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Tools Used: RSoft FullWAVE & Sentaurus TCAD

For photodetector incorporation into the silicon photonic infrastructure, a CMOS-compatible material with efficient near-infrared absorption is essential. Germanium, available in standard front-end CMOS processes, is suitable for making photodetectors due to its high absorption at telecom (1.3-1.5) wavelengths. As such, waveguide-integrated Ge photodetectors amenable for integration within the CMOS device layer stack have become a topic of intense R&D.

Challenge

• For optimum receiver performance, the waveguide-integrated photodetector has to achieve high bandwidth, low capacitance, high responsivity, and ideally single-mode operation at a wavelength of 1.5um. This requirements are mostly in conflict with each other, therefore the photodetector has to be designed by evaluating and minimizing the tradeoffs.
• Of critical importance is to maximize the responsivity for the 100nm thick Ge layer without large increases in length (which would increase the total light absorption, but would also increase the capacitance and the RC bandwidth limitation).
• Photodetector design involves electronic, process, and optical physics. A complete photodetector simulation must incorporate all these effects.