Thermofield Effects in Graphite-like Amorphous Carbon Films with Nanoscale Structure

The paper presents the results of a study on the structure and electrical properties of graphite-like amorphous carbon films deposited by electron-beam evaporation with vacuum heat treatment. The current-voltage characteristics of the films were analyzed in weak and strong electric fields in the temperature range from 25 to 155 °C. For the contact of carbon films with nickel, the Schottky barrier height was calculated based on the obtained current-voltage characteristics. It was found that in the temperature range of 25-45 °C, the mechanism of direct tunneling of charge carriers through the narrow Schottky barrier dominates (φ_b = 0.055 eV). In the range of 55-75 °C, a transition to the thermally assisted tunneling mechanism is observed (φ_b = 0.076 eV). At temperatures above 85 °C, charge carrier transport through the Schottky barrier occurs via thermionic emission (φ_b = 0.3 eV). The analysis of the current-voltage characteristics of graphite-like carbon films allowed us to establish the main mechanisms of hopping conductivity via localized states. It is shown that in the temperature range of 298-348 K, conductivity is determined by states near the Fermi level. The temperature interval of 348-428 K corresponds to conductivity through the band tail of localized states near the conduction band. It is shown that the increase in conductivity in strong electric fields is due to the Poole-Frenkel effect.