Comparison of microstructural and optoelectronic properties of NiO:Cu thin films deposited by ion-beam assisted rf sputtering in different gas atmospheres

NiO thin films have been widely studied recently due to their intrinsic p-type conductivity and potential applications in various domains as transparent conductive oxides. However, the intrinsic p-type resistivity (ρ) of NiO is as high as 1013 Ω·cm, which needs to be optimized. In the current work, we devised an experiment to improve the electrical properties of NiO films through three methods: 1) encouraging monovalent Cu+ ions to substitute for Ni2+ ions in NiO:Cu films deposited from NiO-Cu composite targets; 2) introducing nickel vacancies and interstitial oxygen in the films deposited by oxygen ion assisted rf sputtering in Ar + O2 mixture; 3) adding group-V element N to replace O by employing Ar + N2 mixture as the sputtering gas. The results show that the first two methods can effectively enhance the film's p-type conductivity, while the carrier concentration in the films improves greatly. However, the last method reveals that when N atoms are introduced into NiO:Cu films they will reduce the film's p-type electrical properties. This indicates that N doping hinders the hole generation under our experimental conditions.