# Analysis of single and composite structural defects in pure amorphous silicon: a first-principles study

## TL;DR

This study uses first-principles calculations to analyze structural defects in amorphous silicon, revealing defect stability, electronic effects, and hydrogen passivation mechanisms.

## Contribution

It provides detailed insights into the nature of intrinsic defects and their passivation in amorphous silicon using first-principles simulations.

## Key findings

- Defect complexes can be energetically stable.
- Hydrogen passivation of T5 defects is exothermic.
- Activation energy for hydrogen passivation is 1.05 eV.

## Abstract

The structural and electronic properties of amorphous silicon ($a$-Si) are investigated by first-principles calculations based on the density-functional theory (DFT), focusing on the intrinsic structural defects. By simulated melting and quenching of a crystalline silicon model through the Car-Parrinello molecular dynamics (CPMD), we generate several different $a$-Si samples, in which three-fold ($T_3$), five-fold ($T_5$), and anomalous four-fold ($T_{4a}$) defects are contained. Using the samples, we clarify how the disordered structure of $a$-Si affects the characters of its density of states (DOS). We subsequently study the properties of defect complexes found in the obtained samples, including one that comprises three $T_5$ defects, and we show the conditions for the defect complexes to be energetically stable. Finally, we investigate the hydrogen passivation process of the $T_5$ defects in $a$-Si and show that the hydrogenation of $T_5$ is an exothermic reaction and that the activation energy for a H$_2$ molecule to passivate two $T_5$ sites is calculated to be 1.05 eV.