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.