Network structure and dynamics of hydrogenated amorphous silicon

TL;DR

This paper uses ab initio simulations to explore the structure, defect dynamics, hydrogen motion, and electron-lattice interactions in hydrogenated amorphous silicon, providing insights into defect behavior and the Staebler-Wronski effect.

Contribution

It introduces a detailed simulation approach linking defect fluctuations, hydrogen dynamics, and electron-lattice coupling to phenomena like the Staebler-Wronski effect in a-Si:H.

Findings

Thermal fluctuations affect defect coordination in a-Si:H.

Hydrogen motion mechanisms are elucidated through MD simulations.

Electron-lattice coupling correlates with state localization.

Abstract

In this paper we discuss the application of current it ab initio computer simulation techniques to hydrogenated amorphous silicon (a-Si:H). We begin by discussing thermal fluctuation in the number of coordination defects in the material, and its temperature dependence. We connect this to the ``fluctuating bond center detachment" mechanism for liberating H bonded to Si atoms. Next, from extended thermal MD simulation, we illustrate various mechanisms of H motion. The dynamics of the lattice is then linked to the electrons, and we point out that the squared electron-lattice coupling (and the thermally-induced mean square variation in electron energy eigenvalues) is robustly proportional to the localization of the conjugate state, if localization is measured with inverse participation ratio. Finally we discuss the Staebler-Wronski effect using these methods, and argue that a sophisticated local heating picture (based upon reasonable calculations of the electron-lattice coupling and molecular dynamic simulation) explains significant aspects of the phenomenon.