;Abstract A germanium thin film was grown on a silicon substrate by RF magnetron sputtering to fabricate a near infrared photodetector .Because of the energy gap of germanium is smaller than silicon, its cut-off absorption wavelength can reach NIR up to 1550 nm, and it has high carrier mobility. The advantage of sputtering method is that it is not necessary to use toxic and explosive gas and also a low-cost process. In this research, the sputtering method was applied to grow the film, the thin film quality, and deposit it to fabricate the photodetector to extend the wavelength range to the near-infrared region. A 500-nm single crystal germanium film has been grown at 600 ° C by adjusting the sputtering power, bias voltage, and hydrogen flow rate. After annealed to 700 °C, the full-width- half-maximum of the XRD rocking curve of the germanium film (400) decreased from 2672 arcsec to 2180 arcsec. Its compressive stress was reduced. In addition, the boron-doped germanium thin film with doping concentration of 4.32×1019 cm-3 and carrier mobility of 63.6 cm2/V-s was obtained by using co-sputtering boron particles and annealing process. After 700 °C rapid thermal annealing, the dark current density of the NIR photodetector is about 1.5 mA/cm2 at -1V, and the optical response of the 850- nm band of the 180-μm diameter device is 0.1 A/W at -1 V. It is 0.2 A/W at -3V and 0.18 mA/W and 0.14 mA/W at -3 V for 1310 nm and 1550 nm, respectively.