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. The authors showcase a lateral Si–Ge avalanche photodiode in the O-band. With low dark current, high gain–bandwidth product of 7564 GHz, it supports 100 Gbps NRZ and 200 Gbps PAM4 signals for high-speed optical communication applications.