Exciton localisation in CdSe islands buried in a quantum well of Zn1-xCdxSe

The optical properties of CdSe/ZnSe quantum structures with nominal thickness of the CdSe layer between 1 and 4 monolayers (ML) have been studied. The transition from two- to zero-dimensional quantum confinement can be monitored by photoluminescence (PL), photoluminescence-excitation (PLE), and time-resolved PL experiments. The influence of different degrees of localisation on the relaxation process of excitons is investigated. Experimental results for the excitonic transition energies are in good agreement with theory when strain-, confinement- and alloy-fluctuation-effects are included. The observation of multiple phonon modes indicates the formation of a Zn1−xCdxSe alloy with varying composition as well as the accumulation of CdSe in small islands.