HOPPING CONDUCTION IN NIF2 THIN-FILMS AS A FUNCTION OF THEIR CRYSTALLIZATION DEGREE AND COMPOSITION

The electrical charge transfer through Au-NiF//2-Au thin film structures is investigated as a function of the crystallization degree of the insulating layers. For a constant growth rate, the texture of the samples, prepared by sublimation under vacuum, depends essentially on the substrate temperature during the condensation of the vapours (T//s). Above T//s equals 300 K the NiF//2 thin films are constituted by crystallized grains embedded in an amorphous matter. The average diameter of the grains and the crystallization degree of the layers increase with T//s. Under these conditions, the electrical behaviour of the structures depends on the preparation parameter T//s. However, the charge transfer in NiF//2 thin films is due, over a large temperature range, to a hopping of electrons between localized states situated in their band gap. These states correspond to an atomic disorder and to a weak lack of fluorine.