Dark exciton decay dynamics of a semiconductor quantum dot

We report measurements of the exciton decay dynamics of a single self-assembled quantum dot following non-resonant excitation. The singly charged exciton, the trion, exhibits a simple one component exponential decay corresponding to radiative recombination. Conversely, the neutral exciton exhibits a two component exponential decay. We argue that the secondary component arises from dark exciton creation and subsequent conversion to a bright exciton through a spin flip. The spin flip time is a strong function of the bias applied between a Fermi reservoir close to the dot and a Schottky gate electrode as a result of a Kondo-like spin swap process.