21-GHz-Bandwidth Germanium-on-Silicon Photodiode Using Thin SiGe Buffer Layers

Backside-illuminated germanium photodiodes fabricated on silicon substrate with two SixGe1-xbuffer layers are reported. At 1.3 mum, the responsivity was 0.62 A/W for reverse bias greater than 0.1 V. The 3-dB bandwidth was 21.5 GHz at 10-V reverse bias, achieving a bandwidth-efficiency product of 12.6 GHz