_____________________________________________________________________________________________________ *Corresponding author: Email: sarishbti@gmail.com, drsarishiitk@gmail.com; Original Research Article EFFECT OF EXPOSURE OF LIGHT ON DENSITY OF DEFECT STATE IN Se 96 Bi 4 GLASSY ALLOYS SARISH YADAV 1 , KRISHNA. Ji 2 , S. K. SHARMA 3 R. K. SHUKLA 3 , A. KUMAR 3* . 1 Bharat Institute of Technology, Meerut, India. 2 Sunrise Institute of Engineering Technology & Management, Kanpur, India 3 Harcourt Butler Technological Institute, Kanpur, India. AUTHORS CONTRIBUTION This work was carried out in collaboration between all authors. Author SEA designed the study, wrote the protocol and interpreted the data. Author BA anchored the field study, gathered the initial data and performed preliminary data analysis. Authors while OA and LEI managed the literature searches and produced the initial draft. All authors read and approved the final manuscript. ABSTRACT Amorphous thin films of Se 96 Bi 4 glassy alloy are prepared by vacuum evaporation technique. Space charge limited currents are measured at various fixed temperatures before and after exposure to white light of intensity 990 lux in a vacuum of 10 -2 Torr. Using the theory of space charge limited conduction (SCLC), the density of localized states (DOS) has been calculated after each exposure of light (exposure time 1 -5 hours). The results indicate that DOS increases with the time of light exposure indicating the creation of light induced defects due to exposure of light. Keywords: Chalcogenide glasses, amorphous semiconductors, Light induced defect. 1. INTRODUCTION Due to low phonon vibrations, heavy component elements, chalcogenide glasses are transparent to infrared vibrations including the wavelength 1.3 and 1.55 μm [1]. In addition, they can be doped with rare earth and posses very high intrinsic non-linear properties [2-5]. Another striking and unique property of this family of glasses is their ability to undergo structural changes upon irradiation with an appropriate laser source [6]. These structural alterations produce several effects such as a shift of the optical absorption edge, volume changes, and changes of refractive index n [7-11]. This combination of unique properties has generated a resurgence of interest for the use of chalcogenide glasses in the field of photonics. Potential applications range from all-optical switching, planer waveguide circuits, lasers, optical amplifier to acousto-optic devices [12-14]. Chalcogenide glasses undergo various kinds of photo- structural changes on prolonged exposure to light. The mechanism of the photo-structural change is complex and not completely understood at present. It was recognized that the excitation of electrons from spatially localized states in the band tail induces the formation of several types of defects in the glass structure [15, 16]. Structural defect such as transient bonds, ESR active sites and valance alternation pairs-