CMOS-integrated waveguide photodetectors for communications applications

Waveguide photodetectors, which convert optical signals propagating along waveguides to electrical signals, are a key building block for silicon photonic integrated circuits for communication applications. For operating in the telecom spectral band of 1.3–1.6 µm and for monolithic integration with other electronic and photonic devices on silicon platform within a single CMOS process flow, different absorbers with unique absorbing mechanisms have been developed, including epitaxial Ge-on-Si with band-to-band absorption, metallic silicide with internal photoemission absorption, and defect-assisted silicon with mid-bandgap absorption. This chapter reviews two of them, that is, waveguide-integrated Ge-on-Si and silicide Schottky-barrier photodetectors, developed in our laboratory in terms of performances (bandwidth, responsivity, dark current, etc.), footprint, and integration process, along with the remaining technological issues and the possible solutions.