3 INTERACTING EXCITONS IN 3 COUPLED QUANTUM DOTS

Using a scaled Kohn-Sham formalism, we examine three heavy-and light-h ole excitons, respectively, in three coupled quantum dots to study the effects of competition involving the electron-electron and hole-hole interactions between excitons, the electron-hole interaction within ex citons and the effective masses. The particle-particle interactions pl ay dominant roles in determining the configuration of the excitons in the coupled dots. In the absence of an external electric field, the tw o lowest (occupied) energy states of the heavy-hole excitons are degen erate, and the excitons have an equal probability of residing in eithe r of the two side dots. The corresponding states of the light-hole exc itons exhibit nondegenerate character and the lowest energy exciton is confined predominantly to the centre dot. Under a weak de electric he ld, both the heavy-and light-hole excitons form direct excitons which are localized in the side dots. For large values of the electric held, we find that the electrons associated with the excitons become ionize d as a result of strong confinement by the field and the electron-elec tron repulsion between excitons before the excitons can be transformed into indirect excitons. This result is in contrast to the conclusion that a single exciton in a double-quantum-well structure will be trans formed into an indirect exciton in real space when it is subjected to large fields. Furthermore, we suggest that the wave function overlap b etween interacting excitons may diminish significantly the increase in excitonic lifetime predicted for a single exciton in two coupled quan tum dot systems, implying that it may be difficult to make use of seve ral excitons in coupled structures for nonlinear devices.