Fine structure of excitons in II-VI quantum wells and dots

Applying a magnetic field along principal axes, the fine structure of the groundstate exciton caused by the electron- hole exchange interaction is studied for (Zn,Cd)Se/ZnSe quantum wells and CdSe quantum dots on ZnSe. In quantum wells, the zero-field splitting between optically allowed and forbidden (dark) states is increased by a factor of about two with respect to the bulk ZnSe value (0.25 meV). The localization of excitons gives rise to a finite, but minor contribution from the non-analytical part. For quantum dots, as a result of the 3D confinement, the splitting is further enhanced and reaches values ranging between 1.5 and 2.0 meV. Its weak size dependence is a consequence of the finite barrier height at the CdSe/ZnSe hetero-interface. Our findings signify that dark excitons do not profoundly affect the laser action of these quantum structures.