Germanium-based sensors are disclosed herein. An exemplary germanium-based sensor includes a germanium photodiode and a junction field effect transistor (JFET) formed from a germanium layer disposed on and/or in a silicon substrate. A doped silicon layer, which can be formed by in-situ doping epitaxially grown silicon, is disposed between the germanium layer and the silicon substrate. In embodiments where the germanium layer is on the silicon substrate, the doped silicon layer is disposed between the germanium layer and an oxide layer. The JFET has a doped polysilicon gate, and in some embodiments, a gate diffusion region is disposed in the germanium layer under the doped polysilicon gate. In some embodiments, a pinned photodiode passivation layer is disposed in the germanium layer. In some embodiments, a pair of doped regions in the germanium layer is configured as an e-lens of the germanium-based sensor.