Optical constants of Na-doped ZnO thin films by sol–gel method

The structural and optical properties of pure and Na-doped ZnO thin films have been investigated by X-ray diffraction (XRD), atom force microscopy and UV–Vis spectrophotometer. The crystal structure of all the thin films is the hexagonal wurtzite. The average grain size and surface roughness increases with the increase of the Na/Zn ratio. The optical band gap of the thin films decreases from 3.26 to 3.12 eV by increasing the Na/Zn ratio from 0.0 to 0.10. Transmittance spectra were used to determine the optical constants of the thin films, and the effect of Na/Zn ratio on the optical constants was investigated. With the increase of Na/Zn ratio, the refractive index decreases and the extinction coefficient increases in the 380–700 nm spectral range.

Research Highlights
► Transmittance spectra have been used to determine the optical constants.
► Refractive index decreases with Na/Zn ratio increases.
► Increasing Na/Zn ratio will decrease optical band gap.
► The effect of microstructure on the optical constants has been investigated.