Regulating the Energy Levels of HgTe Colloidal Quantum Dots for High‐performance Extended Shortwave Infrared Photodiodes

A lot of progresses have been reported for the HgTe colloidal quantum dot (CQD) based photodiodes working in the shortwave infrared (SWIR: 1.2– 1.8 µm) and mid‐wave infrared (MWIR: 3– 5 µm) regions. On the other hand, HgTe CQD‐based photodiodes working in extended shortwave (eSWIR: 2.0– 2.6 µm) region still showed poor carrier extraction and high dark current, due to the difficulties in regulating the energy levels of eSWIR HgTe CQDs. HgTe CQDs working eSWIR region usually shows intrinsic conduction, since their Fermi levels locate right in the middle of the gap. In this work, additional PbI 2 was included in the ligand exchange for eSWIR HgTe CQDs to largely regulate their Fermi levels and further improve their n‐type conduction. Due to the balanced diffusion rates of halogen ions and binding strength between halogen ions and surface Hg atoms, coverage rate of halogen ions on CQD surface increased significantly, leading to substantially raised Fermi levels of eSWIR HgTe CQDs, as well as improved surface passivation. When the improved HgTe CQDs were applied in eSWIR photodiodes, their dark currents decreased by more than 1 order, and their external quantum efficiency under small bias achieved 4‐fold enhancement.