Optical properties of Al-doped ZnO thin films obtained by the method of high-frequency magnetron sputtering

The optical constants and thickness of Al-doped ZnO (ZnO:Al(2.5 wt.%)) thin films prepared by high-frequency magnetron sputtering method are determined. ZnO:Al thin films are crystallized in the hexagonal structure from XRD studies. The optical constants and the bandgap of the films under study have been determined. Optical properties (refractive index n(lambda), absorption coefficient alpha(lambda), extinction coefficient k(lambda), dielectric functions ?(lambda) and optical conductivity sigma(lambda)) of thin films and thickness d can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. Single oscillator energy and dispersion energy are obtained from fitting. Optical parameters of the films were determined using the Cauchy, Sellmeier and Wemple models. The increasing value of dispersion parameter for polycrystalline thin films than for single crystals is observed. The fundamental absorption edge position (3.26 eV) in the transmittance spectrum of studied thin films corresponds to the values that are typical for ZnO:Al compound. No significant increase of the bandgap width was revealed by comparing ZnO:Al thin films with the known results of the optical studies of ZnO thin films. Possible reasons of such behavior were analyzed and the influence of bandgap increase on spectral behavior of optical functions are investigated. The material optical parameters such as normalized integrated transmission, zero and high-frequency dielectric constant, density of state effective mass ratio were also calculated.

Automated summary

The optical constants and thickness of Al-doped ZnO thin films were determined using high-frequency magnetron sputtering method. The films were crystallized in hexagonal structure and the optical properties and bandgap were determined. Various optical parameters were analyzed using different models, showing differences between ZnO:Al thin films and known ZnO thin films.