In recent years, extensive researches are going on high-speed low-noise photodetectors for optical communication. A photodetector plays a critical role in the overall performance of the system. III-V based photodetectors for high-performance communication system have already been reported.But, the technology is very expensive.Si is an obvious choice in such cases.Si technology has also the advantage of high reliability and high integrability. However, Si band-gap is not suitable for photodetection around the long-haul communication wavelength.Ge is a good candidate for designing such...