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Hybrid photodetectors with 2D materials and quantum dots (QDs) offer new opportunities for spectral detection given their high mobilities and spectral tunability, respectively. Herein, the study presents a novel architecture of alternating PbS QDs with graphene monolayers positioned at different depths and with independent contacts. This geometry enables the probing of the photocurrent depth profile and therefore of different spectral bands. The study realizes devices with up to five graphene layers and five QD layers intercalated, using only one type of QDs (Single‐Bandgap devices) with an exciton absorption peak at 920 nm, as well as devices with different types of QDs (Multi‐Bandgap devices) with exciton peaks at 850, 1190, and 1350 nm. Since the absorption depth and photoresponse is wavelength dependent, each graphene has a different spectral response, which opens the path for spectral analysis. As expected, it is observed that top graphene layers have stronger response than deeper graphene layers, especially for short wavelengths. However, for the case of Multi‐Bandgap devices, a negative photoresponse coefficient is even observed for longer wavelengths, showing stronger response for deeper layers than for top layers. This intercalated architecture can be used for compact multispectral photodetection without any diffractive or beam splitting component.

 

Hybrid graphene and quantum dots (QDs) photodetectors merge the excellent conductivity and ambipolar electric field sensitivity of graphene, with the unique properties of QDs. The photoresponsivity of these devices depends strongly on the charge transfer at the graphene/QDs interface. Here 1‐pyrene butyric acid (PBA)‐coated PbS QDs with single layer graphene (SLG) are used to investigate the effect of pyrene as a π–π mediator to enhance charge transfer at the SLG/QDs junction under illumination. The surface chemistry at the QD–QD and SLG/QD interface is studied with the conventional tetrabutylammonium iodide (TBAI) QD linker. The hybrid SLG/QD photodetectors with PBA as a SLG‐QD linker demonstrate a photoresponse up to 30% higher than that recorded for devices where only TBAI is used, due to the strong electron coupling between SLG and QDs. Transconductance measurements show that PBA provokes electron depletion in SLG ascribed to the tendency to delocalize the QDs holes, favoring their transfer to SLG. This surface ligand is found to improve the interaction between the QDs light absorbers and the SLG charge collector, leading to an increased photodetection response. This demonstrates that ligand engineering can enhance charge dynamics and boost the performance of the hybrid device.

 

Photodetectors based on colloidal quantum dots (CQDs) and single layer graphene (SLG) have shown high responsivity due to the synergy of strong light absorption from CQDs and high mobility from SLG. However, it is still challenging to achieve high-density and small-footprint devices on a chip to meet the demand for their integration into electronic devices. Even though there are numerous approaches to pattern the chemically fragile CQD films, usually they require non-conventional approaches such as stamping and surface modification that may be non-compatible with semiconductor processing. In this study, we show that conventional lithography and dry etching can be used to pattern QD active films by employing a graphene monolayer passivation/protective layer that protects the surface ligands of CQDs. This protective layer avoids damage induced by lithography process solvents that deteriorate the carrier mobility of CQDs and therefore the photoresponse. Herein we report patterning of CQDs using conventional UV photolithography, achieving reproducible five-micron length PbS CQDs/SLG photodetectors with a responsivity of 10 8 A W −1 . We have also fabricated thirty-six PbS CQDs/SLG photodetectors on a single chip to establish micron size photodetectors. This process offers an approach to pattern QDs with conventional UV lithography and dry etching semiconductor technology to facilitate their integration into current semiconductor commercial technology.