Far-infrared reflection spectra of HgSe

Reflectivity of HgSe (N = 2.0 × 10¹⁸-4.2 × 10¹⁷ cm^-3) was measured in the spectral region from 2–100 μm at temperatures between 95 and 300 K. The frequency of the transverse optical phonon ω_t = 132 ± 2 cm^-1 was determined from Kramers-Kronig analysis. The ω+ mode of the plasmon-LO phonon coupled modes is shown to depend anomalously on temperature. Two extra bands of unknown origin were also observed at about 110 and 120 cm^-1.