Ultra-fast germanium photodiode with 3-dB bandwidth of 265 GHz

By sandwiching a germanium fin between complementary in situ-doped silicon layers, a waveguide-coupled germanium photodiode with a 3-dB bandwidth of 265 GHz, accompanied by high responsivity and low dark current, is realized. On a scalable silicon technology platform, we demonstrate photodetectors matching or even surpassing state-of-the-art III-V devices. As key components in high-speed optoelectronics, photodetectors with bandwidths greater than 100 GHz have been a topic of intense research for several decades. Solely InP-based detectors could satisfy the highest performance specifications. Devices based on other materials, such as germanium-on-silicon devices, used to lag behind in speed, but enabled complex photonic integrated circuits and co-integration with silicon electronics. Here we demonstrate waveguide-coupled germanium photodiodes with optoelectrical 3-dB bandwidths of 265 GHz and 240 GHz at a photocurrent of 1 mA. This outstanding performance is achieved by a novel device concept in which a germanium fin is sandwiched between complementary in situ-doped silicon layers. Our photodetectors show internal responsivities of 0.3 A W-1 (265 GHz) and 0.45 A W-1 (240 GHz) at a wavelength of 1,550 nm. The internal bandwidth-efficiency product of the latter device is 86 GHz. Low dark currents of 100-200 nA are obtained from these ultra-fast photodetectors.

Automated summary

By sandwiching a germanium fin between complementary in situ-doped silicon layers, a high-performance waveguide-coupled germanium photodiode is achieved, showing high internal responsivities and low dark currents at a wavelength of 1,550 nm. This novel device concept enables photodetectors with outstanding performance, with internal bandwidth-efficiency products reaching 86 GHz.