Effect of palladium content on microstructures, electrical and optical properties of NiO films by rf sputtering

• NiO films with p-type conduction were achieved by adding Pd into the films.
• Both electrical resistivity and transmittance of the films decrease when the Pd content increases.
• Crystallinity of the films degrades when the Pd content was over 6.7 at.%.

The Pd-doped nickel oxide (NiO) films with various Pd contents of 0 – 18.3 at.% are deposited on glass substrate. An ultra high electrical resistivity (ρ) is obtained that cannot be detected by four point probe measurement when the Pd content in the film is lower than 2.7 at.%. The ρ value decreases significantly to 34.1 Ω cm as Pd content is increased to 4.6 at.%, and it drops down to 0.001 Ω cm when the Pd content increases to 18.3 at.%. The Hall measurements for all Pd-doped NiO films show p-type conduction. In addition, the transmittance of NiO films declines continuously from 96% to 10% as Pd content rises from 0 to 18.3 at.%. The X-ray diffraction patterns of Pd-doped NiO films show that only NiO peaks appear. Most of the Pd2 + ions substitute for Ni2 + ions in the NiO lattice, which leads to a degradation in the crystallinity of NiO films with higher Pd content.