Structural characterization of polycrystalline Ag–In–Se thin films deposited by e-beam technique T. C ¸ olakog ˘lu, M. Parlak * Department of Physics, Middle East Technical University, 06531 Ankara, Turkey Received 26 January 2007; received in revised form 6 June 2007; accepted 6 July 2007 Available online 18 July 2007 Abstract The Ag–In–Se thin films were deposited by e-beam evaporation of the Ag 3 In 5 Se 9 single crystal powder under high vacuum without intentional doping. Energy dispersive X-ray analysis (EDXA) showed the decreasing behavior of Se and Ag in the structure depending on the annealing. X-ray diffraction (XRD) analysis showed that as-grown films have amorphous structure while annealing the films under nitrogen environment at 200 8C transformed from the amorphous to polycrystalline structure. The crystallinity of the films improved as annealing temperature increases up to 400 8C by 100 8C-step. The polycrystalline films show mixed binary and ternary crystalline phases. Each phase was determined by comparing XRD patterns with complete data cards as Ag 3 In 5 Se 9 , AgInSe 2 , In 4 Se 3 , In 2 Se 3 , InSe, Se 6 and Se. The existence of Se segregation was supported by the formation of Se aggregates in crystalline phases of Se 6 and Se. The X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analysis have been carried out in order to obtain detailed information about the atomic composition, chemical states and morphology of the thin film surface. The decomposition of In 4d, Se 3d and Ag 3d photoelectron peaks revealed the existence of In–In, In–Se, In–Ag, Se–Se and Ag– Ag bondings in as-grown thin films. After annealing the thin films at different temperatures, the concentration of In–Se and In–Ag bonds decreases significantly, which results in an In-rich, but Ag- and Se-deficient thin film structure. The roughness of the film surface as a result of application of post-annealing in between 200 and 400 8C monitored by AFM technique was observed to change from 1.81 to 22.89 nm. # 2007 Elsevier B.V. All rights reserved. Keywords: Silver indium selenide; Ternary compounds; Selenium segregation; XPS; AFM; XRD 1. Introduction Ternary semiconductor compounds have attracted the technological interest owing to their promises for practical application in the areas of visible and infrared light emitting diodes, infrared detectors, optical parametric oscillators, non- linear optics, solar cells, optical frequency conversion, second harmonic generation devices and many other electro-optical devices [1–4]. In the production of stable and radiation resistant polycrystalline thin film photovoltaic solar cells, reasonably high power conversion efficiency values have been achieved by using the ternary chalcopyrite semiconductors as an absorber layer [5]. As a ternary semiconductor compound Ag 3 In 5 Se 9 belongs to the A I 3 B III 5 C VI 9 -type semiconductor family which are the noncubic ternary analogs of A III 2 B VI 3 -type crystalline structures [6]. Along with this fact, these two-cation ternary semiconductor com- pounds are produced by manipulating the sites of In atoms in the binary analog In 2 Se 3 semiconductor crystals together with monovalent Ag atoms, thanks to the distinctive chemical properties of In 2 Se 3 [6]. Clearly, the Ag 3 In 5 Se 9 semiconductor compounds having 4.24 electrons per atom [7] are the isostructural derivatives of In 2 Se 3 binary compounds with 4.80 electrons per atom which is accomplished by replacing the tetrahedral In cations by Ag atoms [8]. According to the studies, Ag 3 In 5 Se 9 ternary compounds crystallize in hexagonal [9] and tetragonal (chalcopyrite) structure having the lattice constants of a ¼ 6:714, b ¼ 6:714 and c ¼ 10:430 A ˚ with possible space group of either P4 or P4mm (c=a ratio is 1.55) [10]. Density of the single crystals was determined from tetragonal lattice parameters as 5.71 g/cm 3 . The relatively low melting point of 825 8C enables the easier preparation of the single crystals and reduces the degree of contamination significantly during growth cycle of the crystal. Ag–In–Se compounds are the highly photosensitive ternary semiconductors with the optical band gap values lying in the visible and near infrared regions and have n-type electrical www.elsevier.com/locate/apsusc Applied Surface Science 254 (2008) 1569–1577 * Corresponding author. Tel.: +90 312 2103280; fax: +90 312 2105099. E-mail address: parlak@metu.edu.tr (M. Parlak). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.07.092