Engineering Vacancies in Bi2S3 yielding Sub‐Bandgap Photoresponse and Highly Sensitive Short‐Wave Infrared Photodetectors

Abstract Defects play an important role in tailoring the optoelectronic properties of materials. Supported by density functional theory (DFT) calculations, herein it is demonstrated that sulphur vacancies are able to engineer sub‐band gap photoresponse in the short‐wave infrared range due to formation of in‐gap states in Bi 2 S 3 single crystals. Sulfurization and subsequent refill of the vacancies result in faster response but limit the spectral range to the near infrared as determined by the bandgap of Bi 2 S 3 . A facile chemical treatment is then explored to accelerate the speed of sulphur deficient (SD)‐based detectors on the order of 10 ms without sacrificing its spectral coverage of the infrared, while holding a high specific detectivity ( D *) close to 10 15 Jones in the visible–near infrared range and 10 12 Jones at 1.6 µm. This work also provides new insights into the role sulphur vacancies play in the electronic structure and, as a result, in sub‐bandgap photoresponse enabling ultrasensitive, fast, and broadband photodetectors.