Distinct Optoelectronic Signatures for Charge Transfer and Energy Transfer in Quantum Dot–MoS₂ Hybrid Photodetectors Revealed by Photocurrent Imaging Microscopy

Abstract

Atomically thin transition metal dichalcogenides (TMDCs) have intriguing nanoscale properties like high charge mobility, photosensitivity, layer‐thickness‐dependent bandgap, and mechanical flexibility, which are all appealing for the development of next generation optoelectronic, catalytic, and sensory devices. Their atomically thin thickness, however, renders TMDCs poor absorptivity. Here, bilayer MoS2 is combined with core‐only CdSe QDs and core/shell CdSe/ZnS QDs to obtain hybrids with increased light harvesting and exhibiting interfacial charge transfer (CT) and nonradiative energy transfer (NET), respectively. Field‐effect transistors based on these hybrids and their responses to varying laser power and applied gate voltage are investigated with scanning photocurrent microscopy (SPCM) in view of their potential utilization in light harvesting and photodetector applications. CdSe–MoS2 hybrids are found to exhibit encouraging properties for photodetectors, like high responsivity and fast on/off response under low light exposure while CdSe/ZnS–MoS2 hybrids show enhanced charge carrier generation with increased light exposure, thus suitable for photovoltaics. While distinguishing optically between CT and NET in QD–TMDCs is nontrivial, it is found that they can be differentiated by SPCM as these two processes exhibit distinctive light‐intensity dependencies: CT causes a photogating effect, decreasing the photocurrent response with increasing light power while NET increases the photocurrent response with increasing light power, opposite to CT case.

Uniform Vapor-Pressure-Based Chemical Vapor Deposition Growth of MoS2 Using MoO3 Thin Film as a Precursor for Coevaporation

“…The coevaporation of Mo and S precursor-based CVD has received much attention for the past few years because of its ability to produce high-quality MoS 2 single crystals with excellent electrical and optical properties. 15−18 The challenging nature of CVD growth of MoS 2 continues to stimulate intense research effort in this field. If the CVD is going to be used for large-scale production of MoS 2 samples, it is important to understand how small variations of CVD process parameters could lead to different results.…”

Device Architecture for Visible and Near-Infrared Photodetectors Based on Two-Dimensional SnSe2 and MoS2: A Review

“…QD-MoS 2 hybrids with interfacial interaction dominated by charge transfer (left) and by non-radiative energy transfer (right), Time-resolved analysis of the normalized rise times of photocurrent at V G = −40 V and V DS = 0 V under 488 nm laser with 37 μW. Reproduced with permission from reference [ 112 ]. ( i , j ) Schematic of the MoS 2 /BN/graphene hetero-structure photodetector for photon absorber/selective hole tunneling layer/bottom electrode, respectively and Time-resolved photoresponse of the 7 h-BN nm device under 405 nm laser irradiation.…”

Light-Induced Interfacial Phenomena in Atomically Thin 2D van der Waals Material Hybrids and Heterojunctions

“…Li et al proposed distinguishing electrically between interfacial CT and ET by using the scanning photocurrent microscopy (SPCM) technique. 53 In SPCM, a tightly focused laser is scanned over a FET containing the 2D material, and at each point, a laser-induced current is measured so that a photocurrent image is composed (Figures 5d,e). Li et al designed two types of 0D−2D hybrids purposely functioning on interfacial hole transfer, core-only CdSe QD−MoS 2 , and on ET, core/shell CdSe/ZnS−MoS 2 , with the shell impeding CT but favoring ET by band gap design (Figure 5c).…”