Heterogeneously integrated waveguide-coupled InGaAs/InP SACM avalanche photodiodes on silicon nitride for 1550 nm

The silicon nitride/silicon (Si₃N₄/Si) photonic platform has attracted significant interest due to its ultra-low-loss waveguides and high-performance optical components. Progress in heterogeneous integration has enabled the development of active photonic devices on Si₃N₄, including PIN waveguide photodiodes. However, to the best of our knowledge, an integrated avalanche photodiode (APD) with internal gain operating at 1550 nm wavelength has not been demonstrated to date. Here, we report on the design, fabrication, and characterization of InP/InGaAs separate absorption, charge, and multiplication (SACM) APDs heterogeneously integrated on Si₃N₄ waveguides. Our APDs have a dark current of 5 nA near breakdown at room temperature, a multiplication gain of 166, and an internal responsivity of 0.61 A/W at unity gain. The 3-dB bandwidth is 4.2 GHz, and we demonstrate open eye diagrams at 7.5 Gbps.