  Lateral quantum dot molecules consist of at least two closely-spaced InGaAs
quantum dots arranged such that the axis connecting the quantum dots is
perpendicular to the growth direction. These quantum dot complexes are called
molecules because the small spacing between the quantum dots is expected to
lead to the formation of molecular-like delocalized states. We present optical
spectroscopy of ensembles and individual lateral quantum dot molecules as a
function of electric fields applied along the growth direction. The results
allow us to characterize the energy level structure of lateral quantum dot
molecules and the spectral signatures of both charging and many-body
interactions. We present experimental evidence for the existence of
molecular-like delocalized states for electrons in the first excited energy
shell.
