Influence of Thermal Annealing on the Physical Properties of Nanostructured NiO Thin Films Fabricated via Chemical Spray Pyrolysis

Nanostructured 900-nm-thick NiO thin films were fabricated via manual chemical spray pyrolysis at 50 °C and post-annealed at 150 °C and 300 °C. X-ray diffraction showed a phase transition from amorphous to face-centered cubic crystalline structures with a preferred (200) orientation and 14.3 nm crystallite size at 300 °C. AFM tracked surface relaxation and grain growth, shifting RMS roughness from 7.46 nm to 2.15 nm, then to 3.21 nm. Optically, direct bandgaps narrowed from 3.95 eV to 3.88 and 3.78 eV due to Urbach tail annihilation. Thus, a 300 °C thermal budget optimizes functional p-type layers for optoelectronics.