Electronic, electrical and optical properties of undoped and Na-doped NiO thin films

The electrical and optical properties as well as the electronic structure of sodium-doped (Na-doped) nickel oxide (NiO) thin films were investigated using X-ray photoelectron spectroscopy (XPS), reflection electron energy loss spectroscopy (REELS), X-ray absorption near edge structure, and extended X-ray absorption fine structure. The XPS results confirmed the presence of NiO bonds of the NiO phase for all films via the Ni 2p spectra. The NiO thin films annealed above 200 °C have both nickel oxide and nickel metal phase. The REELS spectra showed that the band gaps of NiO thin films after Na doping were decreased. Na-doped NiO thin films exhibited relatively low resistivity compared to undoped NiO thin films. In addition, the Na-doped NiO thin films deposited at room temperature have p-type conductivity with a low electrical resistivity of 11.57 Ω cm and high optical transmittance of 80% in the visible light region. Our results demonstrate that Na doping plays a crucial role in enhancing the electrical and optical properties of NiO thin films.