Defect State Density and Orbital Localization in a-Si:H/c-Si Heterojunction and the Role of H

TL;DR

This study uses density functional theory to analyze how hydrogen bonding configurations influence defect states and orbital localization in a-Si:H/c-Si heterojunctions, revealing hydrogen's passivating role at the interface.

Contribution

It provides new insights into the atomic-level effects of hydrogen bonding on defect states and orbital localization in a-Si:H/c-Si interfaces using combined MD and DFT simulations.

Findings

Defect state density is lower at the interface in stable configurations.

Hydrogen atoms can significantly alter atomic structure and reduce defect states.

Hydrogen's passivating effect improves interface quality in heterojunctions.

Abstract

In this paper, we explore the effect of H and its bonding configurations on the defect state density and orbital localization of hydrogenated amorphous Si (a-Si:H)/crystalline Si (c-Si) heterostructures using density functional theory (DFT) studies of model interfaces between amorphous silicon (a- Si)/a-Si:H and c-Si. To model the atomic configuration of a-Si on c-Si, melting and quenching simulations were performed using classical molecular dynamics (MD). Different hydrogen contents were inserted into the a-Si in different bonding configurations followed by DFT relaxation to create the stable structures of a-Si:H representative of hydrogenated a-Si on crystalline Si surfaces. In contrast to crystalline heterojunctions (where the interface density is a maximum at the interface), we find that, in the most energetically stable configurations of H atoms, the defect state density is relatively low at the interface and maximum at the middle of a-Si layer. Our structural analysis shows that in these configurations, H atoms do not necessarily bond to dangling bonds or to interface atoms. However, they are able to significantly change the atomic structure of the heterostructure and consequently decrease the density of defect states and orbital localization at the a-Si layer and more significantly at the interface of a-Si/c-Si. The general form of the modeled defect state distribution demonstrates the passivating role of a-Si:H on c-Si substrates.