Growth and characterization of transparent vanadium doped zinc oxide thin films by means of a spray pyrolysis process for TCO application

Aluminum doped zinc oxides show a high electrical conductivity owing to their high electron concentration in the conduction band, which significantly hinders the development of p-n junction due to the formation of degenerate states. To overcome this limitation, it is proposed to improve the electron mobility rather than the free electron concentration. For this specific aspect, vanadium appears to be one of the most suited alternatives as a doping element. In this work, we report on the preparation of ZnO and vanadium-doped ZnO thin films by spray pyrolysis process. Vanadium loads were varied from 0 to 4 at.% in the ZnO films and its effect on the structural, morphological, chemical, optical, and mechanical properties of the fabricated thin films was investigated through a bench of characterizations techniques, including X-ray diffraction (XRD), atomic force microscope (AFM), X-ray photoelectron spectroscope (XPS), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), UV-Vis spectrophotometer, and digital Vickers microhardness tester. The obtained results demonstrate the successful formation of pristine ZnO films and V-doped ZnO, which were found to be polycrystalline with a hexagonal wurtzite crystal structure. According to the self-correlation function, AFM images reveal that the particle size increases with respect to the V-load. TOF-SIMS analyses confirm the constant distribution of Zn, O and V elements throughout the film thickness. Moreover, our films are found to be optically transparent in the 400–1200 nm range with associated band gaps energy ranging from 3.18 to 3.26 eV. Finally, mechanical measurements have been carried out using a conventional diamond-pyramidal-indenter Vickers test. The results confirmed that by increasing V concentration, the microhardness increases. Graphical abstract Highlights V-doped ZnO films successfully grown by the chemical spray pyrolysis technique. V-doped ZnO films are polycrystalline structure with a dominant (101) orientation. The surface roughness of the films is well controlled with respect to the V concentration and the average optical transmittance of all films was between 60% and 80%. TOF-SIMS analysis confirmed the presence of all the deposited elements over the surface and over the entire film thickness. The energy band gap varies from 3.18 and 3.26 eV w/r to V concentration.