High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition (UHV/CVD). This paper demonstrates efficient germanium-on-silicon p-i-n photodetectors with 0.8 μm Ge, with responsivities as high as 0.38 and 0.21 A/W at 1.31 and 1.55 μm, respectively. The dark current density is 0.37 mA/cm2 and 29.4 mA/cm2 at 0 V and a reverse bias of 0.5 V. The detector with a diameter of 30μm, a 3 dB-bandwidth of 4.72 GHz at an incident wavelength of 1550 nm and zero exteal bias has been measured. At a reverse bias of 3 V, the bandwidth is 6.28 GHz.