High-speed interdigitated Ge PIN photodetectors

In this letter, we report a high-speed PIN photodetector fabricated on Ge with planar interdigitated p/sup +/ - and n/sup +/ -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-/spl mu/m finger width and 2-/spl mu/m spacing with 50 /spl times/ 50 /spl mu/m/sup 2/ active area. At a wavelength of 1.3 /spl mu/m, 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 /spl mu/A at 5 and 15 V, respectively. This photodetector exhibited external quantum efficiencies over 60% in the spectral range 1.0-1.5 /spl mu/m. At a wavelength of 1.3 /spl mu/m, the external quantum efficiency was 67%.