The Atomic Structure of Quantum Dots

In this chapter, the atomic structure of both uncapped and buried quantum dots is described as derived from scanning tunneling microscopy in both top-view and cross-sectional geometry. Important conclusions are drawn also on the growth processes during quantum dot formation as well as during overgrowth. It is demonstrated that uncapped InAs quantum dots on GaAs(001) have a pyramidal shape with dominating {137} side facets and—in the case of larger dots—also {101} and {111} side facets. Buried InAs and InGaAs quantum dots, in contrast, are characterized by a truncated pyramidal shape with a (001) top facet and rather steep side facets. In addition, segregation processes during capping lead to strong intermixing and—under special overgrowth conditions—even to concave top facets or to the formation of nanovoids. Buried GaSb quantum dots are found to be much smaller, but also show a truncated pyramidal shape and strong intermixing effects. The experimental results will be discussed in the framework of the strain-induced segregation processes occurring during the different stages of quantum dot formation and overgrowth.