Germanium on Silicon for Near-Infrared Light Sensing

We review near-infrared detectors in germanium grown on silicon. We discuss pn and pin photodiodes based on Ge deposited on Si by a number of techniques, including thermal evaporation; the optical and electronic characterization of Ge-on-Si heterostructures using various approaches to minimize the density of defects; and compatibility issues with standard fabrication processes for Si electronics. We describe in greater detail the most promising devices realized by us and operating either at normal incidence or in guided-wave geometries, with applications to high-speed optical receivers, as well as image sensors.