Thermoreflectance of IV–VI compounds

We have measured thermoreflectance spectra of epitaxial PbS, PbSe, PbTe, and SnTe films from 0.7 to 5.6 eV, at room temperature and 77 K. Fine structures associated with the usual reflectivity peaks are observed, most of which agree in spectral position with electric field and wavelength modulation results. Δε_r and Δε_i have been obtained through a Kramers-Kronig analysis of our Δ R/R spectra. In the absence of experimental symmetry information, tentative assignments are made based on (1) comparison of temperature coefficients with theoretical deformation potentials, (2) comparison of δε curves with theoretical lineshapes, and (3) matching the structures with existing band structure calculations and related information.