Fine-structure splitting of exciton states in semiconductor quantum dot molecules

Exciton levels and fine-structure splitting in laterally coupled quantum dot molecules are studied. The electron and hole tunnelling energies as well as the direct Coulomb interaction are essential for the exciton levels. It is found that fine-structure splittings of the two lowest exciton levels are contributed by the intra-and interdot exchange interactions which are greatly influenced by the symmetry and tunnel-coupling between the two dots. As the interdot separation is reduced, fine-structure splitting of the exciton ground state is largely increased while those of the second and fourth states are decreased. Moreover, the dependence of the fine-structure splitting in quantum dot molecules on the Coulomb correlation is clearly clarified.