Reverse-Flow-Suppressed Chemical Vapor Deposition Growth of Bi ₂ O ₂ Se Nanosheets: Nanoscale Charge-Transport Analysis and High-Responsivity Photodetection

Two-dimensional Bi₂O₂Se exhibits promising potential for photodetection owing to its high carrier mobility and band gap that can be excited across the visible-to-near-infrared range. Here, a reverse-flow-suppressed chemical vapor deposition strategy is employed to achieve controlled, low-density nucleation of high-quality Bi₂O₂Se nanosheets on mica substrates by tuning the growth temperature, gas flow rate, and reaction time. At 700 °C, 150 sccm, and 20 min, we can reproducibly prepare high-quality Bi₂O₂Se nanosheets with maximum lateral dimensions of 10-25 μm and thicknesses concentrated within the range of 15-25 nm. A Bi₂O₂Se/P-Si heterojunction fabricated via polystyrene-assisted transfer is characterized by Kelvin-probe force microscopy coupled with a carrier statistics model to analyze the built-in electric field at the interface, while conductive atomic force microscopy reveals nanoscale charge-transport properties. On this basis, metal-semiconductor-metal photodetectors are fabricated; the devices exhibit a high responsivity of 103 A/W and a low noise-equivalent power of 7.936 × 10^-17 W/Hz^1/2. Such performance benefits from the two-dimensional nature of the active material and the suppression of intrinsic carrier concentration through growth-condition optimization, which reduces the dark current to ∼10^-10 A. This study preliminarily demonstrates a viable route toward high-performance, low-power optoelectronic devices based on high-quality Bi₂O₂Se nanosheets.