Fine structure of the trion triplet state in a single self-assembled semiconductor quantum dot

The emission from the charged biexciton is used to monitor the energy structure of the trion triplet state in a negatively charged CdSe/ZnSe quantum dot. The isotropic part of the electron–hole exchange interaction regroups the otherwise sixfold degenerated state in three Kramers doublets. The energy separation between the radiative pairs with total spin projection Fz=±3/2 and ±1/2 is 1.6 meV. The anisotropic part mixes states with ΔFz=±2 resulting in a partly linearly polarized transition dipole. Application of magnetic field lifts the degeneracy of the Kramers doublets. The g factors also manifest the anisotropic state mixing.