Some physical investigations on hexagonal-shaped nanorods of lanthanum-doped ZnO

Abstract Lanthanum-doped Zinc oxide (ZnO:La) thin films were successfully grown on glass substrates by the spray pyrolysis technique at 460 °C. Alternatively, some of the obtained films were doped with lanthanum at the molar rates of: 1, 2, 3 and 4%. The structural properties of the prepared samples were characterized by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). It is shown that ZnO:La thin films crystallize in hexagonal wurtzite structure with a preferred orientation of the crystallites along (002) direction. Also, Raman spectroscopy shows the bands corresponding to ZnO structure and confirms the presence of La2O3 secondary phase. Furthermore, it is found that the lattice parameters a and c of La-doped ZnO films decrease with La content. UV-vis measurements show that the average transmittance of the ZnO:La thin films is 75% and the average reflectance is less than 25% in the visible range. In the same line, it is noted that the optical band gap, Urbach energy, and the optical constants are significantly influenced by the lanthanum incorporation. The photoluminescence (PL) measurements exhibit emission in the visible region (a strong band located around 480 nm and a weak band around 420 nm). The intensity of level emission varies with La doping. Moreover, it is observed a significant variation of both electrical resistivity and activation energy with La concentration. The electrical conductivity of films dependence of temperature was measured to reach the dominant conductivity mechanism. © 2015 Elsevier B.V.