TCAD-Assisted Progress on the Cisco Platform Toward Low-Bias 200 Gbit/s vertical-pin Ge- on-Si Waveguide Photodetectors

We discuss the characterization and numerical simulation of vertical Ge-on-Si waveguide photodetectors (VPIN WPDs) of the Cisco platform for data communications in the O-band (1.31 \,\mu \mathrm{m}), with the goal of optimizing their frequency response while integrating them into low-power systems. In a large set of WPDs belonging to 6 different structural variants, at a standard bias voltage of -2 \,\mathrm{V} the best specimens exhibit an intrinsic electro-optic bandwidth of more than 40 \,\mathrm{G}\mathrm{Hz}, which is reduced to about 10 \,\mathrm{G}\mathrm{Hz} at zero bias. A comprehensive 3D multiphysics model, validated through the characterization campaign, provides design guidelines towards intrinsic bandwidths not only wider than 60 \,\mathrm{G}\mathrm{Hz} at -2 \,\mathrm{V}, directly suitable for application in 200 Gbit/s systems, but also wider than 40 \,\mathrm{G}\mathrm{Hz} at zero bias, not including the possible recourse to extrinsic parameter engineering.