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

Amorphous Ge-Sb-Se thin films were co-sputtered from ${{\rm GeSe}_4}$GeSe and ${{\rm Sb}_2}{{\rm Se}_3}$SbSe 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 ${{\rm GeSe}_4} {\text -} {\rm Sb}_2{{\rm Se}_3}$GeSe-SbSe compared to ${{\rm GeSe}_2}{\text -}{\rm Sb}2{{\rm Se}3}$GeSe-SbSe pseudo-binary system and ${{\rm As}2}{{\rm Se}3}$AsSe as reference. The Kerr coefficient was found within the range of $4.9 {\unicode {x2013}}- 21 \times {10^{ - 18}}$4.9--21×10. Quantitatively by means of a figure of merit at 1.55 µm, thin films with compositions of ${{\rm Ge}7}{\rm Sb}{25}{\rm Se}{68}$GeSbSe and ${{\rm Ge}9}{\rm Sb}{20}{\rm Se}{71}$GeSbSe having an estimated Kerr coefficient of about ${10.1} \times {10^{ - 18}};{{\rm m}^2}{{\rm W}^{ - 1}}$10.1×10mW and ${13.4} \times {10^{ - 18}};{{\rm m}^2}{{\rm W}^{ - 1}}$13.4×10mW should be considered for the future nonlinear optical integrated platforms. Such compositions being close to ${({{\rm GeSe}4}){50}}{({{\rm Sb}2}{{\rm Se}3}){50}}$(GeSe)(SbSe) pseudo-binary (i.e., ${\rm Ge}{7.5}{\rm Sb}{25.0}{\rm Se}{67.5}$GeSbSe) provides just the trade-off between a high Kerr coefficient and low optical losses related to two-photon absorption.