Bi₂O₂Se/Xene for Steep-Slope Transistors

Thanks to the unique properties of two-dimensional (2D) materials and their van der Waals (vdW) heterostructures, 2D materials technologies have continued to make big strides. Among various 2D materials semiconductors, the recently discovered bismuth oxyselenide (Bi 2 O 2 Se) is highly attractive because of its high electron mobility, air stability, as well as its ability to form native high- k oxide. Combined with semi-metallic graphene, the Bi 2 O 2 Se/graphene heterostructure has been shown to excel in optoelectronic and electronic applications. Herein, we unveil and demonstrate a new application potential of Bi 2 O 2 Se/Xene heterostructures for making steep-slope transistors, as urgently required in the face of an increasingly challenging power issue. Atomic-scale materials simulations reveal that nearly Ohmic contact is formed between Bi 2 O 2 Se and Xene (graphene and silicene). In forming the heterointerface, Xene is p-type doped with the Fermi level in the lower Dirac cone where density of states of electrons is a decreasing function of energy. This property and the high electrostatic controllability of the barrier height at the vdW interface naturally satisfy the material requirements of the steep-slope “cold-source” transistor. Device modelings confirm that the n-type Bi 2 O 2 Se transistor with graphene or silicene as the source is indeed a steep-slope transistor, with a room-temperature sub-threshold swing below 50 mV/decade. Compared to normal Bi 2 O 2 Se transistor and steep-slope tunneling transistor, the “cold-source” Bi 2 O 2 Se transistor also exhibits a higher drive current. This work provides an atomistic understanding of Bi 2 O 2 Se/Xene-based steep-slope transistors and opens a new direction in precision vdW contact engineering toward achieving nanoscale electronic devices for applications in a low-power integrated circuit.