Terahertz spectroscopic characterization of Ge3Sb2Te6 compounds for active applications

A study of the optical and dielectric properties of the non-volatile chalcogenide phase change material Ge₃Sb₂Te₆ in the terahertz band (0.5–2.5 THz) is presented. Thermally annealed thin films of this material have been characterized with THz time-domain spectroscopy (THz-TDS), in addition to X-ray diffraction (XRD) and Raman spectroscopy. Optical constants, dielectric properties, and THz conductivity were derived from the THz-TDS data using a numerical method that takes into account the strong etalon effect of the thin film. The results are compared to the properties of Ge₂Sb₂Te₅, which is commonly employed in photonics. Remarkably, Ge₃Sb₂Te₆ exhibits considerably lower losses along the metal-to-insulator (MIT) transition. It has also been found that Ge₃Sb₂Te₆ is more robust and that its optical constants are less affected by the substrate material. These results suggest that Ge₃Sb₂Te₆ is potentially a more suitable candidate for high-performance applications requiring high contrast in the refractive index and low loss, such as in THz beam steering.