Stranski–Krastanow growth, modified by the presence of submonolayer coverages of carbon or antimony, is investigated for tensile strained silicon epilayers on Ge(001) substrates. We find a reduction in the wetting layer thickness from >10 monolayers without surfactant, to 7.5 and 4.5 monolayers, respectively, with Sb and C predeposition. Very small islands with an aspect ratio of 0.05 and a narrow size distribution were found for Sb-mediated growth. For both adatom species the wetting layer is free of dislocations, whereas the Si islands are almost completely strain relaxed, mainly via sessile 90° misfit dislocations. We show that early dislocation nucleation is an inherent property of a (001) oriented cubic heterosystem under tensile strain.