Temperature-dependent micro-photoluminescence of individual CdSe self-assembled quantum dots

We use micro- and nano-photoluminescence to study the temperature-dependent excitonic emission from CdSe quantum dots embedded in a ZnSe matrix. By varying the spatial resolution from 200 nm to 1.7 mu m, we are able to study the temperature dependence of the ultranarrow (similar to 200 mu eV) emission from excitons confined to single quantum dots, as well as statistical ensembles of up to 200 dots. By measuring the quenching of the photoluminescence (PL) with temperature, we find compelling evidence that the PL emission from these samples results from two different kinds of states. Similar to previous work, we find that a broad PL line persists to 300 K with an activation energy of similar to 40 meV. However, we find that the ultranarrow lines are quenched at about 60 K, indicating an effective activation energy of only 4.0 meV. (C) 1999 American Institute of Physics. [S0003-6951(99)01228-0].