Linear and nonlinear optical properties of co-sputtered Ge-Sb-Se amorphous thin films

Amorphous Ge-Sb-Se thin films were co-sputtered from ${{\rm GeSe}_4}$GeSe₄ and ${{\rm Sb}_2}{{\rm Se}_3}$Sb₂Se₃ targets. Depending on the film composition, linear optical properties were studied by ellipsometry. The Kerr coefficient and two-photon absorption coefficient were estimated using Sheik-Bahae's formalism for co-sputtered films of ${{\rm GeSe}_4} {\text -} {\rm Sb}_2{{\rm Se}_3}$GeSe₄-Sb₂Se₃ compared to ${{\rm GeSe}_2}{\text -}{\rm Sb}_2{{\rm Se}_3}$GeSe₂-Sb₂Se₃ pseudo-binary system and ${{\rm As}_2}{{\rm Se}_3}$As₂Se₃ as reference. The Kerr coefficient was found within the range of $4.9 {\unicode {x2013}}- 21 \times {10^{ - 18}}$4.9--21×10^-18. Quantitatively by means of a figure of merit at 1.55 µm, thin films with compositions of ${{\rm Ge}_7}{\rm Sb}_{25}{\rm Se}_{68}$Ge₇Sb₂₅Se₆₈ and ${{\rm Ge}_9}{\rm Sb}_{20}{\rm Se}_{71}$Ge₉Sb₂₀Se₇₁ having an estimated Kerr coefficient of about ${10.1} \times {10^{ - 18}}\;{{\rm m}^2}{{\rm W}^{ - 1}}$10.1×10^-18m²W^-1 and ${13.4} \times {10^{ - 18}}\;{{\rm m}^2}{{\rm W}^{ - 1}}$13.4×10^-18m²W^-1 should be considered for the future nonlinear optical integrated platforms. Such compositions being close to ${({{\rm GeSe}_4})_{50}}{({{\rm Sb}_2}{{\rm Se}_3})_{50}}$(GeSe₄)₅₀(Sb₂Se₃)₅₀ pseudo-binary (i.e., ${\rm Ge}_{7.5}{\rm Sb}_{25.0}{\rm Se}_{67.5}$Ge_7.5Sb_25.0Se_67.5) provides just the trade-off between a high Kerr coefficient and low optical losses related to two-photon absorption.