Trench formation in surfactant mediated epitaxial film growth of Ge on Si(100)

We have used STM to study the surface morphology of thin epitaxial Ge films grown on Si(001) in the presence of the surfactant As. The surfactant forces layer-by-layer growth up to 12 ML Ge coverage which could partly be explained by the geometrical surface arrangement of the growing film. Beyond 12 ML coverage we observed a network of trenches which decorate the earlier described V-shaped defects inside the film. Overgrowth of such defects is studied and a mechanism discussed.