Ellipsometric and XPS characterization of transparent nickel oxide thin films deposited by reactive HiPIMS

We have deposited transparent p-type semiconductive NiO thin films by reactive HiPIMS which appeared to be a powerful method to produce thin films exhibiting gradients of chemical compositions and opto-electronic properties. For a fixed amount of oxygen in the discharge (9%), the influence of the pulse duration was investigated. The position of the valence band with respect to the Fermi level was evaluated by X-ray Photoelectron Spectroscopy (XPS), for two different pulse durations, 15 and 30 μs. We have then investigated the dependence of optical properties of NiO films using spectroscopic ellipsometry (1.5–5.0 eV range). Refractive index n, extinction coefficient k, and gap energy of the NiO films were determined with a refractive index gradient decreasing along the film growth direction.