Floating bonds and gap states in a-Si and a-Si:H from first principles calculations

TL;DR

This study uses first-principles calculations to analyze how five-fold coordinated defects in amorphous silicon and hydrogenated amorphous silicon create electronic gap states, and how hydrogenation can mitigate these defects.

Contribution

It provides detailed insights into the formation and evolution of T_5 defects and their role in gap states, highlighting hydrogen's effect in defect passivation.

Findings

T_5 defects contribute to gap states in a-Si and a-Si:H

Hydrogenation reduces gap states by passivating T_5 defects

Electronic structure analysis clarifies defect-related electronic properties

Abstract

We study in detail by means of ab-initio pseudopotential calculations the electronic structure of five-fold coordinated (T_5) defects in a-Si and a-Si:H, also during their formation and their evolution upon hydrogenation. The atom-projected densities of states (DOS) and an accurate analysis of the valence charge distribution clearly indicate the fundamental contribution of T_5 defects in originating gap states through their nearest neighbors. The interaction with hydrogen can reduce the DOS in the gap annihilating T_5 defects.