TCAD-assisted progress on the CISCO platform towards 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 μm), 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 V the best specimens exhibit an intrinsic electro-optic bandwidth of more than 40 GHz, which is reduced to about 10 GHz at zero bias. A comprehensive 3D multiphysics model, validated through the characterization campaign, provides design guidelines towards intrinsic bandwidths not only wider than 60 GHz at -2 V, directly suitable for application in 200 Gbit/s systems, but also wider than 40 GHz at zero bias, not including the possible recourse to extrinsic parameter engineering.