A photo-detecting apparatus includes a semiconductor substrate. A first germanium-based light absorption material is supported by the semiconductor substrate and configured to absorb a first optical signal having a first wavelength greater than 800 nm. A first metal line is electrically coupled to a first region of the first germanium-based light absorption material. A second metal line is electrically coupled to a second region of the first germanium-based light absorption material. The first region is un-doped or doped with a first type of dopants. The second region is doped with a second type of dopants. The first metal line is configured to control an amount of a first type of photo-generated carriers generated inside the first germanium-based light absorption material to be collected by the second region.