A source of free holes in NiO thin films with different nickel content that are prepared using the sol-gel method

The effect of nickel content on the electrical properties of the sol-gel grown NiO films is determined. NiO is a metal-deficient and oxygen-rich metal oxide. An increase in the concentration of nickel acetate during the growth process leads to an increase in the thickness of NiO films, so the crystallite size and the hole concentration increase. There is a change in the hole concentration in NiO films because there is competition between the density of nickel vacancies (VNi), oxygen interstitials and Ni3+. Transformation from Ni2+ to Ni3+ is an offset to the induced lattice relaxation due to transformation from VNi to VNi2−, so VNi and Ni3+ coexist in NiO. The results of this study show the defect-related p-type conductivity of NiO films.