A 42-GHz Bandwidth Avalanche Photodiodes Based on III-V Compounds for 106-Gbit/s PAM4 Applications

This paper describes the design and performance of high-speed avalanche photodiodes (APDs) for 100-Gbit/s PAM4 operation. The APDs are made with InP- lattice- matched III-V compounds, which are suitable for precise band engineering to simultaneously achieve high-speed and high-responsivity performance with a vertical illumination structure. By utilizing a hybrid absorber consisting of p-type and undoped InGaAs layers as well as a 1.1-eV InAlGaAs gap grading layer between the absorber and InAlAs avalanche layer, the peak bandwidth is effectively boosted to 42 GHz with a responsivity of 0.5 A/W at unity gain. An optical receiver made with the APD performed 40-km 106-Gbit/s PAM4 transmissions over a single-mode fiber without an optical amplifier.