Bi₂O₂Se/Xene for Steep-Slope Transistors

Thanks to the unique properties of two-dimensional (2D)materialsand their van der Waals (vdW) heterostructures, 2D materials technologieshave continued to make big strides. Among various 2D materials semiconductors,the recently discovered bismuth oxyselenide (Bi2O2Se) is highly attractive because of its high electron mobility, airstability, as well as its ability to form native high-k oxide. Combined with semi-metallic graphene, the Bi2O2Se/graphene heterostructure has been shown to excel in optoelectronicand electronic applications. Herein, we unveil and demonstrate a newapplication potential of Bi2O2Se/Xene heterostructuresfor making steep-slope transistors, as urgently required in the faceof an increasingly challenging power issue. Atomic-scale materialssimulations reveal that nearly Ohmic contact is formed between Bi2O2Se and Xene (graphene and silicene). In formingthe heterointerface, Xene is p-type doped with the Fermi level inthe lower Dirac cone where density of states of electrons is a decreasingfunction of energy. This property and the high electrostatic controllabilityof the barrier height at the vdW interface naturally satisfy the materialrequirements of the steep-slope "cold-source" transistor.Device modelings confirm that the n-type Bi2O2Se transistor with graphene or silicene as the source is indeed asteep-slope transistor, with a room-temperature sub-threshold swingbelow 50 mV/decade. Compared to normal Bi2O2Se transistor and steep-slope tunneling transistor, the "cold-source"Bi2O2Se transistor also exhibits a higher drivecurrent. This work provides an atomistic understanding of Bi2O2Se/Xene-based steep-slope transistors and opens a newdirection in precision vdW contact engineering toward achieving nanoscaleelectronic devices for applications in a low-power integrated circuit.