Microstructures and optoelectronic properties of nickel oxide films deposited by reactive magnetron sputtering at various working pressures of pure oxygen environment

Thanks to the intrinsic p-type conductivity, NiO films show great potential for applications in various domains. In this work, NiOx films were deposited in three dimensional physical vapor deposition (3D-PVD) system from metallic nickel target in pure oxygen conditions. Optical emission spectroscopy (OES) was employed to analyze the plasma state during the deposition. The variation of the film's structural and optoelectronic properties as a function of the oxygen pressure was investigated. It is found that the oxygen content in NiOx films is more evident for the films deposited with lower oxygen pressure. More Ni3+ ions and interstitial oxygen associated with more Ni2+ vacancies and holes are believed to exist in these films. Therefore, their conductivity is higher than the films deposited at higher oxygen pressure. Additionally, with an increase of oxygen pressure, the film's crystallinity is enhanced, and the film's transmittance as well as the film's band gap improves.