Polarization-Insensitive Waveguide Schottky Photodetectors Based on Mode Hybridization Effects in Asymmetric Plasmonic Waveguides.

Two types of configurations are theoretically proposed to achieve high responsivity polarization-insensitive waveguide Schottky photodetectors, i.e., a dual-layer structure for 1.55 µm and a single-layer structure for 2 µm wavelength band. Mode hybridization effects between quasi-TM modes and modes in plasmonic waveguides are first presented and further investigated under diverse metal types with different thicknesses in this work. By utilizing the mode hybridization effects between quasi-TE mode and mode, and also quasi-TM and mode in our proposed hybrid plasmonic waveguide, light absorption enhancement can be achieved under both TE and TM incidence within ultrathin and short metal stripes, thus resulting in a considerable responsivity for Si-based sub-bandgap photodetection. For 1.55 µm wavelength, the Au-6 nm-thick device can achieve absorptance of 99.6%/87.6% and responsivity of 138 mA·W/121.2 mA·W under TE/TM incidence. Meanwhile, the Au-5 nm-thick device can achieve absorptance of 98.4%/90.2% and responsivity of 89 mA·W/81.7 mA·W under TE/TM incidence in 2 µm wavelength band. The ultra-compact polarization-insensitive waveguide Schottky photodetectors may have promising applications in large scale all-Si photonic integrated circuits for high-speed optical communication.