A method for manufacturing an integrated avalanche photodetector comprising steps of providing a silicon-insulator substrate including a top layer, an insulator layer and a base layer; partially removing the top layer to form an optical waveguide over the insulator layer; forming an opening at least through the cladding layer and the insulator layer extending to a first portion of the base layer; and forming an avalanche photodetector over the first portion of the base layer at least in the opening and optically coupled to the waveguide. In one embodiment, the avalanche photodetector is butt-coupled to the optical waveguide. In another embodiment, the avalanche photodetector is evanescently coupled to the optical waveguide.