Germanium on Silicon Avalanche Photodiode

Silicon photonics is considered as one of the promising technologies for high-speed optical fiber communications. Among various silicon photonic devices, germanium on silicon avalanche photodiodes (Ge/Si APDs) have attracted tremendous attention due to their the properties of high performance and low cost. The sensitivity of 10Gb/s APD reached -29.5dBm at 1550 nm with the bit error rate of 1 × 10-12in 2015, and 25 Gb/s APD reached a highest sensitivity ever reported at about -23.5dBm at 1310 nm in 2016. Furthermore, a linear 28Gbaud APD receiver is found to have about 5dB more sensitivity than PIN solution for both multimode fiber (MMF) and single-mode fiber (SMF). Even with large defect density from lattice mismatch between Ge and Si substrate layer, Ge/Si APD devices demonstrate good reliability and pass all required qualification tests according to GR-468. In this paper, the structure, materials, process, performances, and reliability of APDs will be reviewed.