Effect of strain on surface diffusion in semiconductor heteroepitaxy

We present a first-principles analysis of the strain renormalization of the cation diffusivity on the GaAs(001) surface. For the example of In/GaAs(001)-c(4 × 4) it is shown that the binding of In is increased when the substrate lattice is expanded. The diffusion barrier ∆E(ε) has a non-monotonic strain dependence with a maximum at compressive strain values (ε < 0), while being a decreasing function for any tensile strain (ε > 0) studied. We discuss the consequences of spatial variations of both the binding energy and the diffusion barrier of an adatom caused by the strain field around a heteroepitaxial island. For a simplified geometry, we evaluate the speed of growth of two coherently strained islands on the GaAs(001) surface and identify a growth regime where island sizes tend to equalize during growth due to the strain dependence of surface diffusion.