Structure, Optical and Photocatalytic Properties of ZnO Nanostructures Grown on Ag-Coated Si Substrates

The effect of annealing on the optical properties of zinc oxide nanostructures grown by atmospheric pressure metalorganic chemical vapor deposition on silicon substrates covered with a thin film of silver is investigated. It is shown that annealing at temperatures above 600°C significantly reduces the concentration of oxygen vacancies, and as a result, the ratio of the integrated intensity of ultraviolet emission to visible is improved 4.3 times. As a result of further high-temperature annealing at 900°C, the excitonic emission peak at 378 nm in the photoluminescence spectra is observed to shift towards larger wavelengths to 380 nm. Simultaneously, a decrease in its half-width from 140 to 100 nm is observed, which indicates an improvement in the structural perfection of ZnO/Ag/Si nanostructures. At the same time, an additional band in the region of 475 nm appeared, which, as we suggest, is due to optical transitions from the levels of shallow donors to the acceptor level created by the diffusion of silver in the lattice of zinc oxide. Annealing of ZnO nanostructures grown on silicon substrates as well as Ag-coated Si substrates improves their structure and optical properties, but unfortunately, this leads to a reduction in the photocatalytic activity of prepared ZnO nanostructures.