Photocurrent and photovoltage oscillations in the two-dimensional electron system: Enhancement and suppression of built-in electric fields

We observe microwave-induced photocurrent and photovoltage oscillations around zero as a function of the applied magnetic field in high mobility GaAs 2D electron systems. The photosignals pass zero whenever the microwave frequency is close to a multiple of the cyclotron resonance frequency. They originate from built-in electric fields due to for instance band bending at contacts. The oscillations correspond to a suppression (screening) or an enhancement ("antiscreening") of these fields by the photoexcited electrons.