An avalanche photodiode with a defect-assisted silicon absorption region. An example includes a substrate; a layer of silicon on the substrate, the layer of silicon including a positively-doped region, a negatively-doped region, and an absorption region between the positively-doped and negatively-doped regions, the absorption region including defects in its crystal structure; and contacts in electrical communication with the positively-doped and negatively-doped regions to receive a bias potential.