Optical properties of nanostructures self-organized in CdSe ZnSe fractional monolayer superlattices

We report on optical studies of excitonic transfer and localization in a Cd Se/ZnSe fractional monolayer superlattice with an embedded deeper ZnCdSe qu antum well (QW). Time-resolved selective excitation photoluminescence measu rements reveal a two-step nature of the energy relaxation process. The firs t stage includes hot-exciton cascade relaxation assisted by emission of ZnS e LO phonons, which results in the formation of a narrow nonthermal distrib ution of free excitons. Different mechanisms compete to destroy the distrib ution, including optical- and acoustic-phonon-assisted exciton localization by fluctuations of the random potential, as well as tunneling escape of ho t free excitons towards the embedded deeper QW in the sample. (C) 1999 Else vier Science B.V. All rights reserved.