Fabrication and electrical characterization of solution-processed all-oxide transparent NiO/TiO 2 p-n junction diode by sol–gel spin coating method M. Cavas & R. K. Gupta & Ahmed. A. Al-Ghamdi & Z. Serbetci & Zarah H. Gafer & Farid El-Tantawy & F. Yakuphanoglu Received: 20 February 2013 / Accepted: 8 April 2013 # Springer Science+Business Media New York 2013 Abstract Solution-processed all-oxide transparent NiO/TiO 2 p-n junction was fabricated using sol–gel spin coating method. The optical properties of the NiO and TiO 2 films were studied by transmittance and absorbance spectra. The optical band gaps of NiO and TiO 2 films were determined by optical absorption method and found to be 3.83 eV and 3.74 eV, respectively. The current–voltage characteristics of the oxides based p-n junction showed a rectifying behavior. The junction parameters such as ideality factor and barrier height were calculated using thermionic emission model, Chenug, and Norde method. The barrier height and ideality factor values of the diode were obtained to be 0.59 eV and 9.8, respectively. Keywords p-n junction . NiO . TiO 2 . Sol–gel . Thin films . Oxide semiconductor 1 Introduction Metal oxide semiconductors have been extensively used for transparent spintronics, optoelectronic devices, photovoltaic applications, and sensors due to their high transparency and conductivity [1–3]. Among various oxide semiconductors, zinc oxide, titanium oxide, nickel oxide, tin oxide are par- ticularly attractive materials [4–7]. Titanium oxide (TiO 2 ) is one of the metal oxides, which is used for various applica- tions such as photovoltaic, sensor due to its natural abun- dance, non-toxic nature, and low cost [3, 8]. TiO 2 is an n-type semiconductor with wide band gap of ~3.5 eV [9]. TiO 2 has been used for fabrication of p-n junctions [10]. Nickel oxide (NiO) has been used as a p-type semiconductor with a band gap of 3.6–4.0 eV at room temperature [11]. Nanostructured p-type NiO film has been fabricated from hydrolysis of nickel acetate to use as a photocathode for a solar cell [12]. The cathodic photocurrent is explained by hole injection from dye molecule to the valence band of the p-type NiO electrode. Among the various techniques used for fabrication of these metal oxide films [13–17], sol–gel method offers many advantages such as low temperature processing, low cost, and easy technology [18]. Cavas et al [19]. have used sol–gel spin coating method to fabricate transparent p-n junctions based on NiO and ZnO as p-type and n-type semiconductor, respectively. The variation of photocurrent with wavelength for NiO/ZnO junction has indicated that the device had high efficiency in wavelength range of 450–475 nm. Lee et al [20]. have fabricated TiO 2 /NiO M. Cavas Maden Higher Vocational School, Firat University, Elazığ, Turkey R. K. Gupta (*) Department of Chemistry, Pittsburg State University, 1701 S. Broadway, Pittsburg, KS 66762, USA e-mail: ramguptamsu@gmail.com A. A. Al-Ghamdi : Z. H. Gafer : F. Yakuphanoglu Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia Z. Serbetci Physics Department, Faculty of Arts and Science, Bingol University, Bingol, Turkey F. El-Tantawy Department of Physics, Faculty of Science, Suez Canal University, Ismailia, Egypt F. Yakuphanoglu (*) Physics Department, Faculty of Science, Firat University, Elazig, Turkey e-mail: fyhan@hotmail.com J Electroceram DOI 10.1007/s10832-013-9822-z