Applied Surface Science 301 (2014) 216–224 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Effect of nickel doping on physical properties of zinc oxide thin films prepared by the spray pyrolysis method M. Jlassi a,∗ , I. Sta a , M. Hajji a,b , H. Ezzaouia a a Laboratoire de Photovoltaïque, Centre de Recherche et des Technologies de l’Energie, Technopole de Borj-Cédria, BP 95, 2050 Hammam-Lif, Tunisia b Ecole Nationale d’Electronique et des T´ el´ ecommunications de Sfax, Université de Sfax, BP 1163, CP 3021 Sfax, Tunisia a r t i c l e i n f o Article history: Received 3 September 2013 Received in revised form 12 January 2014 Accepted 10 February 2014 Available online 18 February 2014 Keywords: Physical properties Spray pyrolysis Zinc oxide Nickel doping a b s t r a c t In this study, undoped and nickel-doped zinc oxide thin films (ZnO:Ni) were deposited on glass substrates using a spray pyrolysis technique. The effects of the Zn concentration in the initial solution and the sub- strate temperature on the physical properties of the thin films are studied. The results show that the optimum Zn concentration and substrate temperature for preparation of basic undoped ZnO films with n-type conductivity and high optical transparency are 0.02 M and 350 ◦ C, respectively. Then, by using these optimized deposition parameters, nickel-doped zinc oxide films are prepared. Surface morphol- ogy and crystalline structure of the films are investigated by atomic force microscopy (AFM) and X-ray diffractometer. X-ray diffraction (XRD) patterns show that the films are polycrystalline. The structural analysis shows that all the samples have a hexagonal structure. The crystallite size and the preferred orientation were calculated from the XRD data. From AFM investigations, the surface morphology of the nanostructured films is found to depend on the concentration of Ni. Optical measurements have shown that an increase in the Ni doping results in a reduction in the optical transmission of the layer, but it remains higher than 80% for Ni doping greater than 8 wt%. At the same time, the optical gap increases from 3.4 to 4 eV when the Ni ratio increases. The electrical measurements show that the resistance of the films varies with the duration of pulverization and the nickel content of the film. Low values for the electrical resistivity (around 10 3  cm) were obtained for Ni-doped ZnO thin films. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Nanostructured materials have received much attention because of their novel properties, which differ from those of bulk materials [1,2]. Control of the dimensions and morphology of materials has attracted the interest of researchers in the design of functional devices due to the optical and electronic properties of nanometer and micrometer-size materials, which determine their applications by varying their size and shape [3]. ZnO is a semiconducting material with a direct band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature and has being intensely studied [4,5]. The electrical conductivity of ZnO thin films is natively n-type, originating from Zn atoms in interstitial sites or oxygen vacancies. ZnO nanostructures exhibit novel electronic and optical properties due to a variety of growth planes, formed during creation of the nanostructures. The control ∗ Corresponding author. Tel.: +216 23894370. E-mail address: mohamedjlassilpv@yahoo.fr (M. Jlassi). of ZnO nanostructure properties can be achieved by appropriate doping processes. ZnO doping can be achieved by adding a small amount of group III elements (such as B, Al, In, or Ga) or IV elements (such as Pb, Sn). It is well known that the addition of dopants into a wide gap semiconductor, such as ZnO, can often induce dramatic changes in the optical, electrical, and magnetic properties [6,7]. Therefore, a selective doping element into ZnO has become an important route for enhancing and controlling its optical and electrical performance, which are crucial for practical applications [6]. Several studies on Ni-doped ZnO have been reported, which showed that the optical and electrical properties of ZnO changed after doping with Ni. Recently, special attention has been devoted to the morphology of Ni-doped ZnO for various nanostructures [8,9]. Thermal stability, irradiation resistance, and flexibility of nanostructures are the advantages that expedite their potential wide applications in photodetectors [10], surface acoustic wave devices [11], ultraviolet nanolasers [12], varistors [13], solar cells [14], gas sensors [15], biosensors [16], ceramics [17], field emission [18], and nanogenerators [19]. Self-assembly using physical and chemical methods has been extensively explored for generating http://dx.doi.org/10.1016/j.apsusc.2014.02.045 0169-4332/© 2014 Elsevier B.V. All rights reserved.