Energy shift and line broadening of three-dimensional excitons in electric fields.

We measure electric field induced energy shifts and line broadening of 3D excitons in thin GaAs layers in reflectance and photoluminescence. We observe a small red shift due to the excitonic Stark effect for small electric fields. Subsequently, we find reversal to a blue shift for higher electric fields, due to mixing with continuum states. The exciton line broadens monotonically with increasing field because of field ionization.