Ultrafast avalanche photodiode exceeding 100 GHz bandwidth
Yang Shi, Mingjie Zou, Zuhang Li, Yu Yu, Xinliang Zhang
Abstract
Avalanche photodiodes (APDs) demand multiplication materials with low ionization coefficient ratio (k) for high-speed and high-sensitivity photodetection. Germanium/Silicon (Ge/Si) APDs have been preferred for a decade, leveraging the exceptional multiplication property of Si and inherent complementary metal-oxide-semiconductor (CMOS) compatibility. However, the bandwidth remains tens of gigahertz, fundamentally limited by unexpected dual-carrier multiplication in high-k Ge. Here, we transcend this material limitation by introducing a uni-multiplication-carrier concept. Through a separated absorption-charge-cliff-multiplication structure, we elaborately tailor the electric field to gradient distribution within a thin Ge region, establishing electron-dominated multiplication with a significantly reduced k. Experimentally, the device achieves a record-high bandwidth of 105 GHz at a gain of 7. This enables 8×260 Gb/s signal reception, previously only achieved by gainless photodetectors, while providing 9 dB sensitivity improvement. This work paves the way for amplifier-free optical communications, ultra-precise optical sensing, and large-scale optical computing.