Structure and Electrical Properties of (ZnO/SiO2)25 Thin Films

Abstract

(ZnO/SiO₂)₂₅ thin-film multilayers consisting of nanocrystalline ZnO layers and amorphous SiO₂ spacers with a bilayer thickness from 6 to 10 nm are synthesized in a single deposition process. An analysis of the temperature dependences of the electrical resistivity of (ZnO/SiO₂)₂₅ thin films shows that, in the temperature range of 77–300 K, the dominant conductivity mechanism successively changes from hopping conductivity with a variable hopping length in a narrow energy band near the Fermi level at temperatures of 77–250 K to thermally activated impurity conductivity around room temperature. Using the obtained temperature dependences of the electrical resistivity, the effective density of localized states at the Fermi level and the activation energy of impurity levels are estimated. The effect of heat treatment on the structure and electrical properties of the synthesized films is examined. It is established that in (ZnO/SiO₂)₂₅ thin-film systems at temperatures of 580–600°C, the ZnO and SiO₂ layers chemically interact, which is accompanied by destruction of the multilayer structure and formation of the Zn₂SiO₄ compound with a tetragonal structure (sp. gr. I-42d).