Structural, morphological and electrical properties of nickel oxide thin films deposited by reactive sputtering

Abstract

This paper is devoted to the study of the influence of oxygen content in the nickel oxide films on the film structural, morphological and electrical properties. Nickel oxide films have been synthesized by reactive DC magnetron sputtering discharge by varying the oxygen flow rate (1.9<Q(O2)<3.6sccm) for various deposition time. XRD analyses revealed the polycrystalline nature of the as-deposited films and also a phase transition from nickel oxide (111) to nickel oxide (200) associated with nickel non-stoichiometry in the NiO structure. The polycrystalline films presented an average crystallite size of 15–30nm and a surface roughness of 1–10nm. In-plane stress measurements have established the correlation between crystallite size and intrinsic compressive stress and also the ion-penning effect of negative oxygen ions during the film growth. A maximum stress of 10GPa was found for lower film thickness (10nm). By adjusting the oxygen concentration, conductive AFM (C-AFM) and resistivity measurements by the four point method have revealed at room temperature an electrical transition from insulating to conductive state. C-AFM and four point measurements showed respectively an increase in the collected current and an abrupt decrease of the mean resistivity from 107 to 10Ωcm when the stoichiometry varies from NiO0.96 to NiO1.14. This transition is related to the non-stoichiometry attributed to nickel vacancies. Finally, low-temperature (290–100K) electrical conduction measurements confirmed the weak dependence of Ni-deficient nickel oxide films with film thickness and showed that charge carrier conduction is a thermal-activated process.