  We propose the use of germanium-on-silicon technology for indirect
time-of-flight based three-dimensional sensing, and demonstrate a novel lock-in
pixel featuring high quantum efficiency and large frequency bandwidth. Compared
to silicon pixels, germanium-on-silicon pixels simultaneously maintain a high
quantum efficiency and a high demodulation contrast deep into GHz frequency
regime, which enable consistently superior depth accuracy in both indoor and
outdoor scenarios. Physical model, numerical simulation, device fabrication and
characterization, system performance comparison, and laser safety analysis are
presented. Our work paves a new path to high-performance time-of-flight rangers
and imagers, as well as potential adoption of lasers operated at a longer near
infrared wavelength that falls outside of the operation window of silicon
pixels.
