Optical and Electrical Properties of ZnO/NiO Heterojunctions Obtained by the Spray-Pyrolysis Method

In this work, the effect of thermal annealing on the phase composition, surface morphology, and structural, substructural, optical, and electrical properties of multilayer structures based on p-NiO/n-ZnO heterojunctions obtained by spraying molecular solutions (spray-pyrolysis) is determined. After deposition, the samples were annealed in vacuum at temperatures of 300, 400, 500 °C during 60 min. The multilayer structure was studied using X-ray diffraction analysis, scanning electron microscopy, Hall effect, and optical spectroscopy. The dark current–voltage characteristics of the heterojunctions were also measured. These studies made it possible to determine the main structural, morphological, electrical, and optical properties of the films, such as crystal lattice parameters, dimensions of the coherent scattering regions, microdeformation level, density of dislocations, and band gap width depending on the annealing temperature. The energy band diagram of heterojunctions was constructed from the Anderson and Van Ruyven models.