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

Infrared (IR) photodetectors used in advanced imaging and sensing applications rely on epitaxially grown semiconductors that are expensive to manufacture. Colloidal quantum dots (QDs) offer lower-cost production, with substantial progress using PbS and HgTe QDs. HgSe and HgCdSe QDs offer wide spectral tunability, higher absorption coefficients, and air stability, but their inherent n-type doping has hindered their use. Here, we show that n-type doping can be depleted by neutralizing nanocrystal surfaces by displacing surface metal cations acting as Z-type ligands. Heating with alkanethiols yields QDs coated with protonated thiols and with unfilled conduction bands. Surface-neutralized HgSe and HgCdSe QDs exhibit sharp excitonic absorption features at IR wavelengths up to ∼1700 nm. Photodiodes fabricated from HgCdSe QDs have a room-temperature specific detectivity of 1.4 × 10¹² Jones at 1355 nm, attributable to suppressed doping and low dark current. These air-stable, broadly tunable materials with strong IR absorption may enable low-cost IR sensors.