2, CEA-INAC, Grenoble, , France
3, SPIN, Liège, , Belgium
4, ICB, Dijon, , France
Chalcogenide materials exhibit a unique portfolio of properties which has led to their wide use for non-volatile memory applications such as optical data storage or more recently Phase-Change Random Access Memory . The huge electrical conductivity nonlinearities observed in some chalcogenide glasses (CGs) under electrical field application led the latter as being considered as promising materials to be used as innovative selector element in 3D back-end-of-line memory arrays . Besides, as CGs exhibit a high transparency window in the infrared range and large optical nonlinearities, they offer also opportunities for elaboration of innovative mid-infrared (MIR) components such as MIR supercontinuum (SC) laser sources, optical sensors, IR micro-lens arrays and all-optical integrated circuits . Up to now, the state-of-the-art MIR SC sources have been mainly demonstrated with CGs containing Arsenic such as As2S3, As2Se3 fibers or GeAsSe rib waveguide [4, 5]. However, the REACH European recommendation – which calls for the progressive substitution of the most dangerous chemicals – and the World Health Organization have both identified Arsenic as one of the ten most harmful chemicals for human health. In that context, the linear and nonlinear optical properties of As-free amorphous chalcogenide thin films are investigated here with a particular care on their compatibility with CMOS technologies for future realization of on-chip MIR components. By means of magnetron co-sputtering of chalcogenide compounds targets in an industrial 200 mm deposition tool, we show here how to tailor GeSbwSxSeyTez chalcogenide amorphous thin films aiming to find the best compromise between good glass stability of S-based chalcogenide and the huge nonlinear refractive index of Te-based compositions. Modeling of spectroscopic ellipsometry measurements allowed to determine complex components of linear refractive index and to approximate the optical band gap energy of the different amorphous materials. Optical transmission losses and the real part of refractive index at 1548 nm were obtained using M-line technique. FTIR and Raman spectroscopy in the 100-500 cm-1 range allowed to get information on the amorphous structure of the films. Advanced optical characterizations of nonlinearities in rib and ridge waveguides with a tailored group velocity dispersion were performed and compared to the nonlinear refractive Kerr index n2 of each CGs calculated by means of analytical and empirical models. Finally, the origin of the enhanced optical nonlinearities observed in some of the amorphous GeSbwSxSeyTez chalcogenide compositions will be probed by means of ab initio simulations.
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