Mott–Schottky behavior of strongly pinned double Schottky barriers and characterization of ceramic varistors

Abstract

This work studies the capacitive behavior of an intergranular double Schottky barrier, which describes nonlinear charge transport in polycrystalline semiconductors. It is found that: (i) a widely applied version of the Mott–Schottky equation can be inadequate, and can lead to significant errors; (ii) a property called strong barrier pinning (SBP), underlies most attempts to obtain physical parameters from C–V measurements; and (iii) under SBP, known results from one-sided Schottky barriers can be used to analyze C–V response, showing that correct physical parameters are obtained at low frequency and that high frequency measurements are not advantageous. A new characterization method is introduced, which allows high voltage devices to be directly measured, and yields comparative information about average donor density and barrier height. Besides its technological applicability, the method simplifies the study of scale effects. Experimental results support the theoretical considerations and the proposed characterization method. The usefulness of the method is illustrated by studying the effects of current–pulse degradation on the physical parameters of high voltage varistors.