Double-ended passivator enables dark-current-suppressed colloidal quantum dot photodiodes for CMOS-integrated infrared imagers

Lead sulfide (PbS) colloidal quantum dot (CQD) photodiodes integrated with silicon-based readout integrated circuits (ROICs) offer a promising solution for the next-generation short-wave infrared (SWIR) imaging technology. Despite their potential, large-size CQD photodiodes pose a challenge due to high dark currents resulting from surface states on non-passivated (100) facets and trap states generated by CQD fusion. In this work, we present a novel approach to address this issue by introducing double-ended ligands that supplementally passivate (100) facets of halide-capped large-size CQDs, leading to suppressed bandtail states and reduced defect concentration. Our results demonstrate that the dark current density is highly suppressed by about an order of magnitude to 9.6 nA cm⁻² at −10 mV, which is among the lowest reported for PbS CQD photodiodes. Furthermore, the performance of the photodiodes is exemplary, yielding an external quantum efficiency of 50.8% (which corresponds to a responsivity of 0.532 A W⁻¹) and a specific detectivity of 2.5 × 10¹² Jones at 1300 nm. By integrating CQD photodiodes with CMOS ROICs, the CQD imager provides high-resolution (640 × 512) SWIR imaging for infrared penetration and material discrimination.