Elaboration and Characterization of Mg-Doped ZnO Thin Films by Thermal Evaporation: Annealing Temperature Effect

The annealing temperature effect on the structural, optical, electrical, and mechanical properties of different samples based on ZnO-Mg (MZO) thin films has been investigated. The studied samples were annealed at 300, 400, and 500 °C at atmospheric pressure, and the reference ones were kept without annealing. X-ray diffraction (XRD) analysis confirmed the growth of ZnO hexagonal wurtzite structure at 300 °C, while an increase in the structure crystallinity was observed at 500 °C. Electron-dispersive spectroscopy (EDS) analysis shows the existence of Zn, O, and Mg elements. The Raman spectroscopy reveals the appearance of A1(LO) and LVM modes for all samples. Transmittance spectra in the visible range show an increase in layer transmittance as function of annealing temperature. Similarly, the optical band gap rises from 3.40 to 3.61 eV. The electrical resistance measurements indicate that the as-deposited MZO are conductive films. However, the obtained resistance values for post-annealed MZO confirm the semiconductor behavior of the layer. Results from the mechanical characterization of MZO films, and particularly the proportional relation between hardness and grain size according to the annealing temperature, revealed a behavior disagreement with the Hall-Petch formula.