Temperature-dependent photoluminescence of vertically stacked self-assembled CdSe quantum dots in ZnSe

We studied the optical properties of multiple layers of self-assembled CdSe quantum dots (QDs) embedded in ZnSe, grown by molecular beam epitaxy. The ZnSe barrier thicknesses separating the QD layers ranged from 30 to 60 monolayers (ML). For stacks with thinnest ZnSe barriers photoluminescence (PL) measurements reveal blue shifts as large as 180 meV relative to PL observed for single QD layers. The amount of blue shift decreases with increasing barrier thickness, and for the 60 ML spacer the PL energy returns to that emitted by a single layer of QDs. Temperature dependence of the integrated intensity of the emission spectra reveals that the activation energy for PL quenching is largest for barrier thicknesses of 30 and 45 ML. We tentatively attribute these effects to a decrease in the size of the vertically stacked QDs when the thickness of the barrier layers is small.