Coupling efficiency of monolithic, waveguide-integrated Si photodetectors

A waveguide-integrated photodetector provides a small-footprint, low-capacitance design that overcomes the bandwidth-efficiency trade-off problem of free space optics. High performance silicon devices are critical to the emergence of electronic-photonic integrated circuits on the complementary metal oxide semiconductor platform. We have fabricated vertical p-i-n silicon photodetectors that are monolithically integrated with compact silicon oxynitride channel waveguides. We report over 90% coupling efficiency of 830 nm light from the silicon oxynitride (SiOxNy) channel waveguide to the silicon photodetector. We analyze the dependence of coupling on waveguide index by comparing coupling from low index-contrast waveguides and high index-contrast waveguides.