Controlled Synthesis of a High‐Mobility Bi3O2.5Se2 Semiconductor by Oxidation of Bi2Se3 for Fast and Highly Sensitive Photodetectors

Abstract The search of new high‐mobility two‐dimensional (2D) semiconductors is crucial for the development of next‐generation photodetectors, since current photodetectors based on single 2D semiconductors usually cannot simultaneously own ultrafast response rate and ultrahigh sensitivity. Here, using a facial method of sequentially oxidizing Bi 2 Se 3 at optimal O content, a series of bismuth oxyselenide semiconductors (Bi 3 O 2.5 Se 2 , Bi 2 O 2 Se, Bi 2 SeO 5 ) with appealing electronic applications are successfully synthesized. The crystal and band structures of a superlattice‐free Bi 3 O 2.5 Se 2 phase are resolved by 3D electron diffraction and density functional theory calculations, showing a unique non‐neutral layered structure, moderate band gap, and small effective mass. More importantly, the concept of Bi 2 Se 3 + O 2 can be extended to synthesize the superlattice‐free Bi 3 O 2.5 Se 2 ultrathin films by chemical vapor deposition, whose room‐temperature mobility can be as high as ≈150 cm 2 V −1 s −1 based on Hall measurements. The ultrathin Bi 3 O 2.5 Se 2 photodetectors with a simple device configuration simultaneously own ultrafast response time (≈31 µs), ultrahigh responsivity (≈8 × 10 4 A/W), and large detectivity (≈8 × 10 13 Jones). This work not only introduces a facile way to regulate the phase in the bismuth oxyselenide family, but also provides an alternative candidate for ultrafast and ultrasensitive photodetectors.