Effect of La doping on ZnO thin films physical properties: Correlation between strain and morphology

• Published in: Optik (Stuttgart) 2019-02, Vol.180, p.1018-1026
• Main Authors: Maache, A., Chergui, A., Djouadi, D., Benhaoua, B., Chelouche, A., Boudissa, M.
• Format: Article
• Language: English
• Subjects: Dip coating; La doped ZnO; Surface morphology; Thin films; x-Ray diffraction
• ISSN: 0030-4026; 1618-1336
• DOI: 10.1016/j.ijleo.2018.11.002

•La-doped ZnO thin films with molar rates of La/Zn were elaborated by dip coating process.•Single c oriented 0–5% La-doped ZnO thin films were deposited on 375 °C heated glass.•Transmittance of all thin films, in the visible region, is over 90%.•The surfaces morphologies of the films are affected by the strain/stress values. Single c oriented La-doped ZnO thin films with 0–5% molar rates of La/Zn, were deposited successfully through dip coating process on a glass substrate. Effect of La doping on structural, morphological, and optical properties have been investigated. Hexagonal wurtzite ZnO structure with c-axis orientation was identified by X-ray diffraction (XRD) and La substitution was confirmed by XRD based on the peaks shift towards lower angles. The grain size was about 9–15 nm. The film in-plane stress σ affects strongly the samples surface morphology. Strain and surface morphologies were correlated. SEM images exhibit wrinkle micro-rod (μR) like structures with mean diameter ranged in 0.67–1.68 μm. AFM images reveal obvious variations in the samples surface morphology which confirm what seen in SEM images. The morphologies of such surfaces were affected by the strain/stress values. The transmittance of all films, in the visible region, is over 90%. Calculated optical band gap, from the first derivative of transmittance versus energy, exhibits an important increase upon the amount of La ions in ZnO matrix. Electrically, the films become more resistive with the increasing level of La doping due to grain boundary scattering limitations. As found in this work, the synthesized thin films with single c orientation serve as polarized substrates in water treatment.