Graphene–Quantum Dot Hybrid Photodetectors with Low Dark-Current Readout

Abstract

Graphene-based photodetectors have shown responsivities up to 108 A/W and photoconductive gains up to 108 electrons per photon. These photodetectors rely on a highly absorbing layer in close proximity to graphene, which induces a shift of the graphene chemical potential upon absorption, hence modifying its channel resistance. However, due to the semimetallic nature of graphene, the readout requires dark currents of hundreds of microamperes up to milliamperes, leading to high power consumption needed for the device operation. Here, we propose a different approach for highly responsive graphene-based photodetectors with orders of magnitude lower dark-current levels. A shift of the graphene chemical potential caused by light absorption in a layer of colloidal quantum dots induces a variation of the current flowing across a metal–insulator–graphene diode structure. Owing to the low density of states of graphene near the neutrality point, the light-induced shift in chemical potential can be relatively large, dramatically changing the amount of current flowing across the insulating barrier and giving rise to an alternative gain mechanism. This readout requires dark currents of hundreds of nanoamperes up to a few microamperes, orders of magnitude lower than that of other graphene-based photodetectors, while keeping responsivities of ∼70 A/W in the infrared, almost 2 orders of magnitude higher than that of established germanium on silicon and indium gallium arsenide infrared photodetectors. This makes the device appealing for applications where high responsivity and low power consumption are required.

Recent Advances in 2D Materials for Photodetectors

“…Similarly, De et al. [ 89 ] proposed a high responsive graphene/colloidal quantum dots hybrid photodetector. The chemical potential shift of graphene under laser illumination would bring higher photocurrent across the interface barrier, thus the net current collected by electrode would increase.…”

Silicon/2D-material photodetectors: from near-infrared to mid-infrared

“…As a 2DM with a relatively narrow bandgap, BP has also been combined with TMDCs to form 2DM-heterostructure PDs [92][93][94][95] . For example, a BP-MoS 2 heterostructure PD 103 , © 2020 American Chemical Society; d ref. 135 , © 2018 The Optical Society, under Creative Commons Attribution 4.0 International license (CC BY 4.0, https://creativecommons.org/licenses/by/4.0/); e ref.…”

“…In these PDs, there may be trap states originating from the defect in materials or heterostructure interfaces, resulting in the PG effect-based photoresponse. More recently, a graphene-insulator-metal PD was demonstrated with graphene covered by colloidal quantum dots (CQDs), showing an interesting mixed-photoresponse mechanism 103 . In this PD, the charge trapping upon light absorption in the CQDs layer induces a shift of the chemical potential of graphene (which is analogous to the PG effect).…”

“…In such a PD, the dark current is usually several μA or even sub-μA, which is much lower than that of conventional metal-2DM-metal PDs based on the PG effect. Meanwhile, the PD has a high gain leading to a high responsivity of 70 A W −1 at 1625 nm as well as excellent response linearity for the input power density less than 1.1 W m −2 103 .

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“… 100 , © 2016 Springer Nature Limited, under Creative Commons Attribution 4.0 International license (CC BY 4.0, https://creativecommons.org/licenses/by/4.0/ ); c ref. 103 , © 2020 American Chemical Society; d ref. 135 , © 2018 The Optical Society, under Creative Commons Attribution 4.0 International license (CC BY 4.0, https://creativecommons.org/licenses/by/4.0/ ); e ref.…”