Conductivity inversion of ZnO nanoparticles in ZnO-carbon nanofiber hybrid thin film devices by surfactant-assisted C -doping and non-rectifying, non-linear electrical properties via interfacial trap-induced tunneling for stress-grading applications

Abstract

A special nonrectifying, nonlinear current-voltage characteristic is observed in ZnO nanoparticle-anchored carbon nanofiber (ZnO-CNF) hybrid thin film devices, which has interesting applications in nonlinear stress-grading materials for high-voltage devices and overvoltage protectors in multifunctional electronic circuits. A simple chemical precipitation method is used to fabricate the hybrid films, followed by vacuum annealing at elevated temperatures. Interestingly, the organic surfactant (Triton X-114), used as a binder during the film deposition, manifests unintentional carbon doping into a ZnO lattice, which leads to a conductivity inversion of ZnO from n-type in the lower temperature (300 °C) annealed hybrid into p-type in the higher temperature (600 °C) annealed film. Electrical characterizations reveal that the CNF-ZnO interfaces act as a metal-semiconductor junction with low barrier height, leading to nonrectifying junction properties. Also, the surfactant-induced C-atoms create trap states at the interface which "emit" the trapped charges via interfacial field-assisted tunneling, thus imposing nonlinearity (in both forward and reverse directions) on the I-V curves.