SINGLE ZERO-DIMENSIONAL EXCITONS IN CDSE ZNSE NANOSTRUCTURES/

Zero-dimensional excitons (0DXs) in CdSe/ZnSe nanostructures have been studied by time- and spatially resolved photoluminescence spectroscop y. The three-dimensional confinement is confirmed by an exciton lifeti me up to 550 ps, independent of temperature up to 130 K. By preparing mesa structures with diameters down to 50 nm as local probes, an extre mely high spatial resolution is achieved, giving experimental access t o single 0DXs. A splitting of the ground state into a linearly polariz ed doublet with an energy spacing up to 1.5 meV is found, varying from dot to dot in sign and magnitude. This indicates a noncircular shape with no preferential orientation of the dots. The dot density is estim ated to increase from 5 x 10(10) to 1.5 x 10(11) cm(-2), when changing the nominal CdSe layer thickness from 1 to 3 ML, i.e., close to the c ritical thickness. (C) 1998 American Institute of Physics. [S0003-6951 (98)00647-0].