Obviating Ligand Exchange Preserves the Intact Surface of HgTe Colloidal Quantum Dots and Enhances Performance of Short Wavelength Infrared Photodetectors

Abstract

A large volume, scalable, synthesis procedure of HgTe quantum dots (QDs) capped initially with short‐chain conductive ligands, ensures ligand exchange‐free and simple device fabrication. An effective n‐ or p‐type self‐doping of HgTe QDs is achieved by varying the cation‐anion ratio, as well as shifting the Fermi level position by introducing single‐ or double‐cyclic thiol ligands, i.e., 2‐furanmethanethiol (FMT) or 2,5‐dimercapto‐3,4‐thiadiasole (DMTD) in the synthesis. This allows for the preservation of the intact surface of the HgTe QDs, thus ensuring a one order of magnitude reduced surface trap density compared with HgTe subjected to solid‐state ligand exchange. The charge carrier diffusion length can be extended from 50 to 90 nm when the device active area consists of a bi‐layer of cation‐rich HgTe QDs capped with DMTD and FMT respectively. As a result, the responsivity under 1340 nm illumination is boosted to 1 AW⁻¹ at zero bias and up to 40 AW⁻¹ under ‐1 V bias at room temperature. Due to high noise current density, the specific detectivity of these photodetectors’ reaches up to 10¹⁰ Jones at room temperature and under inert atmosphere. Meanwhile, high photoconductive gain ensures a rise in the external quantum efficiency of up to 1000% under reverse bias.

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