Effect of film thickness on the optical constants and optical absorption properties of NiOx thin films

NiOx (x>1) thin films were deposited by reactive DC-magnetron sputtering from a nickel metal target in Ar+O2 with the relative O2 content 5%. The reflectivity and transmission of the films were measured from 350 to 700 nm. The films coated to thicknesses of 17, 27 and 34 nm had the same absorption mechanism which is a direct allowed transition. The refractive index n and extinction coefficient k of the films were calculated from the measured reflectivity and transmission of these films, and the relationship of the optical band gap with variation in film thickness was studied as well. All results showed that the optical properties of NiOx thin films depended on the film thickness.