Abstract
We report luminescence experiments on excitons in a GaAs-AlGaAs heterostructure with an applied electric field perpendicular to the surface. In the absence of any surface electric field we observe a single emission line centered at the excitonic eigenenergy. With increasing electric field the line shape changes subsequently to a camel-back structure. We explain the field-induced change of the excitonic-emission line shape by absorption in the depletion layer due to field-ionized excitons.