This paper reports on a van der Waals PN heterojunction photodetector, composed of p-type black phosphorus and n-type molybdenum telluride, integrated on a silicon nitride waveguide. The built-in electric field significantly suppresses dark current and improves responsivity. With a 1V bias, the dark current is below 7nA, over two orders of magnitude lower than other waveguide-integrated black phosphorus photodetectors. Responsivity reaches 577 mA/W, increasing to 709 mA/W with electrostatic doping. The device shows a ~1.0 GHz response bandwidth and uniform photodetection from 1500 to 1630 nm.
