Anomalous photomagnetoresistance effect in modulation-doped AlGaAs/GaAs heterostructures

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Abstract
A novel negative photoresistance effect at Al0.3Ga0.7As/GaAs interface in the presence of a magnetic field B is discovered and explained. At low temperatures (T=4.2 K) illumination of the sample leads to a persistent electron accumulation in the GaAs channel (the well-known persistent photoconductivity effect). In the presence of B≳0.3 T the dependence of the longitudinal resistance (as measured by the four-probe method) shows an anomalous behavior in that the resistance increases sharply with the increasing concentration n of carriers provided by light. In the same range of concentrations the longitudinal resistance at fixed n is proportional to B2. It is shown that the observed behavior of the resistance is associated with photoexcitation of electrons from donor vacancy (DX) centers in the highly doped AlGaAs region resulting in the creation of a second conducting layer of high charge density and low mobility.