Etude des couches minces d’Oxyde de Zinc dopé Aluminium et Cobalt élaborées par la technique sol gel-spin coating.

Abstract

In this work, undoped, Cobalt and Aluminum doped ZnO thin films with different amounts of dopants (Co or Al) have been deposited onto glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, cobalt acetate tetrahydrate, Chlorure d'Aluminium hexahydraté, isopropanol and monoethanolamine (MEA) were used as a precursor, doping sources, solvent and stabilizer, respectively. The molar ratio of MEA to metal ions was maintained at 1.0 and a concentration of metal ions is 0.6 mol L-1. The Co (Al) dopant level was defined by the Co (Al) /(Co (Al) + Zn) ratio it varied from 0 to 7 % mol. The structure, morphology and optical properties of the thin films thus obtained were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), ultraviolet–visible (UV–Vis) spectrometry, photoluminescence (PL) spectrometry, Raman spectrometry and the photocurrent measurement. The XRD results showed that all films crystallized under hexagonal wurtzite structure and presented a preferential orientation along the c-axis with the maximum crystallite size was found about 25 nm for undoped film. The results of SEM indicate that the undoped and Al doped ZnO thin films have smooth and uniform surfaces with small ZnO grains, and the Co doped ZnO films shows irregular fiber-like stripes and wrinkle network structure. The topological analysis by AFM shows that the pure and doped films have a similar crystalline morphology consisting of more or less identical grains. roughness tends to increase as one doped with cobalt and decreases by aluminum. The average transmittance of all Co doped films is about 72–97 % and is over 95% for Al doped films in the visible range. the band gap energy increases with Al doping and decreased with Co doping. DRX, EDX and optical transmission confirm the substitution of ions of the dopant for Zn+2 at the tetrahedral sites of ZnO. In addition to the vibrational modes from ZnO, the Raman spectra show, for Co doped films, prominent mode representative of ZnyCo3-yO4 secondary phase at larger values of Co concentration, and longitudinal optical (LO) mode in the Raman spectra was enhanced by the Al doping. Photoluminescence (PL) of all films showed a UV and defect related visible emissions like violet, blue and green, and indicated that cobalt doping resulted in red shifting of UV emission and the reduction in the UV and visible emissions intensity. Photocurrent measurement shows the best photocurrent properties of the thin films, and the doping (notably doping with aluminum) improved the photocurrent films.