High-speed germanium p-i-n avalanche photodetectors on silicon

Integrated silicon nanophotonics has progressed a lot over past decades with great promises for many surging applications in optoelectronics, information and communication technologies, sensing or health monitoring. Enabling low-cost, dense integration, and compatibility with modern semiconductor nanofabrication processes, silicon nanophotonics deliver compact and high-performance devices on single chips. A variety of nanophotonic functionalities, both passive and active, are nowadays available on semiconductor substrates, leveraging the maturity of open-access silicon foundries and epitaxial germanium integration. It encompasses essential functions such as light generation and amplification, fast electro-optical modulation, and reliable conversion of optical into electrical signals. Germaniumbased optical photodetectors are main building blocks within the library of integrated silicon nanophotonics, with performances that are nowadays on par with their III-V-based counterparts. Germanium photodetectors integrated at the end of waveguides are attractive for next-generation on-chip interconnections, because of their compactness, bandwidth and speed, energy consumption and cost. In this work, we present our latest advances on silicon-germanium p-i-n waveguide-integrated photodetectors based on lateral silicon-germanium-silicon heterojunctions. Our hetero-structured photodetectors were fabricated on top of 200-mm silicon-on-insulator substrates using industrial-scale fabrication processes compatible with complementary metal-oxide-semiconductor technology. Silicon-germanium p-i-n photodetectors operated under low bias voltages exhibited low dark-currents (~100 nA), cut-off frequencies beyond 50 GHz, and photo-responsivities of about 1.2 A/W. Photodetector sensitivities of -14 dBm and -11 dBm were achieved for communication data rates of 10 Gbps and 25 Gbps, respectively. P-i-n photodetectors with lateral heterojunction operated in an avalanche regime offered an additional degree of freedom to improve device performances. High-speed and low-noise characteristics were obtained in our p-i-n photodetectors upon avalanche operation, with a gain-bandwidth product of 210 GHz and a low carrier impact ionization ratio of about 0.25. The measured sensitivity of avalancheoperated devices was -11 dBm for 40 Gbps signal detection. As demonstrated in the reported achievements, heterostructured p-i-n photodetectors are thus suitable communication devices in future intra-data center links or high-speed optical interconnects.