  We study the carrier injection into a single InGaAs/GaAs quantum dot
regulated by a radio frequency surface acoustic wave. We find that the time of
laser excitation during the acoustic cycle programs both the emission
intensities and time of formation of neutral $(X^0)$ and negatively charged
$(X^-)$ excitons. We identify underlying, characteristic formation pathways of
both few-particle states in the time-domain experiments and show that both
exciton species can be formed either with the optical pump or at later times by
injection of single electrons and holes "surfing" the acoustic wave. All
experimental observations are in excellent agreement with calculated electron
and hole trajectories in the plane of the two-dimensional wetting layer which
is dynamically modulated by the acoustically induced piezoelectric potentials.
Taken together, our findings provide insight on both the onset of
acousto-electric transport of electrons and holes and their conversion into the
optical domain after regulated injection into a single quantum dot emitter.
