Ultrafast avalanche photodiode exceeding 100 GHz bandwidth

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.