Biexciton versus Exciton Lifetime in a Single Semiconductor Quantum Dot

The decay characteristics of excitons and biexcitons in one single semiconductor quantum dot (QD) are directly monitored using time- and spatially resolved photoluminescence spectroscopy. The experiments are performed on a CdSe/ZnSe QD, occupied by either one or two excitons at a time, allowing a direct comparison between the radiative lifetime of a biexciton and an exciton confined in the same QD. The rather surprising result of comparable recombination rates for both states is related to the spatial wave function distribution and the spin structure of the particles and their coupling to the photon field, i.e., the superradiance effect.