Characterisation of porous doped ZnO thin films deposited by spray pyrolysis technique

• Published in: Applied surface science Vol. 253; no. 23; pp. 9241 - 9247
• Main Authors: Allah, F. Kadi, Abé, S. Yapi, Núñez, C.M., Khelil, A., Cattin, L., Morsli, M., Bernède, J.C., Bougrine, A., del Valle, M.A., Díaz, F.R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 30.09.2007; Elsevier Science
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electrical properties of specific thin films; Electrical properties of specific thin films and layer structures (multilayers, superlattices, quantum wells, wires, and dots); Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Optical and electrical properties; Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity); Optical constants: refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Physics; Scanning electron microscopy; Spray coating techniques; Spray pyrolysis; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; X-ray diffraction; Zinc oxide; X-ray diffraction; Scanning electron microscopy; Zinc oxide; Optical and electrical properties; Spray pyrolysis; Grain boundaries; Disordered systems; Inorganic compounds; Electrical conductivity; Porous materials; XRD; Surface structure; Thin films; Aqueous solutions; Absorption spectra; Grain size; Pyrolysis; Annealing; Transition element compounds; Crystallization; Doped materials; Free carrier; Tin additions; Zinc oxides; Aluminium additions; Porosity; Carrier density
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2007.05.055

Al or Sn doped ZnO films were deposited by spray pyrolysis using aqueous solutions. The films were deposited on either indium tin oxide coated or bare glass substrates. ZnCl 2, AlCl 3 and SnCl 2 were used as precursors. The effect of ZnCl 2 molar concentration (0.1–0.3 M) and doping percentage (2–4% AlCl 3 or SnCl 2) have been investigated. The main goal of this work being to grow porous ZnO thin films, small temperature substrates (200–300 °C) have been used during the spray pyrolysis deposition. It is shown that, if the X-ray diffraction patterns correspond to ZnO, the films deposited onto bare glass substrate are only partly crystallized while those deposited onto ITO coated glass substrate exhibit better crystallization. The homogeneity of the films decreases when the molar concentration of the precursor increases, while the grain size and the porosity decrease when the Al doping increases. The optical study shows that band tails are present in the absorption spectrum of the films deposited onto bare glass substrate, which is typical of disordered materials. Even after annealing 4 h at 400 °C, the longitudinal resistivity of the films is quite high. This result is attributed to the grain boundary effect and the porosity of the films. Effectively, the presence of an important reflection in the IR region in samples annealed testifies of a high free-carriers density in the ZnO crystallites. Finally it is shown that when deposited in the same electrochemical conditions, the transmission of a polymer film onto the rough sprayed ZnO is smaller than that onto smooth sputtered ZnO.