Orthogonal Passivation of Polar Facets for Efficient InSb Quantum Dot SWIR Photodetectors

ABSTRACT

Indium antimonide (InSb) colloidal quantum dots (CQDs) offer a heavy‐metal‐free route to short‐wave infrared (SWIR) photodetection, but their performance still lags behind lead‐ and mercury‐based CQD systems, and the surface chemistry that limits their performance is not well understood. Here, we identify two independent oxide‐derived trap pathways on the polar terminations of zincblende InSb: oxidation of the In‐terminated {111}A and Sb‐terminated {111}B facets creates chemically distinct mid‐gap states, each of which degrades carrier transport. Density functional theory calculations show that metal halides bind strongly to Sb‐terminated facets, but weakly to In‐terminated facets, while thiolates show the opposite preference; this asymmetry leaves single‐ligand passivation incomplete. Exploiting this orthogonality, we develop a facet‐specific exchange that passivates both terminations and removes their surface oxides in a single step. The resulting CQD films show a fivefold reduction in hole‐trap density and a sixfold improvement in hole mobility relative to thiol‐only controls. The photodetectors achieve 50% external quantum efficiency under 1 V reverse bias at 1390 nm, to the best of our knowledge, the highest reported for InSb CQD photodetectors in the 1300–1500 nm range, along with a 580 ns fall time and 95% photocurrent retention after 100 h of continuous operation.