We have fabricated a series of p-i-n Ge/Si heteroijunction photodetectors with different thicknesses of the intrinsic Ge layer, different doping levels of the p and n layers and different diode diameters. Epitaxial Ge was deposited on Si(100) using low-energy plasma-enhanced CVD (LEPECVD) followed by cyclic annealing. Dark current values as low as 0.04 mA/cm(2) were achieved for I pm thick p-i-n photodiodes on lightly doped substrates at -1 V bias, and external quantum efficiencies of 56% at 1.30 mu m and 44% at 1.55 mu m for 3 mu m thick p(+)-i-n(+) photodiodes on highly doped substrates under 0.5 V reverse bias. For a 30 pm diameter diode a RC frequency of 21 GHz is obtained at a reverse bias of 1 V. With such characteristics, these diodes are attractive for telecommunication and optoelectronic applications. (C) 2008 Elsevier B.V. All rights reserved.