Physica B 366 (2005) 44–54 Optical constants of Zn 1x Li x O films prepared by chemical bath deposition technique A. Abu EL-Fadl à , Galal A. Mohamad, A.B. Abd El-Moiz, M. Rashad Physics Department, Faculty of Science, Assiut University, Assiut 71516, Egypt Received 5 May 2005; accepted 12 May 2005 Abstract Zn 1x Li x O films of different Li concentrations x ¼ 0:020:5 were successfully deposited on glass substrates using chemical bath deposition (CBD) technique. Optical properties of the films were studied extensively in the wavelength range 190–800nm from the measurements of the optical transmittance (T) and optical reflectance (R). The mechanism of the optical absorption follows the rule of direct allowed transition. Both the optical energy gap E g and absorption coefficient (a) were found to be Li concentration-dependent. The refractive index values have been fitted to the single- oscillator models. The values obtained for the single-oscillator energy E o are consistent with the optical gap results. The dependence of the optical constants of ZnO on the photon energy (hn) at selected concentrations of Li were discussed. The exponential dependence of the absorption coefficient as a function of the incident photon energy suggests that the Urbach rule is obeyed and indicated the formation of a band tail. It was found that the optical energy gap decreases with increasing Li content; on the other hand the band tail width exhibits the opposite behaviour. r 2005 Elsevier B.V. All rights reserved. PACS: 78.20.e; 78.40.Fy Keywords: Zinc oxide films; Chemical bath deposition technique; Optical constants 1. Introduction ZnO films hold a unique position among materials because they are piezoelectric materials that have been the subject of extensive studies [1–4]. Its piezoelectric properties are exploited in thin films applications, such as a surface acoustic wave (SAW) devices, ultrasonic transducers and sensors [5–7]. The crystal structure of ZnO is hexagonal (wurtzite type) which is suitable for fabrication of high-quality oriented or epitaxial thin film. Each Zn atom is tetrahedrally coordi- nated with four O atoms and the zinc d electrons hybridize with the oxygen p electrons [8]. Now, it ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$-see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2005.05.019 à Corresponding author. Tel.: +20882412244; fax: +20882333837. E-mail address: abulfadl@acc.aun.edu.eg (A. Abu EL-Fadl).