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

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 BiOSe 2D single crystals on a mica substrate. The applied reverse flow significantly suppresses the random nucleation and thus promotes the lateral size of 2D BiOSe crystals up to ∼750 μm. The BiOSe field-effect transistors display high-room-temperature electron mobility up to ∼1400 cm·V·s and a well-defined drain current saturation. The on/off ratio of the BiOSe transistor is larger than 10, and the sub-threshold swing is about 90 mV·dec. The responsivity, response time, and detectivity of BiOSe photodetectors approach up to 60 A·W, 5 ms, and 2.4 × 10 Jones at room temperature, respectively. Our results demonstrate large-size and high-quality BiOSe grown by reverse-flow CVD as a high-performance channel material for next-generation transistors and photodetectors.