Impact of <i>in situ</i> heating on the structure, morphology, and electrical and optical properties of RF-sputtered NiO thin films

In this work, NiO thin films were deposited on glass and n-type Si at different substrate temperatures utilizing reactive RF-sputtering technique. The influence of substrate heating on the crystal structure, surface morphology, and optical and electrical properties of NiO thin films was studied using x-ray diffraction, scanning electron microscopy, UV-vis transmission spectroscopy, and Hall effect measurements. The x-ray diffraction data revealed a significant improvement in crystallinity, with the NiO films preferentially growing along the (111) direction as the substrate temperature increased. The scanning electron microscope images indicated the more explicit grain boundaries above 250 °C. The average light transmittance of the NiO thin film exhibited a significant improvement from 31% to 72% in the visible range. In addition, the optical bandgap was found to increase from 3.19 to 3.51 eV as the substrate temperature increased. The NiO films presented high carrier concentrations ranging from 1.044 × 1019 to 2.847 × 1019 cm−3 and a low surface resistivity of 0.260 Ω.cm. The optimal characteristic parameters of the p-NiO/n-Si diodes (VOC = 0.702 V, n = 4.998, and ΦB = 0.761 eV) were recognized at a substrate temperature of 250 °C. The results demonstrate that sputtered NiO thin films are highly applicable for ultraviolet optoelectronic devices.