(Invited) High Performance Ge/Si Photodetectors for Data Center and 5G Applications

Ge/Si optical devices have been in intense study for many years. In particular, they find themself as one of core optical devices in the Silicon Photonics technologies for high speed optical fiber communications. Among various silicon photonic devices, Germanium on Si photodectors have been widely commercialized in the application for 5G and data center. We have shipped more than millions pcs of Ge/Si optical devices from simple photodiodes to high performance avalanche photodiodes. These devices such as Ge/Si APDs have attracted tremendous attention due to their theoretical better performance than traditional III-V APDs and relatively low cost originally from CMOS foundry. In 2015, we start to ship 10G/25G Ge/Si photodiodes while developing a 10Gb/s APD with 1e-12 sensitivity equal to -29.5dBm at 1550nm; in 2016, we developed a 25Gb/s APD with world record 1e-12 sensitivity equal to -23.5dBm at 1310nm; in 2017, we developed a linear 28Gbaud APD receiver providing 5dB and 5.7dB improvement over PIN solutions for MMF and SMF PAM4 applications respectively; in 2019, we developed a 106 Gb/s (53GBaud PAM4) normal-incidence Ge/Si APDs with sensitivities of -16.8 dBm. Even with large defect density from lattice mismatch between Ge and Si substrate layer, Ge/Si optical devices demonstrate good reliability and passed all required qualification tests according to GR-468. In this paper, we reviewed the structure, materials, process, performance and reliability of the Ge/Si PIN and APD devices. To our knowledge, this is the best sensitivity reported for 100G APD.