Designing High‐Performance Sb₂S₃ Field‐Effect Phototransistor with an Excellent Light‐to‐Dark Current Ratio for Weak Light Detection

Abstract To meet the growing multifunctional flexible applications, developing high‐performance thin film photodetectors, especially based on burgeoning materials, such as antimony sulfide (Sb₂S₃) thin film, is an attractive topic. Although the Sb₂S₃ thin film has lots of advantages, such as high absorption coefficient, excellent stability, and earth abundance, the photodetectors built upon it, especially within a phototransistor framework, are still in a very early stage, let alone working principle, design strategy, and optimization methods. In this work, by performing a finite‐element simulation, the working principle, as well as the effect of the device geometries (channel thickness/length) and the trap density, is investigated to explore a practical strategy to improve the performance of the Sb₂S₃ thin film phototransistor. Benefiting from the extremely low dark current modulated by the gate voltage, the device with a channel thickness of 400 nm and a channel length of 100 µm exhibits an outstanding light‐to‐dark current ratio of > 10⁶, as well as the detectivity of 1.5 × 10¹³ Jones, photosensitivity of 1.2 × 10⁶, and responsivity of 5.8 ×10⁻² A W⁻¹. More importantly, an excellent weak‐light‐detecting ability can be obtained, even with a light intensity of 10 nW cm⁻². These results provide valuable guidance for fabricating high‐performance Sb₂S₃ phototransistors and show great potential for integration within industrial‐mature system‐level devices.