Applied Surface Science 306 (2014) 47–51 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Relevance of annealing on the stoichiometry and morphology of transparent thin films P. Prepelita a,∗,1 , V. Craciun a , G. Sbarcea b , F. Garoi a a National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Street, PO Box MG-36, 077125 Magurele, Ilfov, Romania b ICPE – CA, Splaiul Unirii 313, Sector 3, 74204 Bucharest, Romania a r t i c l e i n f o Article history: Received 26 November 2013 Received in revised form 10 February 2014 Accepted 12 February 2014 Available online 22 February 2014 Keywords: Thin films Polycrystalline Surface morphology ZnO:Al SnO2 ITO Annealing a b s t r a c t Transparent thin films of SnO 2 , ZnO:Al, and ITO were deposited onto glass substrate by vacuum thermal evaporation technique, from 0.5 cm diameter grains (i.e. ITO, ZnO:Al (3%) and SnO 2 ) with 99.99% purity. To improve the quality (i.e. stoichiometry and morphology) of these thin films, they were annealed at 400 ◦ C in air for 2 h. Following this annealing, the samples become suitable to be used as contact electrodes for solar cells. The investigations were performed on samples having a polycrystalline structure, as revealed by X- ray diffraction analysis after annealing process. Moreover, these thin films had a strong orientation with the following planes parallel to the substrate: (1 0 1) for SnO 2 , (0 0 2) for ZnO:Al and (2 2 2) for ITO film respectively. Atomic force microscopy (AFM) investigations of the ZnO:Al (R rms = 2.8 nm) and ITO samples (R rms = 11 nm) show they are homogeneous and a slightly higher roughness (R rms = 51 nm) for the SnO 2 thin film surface. The size and shape of the grains were also observed and investigated by scanning elec- tron microscopy (SEM). All SnO 2 , ZnO:Al and ITO transparent thin films are uniform and dense.The values obtained for electrical resistivity, transmission and energy bandgap as well as conductivity and trans- parency properties of these thin films, make them suitable to be used as transparent contact electrodes for solar cells. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Transparent and conductive oxide (TCO) thin films, such as alu- minum doped zinc oxide (ZnO:Al), indium tin oxide (ITO) and tin oxide (SnO 2 ), are the target for advanced research technolo- gies due to their versatile properties than can be applied to gas sensors [1], optoelectronics [2], solar cells [3], and displays. Occu- pying one of the priority fields of the worldwide scientific research, these materials are integrated within the structures of solar cells as transparent contact electrodes. Equally, used as transparent con- tact electrodes, these layers illustrate a possible improvement in performance of the solar cell [3]. N. Baydogan [2] showed that ZnO thin films doped with 1.2 at% Al have decreasing resistivity with increasing annealing temper- ature, and T.L. Chen [4] obtained highly stable Al-doped ZnO transparent conductors using an oxidized ultrathin metal capping layer at its percolation thickness. The properties of ZnO:Al thin films ∗ Corresponding author. Tel.: +40 21 4574467; fax: +40 21 4574467. E-mail address: prepelitapetro@yahoo.co.uk (P. Prepelita). 1 Married as Garoi. make them suitable for their use in various electronic applications, as well as their integration in solar cells as window layer [5]. The excellent electrical and optical properties of ITO thin films have been exploited in many applications [6]. However, the thicker the layer the higher the charge carriers concentration as well as the conductivity, but the lower the transparency of the material. The conductivity of ITO thin films is increased by improvements in crystalline structure. Therefore, it is important to choose a proper deposition technique followed by an appropriate annealing treat- ment to further improve their optical and electrical properties [6,7]. Note that tin oxide (SnO 2 ) thin films have a bandgap of 3.6 eV, as well as other noteworthy properties [1,8]. All these oxide thin films can be deposited by several meth- ods, such as: vacuum thermal evaporation [9], spray pyrolysis [10], pulsed laser deposition [6,11], sol gel [12], spin coating [13] or radio frequency (RF) magnetron sputtering [14]. Post-deposition annealing in various ambient conditions reduces defect concentration in amorphous and crystalline films, leading to a higher electron mobility. SnO 2 thin films showed a compact and homogeneous structure, with an optical transmis- sion around 80% in the visible range of the spectrum [15]. It has been used as transparent conductive contact on glass substrate to achieve ZnTe/CdSe heterojounctions [9]. http://dx.doi.org/10.1016/j.apsusc.2014.02.063 0169-4332/© 2014 Elsevier B.V. All rights reserved.