Microstructural and piezoelectric properties of ZnO films

Using the chemical spray pyrolysis method, nanostructured ZnO films have been synthesized on p-type silicon substrates. The fabricated films are grown at different deposition temperatures (300–500 °C) and are characterized using a combination of microstructural, electrical, and nanoscopic piezoelectric techniques. The X-ray diffraction results, in agreement with piezoresponse force microscopy, confirm that the deposits have a hexagonal wurtzite structure with a change in preferred orientation from (0 0 2) to (1 0 1) with an increase in the deposition temperature above 350 °C. ZnO nanostructures with the optimal crystallinity, electrical mobility, and carrier concentration are obtained at 450 °C. XPS spectra are used to determine the chemical state and elemental composition of the films. The decrease in bandgap with the increase in temperature is well correlated with calculated crystallite size. The samples deposited at lower temperatures show the strongest blue emission due to its defective nature. A comparative nanoscale piezoelectric investigation reveals enhanced piezoelectric response at 350 °C compared to samples fabricated at other deposition temperatures. Our study thus sheds light on the important role of the deposition temperatures in control and tuning the microstructural and piezoelectric properties of the spray pyrolyzed ZnO films.