Enhanced instability of strained alloy films due to compositional stresses

A single-component strained film is known to be unstable to the stress-driv en morphological instability. Here, we determine how the instability is mod ified in an alloy film by considering the effect of compositional stresses due to an atomic size difference. We find that the coupling of composition to stress always makes the film more unstable to the formation of stress-dr iven surface undulations. The destabilization is greatest over a range of i ntermediate deposition rates.