Spectrally Tunable Germanium-on-silicon Photodetectors: Design and Simulations

Germanium-based photodetectors represent the state-of-the-art in Near Infrared (NIR) detection systems when it comes to the monolithic integration with silicon electronics and CMOS compatibility. Germanium-on-silicon devices have been widely studied and several different photodetection schemes have been employed, such as Shottky junctions, pn diodes and phototransistors. Typically, germanium-based photodetectors provide a sensitivity spectrum ranging from the visible to the near infrared (NIR) and their responsivity at shorter wavelengths can be slightly tuned by the applied bias due to the varying extension of the electric field inside the Ge film. In this paper we propose a novel Ge-on-Si photodetector architecture whose spectral response can be completely switched from the visible to the NIR with the application of a proper bias. We provide Technology Computer Aided Design (TCAD) simulations of the device showing how the photodetection performance depend on different fabrication parameters. Finally, we show preliminary results obtained on sample devices.