Effect of heat treatment on the properties of non-stoichiometric p-type nickel oxide films deposited by reactive sputtering

Non-stoichiometric p-type NiO thin films were deposited by radio frequency reactive magnetron sputtering from a Ni target with equal Ar and O₂ flow rates. The non-stoichiometry of as-deposited NiO presented an O-rich NiO phase analyzed by Rutherford backscattering spectrometry. The properties of sputtered NiO films, such as crystallinity, transmittance, bonding configuration, and hole carrier concentration after annealing at various temperatures in nitrogen were examined using X-ray diffractometry, ultraviolet-visible spectroscopy, X-ray photoelectron spectrometry and Hall measurement, respectively. Furthermore, the weight change and phase transition of sputtered NiO heated in nitrogen ambient were measured by thermogravimetric analysis and differential scanning calorimetry. Our results reveal that the heat treatment on NiO films leads to the out-diffusion of excess oxygen atoms, which may be attributed to their interstitial nature in the sputtered NiO structure.