Optical Studies of Al2O3:ZnO and Al2O3:TiO2 Bilayer Films in UV-VIS-NIR Spectral Range

In this work, the results of ellipsometric studies of bilayer films of broadband oxides (Al2O3:ZnO, Al2O3:TiO2) are presented. Thin layers of Al2O3,ZnO and TiO2 were deposited on silicon substrate using the atomic layer deposition (ALD) method. The desired ranges of antireflective properties were selected, and then, based on optical modeling, the appropriate thicknesses of individual layers were determined. Optical constants were determined based on ellipsometric measurements in the spectral range of 193–1690 nm. For several selected samples, this range has been extended to 470–6500 cm−1. B-spline function, Tauc–Lorentz, Cody–Lorentz and Psemi-M0 oscillator models were used to describe the optical properties of the investigated films. Reflectance spectra for layers on a silicon substrate were determined in the range from 200 to 2500 nm. Additionally, complementary studies, SEM and EDS analyses, were also performed. The EDS investigations enabled the determination of the composition of the bilayer films. Spectrophotometric analysis demonstrated consistency between the obtained experimental data and theoretical predictions, confirming the validity of the applied model. The studies showed significant improvement in antireflective properties depending on the thickness of the prepared layers while maintaining an extinction coefficient close to zero, across much of the investigated spectral range, regardless of the layer thickness.