An avalanche photodiode includes a silicon layer on a substrate; a germanium layer on the silicon layer; a cathode and an anode on any of the silicon layer and the germanium layer; and a plurality of contacts on the germanium layer, in addition to the cathode and the anode. The silicon layer can include a highly doped region at each end, an intrinsic doped region in a middle, and an intermediately doped region between the highly doped region at each end and the intrinsic doped region, and the cathode and the anode are each at a respective a highly doped region at each end. The germanium layer can include a plurality of highly doped regions with each including one of the plurality of contacts.