Amorphous Ge-Sb-Se-Te chalcogenide films fabrication for potential environmental sensing and nonlinear photonics

Quaternary Ge-Sb-Se-Te chalcogenide thin films were fabricated by rf magnetron sputtering from Ge₁₉Sb₁₇Se_64−xTe_x (x = 5, 10, 15, 20) sputtering targets in order to select appropriate compositions for infrared sensor and optical nonlinear applications. An influence of chemical composition and deposition parameters on the optical properties, structure and wettability was thus studied. The amorphous thin films seem to be constituted by selenide entities that can include tellurium atoms in variable proportion such as [GeSe_4−xTe_x] and [SbSe_3−xTe_x] (x = 0, 1, 2) and Ge(Sb)-Ge(Sb) bonds according to Raman spectroscopy. Contact angle measurements of the thin films showed values of 68–71° for water and their surface energies in the range of ~36–39 mJ·m⁻² seem suitable for surface functionalization required for photonic sensor development. Furthermore, the maximum nonlinearity at the telecom wavelength with respect to the highest figure of merit value was found for the thin film with composition Ge₁₉Sb₁₇Se₅₆Te₈ having nonlinear refractive index of 28 × 10⁻¹⁸ m²·W⁻¹. Due to their low optical bandgap energies, they may find their full interest for nonlinear optics in the mid-infrared range. Wide IR transparency in combination with high (non)linear refractive indices make these materials attractive in the field of mid-IR sensing and optical nonlinear devices.