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

Thermoreflectance spectra of semiconducting CdO single crystals at 100^∘{}K with carrier concentrations in the range (2-40) X 10¹⁸/cm³ give 2.28 eV for the direct Γ₁₅-Γ₁ gap. Two indirect gaps are found: L₃-Γ₁ at 1.09 eV and Σ₃-Γ₁ 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.