Quantum Dot Exciton Dynamics through a Nanoaperture: Evidence for Two Confined States

Excitons confined to CdSe/ZnSe self-assembled quantum dots are probed through a nanoaperture using time-resolved photoluminescence. Significant evidence is shown that two different electronic states are associated with these dots, with binding energies which differ by an order of magnitude. The first has a short 450 ps lifetime, exhibits a relatively broad emission line, and persists nearly to room temperature; the second exhibits a long (>4ns) lifetime and is responsible for the sharp (~100μeV) lines seen at low temperatures (<60K). These results are completely unlike those seen in III-V dots, and reveal the complexity of the electronic structure in CdSe dots.