Phonon-assisted biexciton generation in a single quantum dot

We investigate absorption of a single InGaAs/GaAs quantum dot by multi-channel photoluminescence excitation spectroscopy as a function of magnetic field. We find strong resonances corresponding to GaAs LO phonon-assisted absorption and unexpected phonon-assisted generation of biexciton states. Magnetic field induced detuning of the resonance conditions results in a twofold diagonal splitting of the exciton line. This indicates spin conservation in the phonon-assisted absorption process and the successive recombination process. In contrast to the exciton line a symmetric fourfold splitting is observed for the biexciton resonances. Those findings are explained in terms of sequential biexciton generation followed by sequential biexciton decay.