Structural, electrical and optical properties of K-doped NiO films prepared by rapid pyrolysis sol-gel technique

K-doped NiO films (Ni1 − xKxO) were deposited on glass substrates using a rapid pyrolysis sol-gel technique. The structural, morphological, electrical and optical properties of the films were investigated using X-ray diffraction, scanning electron microscopy and atomic force microscope, Hall effect measurement system, and ultraviolet-visible spectrophotometer, respectively. All the deposited films were cubic structure, and the residual stress in the films changed with increasing K doping concentration from residual compressive stress to residual tensile stress. The morphologies and compactability of the films were seriously affected by the K doping concentration, and the cause of the formation of the morphologies was discussed detailedly. The lowest root-mean-square roughness of the films was obtained at x = 0.06 and was about 2.6 nm. The carrier concentration of the films was very similar, but the carrier mobility of the films was seriously affected by the compactability of the films. The lowest resistivity of about 23.7 Ω ⋅ cm was obtained at x = 0.06. The transmittance decreased on the whole with increasing K doping concentration, but the optical energy bandgaps of the films were almost constant.