Non-linear I–V characteristics of double Schottky barriers and polycrystalline semiconductors

An attempt to determine theoretically the highly nonlinear current-voltage (V–V) characteristics of polycrystalline semiconductors, such as ZnO-based varistors, is made from the electrical properties of individual grain boundaries under DC bias. The role played by the fluctuations of double Schottky barrier heights at grain interfaces on driving electrical breakdown phenomena of macroscopic samples is pointed out in terms of a binary mixture model. An alternative trial form for the double Schottky barrier height is introduced to reproduce the breakdown voltage as well as the high nonlinear coefficient α, where I ∝ Vα.