We demonstrate, for the first time, the application of dopant-segregation (DS) technique in metal-germanium-metal photodetectors for dark-current suppression and high-speed performance. Low defect density and surface smooth epi-Ge (similar to 300 nm) layer was selectively grown on patterned Si substrate using two-step epi-growth at 400 degrees C/600 degrees C combined with a thin (similar to 10 nm) low-temperature Si/Si0.8Ge0.2 buffer layer. NiGe with DS effectively modulates the Schottky barrier height and suppresses dark current to similar to 10(-7) A at -1 V bias (width/spacing: 30/2.5 mu m). Under normal incidence illumination at 1.55 mu m, the devices show photoresponsivity of 0.12 A/W. The 3 dB bandwidth under -1 V bias is up to 6 GHz.