Universal shapes of self-organized semiconductor quantum dots

The model systems for self-organized quantum dots formed from elemental and compound semiconductors, namely Ge grown on Si(001) and InAs on GaAs(001), are comparatively studied by scanning tunneling microscopy. It is shown that in both material combinations only two well-defined families of faceted and defect-free nanocrystals exist (and coexist). These three-dimensional islands, pyramids and domes, show common morphological characteristics, independently of the specific material system. A universal behavior is further demonstrated in the capping-passivation process that turns the nanocrystals in true quantum dots.