Optical Power Screening Effects in Ge-on-Si Vertical Pin Photodetectors

We present an experimental and numerical study on the effects of the input optical power on the electro-optic frequency response of a Ge-on-Si vertical pin waveguide photodetector. Experimental results were provided by Cisco Systems, which characterized several nominally identical devices. Increasing the optical power from −2 dBm to 3 dBm, a significant decrease of the electro-optic frequency response was observed in the O-band, from about 40GHz down to approximately 32GHz. This trend is accurately predicted by our 3D multiphysics model, where Maxwell’s equations are solved with the FDTD method to evaluate the spatial distribution of photogenerated carriers, which is then converted in an optical generation rate included in the drift-diffusion solver. The 3D model provides a detailed explanation of the experiments by showing the effects of carrier screening on the magnitude of the electric field profile, which is reduced for high optical power, slowing the photogenerated carriers and reducing the bandwidth.