Tensile-Strained Ge/SiGeSn Quantum Wells for Polarization-Insensitive Electro-Absorption Waveguide Modulators

We present design and modeling of a polarization-insensitive electro-absorption waveguide modulator operating at 1550 nm. Our design uses tensile-strained Ge-SixGeySn_1-x-y quantum wells as the active material grown on a relaxed SiGeSn buffer on a silicon substrate, compatible with complementary metal-oxide semiconductor (CMOS) processes. Introducing tensile strain in the Ge wells can effectively reduce the direct bandgap for optimal modulation at the critical 1550 nm wavelength, and provide polarization-insensitive electro-absorption properties. We present a theoretical model for the electronic band structure, excitonic absorption coefficient, and polarization-dependent optical confinement factor. We also bring forth a waveguide design based on index guidance, where we calculate the optical confinement factors of various regions to determine the extinction ratio and insertion loss. The proposed modulator operating at 1550 nm can offer unique advantages for use in high-performance, CMOS-compatible electronic-photonic integrated circuits.