Modeling the optical properties of sapphire ( α-Al 2O 3)

Abstract

Optical properties of sapphire α-Al 2O 3 for parallel and perpendicular polarization are modeled in the spectral range 0.2–20 eV. The modified Lorentz model with frequency dependent damping, which enables adjusting the broadening function over a range of functions with similar kernels but different wings, is employed. Due to greater flexibility of the employed model, we obtain excellent agreement with experimental data for both polarizations in the entire investigated spectral range with a total of 8 oscillators, i.e. 33 parameters. In the previous study reporting modeling of the optical constants of sapphire in the range 1–30 eV using conventional damped harmonic oscillator model, 13 oscillators with a total of 40 parameters were used. Good agreement with the imaginary part but significant discrepancies for the real part of the dielectric function obtained in the previous study were attributed to possible inconsistencies in the experimental data, based on the fact that a damped harmonic oscillator model automatically satisfies KK relations. However, we obtain good agreement with experimental data for both real and imaginary parts of the dielectric function using our model. Therefore, we conclude that the main reason for the discrepancy in the previous study is inadequacy of the assumption of Lorentzian line broadening.