Optical study of Ge 10 Se 90-x Te x glassy semiconductors Pankaj Sharma ⁎ , S.C. Katyal Department of Physics, Jaypee University of Information Technology, Waknaghat, Solan, HP-173215, India Received 1 June 2006; received in revised form 5 February 2007; accepted 22 March 2007 Available online 31 March 2007 Abstract Chalcogenide glasses are interesting materials from their infrared transmitting properties and photo-induced effects exhibited by them. Thin films of the glasses Ge 10 Se 90-x Te x (x = 0, 10, 20, 30, 40, 50) prepared by melt quench technique were evaporated at a pressure of ~10 - 4 Pa. The amorphous nature of bulk as well as thin films was detected by X-ray diffraction. Optical transmission spectra of thin films were obtained in the range 400–2400 nm. The optical constants i.e. optical band gap, absorption coefficient and refractive index are calculated using the Swanepoel method. The optical band gap is found to decrease with the increase of Te content. The absorption coefficient and refractive index decrease with the increase of wavelength. The refractive index first decreases (up to 30 at.%) and thereafter increase with Te content. © 2007 Elsevier B.V. All rights reserved. Keywords: Chalcogenide glasses; Optical properties; Band gap; Absorption coefficient; Refractive index 1. Introduction Chalcogenide glasses are interesting materials because of their technological applications [1] and commercial importance [2]. They are recognized as promising materials for infrared optical elements, infrared optical fibres, xerography, switching and memory devices, photolithography and in the fabrication of inexpensive solar cells and more recently for reversible phase change optical records [3–14]. The influence of impurities on electrical, optical and the structural properties of chalcogenide glasses are of important concern with respect to their application. This influence can be widely different for different impurities. Many approaches were proposed to explain the compositional dependence of various physical properties of chalcogenide networks [1,15–18]. Amorphous semiconductors of Se based systems such as Ge–Se have attracted much attention in recent years. This family of chalcogenide glasses provides an ideal system for investigation. The chemical composition and energy band structure changes as a result of introducing the Ge atoms into the Se matrix. The variation of the Ge–Se structure is reflected in different properties such as the glass forming regions, glass transition temperature, photoluminescence, IR and Raman spectra and the optical properties [19–21]. Optical properties of IV–VI compounds have been studied by various researchers [22,23]. The optical band gap and the localized states width were found to depend on the composition. The optical band gap and refractive index are the most significant parameters in amorphous semiconducting thin films. The optical behaviour of material is utilized to determine its optical constants. Films are ideal specimen for absorbance and transmittance type measurements. Therefore, accurate measure- ments of the optical constants are extremely important. The optical properties of amorphous semiconductors have been extensively studied [22,23] on Ge–Se system because of their wide range of applications and strong dependence on composition. In Ge 10 Se 90 system the average coordination number brN is 2.2 i.e. the system is in floppy mode. Alloying of Ge 10 Se 90 with a fourth element of group VI (Te) is very important from the basic as well as application point of view because for Ge 10 Se 90-x Te x (x =0, 10, 20, 30, 40, 50) compositions brN varies from 2.2 to 2.7 i.e. the system varies from floppy mode to rigid mode with a change in mode at 2.4 [16,18]. In the present work, therefore, the effect of Te additive on the optical properties of such a technically important system Ge 10 Se 90 has been studied. The optical parameters optical band gap (E g opt ), Thin Solid Films 515 (2007) 7966 – 7970 ⁎ Corresponding author. Tel.: +91 1792 239220; fax: +91 1792 245362. E-mail address: pks_phy@yahoo.co.in (P. Sharma). 10.1016/j.tsf.2007.03.080 doi: