High-field electrical conduction in thin-film sandwich structures of the metal/organic semiconductor/metal type

Abstract

The investigated organic compounds are derivatives of the asparagic acid. Thin films of respective compounds were deposited from dimethylformamide solutions. The temperature dependences of the electrical conductivity and Seebeck coefficient are investigated. All compounds have semiconducting properties. The values of some characteristic parameters (activation energy, ratio of carrier mobilities, etc.) have been determined. Using sandwich cells of the type Al/organic compound/Al, the static current–voltage ( J– U) characteristics have been studied. For lower values of intensity of electric field E ( E ≅6×10 2–2×10 3 V cm −1), J– U characteristics are ohmic. At higher values of E , the current density J increases faster than linear. For E ≅10 3–10 4 V cm −1, the obtained experimental data are in good agreement with the Richardson–Schottky law. At fields E >10 5 V cm −1, the experimental points deviate more and more from Schottky characteristics in direction of larger values of J. For explanation of these behaviours, the electron transitions through and over the potential barrier at metal-organic film interface are taken into account.