Electronic structure and optical properties of ultrathin CdS/ZnS quantum wells grown by molecular-beam epitaxy

We investigate in detail the optical properties of ultrathin, highly strain ed, cubic CdS/ZnS single and multiple quantum well structures using mainly photoluminescence, photoluminescence-excitation, and absorption spectroscop y. An effective model within the envelope function approximation is present ed, taking into account strain and excitonic effects. Using an improved par ameter set for cubic CdS this model successfully describes the observed exc iton transition energies. A fit to experimental data taking into account th e Stokes shift between luminescence and absorption yields some information about the model parameters, namely, the CdS/ZnS band alignment and the tetr agonal deformation potential of CdS in the zinc-blende modification. Finall y, we investigate the influence of localization effects due to well width f luctuations on the dimensionality of exciton confinement. A strong enhancem ent of the excitonic exchange interaction is found for deeply localized sta tes in extremely narrow quantum wells, suggesting a Significant lateral con finement and the formation of quasi-zero-dimensional states. [S0163-1829(99 )08715-9].