Optical absorption of Zn(V,Al)O thin films studied by spectroscopic ellipsometry from 1 to 6 eV

¹ Department of Physics, Faculty of Science, King Abdulaziz University, North Jeddah Branch, P.O. Box 80203, 21589 Jeddah, Saudi Arabia
² Equipe de Spectroscopie Raman, Département de Physique, Faculté des Sciences de Tunis, Campus Universitaire, El-Manar, 2092 Tunis, Tunisie
³ Department of Physics and Chemistry, College of Sciences, Al Imam Mohammad Ibn Saud Islamic University (IMSIU), 11623 Riyadh, Saudi Arabia
⁴ Laboratory of Physics of Materials and Nanomaterials Applied at Environment (LaPhyMNE), Faculty of Sciences in Gabes, Gabes University, Gabes, Tunisia
⁵ Department of Physics, Faculty of Science, King Abdulaziz University, P.O. Box 80203, 21589 Jeddah, Saudi Arabia

^a e-mail: amor.sayari@laposte.net

Received: 9 November 2012
Revised: 17 May 2013
Accepted: 21 May 2013
Published online: 13 June 2013

Abstract

Aerogel nanoparticles prepared with various Al concentrations were used as a target for the deposition of (V,Al) co-doped ZnO films by rf-magnetron sputtering on glass substrates. The influence of Al content on the structural and the optical properties of the Zn(V,Al)O films was investigated by X-ray diffraction and spectroscopic ellipsometry (SE). It is found that all films exhibit one high intensity (0 0 2) peak, indicating that they have c-axis preferred orientation due to self-texturing mechanism. SE measurements, used to determine the complex pseudo dielectric functions, were carried out at room temperature in the 1–6 eV photon energy region. The excitonic edge of the fundamental band gap (E0) transition in the imaginary part of the dielectric function of the Zn(V,Al)O films is observed around 3.5 eV and shows a dependence on the Al content. The E₀ absorption edge of the Zn_0.9−x V_0.1Al_xO alloys shows a blueshift from that of pure ZnO, reaching 389 meV for x = 0.02. This blueshift is interpreted by the Burstein-Moss effect. By analyzing the dielectric function, reduced effective mass m^* of the Zn_0.9−x V_0.1Al_xO alloy is extracted and shows good agreement with literature values.