Controlled Synthesis of a High-Mobility Bi₃O_2.5Se₂ Semiconductor by Oxidation of Bi₂Se₃ for Fast and Highly Sensitive Photodetectors

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 Bi2Se3 at optimal O content, a series of bismuth oxyselenide semiconductors (Bi3O2.5Se2, Bi2O2Se, Bi2SeO5) with appealing electronic applications are successfully synthesized. The crystal and band structures of a superlattice-free Bi3O2.5Se2 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 Bi2Se3 + O-2 can be extended to synthesize the superlattice-free Bi3O2.5Se2 ultrathin films by chemical vapor deposition, whose room-temperature mobility can be as high as approximate to 150 cm(2) V-1 s(-1) based on Hall measurements. The ultrathin Bi3O2.5Se2 photodetectors with a simple device configuration simultaneously own ultrafast response time (approximate to 31 mu s), ultrahigh responsivity (approximate to 8 x 10(4) A/W), and large detectivity (approximate to 8 x 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.