High-Performance Phototransistor Based on Ultrathin Two-Dimensional Single-Crystalline Bi₂S₃

We have grown ultrathin Bi2S3 with a layered structure and single crystallinity. The two-dimensional Bi2S3 crystals were synthesized by using a chemical vapor deposition (CVD) technique, resulting in a thickness of approximately down to 9 nm and lateral dimensions exceeding several tens of micrometers. Phototransistors based on this ultrathin Bi2S3 exhibit superior photoelectric properties due to strong Coulomb interactions. Specifically, the Bi2S3 device demonstrates a high photoresponsivity of 2.35 × 105 A/W, a high detectivity of 7.5 × 1014 Jones, and a rapid response time of 60 ms. The Bi2S3 crystals also feature a tunable direct bandgap ranging from 1.3 to 1.9 eV, which enables the generation of substantial photocurrent due to its high quantum efficiency. Furthermore, the material’s single-crystalline, anisotropic structure, combined with its low effective electron mass, contributes to high charge mobility and enhanced photoresponsivity. CVD-grown Bi2S3 phototransistors are therefore promising candidates for various applications, including next-generation photodetectors, optical fibers, and image sensors, owing to their inherent flexibility and structural anisotropy.