Improved Facet and Edge Passivation in Near-Infrared III-V Colloidal Quantum Dot Photodetectors

Lead-free III-V colloidal quantum dots (CQDs) are of significant interest for their potential in near-infrared (NIR) to short-wave infrared (SWIR) photodetection. However, achieving effective surface passivation remains challenging, especially as larger CQD sizes introduce more complex surface facets and compositions while shifting the absorption peak from the NIR to the SWIR range. In this study, a mixed-halide passivation strategy is developed for large InAs CQDs, an approach that led to a doubling in anti-oxidation ability and achieves a hole mobility of 0.03 cm² Vs^-1. These in turn led to a T90 lifetime of 50 h and enhanced operating stability in photodetectors operating at 1140 nm. Density functional theory (DFT) simulations and facet characterization indicate that exposed facets and edges are well passivated using a mixture of indium halides, which provide a stronger desorption energy compared to single-halide passivation. This approach yields photodetectors with an external quantum efficiency (EQE) of 75% and a response time of 10 ns, an advance for InAs photodetectors operating at 1140 nm.