Chloride-passivated lead sulfide thin film for high-performance extended short wavelength infrared photodiode

Liquid-phase chemically deposited lead sulfide as a narrow-bandgap semiconductor holds great potential for extended short-wavelength infrared sensing. However, lead sulfide thin films typically contain massive sulfur vacancies and oxygen impurities, which form during chemical deposition, leading to inferior device performance. Here, for the first time, we report on the in-situ passivation of lead sulfide polycrystalline film with chloride ions as an additive during liquid-phase chemical deposition. Due to the similar ionic radius of chloride ions to sulfur ions and their ability to coordinate with lead ions, the addition of chloride ions effectively reduces sulfur vacancy and oxygen-in-sulfur defect densities. The reduction of bulk defect densities lowered the dark current density of homojunction photodiodes made from the passivated film by more than threefold. The photodiode exhibited a high responsivity of 0.79 A/W at 2.5 µm and a fast response speed of 19.6 µs. At room temperature, the 1 mm² photodiodes exhibited a resistance-area product of 8.78 Ω cm² and a specific detectivity of 8.79 × 10⁹ Jones at 2.5 µm, among the best-reported performance of lead sulfide bulk thin film photodiode. At 80 K, the resistance-area product was 6.16 kΩ cm². This research paves a new path for high-performance extended short-wavelength infrared photodetector.