Effect of RF power on the structural and optical properties of RF-sputtered ZnO thin films

¹ Solid State Physics and Thin Films Laboratory, Faculty of Sciences Semlalia, Cadi Ayyad University, PO Box 2390, Marrakech 40000, Morocco
² Laboratory of Coordination Chemistry and Catalysis, Faculty of Sciences Semlalia, Cadi Ayyad University, PO Box 2390, Marrakech 40000, Morocco

^a e-mail: lahcen.com@hotmail.fr

Received: 10 March 2014
Revised: 11 April 2014
Accepted: 2 May 2014
Published online: 10 June 2014

Abstract

ZnO thin films were deposited by reactive cathodic radio-frequency (RF) sputtering from a pure Zn target in a gas mixture of 30% O₂ and 70% Ar and at different RF powers. The structural properties of the as-deposited thin films were studied by X-ray diffraction (XRD). The optical properties (especially the refractive index, absorption coefficient and optical band gap) were investigated by optical transmission measurements in the ultraviolet-visible-near Infrared wavelength range. The XRD patterns showed that the as-deposited ZnO thin films are polycrystalline. The crystallite size varied with RF power reaching a maximum at 200 W. These results were correlated with X-ray refectometry measurements which revealed a minimum in the film density at 200 W. The deposition rate of these films varied from 2.53 to 5.27 nm/min depending on the RF-power, with a maximum at 200 W. On the other hand, the optical band gap E_g was quasi-constant (about 3.28 eV) when the RF power was increased from 100 to 300 W.