We propose a Ge/Si photodetector based upon photovoltaic field effect transistor (PVFET) for low-power silicon photonics. The device realizes detection by modulating the conductivity of the FET channel through photo-induced gate voltage, exhibiting ultra-high responsivity. The responsivity can reach about 104 A/W at operating voltages lower than 1.5 V. Furthermore, its light-to-dark (on/off) current ratio and temporal response characteristics are studied numerically. A maximum on/off ratio up to 193 can be obtained by optimizing the doping concentration of Ge gate.
