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The control of native defects in the ZnO material is strongly important for a wide range of technological applications. In this paper, native defects are tuned via the post-thermal treatment of ZnO films in a high vacuum atmosphere. The microstructure of the as-grown ZnO film shows columnar growth and strongly polar-oriented grains along the c-plane (002). Also, the obtained results indicate that the as-grown film contains a high amount of intrinsic defects and strong lattice distortions. After the thermal annealing, the ZnO films display significant structural changes, which are reflected in their electrical, vibrational, and optical properties. Our findings suggest that these changes were attributed to the selective cleanup effect of the native defects and the partial deoxidation process mainly on the exposed particle surface (at high temperatures) tuned up by the thermal annealing temperature. According to DFT calculations, oxygen vacancies (VO) show lower energy, followed by zinc vacancies (Oi) and oxygen interstitials (VZn) indicating that VO defect is the most stable in ZnO. That sequence of stability could suggest the sequence of the annihilation of those defects, which is in line with our experimental findings.

In this work, we present the study of undoped and Fe-doped SnO2 polycrystalline films grown by direct-current sputtering on glass substrates. X-ray diffraction (XRD) analysis revealed that the as-deposited films exhibit an amorphous phase, whereas, after 2 h of thermal annealing at 500 °C, the films showed a rutile-type structure with no evidence of secondary phases. Rietveld refinement analyses of the XRD patterns revealed that the undoped films do not reveal a preferred orientation as is displayed in the bulk system, whilst the Fe-doped films showed a (1 0 1) preferred orientation which is enhanced with the deposition time (film thickness). A detailed analysis revealed a clear dependence of the unit cell volume on the crystallite size. The latter effect was mainly associated with strain effects occurring during the film deposition. Additionally, the growth of columnar-shaped structures was determined by cross-section scanning electron microscopy images. Interesting features of the fundamental absorption were determined via UV–vis spectroscopy. The obtained results revealed a monotonous decrease of the band gap with film thickness, which becomes larger for the Fe-doped SnO2 films and is associated with a change in the residual strain, in good agreement with the XRD analysis and Raman spectroscopy measurements.