Gradient bandgap engineering for performance enhancement in PbSe photodetectors

Short-wave infrared (SWIR) photodetectors are essential for applications ranging from industrial inspection to biomedical imaging. However, conventional detectors based on Ge, InGaAs, or HgCdTe face challenges such as high cost, complex processing, and limited compatibility with silicon technology. PbSe has emerged as a promising alternative due to its strong infrared absorption and room-temperature operation. Despite progress, PbSe thin film photodetectors still suffer from high dark current and slow response. Herein, we report a PbSe-Sb₂Se₃ gradient-alloyed thin film fabricated via dual-source vapor transport deposition (VTD), achieving a quasi-homojunction with suppressed carrier recombination and enhanced carrier transport. The wide bandgap of Sb₂Se₃ (1.17 eV) enables gradient bandgap engineering, effectively reducing dark current and enhancing photoresponse. The resulting photodetectors exhibit a low dark current density of 1.97 × 10^-9 A cm^-2, high responsivity of 138.7 mA W^-1, and ultrafast response times of 11.8 μs (rise) and 18.3 μs (fall), with excellent thermal stability up to 90 °C. This work offers a promising pathway for the development of high-performance, low-cost, and room-temperature-operable SWIR photodetectors.