Applied Surface Science 257 (2011) 10072–10077 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om epa g e: www.elsevier.com/locate/apsusc Investigations on structural, vibrational, morphological and optical properties of CdS and CdS/Co films by ultrasonic spray pyrolysis S. Aksay a,∗ , M. Polat b , T. Özer a , S. Köse b , G. Gürbüz b a Department of Physics, Anadolu University, TR-26470, Eskis ¸ ehir, Turkey b Department of Physics, Eskis ¸ ehir Osmangazi University, TR-26020, Eskis ¸ ehir, Turkey a r t i c l e i n f o Article history: Received 7 February 2011 Received in revised form 29 June 2011 Accepted 30 June 2011 Available online 7 July 2011 Keywords: Cds/co films X-ray diffraction Optical materials AFM FTIR Raman a b s t r a c t CdS and CdS/Co films have been deposited on glass substrates by an ultrasonic spray pyrolysis method. The effects of Co incorporation on the structural, optical, morphological, elemental and vibrational properties of these films were investigated. XRD analysis confirmed the hexagonal wurtzite structure of all films and had no impurity phase. While CdS film has (0 0 2) as the preferred orientation, CdS/Co films have (1 1 0) as the preferred orientation. The direct optical band gap was found to decrease from 2.42 to 2.39 eV by Co incorporation. The decrease of the direct energy gaps by increasing Co contents is mainly due to the sp–d exchange interaction between the localized d-electrons of Co 2+ ions and band electrons of CdS. After the optical investigations, it was seen that the transmittance of CdS films decreased by Co content. The Raman measurements revealed two peaks corresponding to the 1LO and 2LO modes of hexagonal CdS. The vibrational modes of Cd–S were obtained in the wavenumber range (590–715 cm -1 ) using Fourier transform infrared spectroscopy (FTIR). The elemental analysis of the film was done by energy dispersive X-ray spectrometry. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Cadmium sulphide (CdS) is an n-type semiconductor with a direct band gap of 2.4 eV, which falls in the visible spectrum at room temperature. Because of its wide band gap, CdS is used as a window material for heterojunction solar cells. It has also application in light-emitting diodes (LED) [1], gas detectors [2], photovoltaic cells [3–5], nonlinear optics [6], and thin film tran- sistors [7]. Transition-metal (TM) doped CdS systems are highly promising diluted magnetic semiconductors (DMSs) for applica- tions requiring ferromagnetism near room temperature. DMSs in II–VI semiconductors systems have attracted much interest for potential applications in spintronics and microelectronics [8–13]. Particularly in recent years, spintronic devices such as spin-valve transistors, ultrafast optical switches and optical isolators have stimulated great passions of many researchers for introducing room temperature ferromagnetism in CdS materials [12,13]. Dop- ing with TM elements leads to many interesting properties of CdS. Doping of CdS films incorporating various elements such as Sn [14], Sb [15], Cu [16,17], B [18], Mn [9,19], Fe [20], Co [8,10,12,13,21,22], ∗ Corresponding author. Tel.: +90 222 3350580; fax: +90 222 3204910. E-mail address: saksay@anadolu.edu.tr (S. Aksay). In [23,24] and Ni [25] have already been studied. The properties (electrical, optical and magnetic) of CdS is strongly modified by the doping of Fe 2+ , Mn 2+ , Ni and Co 2+ [20,21,26,27] because of the sp–d exchange interaction between the localized d electrons of the transition metal magnetic ions and the mobile carriers in the con- duction or valance band. Among these metallic elements, Co is an important transition metal element. The ion radius of Co 2+ (0.74 ˚ A) is smaller than that of Cd 2+ (0.97 ˚ A), which means that Co 2+ can easily penetrate into CdS crystal lattice or substitute Cd 2+ position in crystal [8]. CdS and Co-doped CdS films with good structural, magnetic and optical qualities have been reported from a vari- ety of techniques such as ion implantation [21], aqueous chemical coprecipitation [13], high energy electron irradiation [22], spray pyrolysis [12] and surfactant-assisted synthesis [8]. Among these, the spray pyrolysis method is simple, cost effective and suitable for large area thin film preparation with homogenous doping level [14,15,23,25,26]. Raman scattering and FTIR vibrations mode are sensitive to different features such as stress, defects, structural disor- der and local atomic arrangement [15]. -CdS belongs to the hexagonal (wurtzite) per primitive cell where all the atoms occupy C 6  (P6 3 mc) sites. Group theory predicts, at the Ŵ point of the Brillouin zone, the existence of following optic modes:  opt = A 1 + 2B 1 + E 1 + 2E 2 [21,28], where A 1 and E 1 modes are polar 0169-4332/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2011.06.142