PERSISTENT DECREASE OF DARK CONDUCTIVITY DUE TO ILLUMINATION IN ALGAAS GAAS MODULATION-DOPED HETEROSTRUCTURES/

We report on a persistent decrease of the dark conductivity in AlGaAs/ GaAs heterostructures due to illumination. The decrease was observed f or photon energies between 0.7 and 1.15 eV and larger than 1.4 eV in t he temperature range 170 < T < 300 K. Using proper bias conditions the dark conductivity after illumination can be 20% smaller than the dark conductivity in thermal equilibrium. The studies have been performed on samples with different doping species and compositions. A possible model for the observed behavior is discussed.