Observation of negative persistent photoconductivity in an n-channel GaAs/Al_xGa_1-xAs single heterojunction

We report the first observation of negative persistent photoconductivity at 4.2 K in an n-channel modulation doped GaAs/Al_0.33Ga _0.67As single heterostructure, where two-dimensional electrons have a mobility of ∼550 000 cm²/V s when density is ∼3.0×10¹¹ cm^-2. Based on extensive magnetotransport measurements, we conclude that the negative persistent photoconductivity effect comes from the time dependence of (1) the annihilation of two-dimensional electrons by photoexcited holes, and (2) the trapping and de-trapping of photoexcited electrons by shallow donors in doped Al _0.33Ga_0.67As. A model that quantitatively explains the nonexponential recovery time is presented.