Magneto-optics on single quantum dots

We report about magneto-optical experiments on single self-assembled InGaAs quantum dots. In the first part of our contribution we concentrate on phonon assisted absorption studied by photoluminescence excitation spectroscopy. We observe phonon assisted absorption via InGaAs and GaAs LO phonons, as well as sequential phonon assisted biexciton generation followed by sequential biexciton decay. The magnetic field dependence of the observed phonon resonances exhibits distinct differences between exciton and biexciton lines, which are caused by spin conservation and decay statistics. In the second part, we report about controlled single electron charging of a single quantum dot investigated by magneto-photoluminescence spectroscopy on electric field tunable structures. We observe the emission lines of neutral, single, and double charged exciton states for different bias conditions. The application of high magnetic fields results in fully resolved Zeeman splittings and diamagnetic shifts. The upper Zeeman component of the single charged exciton is found to be quenched at higher electric fields. This behavior is explained in terms of an enhanced tunneling probability of the triplet versus the singlet configuration.