Chloride-Passivated Lead Sulfide Thin Film for High-Performance Extended Short-Wavelength Infrared Photodiode
Liquid-phase chemically deposited lead sulfide (PbS) thin films are a cost-effective platform for extended short-wavelength infrared (eSWIR) detection, yet their performance is constrained by high densities of sulfur vacancies and oxygen-in-sulfur defects formed during deposition. This work introduces chloride ions as an in-situ additive during chemical bath deposition to passivate these defects. The similar ionic radius of Cl⁻ (176 pm) to S²⁻ (179 pm) and its coordination with Pb²⁺ enable substitutional incorporation without significant lattice distortion. The passivated films exhibit a near-unity Pb/S atomic ratio, a photoluminescence full-width at half-maximum of 75 meV, and a carrier lifetime increase exceeding 20-fold. Homojunction photodiodes fabricated from these films demonstrate a dark current density of 3.1 μA/cm² at 0 V, a responsivity of 0.79 A/W at 2.5 μm, a specific detectivity of 8.79 × 10⁹ Jones, and a response time of 19.6 μs. The resistance-area product (R₀A) reaches 8.78 Ω cm² at 300 K and 6.16 kΩ cm² at 80 K. Activation energy analysis reveals trap-assisted tunneling as the dominant dark current mechanism at higher reverse biases, attributed to grain boundaries. These results represent among the best reported performance for PbS bulk thin-film photodiodes and offer a scalable route to high-performance eSWIR sensors.