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 Ge_(19)Sb_(17)Se_(64-x)Te_(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-x)Te_(x)]and[SbSe_(3-x)Te_(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 68e71for water and their surface energies in the range of~36e39 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 Ge_(19)Sb_(17)Se56Te8 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 midIR sensing and optical nonlinear devices.

Insight into the photoinduced phenomena in ternary Ge-Sb-Se sputtered thin films

The kinetics of photoinduced changes,namely,photobleaching and photodarkening in sputtered ternary GeSbSethin films,was studied.The study of time evolution of the absorption coefficientΔα(t)upon roomtemperature near-bandgap irradiation revealed several types of photoinduced effects.The as-deposited films exhibited a fast photodarkening followed by a dominative photobleaching process.Annealed thin films were found to undergo photodarkening only.The local structure studied by Raman scattering spectroscopy showed significant structural changes upon thermal annealing,which are presumably responsible for a transition from the photobleaching observed in as-deposited and reversible photodarkening in annealed thin films.Moreover,a transient photodarkening process was observed in both as-deposited and annealed thin films.The influence of the initial film thickness and laser optical intensity on the kinetics of photoinduced changes is discussed.