  Time-resolved resonance fluorescence (RF) on a single self-assembled quantum
dot (QD) is used to analyze the generation and capture of photoinduced free
charge carriers. We directly observe the capture of electrons into the QD in an
intensity reduction of the exciton transition. The exciton transition is
quenched until the captured electron tunnels out of the dot again in the order
of milliseconds. Our results demonstrate that even under resonant excitation,
excited, free electrons are generated, which can negatively influence the
optical properties of a QD. This detrimental effect has been neglected before
for dots that are optimized for maximum efficiency and minimum spectral
diffusion.
