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

Abstract

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., ${\rm Ge}_{7.5}{\rm Sb}_{25.0}{\rm Se}_{67.5}$Ge7.5Sb25.0Se67.5) provides just the trade-off between a high Kerr coefficient and low optical losses related to two-photon absorption.