Electronic interface states at grain boundaries in ZnO : Pr varistors by single grain boundary measurements

Electronic interface states at grain boundaries in ZnO:Pr varistors were di rectly observed by single grain boundary measurement. Photo-capacitance spe ctroscopy and photo-isothermal capacitance transient spectroscopy(photo-ICT S) were applied to these experiments. Photo-capacitance spectrum in the nea r infrared region showed a peak at 1380 nm, i.e. 0.9 eV. Since this peak is originated by electron excitation from the interface states at the grain b oundary, the energy for this peak indicates that the electronic states at t he grain boundaries are located at 0.9 eV below the top of the double Schot tky barrier. This result is the direct evidence which shows the value of th e energy level of the interface states in ZnO varistors. Moreover the ICTS peak shifted to shorter range by the irradiation of 1380 nm light. The phot o-intensity change of ICTS peaks revealed the linear relation between emiss ion rate of the interface states and the light intensity. (C) 2001 Elsevier Science Ltd. All rights reserved.