Direct simulation of ion beam induced stressing and amorphization of silicon

TL;DR

This study uses molecular dynamics simulations to explore how silicon responds mechanically to ion irradiation, revealing stress behaviors, amorphization processes, and defect dynamics consistent with experimental data.

Contribution

It introduces a realistic simulation model for ion beam induced amorphization of silicon and compares structural properties with experimental results, highlighting the role of deformation rate and defects.

Findings

Amorphous silicon expands upon irradiation at realistic deformation rates.

Stress state depends on the material's ability to relax, leading to either compression or tension.

Annealing reduces local defects without large-scale network rearrangement.

Abstract

Using molecular dynamics (MD) simulation, we investigate the mechanical response of silicon to high dose ion-irradiation. We employ a realistic and efficient model to directly simulate ion beam induced amorphization. Structural properties of the amorphized sample are compared with experimental data and results of other simulation studies. We find the behavior of the irradiated material is related to the rate at which it can relax. Depending upon the ability to deform, we observe either the generation of a high compressive stress and subsequent expansion of the material, or generation of tensile stress and densification. We note that statistical material properties, such as radial distribution functions are not sufficient to differentiate between different densities of amorphous samples. For any reasonable deformation rate, we observe an expansion of the target upon amorphization in agreement with experimental observations. This is in contrast to simulations of quenching which usually result in denser structures relative to crystalline Si. We conclude that although there is substantial agreement between experimental measurements and most simulation results, the amorphous structures being investigated may have fundamental differences; the difference in density can be attributed to local defects within the amorphous network. Finally we show that annealing simulations of our amorphized samples can lead to a reduction of high energy local defects without a large scale rearrangement of the amorphous network. This supports the proposal that defects in amorphous silicon are analogous to those in crystalline silicon.