Near-field optical spectroscopy of localized excitons in strained CdSe quantum dots

Control of the growth dynamics during the epitaxy of coherently strained ZnSe/CdSe quantum structures results in a varied interfacial texture that broadly defines two qualitatively different regimes for exciton localization. An island growth mode produces quantum dot regions in which the lateral confinement of excitons is directly revealed through the observation of resolution-limited (full width at half maximum of 0.8 meV) emission peaks in near-field photoluminescence spectra. By contrast, layer-by-layer growth produces potential fluctuations at length scales small compared to the exciton diameter, so that the localization of excitons is driven by a random interfacial potential with a smooth density of states.