Controlled Ge quantum dots positioning with nano-patterned Si(001) substrates

International audienceA square nanometric patterned substrate (period 20 nm) is obtained by direct twist bonding of two twin Si(001) surfaces, thinning and preferential chemical etching. Molecular beam epitaxy of Ge is carried out on a sample having heterogeneous trench depths to analyse islands positioning as a function of the surface morphology. Scanning electron microscopy observations show that small single dots per mesa or large dots covering several mesas can be observed. It highlights the influence of the mesa aspect ratio on the control of Ge islands self‐organization, and suggests the occurrence of an effective activation barrier depending on the surface profile. The position‐dependent energy stored in a dot for a given surface profile is estimated from a very simple model based on the balance between capillarity and elastic relaxation terms. By choosing a cycloid‐like profile, experimental observations can be explained without fitting parameters