Stress-Driven Alloy Decomposition during Step-Flow Growth

A surface under stress is morphologically unstable. In normal step-flow growth, this is manifested as a step-bunching instability. Here it is shown that for alloy growth the resulting inhomogeneous strain drives decomposition of the alloy. At the same time, this decomposition ``screens'' the inhomogeneous strain, partially suppressing the instability. In contrast to a previous continuum model, stress-driven alloy decomposition during step flow is never destabilizing, nor does it ever fully stabilize the surface. A possible mechanism for spontaneous superlattice formation is suggested.