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Nanohybrids of graphene and colloidal semiconductor quantum dots (QDs/Gr) provide a promising quantum sensing scheme for photodetection. Despite exciting progress made in QDs/Gr photodetectors in broadband from ultraviolet to short-wave infrared, the device performance is limited in middle-wave infrared (MWIR) detection. A fundamental question arises as to whether the thermal noiseinduced dark current and hence poor signal-to-noise ratio in conventional uncooled MWIR photodetectors persist in QDs/ Gr nanohybrids. Herein, we investigated noise, responsivity (R*), and specific detectivity (D*) in HgTe QDs/Gr nanohybrids, revealing that the noise and R* are decoupled in nanohybrids and each can be optimized independently toward its theoretical limit. Specifically, the noise in the QDs/Gr nanohybrids is dominated by that of graphene with a negligible effect from the dark current in HgTe QDs and can be optimized to its intrinsic limit by removing charge doping of adsorbed polar molecules on graphene. Furthermore, the R* is proportional to the photoconductive gain enabled by the strong quantum confinement in QDs and Gr. Achieving high gain in the MWIR spectrum, however, is challenging and requires elimination of charge traps primarily from the surface states of the narrow-bandgap semiconductor HgTe QDs. Using grain-rotation-induced grain-coalescence growth of single-layer and core/shell HgTe QDs, we show the that HgTe QDs surface states caused by Te deficiency can be dramatically suppressed, resulting in high gain up to 4.0 × 107 in the MWIR spectrum. The optimized noise and R* have led to high uncooled MWIR D* up to 2.4 × 1011 Jones, making nanohybrids promising to surpass the fundamental dark-current limit in conventional photodetectors. 

Abstract Nanohybrids based on van der Waals (vdW) heterostructures of two dimensional (2D) atomic materials have recently emerged as a unique scheme for designing high‐performance quantum sensors. This work explores vdW nanohybrids for photodetection, which consist of graphene decorated with intermingled transition‐metal dichalcogenide (TMDC) nanodiscs (TMDC‐NDs) obtained using wafer‐size, layer‐by‐layer growth. The obtained TMDC‐NDs/graphene nanohybrids take advantage of strong quantum confinement in graphene for high charge mobility and hence high photoconductive gain, and localized surface plasmonic resonance (LSPR) enabled on the TMDC‐NDs for enhanced light absorption. Since the LSPR depends on the nanostructure's size and density, intermingled TMDC‐NDs of different kinds of TMDCs, such as WS₂(W) and MoS₂(M), have been found to allow small‐size, high‐concentration TMDC‐NDs to be achieved for high photoresponse. Remarkably, high photoresponsivity up to 31 A/W (550 nm wavelength and 20 µW cm⁻²light intensity) has been obtained on the WMW‐NDs/graphene nanohybrids photodetectors made using three consecutive coatings of WS₂(1st and 3rd coating) and MoS₂(2nd coating), which is considerably higher by a factor of ≈4 than that of the counterparts MoS₂‐ND/graphene or WS₂‐NDs/graphene devices. This result provides a facile approach to control the size and concentration of the TMDC‐NDs for high‐performance, low‐cost optoelectronic device applications.