The effect of magnetron power and oxygen pressure on the properties of NiO films deposited by magnetron sputtering in layer-by-layer growth regime

Nickel oxide (NiO) is an attractive material for photovoltaic applications due to its p-type conductivity. This paper investigates the structure, morphology, and optical properties of NiO films deposited by magnetron sputtering. The magnetron power and oxygen pressure were varied in the range of 200-250 W and 0.3-0.7 Pa, respectively, while other growth parameters remained constant. The average transmittance of the deposited NiO films was found to be between 43 and 53% in the wavelength range of 400-800 nm, and the optical band gap varied from 3.28 to 3.33 eV. AFM measurements revealed that the grain size and surface roughness changed in the range of 16-43 nm and 1.3-4.0 nm, respectively. XRD pattern showed reflection from (111), (200), (220), (311), and (222) planes of cubic NiO. We also observed the presence of rhombohedral NiO2 phase in some XRD patterns. We can conclude that the formation of the NiO2 phase in NiO films is more favorable at magnetron power of 200 W. However, this unstable NiO2 phase transforms to NiO phase over time. NiO films deposited by layer-by-layer magnetron sputtering demonstrate appropriate structure and optical properties for their applications in heterostructure design with ZnO films.