Epitaxial growth in dislocation-free strained alloy films: Morphological and compositional instabilities

TL;DR

This paper develops a continuum model to analyze morphological and compositional instabilities in dislocation-free strained alloy films during epitaxial growth, revealing how various factors influence stability and instability onset.

Contribution

It introduces a comprehensive stability analysis considering realistic factors like elastic moduli dependence and surface-bulk coupling, providing new insights into epitaxial film stability.

Findings

Identification of stability diagrams above and below the spinodal temperature

Calculation of kinetic critical thickness for instability onset

Scaling laws for critical thickness with strain and deposition rate

Abstract

The mechanisms of stability or instability in the strained alloy film growth are of intense current interest to both theorists and experimentalists. We consider dislocation-free, coherent, growing alloy films which could exhibit a morphological instability without nucleation. We investigate such strained films by developing a nonequilibrium, continuum model and by performing a linear stability analysis. The couplings of film-substrate misfit strain, compositional stress, deposition rate, and growth temperature determine the stability of film morphology as well as the surface spinodal decomposition. We consider some realistic factors of epitaxial growth, in particular the composition dependence of elastic moduli and the coupling between top surface and underlying bulk of the film. The interplay of these factors leads to new stability results. In addition to the stability diagrams both above and below the coherent spinodal temperature, we also calculate the kinetic critical thickness for the onset of instability as well as its scaling behavior with respect to misfit strain and deposition rate. We apply our results to some real growth systems and discuss the implications related to some recent experimental observations.