Physica B 325 (2003) 308–318 Determination and analysis of optical constants for Ga 2 Se 3 films near absorption edge M.A. Afifi, A.E. Bekheet*, H.T. El-Shair, I.T. Zedan 1 Physics Department, Faculty of Education, Semiconductor Laboratory, Ain Shams University, Cairo, Egypt Received 12 June 2002; received in revised form 28 August 2002 Abstract Ga 2 Se 3 has been prepared in bulk and thin film forms. The composition of films has been checked using energy dispersive X-ray spectroscopy technique. X-ray diffraction measurements have shown that Ga 2 Se 3 films evaporated at room temperature substrates were amorphous. The transmittance ðT Þ of Ga 2 Se 3 thin films has been measured over the wavelength range (400–900 nm). The optical constants, the refractive index ðnÞ and the absorption index ðkÞ have been determined from the analysis of the transmittance data. Analysis of the refractive index ðnÞ yields the values of the long wavelength dielectric constant ðe N Þ; the average oscillator wavelength ðl o Þ; average oscillator strength ðS o Þ; average oscillator energy E o ; the refractive index dispersion parameter ðE o =S o Þ and the dispersion energy ðE d Þ: Analysis of absorption index ðkÞ yields both direct and indirect allowed transitions with optical energy gaps of 2.65 and 2:056 eV; respectively. The effect of annealing at different temperatures on optical constants is also investigated. r 2002 Elsevier Science B.V. All rights reserved. PACS: 78.20.C; 73.61.J; 78.66 Keywords: Optical properties; Ga 2 Se 3 films; Optical constants 1. Introduction Studies of M III 2 X VI 3 (M ¼ Ga; In, Tl and X ¼ S; Se, Te) compounds are attracting wide attention because of their importance as good photovoltaic materials. Moreover, these compounds have at- tractive properties for applications in electrother- mal devices [1] such as solid solution electrodes. Many papers have dealt with the ordering of these compounds and it has been found that annealing affects the degree of ordering [2–4]. Ga 2 Se 3 is a member of the above family and has become a matter of great interest, because it serves as a good candidate for optoelectronic applications [5,6]. It has three phases (a; b; and g). Two of them, named a and g phases, have a disordered sphalerite-type structure, the first being tetragonal with slight difference between the a and c parameters and the second is cubic. In the third phase, named b phase, a certain ordering of vacancies in the metallic sublattice takes place leading to a superstructure formation. Mikkelsen [7] showed by differential thermal analysis (DTA) that a phase was obtained by isothermal crystal growth of the melt above *Corresponding author. Tel.: +20-245-52138; fax: +20-245- 52138. E-mail address: ashraf bekheet@hotmail.com (A.E. Bekheet). 1 Ministry of Education, Science teacher in preparatory school. 0921-4526/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0921-4526(02)01544-2