Chalcogenide Letters Vol. 5, No. 3, March 2008, p. 27 - 33 PREPARATION AND OPTICAL PROPERTIES OF SeS THIN FILMS SEMICONDUCTING CHALCOGENIDE GLASSES M. Abdel Rafea * , A. A. M. Farag a Institute of Advanced Technology and New Materials, Mubarak City for Scientific Research and Technology Applications, New Borg El Arab city, Alexandria, Egypt. a Faculty of Education, Ain shams university, Heliopolis, Roxy, Cairo 11757, Egypt Se 1-x S x glassy films have been prepared in the thin films form with x in the range 0.0-0.4 and thickness in the range 500-600 nm by thermal vacuum evaporation technique. The amorphous structure of the films was confirmed by XRD measurements. The surface morphology and the thickness of the films were studied by SEM. The optical properties of the films were studied by transmittance method, it was found that the optical constants of the films are sensitive to composition. The refractive index was determined and the data was discussed in the Wemple and DiDomenico model for single effective oscillator. The resultant oscillator energy and strength were then calculated and found to be increased as the composition increases. A blue shift in the absorption edge was observed by increasing the sulfur content and the band gap increases from 1.85 to 2.03 eV as the composition increases from 0.0 to 0.4. (Received February 14, 2008; accepted February 20, 2008) Keywords: Chalcogenide glasses, Thermal vacuum evaporation, Optical properties 1. Introduction Chalcogenide glasses "sulfide, selenide and telluride" in the binary and multi component systems are promising materials for various electronic, optoelectronic, optical memory switching devices, optical recording media and photonic applications. Selenium based chalcogenide glasses have high transparency in the broad middle and far infrared region and have strong non-linear properties. The glassy state Se-S exhibits an electronic conductivity of p-type semiconductor. The addition of S to Se leads to a decrease in the density as well as an increase in the glass transition temperature [1-3]. Substitution of chalcogenide partially by Ge and As increases their thermal stability, while Sb increases their fast phase transformation for optical memory recording media. When Se content increases in the Ge 0.23 Sb 0.07 S 0.70-x Se x glass system from 0.0 to 0.7, a red shift of the optical absorption edge occurs. The laser irradiation results in near-surface photo-expansion and glass structure modification as a function of S/Se ratio takes place [4]. In Ge 30-x Sb x S 70 glass thin films, the band gap decreases from 2.04 to 1.74 as Sb increases from 0 to 30 which was explained by the change of the binding energies of Ge-S and Sb-S. The Wemple & DiDomenico model (WDD) determines the oscillator energy, E 0 , and oscillator strength, E d , for single effective oscillator using the following formula d d E E h E E n 0 2 0 2 ) ( 1 1 ν − = − (1) Both E 0 and E d decreases linearly as Sb content increase[5]. Replacing Ge-Sb by As, in the As 33 S 67-x Se x glass of spin coated films of x = 0 - 67, the increase of Se content decreases the band gap from 2.45 to 1.8 eV. Also a red shift in the absorption edge takes place by annealing the films at T=150 o C for 30 and 60 min [6]. In As 100-x S x glass system, the band gap increases as x decreases. The refractive index is fitted also to the (WDD) dispersion relationship of the single oscillator model [7]. In the As 40 S 60-x Se x glass system, the glass transition * Corresponding author: m.abdelrafea@mucsat.sci.eg