Structural and Optical Properties of ZnO:Al Thin Films Produced by Magnetron Sputtering with Different Oxygen Flow: An Experimental and Ab Initio Study

Abstract

This work addresses, in an experimental and theoretical way, the influence of different oxygen pressure values on the physical and electronic properties of thin conductive and transparent oxide films of Al‐doped ZnO, with different thicknesses. A series of characterization techniques, which include X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), optical spectrophotometry, and Hall measurements are conducted. All films have a hexagonal wurtzite structure characteristic of ZnO, with preferential orientation along the plane (002) and transmittance values, in the visible range, greater than 80%. The increase in flow oxygen up to 25% provides an increase in the film's density resulting in a decrease in electrical resistivity from 9.58 × 10−3 Ω cm to 8.14 × 10−3 Ω cm. The ab initio calculations allow to observe the distortions in the microstructure of the films attributed to the presence of impurities and to obtain the values of the total and formation energies. The values of the Mulliken population and chemical bond length are notoriously influenced by the concentration of oxygen in the atmosphere. The displacement of the valence band (VB) and the Fermi level, together with the decrease in the gap energy, reinforce the influence of oxygen gas on the electronic structure of the films.

Synthesis of AZO-Coated ZnO Core–Shell Nanorods by Mist Chemical Vapor Deposition for Wastewater Treatment Applications

“…Compared to the hexagonal wurtzite facets for ZnO nanorods with an average diameter of 104 nm before the coating process, the surfaces of ZnO nanorods gradually grew and transformed into an almost-circular shape with an increase in AZO coating time. The surface morphology change might be due to the difference in ionic radius between Zn 2+ (0.74 Å) and Al 3+ (0.53 Å) [ 26 ]. When the AZO was coated on the ZnO nanorods during the mist CVD process, the high concentration of Al ions might replace the Zn ion sites, resulting in structural changes.…”