Normal-incidence SiGe/Si p-i-n photodetectors with relaxed GeSi alloy layers grown on Si buffer layers at low temperature and fraction-graded Si1-xCex buffers were fabricated by rapid thermal process/very-low-pressure: chemical-vapor deposition. The response wavelength of these detectors ranges from 0.7 to 1.55 mu m. The peak wavelengths are 0.98 and 1.06 mu m, at which the responsivities are 2.7 and 1.8 A/W (-2 V), respectively, The responsivities at 1.3 mu m are 0.15 and 0.07 A/W (-5 V), and the dark current densities are 0.05 and 0.03 mu A/mm(2) (-2 V), respectively. The influences of the Ge fraction, epilayer thickness, and bias voltage on the detectors are discussed.