Eur. Phys. J. Appl. Phys. (2013) 63: 10301 DOI: 10.1051/epjap/2013130099 THE EUROPEAN PHYSICAL JOURNAL APPLIED PHYSICS Regular Article Optical spectroscopy and dispersion parameters of Ge 15 Se 60 X 25 (X = As or Sn) amorphous thin films Heba E. Atyia a and N.A. Hegab Physics Department, Faculty of Education, Ain Shams University, Cairo, Egypt Received: 22 February 2013 / Received in final form: 19 May 2013 / Accepted: 21 May 2013 Published online: 5 July 2013 – c  EDP Sciences 2013 Abstract. In the present work the optical properties of Ge15Se60X25 (X = As or Sn) films have been studied. Optical reflectance and transmittance of films were obtained at normal incident in the wavelength range (500–2500 nm). The transmittance measurements were used to calculate the refractive index n and the absorption index k depending on Swanepole’s method. The analysis of the optical absorption data revealed that the optical band gap E opt g was allowed indirect transitions. The optical constants such as complex dielectric constant, dispersion parameters (E0 and E d ), ε∞, VELF, SELF and dissipation factor tan δ were determined. It was found that E opt g and the oscillator energy E0 decreased with As addition than Sn addition. Whereas, the Urbach tail energy Ee, the dispersion energy E d , the real and imaginary dielectric constants ε1 and ε2, the high frequency dielectric constant ε∞ and the dissipation factor tan δ increased with As addition than Sn addition. 1 Introduction The chalcogenide glasses are very promising materials for use in many technological application [1, 2]. These materi- als have glass formation ability over a wide compositional range [3], which make them exhibit a number of interest- ing changes in their physical properties such as switching and memory effects [4–7]. The knowledge of the optical properties of these glasses is obviously necessary for the use of these materials in the fabrication of a great num- ber of optical devices [8]. Chalcogenides like Se-Ge are known to be very good covalent bonded glass formers. It has been established that the physical properties of this system are highly compositional dependent [9]. It is found that the addition of some impurities as a third element to binary chalcogenide glasses changes their structure and new properties are expected for these glasses. From this point of view the addition of As or Sn to the Se-Ge system can markedly affect its structural, electrical and optical properties [10, 11]. In the present work reports a systematic study of the optical reflectance and transmittance for Ge 15 Se 60 X 25 (X = As or Sn) films. The optical parameters like refrac- tive index n, absorption index k, absorption coefficient α, high frequency dielectric constant ε ∞ , oscillator strength E d , oscillator energy E o and the optical energy gap E opt g have been calculated. The effect of X (X = As or Sn) ad- dition to Ge-Se on the optical properties has been studied also. a e-mail: Hebaelghrip@hotmail.com 2 Experimental technique Bulk Ge 15 Se 60 X 25 (X = As or Sn) materials were pre- pared by melting together the stoichiometric amounts of the constituent elements Ge, Se and X (X = As or Sn) of purity 99.999% in a sealed evacuated (10 −5 torr) silica tube (length 15 cm, internal diameter 12 mm and weight 7 g). The content of each tube was heated gradually in an oscillatory furnace and kept constant at melting point of Se, Sn, Bi and As for 1 h, then it was raised to 1273 K and kept constant for 24 h [6]. Long time of synthesis and oscillation of the tube are necessary for the homogeneity of the synthesized samples. The tube is then quenched in icy water to obtain the samples in the glassy. Thin films of the investigated samples were obtained from bulk sam- ples by thermal evaporation technique under vacuum and subsequent deposition on highly cleaned glass substrates. The substrate temperature was held at that of the room temperature during deposition. The thickness of film sam- ples was measured after deposition by Tolansky’s inter- ferometric method [12]. The chemical composition of the investigated samples was checked by energy dispersive X-ray analysis (EDX) using a JEOL 5400 scanning elec- tron microscope. The EDX diagrams of our compositions in thin film forms of different thicknesses (not shown) possess a nearly stoichiometric composition (Ge 15 Se 60 X 25 (X = As or Sn)). The structure of the investigated film compositions was examined by X-ray diffraction and dif- ferential thermal analysis. The obtained patterns reveals the amorphous nature of the studied film compositions. The same behavior was obtained for all studied films. 10301-p1