Impact-Ionization-Induced Bandwidth-Enhancement of a Si–SiGe-Based Avalanche Photodiode Operating at a Wavelength of 830 nm With a Gain-Bandwidth Product of 428 GHz

We demonstrate a high-performance Si-SiGe-based vertical-illuminated avalanche photodiode (APD) operating in the 830-nm wavelength regime. The trade-off between the gain and bandwidth performance of a traditional APD can be overcome due to the impact-ionization-induced resonant effect in the measured frequency responses with an internal radio-frequency gain. Furthermore, under avalanche operation, the low-frequency (<100MHz) roll-off caused by the slow diffusion current from the n⁺ silicon substrate can also be minimized. A wide 3-dB bandwidth (15.3 GHz) and an extremely high gain-bandwidth (428 GHz), with 18% external efficiency, can be achieved simultaneously in our device, without using complex silicon-on-insulator or germanium-on-insulator substrates to block the slow photocurrent from the silicon substrate