Effect of Annealing on Surface Morphology and Bandgap Shift of Sol–Gel-Derived Mg-Doped ZnO Thin Films Grown on Mica Substrates

We studied the effect of annealing temperature on the surface morphology and bandgap energy of Mg-doped ZnO (MZO) thin films grown on muscovite mica substrates using sol–gel spin-coating. Both the un-annealed and the MZO thin film annealed at 300 °C exhibited cracked and flat surfaces consisting of very small particles, while a uniform and dense morphology consisting of spherical nanoscale grains was observed in the films annealed at temperatures above 400 °C. All the films exhibited strong ultraviolet emissions in the range of 3.2–3.4 eV and broad defect-related emissions in the visible region. An average transmittance of over 80% in the visible region was observed for all the films. The absorption edges in the transmittance and absorption coefficient spectra were found to be shifted toward lower wavelengths with an increase in the annealing temperature. The optical bandgap and Urbach energy of the films were calculated from the absorption coefficients.