The Nature of Unintentional Deep Level Clusters Responsible for Persistent Photoconductivity Effect in GaAs/AlGaAs MQW Photodetectors

Abstract

GaAs/AlGaAs multiple quantum well (MQW) structures are among the most perspective materials for long wavelength infrared photodetectors arrays. It is shown2 that dark and photo currents in GaAs/AlGaAs MQW grown by MBE, having asymmetry in dependence on polarity of bias voltage, in whole correspond to model of the rectangular AlGaAs potential barrier. The excess dark current in GaAs/Al_xGa_1-xAs MQW with a composition x < 0.3 caused by presence of defects in the barriers is usually small and was observed only at temperature T < 77 K ⁶. In MQW with x > 0.3 the considerable excess current was observed at T > 77 K. The excess current is increased on 2–3 order after illumination of MQW by optical radiation with a wave length λ <1.3 μm. This current is conserved for a long time at lowered temperatures and is decreased to the initial value after heating of the sample more than 170 K ¹ This persistent photoconductivity effect was explained within the framework of the model of AlGaAs barrier with local sagging of the conduction band that facilitates electron tunneling. The values of the sagging and excess current increase at photo-ionization of a local unintentional deep levels (DL) located in the barriers and decrease at the subsequent capture on them of conduction band electrons ¹.