Reflectance and Thermoreflectance of GeTe

The reflectance spectra of p‐type GeTe crystals are measured in the energy range 0.4 to 3.0 eV at liquid nitrogen and room temperature. The principal optical constants are obtained by inverting the spectra using the Kramers‐Kronig technique. The thermoreflectance spectra at room and liquid nitrogen temperature are measured over the energy range from 0.8 to 3.0 eV. The results are quantitatively interpreted. The relatively large and sharp changes in the thermoreflectance spectra near 1 eV are explained with the thermal width of the Fermi function, and with δ‐type transitions at 1.36 eV.