Spectroscopic ellipsometry determined dielectric function from 0.74 to 9.25 eV and band-to-band transitions in zirconia thin films fabricated by electron-beam-assisted deposition

Zirconia (ZrO2) thin films were fabricated using an ultra-high-vacuum electron-beam physical vapor deposition technique. Spectroscopic ellipsometry (SE) data from multiple samples with different thicknesses were acquired over a broad photon-energy range of 0.74–9.25 eV to determine the frequency-dependent complex dielectric function of ZrO2 thin films. Atomic force microscopy (AFM) analysis confirms the formation of highly uniform films with an average height variation below 2 nm across the scanned areas. In the SE-based optical analysis, a five-layer model consisting of the substrate, native oxide, ZrO2 thin film, surface roughness layer, and ambient was employed within a multi-sample analysis framework. The surface roughness layer was modeled using a 50:50 effective medium approximation of the film and ambient, yielding roughness thicknesses consistent with those obtained from AFM measurements. By parameterizing the intrinsic dielectric response using a set of oscillators, a critical-point model dielectric-function analysis was applied to identify band-to-band transition parameters. These results provide a comprehensive parameterization of the dielectric function of electron-beam-deposited ZrO2 thin films and establish a robust ellipsometry-based framework for correlating thin-film structure and optical properties in ultra-wide-bandgap oxide materials.