An effect of lanthanum doping on physical characteristics of FTO thin films coated by nebulizer spray pyrolysis technique

Abstract

In order to enhance the optoelectronic properties of the FTO material, the rare earth element lanthanide (La) was doped at various doping concentrations (0–1.5 wt. %) by a simple and low-cost nebulizer spray pyrolysis (NSP) technique. X-ray diffraction, Raman spectrum, AFM, EDAX, UV–Vis, Photoluminescence (PL), and Hall Effect measurements were used to study the influence of La on FTO. From the XRD, the films prepared were polycrystalline with the tetragonal crystal structure. By increasing La doping concentration, the intensity of the predominant peak (110) and the crystalline size were decreased. The peaks at 467 cm−1, 573 cm−1, and 780 cm−1were observed in low-frequency regions associated with Eg, Eu, and B2g vibration modes respectively. AFM study confirmed the decreasing nature of the surface roughness for the doped films. 1.5 wt. % of La-doped thin film showed high optical transmittance, minimum reflectance with absorbance and further noticed that the increasing band gap values (3.75eV–3.92eV) with increasing La content. The values of the refractive index, extinction coefficient, the real and imaginary part of dielectric constants were calculated and discussed in detail. Photoluminescence spectra displayed the highest emission peak at 370 nm is due to near band edge emission. Hall measurement showed high carrier concentration (7.14 × 1019 cm−3) and low resistivity (3.04 × 10−3 Ω cm) values for 1.5 wt. % La-doped film. The figure of merit 1.1 × 10−3 Ω-1 was also obtained for the same film which perfectly can be used for optoelectronic devices.