Surface Passivation of HgTe Nanocrystals Enabling E_G/2 Open-Circuit Voltage and Their Coupling to Dielectric Cavity...

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 SnO₂ 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.