Optical and structure properties of amorphous Ge-Sb-Se films for ultrafast all-optical signal processing

In this paper, we deposited amorphous chalcogenide Ge-Sb-Se films using the RF sputtering method, then measured their optical and structural properties using various diagnosis tools. The linear refractive index and optical band-gap for as-deposited films were analyzed as a function of the chemical composition and the mean coordination number (MCN). The third-order optical nonlinearities were predicted by applying the Z-scan method combined with a model developed by Sheik-Bahae. The relationship between film compositions and the optical properties was analyzed by Raman spectra in terms of structural evolution. The data suggests that the "defect" gap states in the network play an important role in the thirdorder optical nonlinearity of these chalcogenide films. The Ge20Sb15Se65 films most suitable for all-optical signal processing applications had large nonlinear refractive indices (8.735 1015 m2/W), moderate nonlinear absorption (8.592 109m/W) and showed an ultrafast nonlinear response time (66 fs).