High-performance waveguide Ge/Si avalanche photodiode with a lateral separate-absorption-charge-multiplication (SACM) structure

A high-performance waveguide Ge/Si avalanche photodiode operating at the O-band (1310 nm) is designed with a Ge/Si ridge waveguide defined by two shallow trenches in the active region and fabricated with simplified processes. The device shows a high primary responsivity of 0.96 A/W at the unit-gain voltage of -7.5 V. It has a large 3-dB bandwidth of >27 GHz and a low dark current of 1.8 µA at a reverse bias voltage of -13 V. When the present Ge/Si APD is used for receiving 25 Gbps data, the eye-diagram is open even for an optical power as low as -18 dBm. Furthermore, 50 Gbps data receiving is also demonstrated with an input optical power of -15 dBm, showing the great potential of the present Ge/Si APD for the application in future high-speed data transmission systems.