Surface Passivation of HgTe Nanocrystals Enabling E _G /2 Open‐Circuit Voltage and Their Coupling to Dielectric Cavity for Narrow Detection

ABSTRACT Colloidal HgTe nanocrystals (NCs) offer a versatile, solution‐processable platform for infrared optoelectronics, yet their integration into high‐performance diodes has long been hindered by surface‐trap‐limited open‐circuit voltage ( V _OC ), high dark currents, and insufficient thermal robustness. Here, we demonstrate that ultrathin CdS shells grown around HgTe cores, combined with an optimized cation‐exchange protocol, enable unprecedented passivation of trap states while reducing species interdiffusion and simultaneously improving interfacial band alignment. Implemented in a diode architecture employing SnO ₂ electron‐transport layers and Ag‐doped CdTe hole‐selective contacts, these HgTe/CdS NCs yield a two orders of magnitude reduction in dark current and a V _OC of 420 mV; exceeding half the optical bandgap for the first time in HgTe‐based NC photodiodes. Operated at room temperature, the devices exhibit detectivities up to 1.5 × 10 ^{1 1} Jones and fast response times below 200 ns. Leveraging the reduced dark current and improved film homogeneity, we further integrate the photodiodes into a dielectric Bragg cavity to achieve ultranarrow detection linewidths down to 90 cm ⁻¹ at 1.55 µm. This diode design benefits from a strong field enhancement, while the device absorption limits the linewidth. Our results establish surface‐passivated HgTe NCs as a viable route toward compact, narrowband, and thermally stable infrared photodetectors.