Far-infrared spectroscopy of CdTe1−xSex(In): Phonon properties

•Optical properties were investigated applying far-infrared spectroscopy.•Dielectric function which includes spatial distribution of free carriers were used.•The long wavelength optical phonons exhibit a two-mode behavior.•The local In mode at about 160 cm−1 is observed.•Surface layers with a low concentration of free carriers are formed.

The far-infrared reflectivity spectra of CdTe0.97Se0.03 and CdTe0.97Se0.03(In) single crystals were measured at different temperatures. The analysis of the far-infrared spectra was carried out by a fitting procedure based on the dielectric function which includes spatial distribution of free carriers as well as their influence on the plasmon–phonon interaction. We found that the long wavelength optical phonon modes of CdTe1−xSex mixed crystals exhibit a two-mode behavior. The local In mode at about 160 cm−1 is observed. In both sample, a surface layer with a low concentration of free carriers (depleted region) are formed.