Surface-Neutralized HgCdSe Quantum Dots for High-Detectivity Infrared Photodetectors

Infrared (IR) photodetectors are essential components of devices for night vision, autonomous driving, and machine vision, but are composed of epitaxially grown semiconductors that are expensive to manufacture.Colloidal quantum dots (QDs) with IR bandgaps offer an alternative route to low-cost, scalable IR device fabrication, with substantial progress to date using QDs composed of PbS and HgTe.HgSe and HgCdSe are alternative materials that provide broad IR bandgap tunability, higher absorption coefficients, and stability in air, but exhibit intrinsic n-type doping that has hindered applications in optoelectronics.Here we show that n-type doping can be fully depleted from HgSe and HgCdSe QDs by neutralizing their nanocrystal surfaces using surface ligand treatments that displace metal cations functioning as Z-type ligands.We apply QDs deriving from interdiffusion-enhanced cation exchange and find that heating in the presence of alkanethiols yields QDs stabilized by protonated thiols that are stable as dispersions and have unfilled conduction bands.Binary and ternary HgSe and HgCdSe QDs are now available with sharp excitonic absorption features at IR wavelengths up to ~1700 nm.Photodiodes fabricated from surface-neutralized HgCdSe QDs exhibit a high roomtemperature specific detectivity of 1.4 10 12 Jones at 1355 nm, attributable to suppressed ntype doping and low dark current.These air-stable, broadly tunable materials with strong IR absorption may enable low-cost manufacturing routes to IR sensors.