Self-assembly of steps and vacancy lines during the early stages of Ge∕Si(001) heteroepitaxy

The wetting layer formed during the early stages of Ge∕Si(001) growth has been found in recent experiments to undergo a roughening process, where the SA surface steps affect the spatial organization of vacancy lines (VLs) by increasing (stretching) or decreasing (squeezing) their average spacing. Using a combination of atomistic simulations and elastic theory of surface defects, we have computed the interaction energy of the SA steps and VLs for each of the observed defect configurations. We find that the repulsive SA-VL interactions lead to an increase in the spacing of the VLs in the “stretch” arrangement, but do not significantly affect the VL spacing in the “squeeze” configuration, providing an explanation for the observed correlations in the wetting layer roughness.