Optical Characterization of As₅Se₄₅Te₃₅Ge₁₅ Chalcogenide Glass: Absorption, Band Gap, and Dispersion Properties

Abstract

An exhaustive optical characterization of melt-quenched As₅Se₄₅Te₃₅Ge₁₅ chalcogenide glass was carried out with ultraviolet-visible-near infrared spectroscopy in the 200-1100 nm region. Absorption spectra show strong absorption in the ultraviolet region (10⁴-10⁵ cm-¹), followed by gradually decreasing absorption in the visible and near infrared region. This behavior indicates it is an amorphous semiconducting glass with localized band tail states. Tauc plots indicate indirect optical band gap transitions, whereas Urbach plots indicate disorder-induced exponential absorption tails. Refractive index measurements indicate normal dispersion characteristics and high electronic polarizability due to As-Se/Tebonding and the presence of heavy chalcogen atoms. It was observed that the extinction coefficient diminishes monotonically with increments in wavelength, indicating lowered optical loss in the visible and NIR region. Also, the real and imaginary parts of the complex dielectric constant diminish with increments in wavelength, along with reduced dielectric loss. It was observed that the addition of arsenic increases cross-link density in the Se-Te-Ge network, enabling tailoring of its electronic structure and optical parameters. These results ascertain that As₅Se₄₅Te₃₅Ge₁₅ glass has the potential to be utilized for infrared photonics, nonlinear optics, and phase-change memory.