PHOTO-HALL MODEL FOR SPACE-CHARGE EFFECTS IN N-ZNSE/GAAS-CR HETEROSTRUCTURES

We describe a model to explain an anomolous mobility behavior observed in our Hall experiments with unintentionaly doped n-ZnSe MBE layers on semi-insulating GaAsP:Cr substrates. In the dark, the room temperature electron mobility in many of our n-ZnSe layers had unexpectedly low values. We found a positive correlation between the values of the dark mobility and the net areal carrier concentration. upon illumination with the 458 nm Ar laser line, the anomalously low mobility values showed a pronounced increase towards normal values around 450 cm2/V · s. The mobility increases, roughly logarithmically with the light intensity over 5 decades, were accompanied by a similar increase in the real electron concentration. These results indicate that the cause of the anomalous mobility reduction is the presence of space charge regions associated with defects either in the ZnSe epilayers or at the interface. Our model determines the behaviour of the band bendinng in the n-ZnSe/GaAs:Cr heterostructure under illumination, in the presence of both interface and surface bandgap-states and also extended defects in the epilayer. The photo-induced change in the band-bending at the interface or near defects explains the logarithmic light intensity dependence of the observed photo-Hall effect. © 1989.