first principles calculations to explore hydrogen diffusion mechanisms in hydrogenated amorphous silicon, revealing that structural fluctuations intrinsic to the amorphous phase dominate hydrogen dynamics.

Contribution

It introduces a new FBCD mechanism for Si-H bond breaking and provides detailed insights into hydrogen diffusion driven by host atom motion.

Findings

Si-Si bond and ring centers are local energy minima

FBCD is a new diffusion mechanism for free hydrogen release

Hydrogen dynamics are dominated by amorphous structural fluctuations

Abstract

We report first principles ab initio density functional calculations of hydrogen dynam- ics in hydrogenated amorphous silicon. Thermal motion of the host Si atoms drives H diffusion, as we demonstrate by direct simulation and explain with simple models. Si-Si bond centers and Si ring centers are local energy minima as expected. We also describe a new mechanism for break- ing Si-H bonds to release free atomic H into the network: a fluctuation bond center detachment (FBCD) assisted diffusion. H dynamics in a-Si:H is dominated by structural fluctuations intrinsic to the amorphous phase not present in the crystal.