High-speed interdigitated Ge PIN photodetectors

In this letter, we report a high-speed PIN photodetector fabricated on Ge with planar interdigitated p⁺ - and n⁺-fingers that were formed by ion implantation into a Ge substrate. The 3-dB bandwidth and the external quantum efficiency were measured on a photodetector having 1-μm finger width and 2-μm spacing with 50 × 50 μm² active area. At a wavelength of 1.3 μm, the bandwidth was 1.8, 2.6, and 3 GHz at bias voltages of 5, 10, and 15 V, respectively. The dark current was 0.9 and 10 μA at 5 and 15 V, respectively. This photodetector exhibited external quantum efficiencies over 60 % in the spectral range 1.0-1.5 μm. At a wavelength of 1.3 μm, the external quantum efficiency was 67%.