Temperature-driven band inversion in Pb0.77Sn0.23Se: Optical and Hall effect studies

Optical and Hall effect measurements have been performed on single crystals of Pb0.77Sn0.23Se, a IV-VI mixed chalcogenide. The temperature-dependent (10-300 K) reflectance was measured over 40-7000 cm-1 (5-870 meV) with an extension to 15 500 cm-1 (1.92 eV) at room temperature. The reflectance was fitted to the Drude-Lorentz model using a single Drude component and several Lorentz oscillators. The optical properties at the measured temperatures were estimated via Kramers-Kronig analysis as well as by a Drude-Lorentz fit. The carriers were p type with the carrier density determined by Hall measurements. A signature of valence intraband transition is found in the low-energy optical spectra. It is found that the valence-conduction band transition energy as well as the free-carrier effective mass reach minimum values at 100 K, suggesting temperature-driven band inversion in the material. Density functional theory calculations for the electronic band structure are also presented.