Charge-triggered switching mechanism in selenium selector enabling ultralow leakage current

The rapid growth of artificial intelligence models has outpaced the capabilities of current dynamic random-access memory/flash storage systems in speed, density and energy efficiency. Three-dimensional phase-change memory offers a scalable solution, yet cross-point integration is limited by selector performance. Here, by reverse-tracing previously reported ovonic threshold switch (OTS) materials, we identify amorphous elemental selenium as a highly effective OTS selector. It exhibits an ultralow leakage current (4 × 10^-12 A), an on/off current ratio exceeding 10⁸, high drive current density (21.2 MA cm^-2), fast switching speed (~20 ns) and endurance up to 2 × 10⁹ cycles. Photoexcitation spectroscopy and density functional theory calculations reveal a charge-triggered mechanism: dense trap pairs in amorphous selenium strongly pin the Fermi level and suppress leakage, while full carrier excitation in these traps near threshold, together with impact-ionization-induced avalanche multiplication, enables abrupt switching and high on-current. Integrated selenium-selector/phase-change memory arrays demonstrate reliable write/erase operations with a 0.75-V read margin. These results clarify the OTS mechanism and establish amorphous selenium as a leading selector material for three-dimensional memory.