Ultrahigh Photo‐Responsivity and Detectivity in 2D Bismuth Sulfide Photodetector for Vis–NIR Radiation

Abstract Bismuth sulfide (Bi2S3) exhibits a direct energy bandgap and an exceptional optical absorption capability over a broadband radiation, thus presents a novel class of 2D photodetector material. The field effect transistor (FET) photodetector device is fabricated from 2D Bi2S3. An anomalous variation in the transport characteristics of 2D Bi2S3 is observed with the variation in temperature. The electrical resistance reduces by 99.26% at 10 K compared to the response at 300 K. Defects due to the bismuth and sulfur vacancies play a critical role in the dramatic behavior, which is confirmed using photoluminescence, time‐resolved photoluminescence, Hall measurements, and energy dispersive X‐ray spectroscopy. The density functional theory calculations provide a significant insight into the thermodynamic properties of intrinsic defects in Bi2S3. Moreover, the effect of gate bias on responsivity additionally confirms its invariance at low temperature. The Bi2S3 based FET photodetector achieves ultrahigh responsivity in the order of ≈106 A W−1 and detectivity of ≈1014 Jones. Moreover, the external quantum efficiency of ≈107% is measured in a wide spectrum of optical illumination (532 to 1064 nm) with a noise‐equivalent power of 3.5 × 10−18 W/√Hz at a bias of 0.2 V. The extraordinary performance of Bi2S3 photodetector outstands 2D photodetectors.