Study of persistent photoconductivity in semimetallic Al0.2Ga0.8Sb/InAs quantum wells

Abstract

The “positive” persistent photoconductivity (PPC) and “negative” persistent photoconductivity (NPPC) have been observed in Al0.2Ga0.8Sb/InAs quantum wells. The decay kinetics of the PPC and NPPC effects can be well described by stretched-exponential functions and the activation energy of the thermally activated relaxation was obtained. Through the studies of the NPPC and PPC effects under various conditions, such as different temperature and different photon energy of excitation, we suggest that the NPPC and PPC effects are caused by two competing processes. At T≤40K, the electrons in the InAs wells are excited into the valence band of the AlGaSb layer, the recovery to the original state is prohibited by the barrier due to interface band bending and hence NPPC effects occur. At T≥140K, the photoexcited holes are trapped by the deep defects in the InAs well and the remaining electrons contribute to the observed PPC. For 40K<T<140K, these two mechanisms compete with each other. The previously proposed model that describes the NPPC resulting from the capture of the photoexcited electrons by the DX-like deep donors in AlGaSb fails to explain our observation here.