Ordinary and extraordinary dielectric functions of rutile SnO2 up to 20 eV

Abstract

Spectroscopic ellipsometry at room temperature is applied in order to determine the ordinary (ε⊥) and extraordinary (ε∥) dielectric functions (DFs) of rutile SnO2 corresponding to electric field (E) polarization perpendicular (E⊥c) and parallel (E∥c) to the optical axis (c), respectively. Strong anisotropic behavior is found for the full spectral range from 0.5 up to 20 eV. The onsets of strong absorption are found at 4.28 eV and 5.42 eV for E⊥c and E∥c, respectively. A dipole-forbidden band gap at (3.59 ± 0.2) eV at room temperature is found by line shape fits to the imaginary parts of the DFs. Further high-energy transitions are resolved. Their accurate energy values are obtained by fitting the second derivatives of the DFs. Comparison to published DFs calculated by ab-initio theory demonstrates that the electron-hole interaction in SnO2 is strong and has to be included for interpretation.