Negative and positive persistent photoconductivity effects in AlxGa1−xAsySb1−y/InAs quantum wells

Both negative and positive persistent photoconductivity (NPPC and PPPC) effects on the low-temperature transport properties were studied in the AlxGa1−xAsySb1−y/InAs quantum wells with a well width of Lw=15 and 50 nm. The irradiation of light with λ<1.0 μm causes the NPPC, while the light with λ=1.6 μm causes the PPPC. The Hall coefficient RH(B) in the dark or after illumination considerably increases with increasing B, indicating the coexistence of majority electrons and minority holes and allowing to analyze it by means of the two-carrier model. The PPPC effect leads to an increase in both density (n and p) and mobility of electrons and holes, while the NPPC inversely leads to their decrease, which was confirmed by the PPC effects on the SdH oscillations and the Hall resistance in the regime of quantum Hall effect in high magnetic fields. We have found the experimental relation, pμn3, so that the minority holes increases (decreases) much more rapidly than the majority electrons increases (decreases) in the PPPC (NPPC).