Temperature dependence of the Schottky barrier capacitance in α- and β-zinc phthalocyanine

Abstract

Capacitance measurements of Schottky barrier devices have proved useful in the past for probing properties of dopant distribution and charge carrier detrapping. In this paper the temperature variation of the Schottky barrier capacitance of cells constructed with either α-zinc phthalocyanine or β-zinc phthalocyanine is compared. The α phase is found to differ markedly from the β phase. The α phase shows a Schottky barrier capacitance down to 150 K, however the slope of the 1/C2 vs V plots is temperature dependent. This temperature dependence is explained in terms of a two-site model for the dopant, oxygen. In this model only one site is active in charge carrier generation. The β phase, on the other hand, shows a hindered response of the charge carriers to the oscillating applied voltage. The dopant density in the β phase film is found to be comparable to dopant densities in α phase film.