First-principles study of the electronic structure of CdS/ZnSe coupled quantum dots

We have studied the electronic structure of CdS/ZnSe coupled quantum dots, a novel heterostructure at the nanoscale. Our calculations reveal CdS/ZnSe coupled quantum dots are type II in nature where the anion p states play an important role in deciding the band offset for the highest occupied molecular orbitals (HOMO). We show that the offsets of HOMO as well as the lowest unoccupied molecular orbitals (LUMO) can be tuned by changing the sizes of the components of the coupled quantum dots, thereby providing an additional control parameter to tune the band gap and the optical properties. Our investigations also suggest that the formation of an alloy near the interface has very little influence on the band offsets, although it affects the spatial localization of the quantum states from the individual components. Comparing the influence of strain on coupled quantum dots and core-shell nanowires, we find strain practically has no role in the electronic structure of coupled quantum dots as the small effective area of the interface in a coupled quantum dot helps a large part of the structure remain free from any substantial strain. We argue that in contrast to core-shell nanowires, quantum confinement is the key parameter that controls the electronic properties of coupled quantum dots and should therefore be an ideal candidate for the design of a quantum device.