Transport and magnetic phenomena in ZnO-C thin-film heterostructures

ZnO- and C-based heterostructures were fabricated by the layer-by-layer deposition technique using the ion-beam sputtering process. Structure, electrical and magnetic properties of fabricated heterostructures are discussed. The two-phase (ZnO and C) films are evolved into a multilayer structure, consisting of amorphous carbon and crystalline ZnO layers when the bilayer thickness increases. When carbon is added to ZnO, its electrical resistivity reduces. The conduction mechanism changes from the variable-range hopping in a narrow energy band to the nearest neighbors hopping in ZnO-C films with a thickness of h < 150 nm. The temperature dependence of conductivity changes from the Arrhenius-like to logarithmic law, indicating that the strong charge localization turns into a weak one when the film thickness is about 150 nm. The negative magnetoresistance of up to 1%was detected at 77 K. The film ferromagnetism at the temperature of 10 K was not found.