Optical properties of tellurium-based chalcogenide alloys in the far infrared region ($\lambda$ > 30 $\mu$m)

Ternary telluride alloys of Ge–Se(Sb)–Te and Si–Ge(Ga)–Te systems are synthesized in glassy and crystalline states for use in the terahertz frequency range. The transmission spectra of the obtained alloys are measured and studied in a wide wavelength range from 0.75 to 300 $\mu$m. The possible mechanisms of their formation are discussed. A comparative analysis of the results shows that the Ge$_{14}$Sb$_{28}$Te$_{56}$ alloy of the GST system is most promising. Its phonon spectrum is in the range of 40–280 cm$^{-1}$, limiting the long-wavelength transmission window of this alloy by 35 $\mu$m. Optimization of the Ge$_{14}$Sb$_{28}$Te$_{56}$ composition, the removal of impurities, and heat treatment will promote a further decrease in the absorbance in the far-infrared spectrum of this alloy.