Nature of persistent photoconductivity in GaAs0.7Sb0.3∕GaAs multiple quantum wells

Abstract

The optoelectronic properties of undoped type-II GaAs0.7Sb0.3∕GaAs (100) multiple quantum wells have been investigated by photoluminescence (PL), and photoconductivity measurements. Quite interestingly, persistent photoconductivity (PPC) has been discovered in this material. The decay kinetics of the PPC effect can be well described by the stretched-exponential function IPPC(t)=IPPC(0)exp[−(t∕τ)β], (0<β<1), which is similar to the behavior observed in many disorder systems. Through the study of the PPC effect under various conditions, and combining with the characteristics of the PL spectra, we identify that the origin of the PPC effect arises from the spatial separation of photoexcited electrons and holes. Here, the photoexcited electrons fall into the GaAs layer, and holes are trapped by local potential minima due to alloy fluctuations in the GaAsSb layer. This process prevents the recombination of electrons and holes, and thus the PPC occurs. In order to return to the initial states, photoexcited electrons have to overcome the energy barrier caused by the conduction band offset.