Observation of persistent negative photoconductivity effect in AlGaAs/GaAs modulation-doped structures

We report on the observation of a persistent ``negative'' photoconductivity effect exhibited in Alₓ{Ga}_{1{{-}}x}$As/GaAs heterostructures over the temperature range 170T300 K. We believe this to be the first observation of persistent ``negative'' photoconductivity, particularly at these relatively high temperatures. A possible source of the phenomenon is discussed, and suggested to originate from an interaction between the two-dimensional electron gas and EL2 centers.