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

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.