▎ 摘　　要

Maintaining the rapid development of information technology by scaling down a metal-oxide semiconductor field-effect transistor faces two serious challenges. First, the gate field loses control of the channel as it continuously decreases. Second, the fundamental thermionic limit restricts the reduction in supply voltage. Thus, further scaling down necessitates alternative device structures and different switching mechanisms. Here, we report impact-ionization transistors (IITs) based on nanoscale (similar to 30 nm) vertical graphene/black phosphorus (BP)/indium selenide (InSe) heterostructures. By facilitating the carrier multiplication of the ballistic impact-ionization process as the internal gain mechanism in sub-mean-free-path (sub-MFP) channels, the IITs exhibit a low average subthreshold swing (SS < 1 mV/dec) over five current levels. High stability (>10 000 cycles) and small hysteresis (<1%) switching properties are also obtained. The experimental demonstration of such transistor combining steep SS, high ON-state current density, reliable robustness, miniature footprint, and low bias voltage approaches fulfillments of targets for next-generation devices in the International Technology Roadmap for Semiconductors.