Investigation of the Changes in Electronic Properties of Nickel Oxide (NiO_<i>x</i>) Due to UV/Ozone Treatment

Drastic reduction in nickel oxide (NiO_x) film resistivity and ionization potential is observed when subjected to ultraviolet (UV)/ozone (O₃) treatment. X-ray photoemission spectroscopy suggests that UV/O₃ treatment changes the film stoichiometry by introducing Ni vacancy defects. Oxygen-rich NiO_x having Ni vacancy defects behaves as a p-type semiconductor. Therefore, in this work, a simple and effective technique to introduce doping in NiO_x is shown. Angle-resolved XPS reveals that the effect of UV/O₃ treatment does not only alter the film surface property but also introduces oxygen-rich stoichiometry throughout the depth of the film. Finally, simple metal/interlayer/semiconductor (MIS) contacts are fabricated on p-type Si using NiO_x as the interlayer and different metals. Significant barrier height reduction is observed with respect to the control sample following UV/O₃ treatment, which is in agreement with the observed reduction in film resistivity. From an energy band diagram point of view, the introduction of the UV/O₃ treatment changes the defect state distribution, resulting in a change in the pinning of the Fermi level. Therefore, this work also shows that the Fermi level pinning property of NiO_x can be controlled using UV/O₃ treatment.