Picosecond photoresponse in van der Waals heterostructures

Abstract

performance. Here we demonstrate that graphene/WSe2/graphene heterostructures ally the high photodetection efficiency of TMDs 5,6 with a picosecond photoresponse comparable to that of graphene 7-9 , thereby optimizing both speed and efficiency in a single photodetector. We follow in time the extraction of photoexcited carriers in these devices using timeresolved photocurrent measurements and demonstrate a photoresponse time as short as 5.5 ps, which we tune by applying a bias and by varying the TMD layer thickness. Our study provides direct insight into the physical processes governing the detection speed and quantum efficiency of these van der Waals (vdW) heterostuctures, such as out-of-plane carrier drift and recombination.The observation and understanding of ultrafast and efficient photodetection demonstrate the potential of hybrid TMD-based heterostructures as a platform for future optoelectronic devices. 2The optoelectronic response of 2D crystals is currently the subject of intense investigation [1][2][3][5][6][7][8][9][10][11][12][13][14][15][16] prompted by the need for next-generation photodetectors with superior performance in terms of efficiency, detection speed, as well as flexibility and transparency 17 . High photon absorption 5,18 and large photoconducting gain 11,12,14 have been observed in devices based on semiconducting 2D crystals. Yet, the observed response time typically ranges from nanoseconds 16 to seconds 11,14 , with faster devices often displaying lower responsivity 11 . Therefore, the main challenge is to develop and assess photodetectors based on 2D semiconductor crystals that simultaneously possess a large active area, high internal efficiency, and fast response time.A promising approach to create such versatile devices is to sandwich a TMD layer between two graphene sheets serving as charge extraction contacts. In contrast to lateral photodetectors, such vertical van der Waals (vdW) heterostructures 4 have the advantage of possessing a large, scalable active area and an atomically short charge extraction channel, potentially enabling both efficient and fast photodetection. Whereas the quantum efficiency of these vdW devices 5,6,13 and the dynamics of photocarrier creation and relaxation in TMDs [19][20][21][22][23][24][25][26][27] have been addressed, the response time of TMD-based photodetectors, as well as the dynamic processes governing their quantum efficiency remain elusive.Here, we report on the intrinsic processes that limit the performance of photodetectors based on high-quality G/WSe2/G (with G representing graphene) vdW heterostructures encapsulated in hexagonal boron nitride (hBN) 28 . We perform time-resolved photocurrent measurements 7,29 on devices consisting of WSe2 flakes with a range of thicknesses (monolayer and multilayers from 2.2 to 40 nm). This technique, which combines electronic detection with subpicosecond optical excitation, allows probing of the extraction ( Figure 1a) and loss dynamics of the photoexcited charge carriers in the photoactive TMD layer. We ...

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Photogating in Low Dimensional Photodetectors

“…Responsivity and response time of part current state‐of‐the‐art low dimensional photodetectors 17, 31, 32, 39, 40, 44, 47, 67, 99, 100, 101, 102, 103, 104. The blue line represents a typical magnitude order of GBP for traditional high‐performance thin‐film photodetectors.…”

Two-Dimensional MoS2-Graphene-Based Multilayer van der Waals Heterostructures: Enhanced Charge Transfer and Optical Absorption, and Electric-Field Tunable Dirac Point and Band Gap

“…These heterogeneous stacks have unusual properties that are not present in individual layers and encompass a wide spectrum of physical and chemical phenomena exemplified by new van Hove singularities [4][5][6][7] , Fermi velocity renormalization 8,9 , unconventional quantum Hall effects 10 , Hofstadter's butterfly pattern [11][12][13][14] , and others. Peculiar electronic [15][16][17] and optoelectronic properties 18,19 have been revealed in diverse 2D heterostructures based on layered materials such as GR, semiconducting transition metal dichalcogenides (TMDs) and insulating hexagonal boron nitride (h-BN). Interestingly, these heterostructures are also tunable hyperbolic metamaterial 20 and memory device with ultrahigh on/off ratio 21 , or have gate-induced superconductivity 22 and high-temperature superfluidity 23 .…”