Thermal annealing effect on optical properties of electrodeposited ZnO thin films

7pp; International audience; ZnO thin films were electrodeposited in aqueous solution on gilded p-type Si wafer substrates. Thermal treatments were carried out on different films in Ar atmosphere at different temperatures, between 200 and 600 ◦C. Surface morphology studies using scanning electron microscopy and atomic force microscopy show a smooth surface for an annealing temperature of 400 ◦C with a roughness mean square value of about 15 nm and a precipitation of ZnO microcrystals on the deposit surface at 600 ◦C. X-ray diffraction experiments reveal a decrease in the c-parameter value from 5.223 to 5.206Å after treatment at 600 ◦C, due to the removal of hydrogen from the film. Raman spectroscopy analyses show an improvement in the crystal quality of the film and a decrease in the compressive stress inside the deposit. Photoluminescence observations reveal an important change in the UV emission band after annealing at 200 ◦C. A visible region emission band at 580 nm, ascribed to interstitial oxygen, is observed for the as-grown deposit and decreases as the annealing temperature increases. An emission band appears near 525 nm for samples annealed at 400 and 600 ◦C; this band is ascribed to oxygen vacancies created during annealing treatment. This result is in agreement with the energy dispersive x-ray spectroscopy experiments which revealed loss of oxygen.