Electronic characterization of single grain boundary in ZnO:Pr varistors

Isothermal capacitance transient spectroscopy (ICTS) has been applied to study single grain boundaries of ZnO:Pr varistors using micro-electrodes prepared on the surface of the ZnO ceramic. A similar ICTS peak was observed as in the case of bulk measurement. This peak has directly proved the existence of the electronic interface states and formation of double Schottky barrier (DSB) at the grain boundary. The quantitative analysis of ICTS peak height revealed that the higher density of the interface states gave the higher nonlinearity of a I–V relation. Photo-ICTS spectra were also examined for the single grain boundary. The peaks shifted to shorter time compared with the dark-ICTS spectrum when the irradiated light brought about an increase of the junction capacitance. This result gave detailed information about deep electronic interface states of DSB.