Effect of post-annealing treatment on the microstructure and optical properties of ZnO/PS nanocomposite films

• ZnO films were deposited on PS substrates by RF magnetron sputtering.
• Post-annealing has effect on the microstructure and optical properties of ZnO/PS films.
• The intensity of PL peak has obviously increased with the annealing temperature increasing.
• ZnO films formed a broad PL band including the violet, blue, green and red–orange emission.

In this study, porous silicon (PS) templates were formed by electrochemical anodization on p-type (1 0 0) silicon wafer and ZnO films were deposited on PS substrates using radio frequency reactive magnetron sputtering technique. The effects of annealing temperature on the microstructure and optical properties of the ZnO/PS nanocomposite films were systematically investigated by X-ray diffraction (XRD), UV–Visible spectroscopy and fluorescence spectrophotometry. XRD results indicated that all ZnO films were polycrystalline in nature with a hexagonal wurtzite structure and the (0 0 0 2) oriented ZnO films deposited on PS substrates had the best crystal quality under annealing at 700 °C. It was demonstrated that the optical band edge shifted to longer wavelength as the annealing temperature shifted from room temperature (RT) to 700 °C due to the quantum confinement effect. Furthermore, the optical band gaps calculated based on the quantum confinement model were in good agreement with the experimental values. Photoluminescence (PL) measurements at RT revealed that ZnO/PS films formed a broad PL band including the violet, blue and green emissions from ZnO and red–orange emission from the PS. The mechanism and interpretation of broadband PL of the films were discussed in detail.