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

• GeSe4, Ge15Sb15Se70, Ge20Sb15Se60, Ge27Sb13Se60, Ge28Sb12Se60 films were fabricated.
• Films have large nonlinear refractive index and moderated nonlinear absorption.
• The ultrafast nonlinear response of the chalcogenide film is presented.
• The homopolar bonds in the network play an important role in the optical properties.

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 third-order optical nonlinearity of these chalcogenide films. The Ge20Sb15Se65 films most suitable for all-optical signal processing applications had large nonlinear refractive indices (−8.735 × 10−15 m2/W), moderate nonlinear absorption (8.592 × 10−9m/W) and showed an ultrafast nonlinear response time (66 fs).