Normal-incidence SiGe/Si p -i -n photodetectors with relaxed GeSi alloy layers grown on Si buffer layers at low temperature and fraction-graded Si 1Ϫx Ge x 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 m. The peak wavelengths are 0.98 and 1.06 m, at which the responsivities are 2.7 and 1.8 A/W ͑Ϫ2 V͒, respectively. The responsivities at 1.3 m are 0.15 and 0.07 A/W ͑Ϫ5 V͒, and the dark current densities are 0.05 and 0.03 A/mm 2 ͑Ϫ2 V͒, respectively. The influences of the Ge fraction, epilayer thickness, and bias voltage on the detectors are discussed.