High Mobility Two-Dimensional Bismuth Oxyselenide Single Crystals with Large Grain Size Grown by Reverse-Flow...

2D semiconductors with atomically thin body thickness have attracted tremendous research interest for high-performance nanoelectronics and optoelectronics. Most of the 2D semiconductors grown by chemical vapor deposition (CVD) methods suffer from rather low carrier mobility, small single-crystal size, and instability under ambient conditions. Here, we develop an improved CVD method with controllable reverse-gas flow to realize the direct growth of quality Bi₂O₂Se 2D single crystals on a mica substrate. The applied reverse flow significantly suppresses the random nucleation and thus promotes the lateral size of 2D Bi₂O₂Se crystals up to ∼750 μm. The Bi₂O₂Se field-effect transistors display high-room-temperature electron mobility up to ∼1400 cm²·V^-1·s^-1 and a well-defined drain current saturation. The on/off ratio of the Bi₂O₂Se transistor is larger than 10⁷, and the sub-threshold swing is about 90 mV·dec^-1. The responsivity, response time, and detectivity of Bi₂O₂Se photodetectors approach up to 60 A·W^-1, 5 ms, and 2.4 × 10¹⁰ Jones at room temperature, respectively. Our results demonstrate large-size and high-quality Bi₂O₂Se grown by reverse-flow CVD as a high-performance channel material for next-generation transistors and photodetectors.