Thermoreflectance spectra of CdO: Band gaps and band-population effects

Abstract

Thermoreflectance spectra of semiconducting CdO single crystals at 100\ifmmode^\circ\else\textdegree\fi{}K with carrier concentrations in the range (2-40) X ${10}^{18}$/${\mathrm{cm}}^{3}$ give 2.28 eV for the direct ${\ensuremath{\Gamma}}_{15}\ensuremath{-}{\ensuremath{\Gamma}}_{1}$ gap. Two indirect gaps are found: ${L}_{3}\ensuremath{-}{\ensuremath{\Gamma}}_{1}$ at 1.09 eV and ${\ensuremath{\Sigma}}_{3}\ensuremath{-}{\ensuremath{\Gamma}}_{1}$ at 0.84 eV. Theoretical calculations of the shape of the spectrum, taking explicitly into account the band-population effects, are in qualitative agreement with the experimental results. The spectra of sputtered films of CdO differ substantially from single-crystal spectra, suggesting structural differences between films and crystals.