Vacuum 82 (2008) 608–612 Optical characterization of vacuum evaporated a-Se 80 Te 20x Cu x thin films Anis Ahmad a , Shamshad A. Khan b , Kirti Sinha a , Lokendra Kumar c , Zishan H. Khan d , M. Zulfequar e , M. Husain e,Ã a Department of Physics, University of Lucknow, Lucknow, U.P. 226007, India b Department of Physics, St. Andrew’s College, Gorakhpur, U.P. 273001, India c Department of Physics, University of Allahabad, Allahabad, U.P. 211002, India d Department of Applied Sciences and Humanities, Faculty of Engineering and Technology, Jamia Millia Islamia, New Delhi 110025, India e Department of Physics, Jamia Millia Islamia, New Delhi 110025, India Received 18 April 2007; received in revised form 28 August 2007; accepted 3 September 2007 Abstract Thin films of a-Se 80 Te 20x Cu x (where x ¼ 2, 6, 8 and 10) were deposited on glass substrates by vacuum evaporation technique. The absorbance, reflectance and transmittance of as-deposited thin films were measured in the wavelength region 400–1000 nm. The optical band gap and optical constants of amorphous thin films have been studied as a function of photon energy. The optical band gap increases on incorporation of copper in Se 80 Te 20x Cu x system. The value of refractive index (n) decreases while the value of the extinction coefficient (k) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states. r 2007 Published by Elsevier Ltd. Keywords: Amorphous semiconductors; Thin films; Optical band gap; Optical constants 1. Introduction Due to their specific electrical and optical properties, chalcogenide glasses have conquered an important place for the applications of the non-crystalline materials. Chalcogenide glasses are promising optical materials due to their transparency in IR region, relatively good thermal, mechanical and chemical properties and the low optical losses having their application in the field of fiber optics, xerography and novel memory devices [1–6]. The interest in optical properties of amorphous semiconductor and glasses has also been stimulated by their possible applications as switching elements and optical transmission media, as well as the passivating materials for integrated circuits [7]. It is well known that the glassy amorphous materials relax towards an amorphous state of lower free energy at temperature far below the glass transition temperature. Optical memory effects in amorphous semiconducting films have been investigated and utilized for various applications such as large packing density, mass replication, fast data rate, high signal-to-noise ratio and high immunity to defects [8–12]. Glassy chalcogenide semiconductors have great varieties of band gaps and are transparent in the infrared region [13]. Continuous variation of discreet structural, optical and electronic properties, if achieved in semiconducting materials in a controlled manner, could enhance their employability in the fabrication of devices with predetermined characteristics. Ternary alloy semicon- ductors do provide such a class of materials. The present communication reports the optical properties of. Se 80 Te 20x Cu x where x ¼ 2, 6, 8 and 10. Here, selenium has been chosen as an additive material due to its wide commercial importance. We have chosen Te based alloys because they have been used as optical storage media, although they are known to degrade in moist atmosphere [14]. Se–Te films are attractive for archival recording because they form micro pits or bubbles [15] through a process of melting or ablation due to localized heating by the intense laser beam. But they require greater laser power ARTICLE IN PRESS www.elsevier.com/locate/vacuum 0042-207X/$ - see front matter r 2007 Published by Elsevier Ltd. doi:10.1016/j.vacuum.2007.09.006 Ã Corresponding author. E-mail address: mush_reslab@rediffmail.com (M. Husain).