Atomistic study of dislocation formation during Ge epitaxy on Si

TL;DR

This study uses atomistic simulations to understand how dislocations form during the epitaxial growth of germanium on silicon, revealing the role of amorphous regions and surface morphology in dislocation dynamics.

Contribution

It provides detailed atomistic insights into dislocation formation mechanisms during Ge/Si epitaxy, linking surface features to dislocation pathways.

Findings

Dislocations originate in amorphous regions under surface valleys.

Atoms are expelled to the surface, relieving stress and smoothing the film.

Dislocation half-loops propagate along valleys, influenced by surface morphology.

Abstract

We performed classical molecular dynamics simulations to investigate, from an atomistic point of view, the formation of dislocations during the epitaxial growth of Ge on Si. We show that simulations at 900 and 1000 K with deposition rates of 10$^8$ monolayers per second provide a good compromise between computational cost and accuracy. In these conditions, the ratio between the Ge deposition rate and the ad-atom jump rate is analogous to that of out-of-equilibrium experiments. In addition, the main features of the grown film (intermixing, critical film thickness, dislocation typology, and surface morphology) are well described. Our simulations reveal that dislocations originate in low-density amorphous regions that form under valleys of the rough Ge film surface. Atoms are squeezed out of these regions to the surface, releasing the stress accumulated in the film and smoothing its surface. Amorphous regions grow until atoms begin to rearrange in dislocation half-loops that propagate throughout the Ge film. The threading arm ends of the dislocation half-loops move along the surface following valleys and avoiding islands. The film surface morphology affects the propagation path of the dislocation half-loops and the resulting dislocation network.