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Published online by Cambridge University Press: 10 February 2011
Isothermal capacitance transient spectroscopy(ICTS) measurement is applied to ZnO:Pr varistors. A simple peak corresponding to the interface states at grain boundaries was obtained and the energy level of the interface states revealed to be monoenergetic and located around 0.9eV below the conduction band. The cross section was calculated as around 10−14 cm2. Quantitative treatment of the ICTS intensity in relation to the density of interface states at grain boundaries was established. The density of interface states was obtained from the linear relation between ICTS intensity and reciprocal carrier density(ND). According to experiments on series of rare-earth doped ZnO varistors, the interface states of Pr, Tb or Nd doped ZnO varistors had higher density of states than La or Er doped varistors. Moreover, application of ICTS measurement to single grain boundary using microelectrodes revealed that higher density of interface states gave higher nonlinearity in I-V characteristics.