Atomistic Structures of Amorphous Si1-xGex Alloys: A Molecular-Dynamics Study

Abstract

Although extensive studies have been carried out on structural analyses of amorphous silicon-germanium (a-Si1-xGex) alloys, there are still controversies concerning short-range order in a-Si1-xGex alloys. In this study, we examined amorphous structures of Si1-xGex alloys by molecular-dynamics (MD) simulations using the Tersoff interatomic potential. Amorphous networks were prepared by rapid quenching from liquid Si1-xGex alloys. Computer-generated atomic configurations consisted of tetrahedral networks with complete chemical disorder in the first coordination shell. The bond lengths of Si-Si, Si-Ge and Ge-Ge pairs slightly increased with the Ge composition, and a weaker composition dependence was observed in the bond lengths of Si-Si and Si-Ge pairs than that for Ge-Ge pair. These results were in good agreement with those obtained experimentally, suggesting that the MD calculations based on the Tersoff potential is useful for the structural analysis of a-Si1-xGex alloys. It was confirmed that the Ge-Ge bond length and bond angle surrounding Ge atoms are more distorted. This is attributed to the difference between Si and Ge in the bond-stretching and in the bond-bending forces.