Frequency-Dependent Impedance Responses of ZnO Using UV Light

Abstract

Impedance spectroscopy data show that polycrystalline ZnO films can show either increases or decreases in their effective resistances after UV exposure, depending on the frequency of the applied AC excitation. Simple equivalent circuit models, based on resistance (R) and capacitance (C) in parallel, are sufficient to confirm the observed experimental trends. Simulated data demonstrate that that arbitrary R and C values will not produce the sign change, but that typical resistance and capacitance characteristics for photoconductive semiconductors like ZnO can cause the sign change. These results suggest that it could be desirable to manipulate the R and C values of photodetector materials to either control – or eliminate – such frequency-dependent UV responses.