Sol–gel derived amorphous/nanocrystalline MgZnO thin films annealed by atmospheric pressure plasma jets

This paper reports the characterization of sol–gel derived MgZnO thin films annealed by atmospheric pressure plasma jets (APPJs). MgxZn1−xO films exhibit high transparency (> 80%) in the visible light wavelength region. When 20 at% Mg is incorporated into the film, the optical bandgap reveals a blue shift from ~3.25 to ~3.5 eV and the resistivity increases by three to four orders of magnitude, owing to the substitution of Mg atoms into the Zn lattice sites. The absorption band edge becomes sharper and the bandgap becomes slightly narrower as the APPJ treatment time increases. This can be attributed to slight grain growth in the films. When the material is amorphous/nanocrystalline, the quantum confinement effect causes a slight decrease in the bandgap as the grain size increases, resulting in slope alteration at the absorption edge. Compressive stresses caused by the difference in the thermal expansion coefficients between the film and the substrate are generated during the drying process. This leads to surface wrinkling on the sol–gel derived Mg0.2Zn0.8O thin films.