Observation of negative persistent photoconductivity in an n-channel GaAs/AlxGa1−xAs single heterojunction

We report the first observation of negative persistent photoconductivity at 4.2 K in an n-channel modulation doped GaAs/Al0.33Ga0.67As 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 Al0.33Ga0.67As. A model that quantitatively explains the nonexponential recovery time is presented.