High-efficiency, Ge-on-SOI lateral PIN photodiodes with 29 GHz bandwidth

Ge has tremendous potential for high-speed operation at λ=850 nm, an important wavelength for short range highly-parallel interconnects, because the absorption length of Ge is only a few hundred nm. However, for thin Ge-on-Si detectors, the Ge film must be isolated from the underlying Si in order to prevent collection of slow carriers generated deep within the substrate. In this work, we present results of lateral PIN photodetectors fabricated using Ge films deposited on ultra-thin silicon-on-insulator (SOI) substrates. These devices have bandwidths as high as 29 GHz, and the highest bandwidth-efficiency product reported to date for a group-IV photodetector.