Optical and structural properties of aluminium nitride thin-films synthesized by DC-magnetron sputtering technique at different sputtering pressures

Abstract

Aluminium nitride thin-films (AlN) were fabricated by a DC-magnetron sputtering technique at different background pressures while maintaining the same deposition conditions. The influence of varying sputtering pressure on the structural and optical properties of AlN thin-films was investigated. XRD measurements were utilized to determine the structural properties of the deposited AlN thin-films such as strain, stress, crystallite size, and crystalline density. They confirmed the hexagonal wurtzite structure of AlN thin-films and the increase in the degree of c-axis orientation as the sputtering pressure decreases. The optical properties of AlN thin-films, deposited on glass substrates, were analyzed by means of transmittance and absorption spectra using a UV–Vis spectrophotometer. The results have shown that an increase in the sputtering pressure leads to a shift of the threshold transmittance towards the lower wavelength range. This results in widening the optical bandgap and decreasing both the refractive index and the extinction coefficient. The dispersion of the refractive index is investigated according to the Wemple–DiDomenico single oscillator model and the model parameters (such as effective single oscillator E0, dispersion energy Ed, zero-frequency dielectric constant e0 and optical moments) were estimated accordingly.