Non-ohmic behavior of metal-insulator granular thin films in low-field regime (eDV kBT)

Abstract

Non-ohmic behavior is not expected in metal–insulator granular systems in a low-field regime. There is no model to explain this behavior, even though it has been reported in several metalinsulator granular thin films (Fe-Al2O3, Co-Al2O3, and Ti-SiO2). In this paper, we show additional experimental results of Fe-SiO2 granular films and propose an explanation for the electrical properties of all above mentioned systems, based on Mott variable range hopping. The experimental results show that the localization length increases and the electrical resistance decreases with the increase of electrical potential or current. The non-ohmic behavior of the resistance and the increase of the localization length with increasing current are explained by the activation of new pathways for electrons in granular thin films that contain variable grain sizes and/or have different distances between grains.