Structural Simplicity as a Restraint on the Structure of Amorphous Silicon

TL;DR

This paper demonstrates that enforcing structural simplicity in modeling amorphous silicon leads to models that are consistent with experimental data and exhibit electronic properties, highlighting the importance of local homogeneity in amorphous materials.

Contribution

The study introduces a simplicity-based refinement approach that produces realistic amorphous silicon models without chemically specific restraints.

Findings

Simplest models are continuous random networks consistent with PDF data.

Structural simplicity correlates with electronic homogeneity and a pseudogap formation.

Method approaches state-of-the-art models using only homogeneity assumptions.

Abstract

Understanding the structural origins of the properties of amorphous materials remains one of the most important challenges in structural science. In this study we demonstrate that local 'structural simplicity', embodied by the degree to which atomic environments within a material are similar to each other, is powerful concept for rationalising the structure of canonical amorphous material amorphous silicon (a-Si). We show, by restraining a reverse Monte Carlo refinement against pair distribution function (PDF) data to be simpler, that the simplest model consistent with the PDF is a continuous random network (CRN). A further effect of producing a simple model of a-Si is the generation of a (pseudo)gap in the electronic density of states, suggesting that structural homogeneity drives electronic homogeneity. That this method produces models of a-Si that approach the state-of-the-art without the need for chemically specific restraints (beyond the assumption of homogeneity) suggests that simplicity-based refinement approaches may allow experiment-driven structural modelling techniques to be developed for the wide variety of amorphous semiconductors with strong local order.