Simulation and modeling of the electronic structure of GaAs damage clusters

TL;DR

This study uses atomistic simulations to analyze the electronic properties of radiation damage clusters in GaAs, revealing how damage affects electronic structure and the transition to metallic states.

Contribution

It introduces a combined molecular dynamics and density functional theory approach to characterize damage clusters in GaAs, providing new insights into their electronic behavior.

Findings

Damage clusters' electronic properties are well described by a classical charging model.

The band gap closes with increasing damage, leading to metallic behavior.

Estimated Fermi level of high-damage clusters is 0.46 eV above the valence band.

Abstract

In an effort to build a stronger microscopic foundation for radiation damage models in gallium arsenide (GaAs), the electronic properties of radiation-induced damage clusters are studied with atomistic simulations. Molecular dynamics simulations are used to access the time and length scales required for direct simulation of a collision cascade, and density functional theory simulations are used to calculate the electronic properties of isolated damaged clusters that are extracted from these cascades. To study the physical properties of clusters, we analyze the statistics of a randomly-generated ensemble of damage clusters because no single cluster adequately represents this class of defects. The electronic properties of damage clusters are accurately described by a classical model of the electrical charging of a semiconducting sphere embedded in an uniform dielectric. The effective band gap of the cluster depends on the degree of internal structural damage, and the gap closes to form a metal in the high-damage limit. We estimate the Fermi level of this metallic state, which corresponds to high-energy amorphous GaAs, to be 0.46 +/- 0.07 eV above the valence band edge of crystalline GaAs.