La-doping content effect on the optical and electrical properties of La-doped ZnO thin films

La-doped ZnO films with a series of La content were deposited by a chemical solution deposition and characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray energy dispersion spectrometry, ultraviolet–visible and luminescent spectrophotometries, and electrical resistance measurement. The transmittance and electrical conductivity of the films increased and then decreased with increasing La content. The film with actual La content of 0.14 at.% showed a lowest optical absorbance, a widest bandgap of 4.08 eV, and a minimal resistance of 3.3 × 10−1 Ω cm. The films showed a strong near band gap emission and some weak emissions related to intrinsic defects, implying near perfect crystal structure. The refractive index, extinction coefficient, optical conductivity, dielectric constant of the films were calculated with the transmittance and reflectance spectra.