Surface roughness and alloy stability interdependence in lattice-matched and lattice-mismatched heteroepitaxy

How the possibility of a better strain relaxation introduced by the surface roughness can modify alloy demixing is investigated here. We propose a step-by-step model to simulate the growth process on a rough surface. We use an atomistic description and also consider the surface tension difference between the two binaries that form the ternary alloy. This study clearly shows how and why—in the lattice-matched case—the atoms corresponding to the binary materials with the lowest surface tension naturally tends to segregate towards initially sloping areas, whereas—in the mismatched case—upper areas are enriched in the more strained binary. The results are exemplified by ${\mathrm{Al}}_{0.5}{\mathrm{In}}_{0.5}\mathrm{As}$ lattice matched or not to its substrate. Throughout this article, we discuss the balance among mixing enthalpy, strains, and the difference of surface tension between the two binaries that form the ternary alloy.