Short‐Wave Infrared Colloidal QDs Photodetector with Nanosecond Response Times Enabled by Ultrathin Absorber Layers

Ultrafast short-wavelength infrared (SWIR) photodetection is of great interest for emerging automated vision and spatial mapping technologies. Colloidal quantum dots (QDs) stand out for SWIR photodetection compared to epitaxial (In,Ga)As or (Hg,Cd)Te semiconductors by their combining a size-tunable bandgap and a suitability for cost-effective, solution-based processing. However, achieving ultrafast, ns-level response time has remained an outstanding challenge for QD-based SWIR photodiodes (QDPDs). Here, we report on record 4 ns response time in PbS-based QDPDs that operate at SWIR wavelengths, a result reaching the requirement of SWIR LiDAR based on colloidal QDs. These ultrafast QDPDs combine a thin active layer to reduce the carrier transport time and a small area to inhibit slow capacitive discharging. By implementing a concentration gradient ligand exchange method, high-quality p-n junctions are fabricated in these ultrathin QDPDs. Moreover, these ultrathin QDPDs attain an external quantum efficiency of 42% at 1330 nm, due to a 2.5-fold enhanced light absorption through the formation of a Fabry-Perot cavity within the QDPD and the highly efficient extraction (98%) of photogenerated charge carriers from the PbS QD film. Based on these results, we estimate that a further increase of the charge-carrier mobility can lead to PbS QDPDs with sub-ns response time. This article is protected by copyright. All rights reserved.