Critical-point model dielectric function analysis of WO₃ thin films deposited by atomic layer deposition techniques

WO₃ thin films were grown by atomic layer deposition and spectroscopic ellipsometry data gathered in the photon energy range of 0.72-8.5 eV, and from multiple samples were utilized to determine the frequency dependent complex-valued isotropic dielectric function for WO₃. We employ a critical-point model dielectric function analysis and determine a parameterized set of oscillators and compare the observed critical-point contributions with the vertical transition energy distribution found within the band structure of WO₃ calculated by the density functional theory. The surface roughness was investigated using atomic force microscopy, and compared with the effective roughness as seen by the spectroscopic ellipsometry.