Transport and persistent photoconductivity in atomic-planar-doped GaAs-AlAs/GaAs heterostructures

We have observed a striking photoeffect in an atomic-planar-doped GaAs-AlAs/GaAs heterostructure in Shubnikov–de Haas measurements at 4.2 K. After successively illuminating the sample with a GaAs0.6P0.4 red light-emitting diode (LED), both the 2D electron density and mobility decrease initially before they start to increase upon futher illumination. This negative persistent photoconductivity is not observable when the sample is illuminated with GaAs and In0.53Ga0.47As LEDs. On the other hand, when the light dosage is large enough the usual positive persistent photoconductivity is observed with all three LEDs used. The existence of both donorlike traps and acceptorlike traps in our sample is proposed to explain these observations.