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 ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs heterostructures over the temperature range 170<T<300 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.