High-speed Si-Ge avalanche photodiode with a gain-bandwidth product of 7564 GHz.

Avalanche photodetectors are renowned for their exceptional sensitivity and high gain-bandwidth product, making them highly promising for optical communications, quantum technologies, LiDAR, and biosensing. This paper presents a lateral separate absorption charge multiplication silicon-germanium avalanche photodiode designed for O-band operation. The electric field distribution was strategically designed to minimize dark current and enhance gain. A tapered input waveguide and a distributed Bragg reflector were integrated to improve responsivity. The device achieves a dark current of only 8.4 μA at 12.5 V reverse bias with an input optical power of -24 dBm and demonstrates a record-high gain-bandwidth product of 7564 GHz. High-speed eye diagram measurements confirm its support for 100 Gbps NRZ and 200 Gbps PAM4 signals, with sensitivities of -17.1 dBm and -9.6 dBm, respectively. Eye diagram validation at 200 Gbps PAM4 was also conducted across eight avalanche photodiodes aligned with an eight-channel dense wavelength division multiplexing system.