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A Si-based waveguide photodetector with a response in the 1.3-1.55-μm wavelength range is demonstrated. The active absorption layer of the pin photodiode consists of a SiGeC alloy epitaxially grown on a Si substrate with a Ge content of 55% and a thickness of 800 /spl Aring/. The external quantum efficiency for a 400-μm-long waveguide, measured by using a single-mode fiber coupled to the waveguide facet, is 0.2% at 1.55 μm. The dark current density at peak photoresponse is 40 pA/μm2. The quantum efficiency can be further enhanced by using multiple SiGeC layers as the absorber. Direct measurements of the absorption coefficient for the alloy layer are also reported.