An Atomically Thin Air-Stable Narrow-Gap Semiconductor Cr₂S₃ for Broadband Photodetection with High Responsivity

Infrared (IR) photodetectors are essential for optical communication, imaging, and medical and environmental monitoring technologies. However, current IR photodetectors relying on conventional narrow-gap semiconductors require strict lattice match epitaxy and expensive manufacturing methods, and the incompatibility with complementary metal-oxide-semiconductor technique cannot meet the requirement of high integration and miniaturization. Here, the controllable growth of an ultrathin narrow-gap semiconductor Cr₂S₃, with thickness down to unitcell of ≈1.85 nm, is reported using chemical vapor deposition method. The as-grown 2D Cr₂S₃ exhibits outstanding environmental stability with negligible degradation even after exposure in air for more than two months. By combining the optics Fourier transfer infrared spectrometer with density functional theory calculations, the bandgap of the synthesized Cr₂S₃ nanoflakes is determined to be 0.15 eV. A photodetector based on the 2D Cr₂S₃ exhibits a high responsivity (14.4 A W⁻¹ at 520 nm, 6.0 A W⁻¹ at 808 nm, and 3.0 A W⁻¹ at 1550 nm) and excellent detectivity (4.0 × 10¹⁰ Jones at 520 nm, 1.7 × 10¹⁰ Jones at 808 nm, and 8.3 × 10⁹ Jones at 1550 nm) under ambient conditions. These findings indicate that the air-stable 2D narrow-gap semiconductor Cr₂S₃ can act as a highly competitive candidate for broadband photodetector application and fundamental photophysics investigation.