Chapter 2 - Vertical diatomic artificial quantum dot molecules

Abstract

Circular vertically coupled semiconductor double quantum dots can be employed to study the filling of electrons in quantum dot artificial molecules. When the dots are quantum mechanically strongly coupled, the electronic states in the system are substantially delocalized, and the Coulomb diamonds and the addition energy spectra of the artificial molecule resemble those of a single quantum dot artificial atom in the few-electron limit. When the dots are quantum mechanically weakly coupled, the electronic states in the system are substantially localized on one dot or the other, although the dots can be electrostatically coupled, and this leads to a pairing of the counductance peaks in the several-electron regime. The chapter also describes the dissociation of the few-electron artificial molecules at 0 T as a function of interdot distance from the strong coupling limit to the weak coupling limit. Slight mismatch unintentionally introduced in the fabrication of the artificial molecules from materials with nominally identical constituent quantum wells is responsible for electron localization as the interdot coupling becomes weaker. This offsets the energy levels in the quantum dots by up to 2 meV, and this plays a crucial role in the appearance of the addition energy spectra as a function of coupling strength particularly in the weak coupling limit.