Optical band gap and optical constants in a-Se 80 Te 20x Pb x thin films Shamshad A. Khan 1 , M. Zulfequar, M. Husain * Department of Physics, Jamia Millia Islamia, New Delhi 110025, India Received 2 March 2004; accepted 28 July 2004 Available online 17 September 2004 Abstract The optical constants (absorption coefficient, refractive index, extention coefficient, real and imaginary part of dielectric con- stant) have been studied for a-Se 80 Te 20x Pb x (where x = 0,2,6,10) thin films as a function of photon energy in the wave length range (500–1000nm). It has been found that the optical band gap increases while the refractive index and the extinction coefficient (k) decreases on incorporation of lead in Se–Te system. The value of absorption coefficient (a) and the extinction coefficient (k) increases, while the value of refractive index (n) decreases with incident photon energy. The results are interpreted in terms of the change in concentration of localized states due to the shift in fermi level. Ó 2004 Elsevier B.V. All rights reserved. PACS: 78.20.Cl; 61.43.Fs Keywords: Amorphous semiconductor; Optical constants; Chalcogenides; Optical band gap; Thin films 1. Introduction It is well known that the impact of amorphous semi- conductors on science and technology is considerable, with these materials having application in solar cells, IR detectors, electronics and optical switches, inorganic resist, optical recording media and image processing sys- tems [1–4]. During the last decade, efforts have been made to develop new vitreous materials, especially glassy chalcogenide materials because of their attractive IR properties. Discovery and study of new materials, whose properties can be tailored-made, constitute the core of development of solid state technology. In spite of well-established technologies for preparation of these semiconductors and devices fabricated, utility of such materials is restrained due to their discrete structural and electronic properties. Impurity effects in chalcoge- nide glasses may have importance in fabricating glassy semiconductors. The most important applications of chalcogenide glasses are now in the field of optics and arise chiefly from either their infrared-transmitting properties or photo-induced effects they exhibit. They have potential uses in integrated optics, optical imaging, optical data storage and infrared optics. The optical band gap, refractive index and extinction coefficient are the most significant parameters in amor- phous semiconducting thin films. The optical behavior of a material is utilized to determine its optical con- stants. Films are ideal specimens for reflectance and transmittance type measurements. Therefore, an accu- rate measurement of the optical constants is extremely important. Chalcogenide glasses have been found to ex- hibit the change in refractive index under the influence of light, which makes it possible to use these materials to record not only the magnitude but also the phase of illumination. The latter is especially important in holo- graphic optical data storage and in the fabrication of various integrated components and devices such as selective optical filters, mixers, couplers and modulators [5–7]. 1567-1739/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2004.07.002 * Corresponding author. Tel.: +91 11 26988332; fax: +91 11 26980229. E-mail address: mush_reslab@rediffmail.com (M. Husain). 1 Department of Physics, St. AndrewÕs College, Gorakhpur, U.P., India. www.elsevier.com/locate/cap Current Applied Physics 5 (2005) 583–587