Low Residual Carrier Concentration and High Mobility in 2D Semiconducting Bi₂O₂Se

The air-stable and high-mobility two-dimensional (2D) Bi₂O₂Se semiconductor has emerged as a promising alternative that is complementary to graphene, MoS₂, and black phosphorus for next-generation digital applications. However, the room-temperature residual charge carrier concentration of 2D Bi₂O₂Se nanoplates synthesized so far is as high as about 10¹⁹-10²⁰ cm^-3, which results in a poor electrostatic gate control and unsuitable threshold voltage, detrimental to the fabrication of high-performance low-power devices. Here, we first present a facile approach for synthesizing 2D Bi₂O₂Se single crystals with ultralow carrier concentration of ∼10¹⁶ cm^-3 and high Hall mobility up to 410 cm² V^-1 s^-1 simultaneously at room temperature. With optimized conditions, these high-mobility and low-carrier-concentration 2D Bi₂O₂Se nanoplates with domain sizes greater than 250 μm and thicknesses down to 4 layers (∼2.5 nm) were readily grown by using Se and Bi₂O₃ powders as coevaporation sources in a dual heating zone chemical vapor deposition (CVD) system. High-quality 2D Bi₂O₂Se crystals were fabricated into high-performance and low-power transistors, showing excellent current modulation of >10⁶, robust current saturation, and low threshold voltage of -0.4 V. All these features suggest 2D Bi₂O₂Se as an alternative option for high-performance low-power digital applications.