Time-Resolved Observation of Hole Tunneling in van der Waals Multilayer Heterostructures

Abstract

We reported a time-resolved study of quantum-mechanical tunneling of holes between two MoSe2 monolayers that are separated by a monolayer WS2 energy barrier. Four-layer heterostructures of MoSe2/WS2/MoSe2/graphene, as well as control samples, were fabricated by mechanical exfoliation and dry transfer techniques. To time-resolve the hole tunneling process, an ultrashort laser pulse was used to excite electrons and holes in both MoSe2 layers. By utilization of the graphene layer to eliminate carriers in the third MoSe2 layer, the first MoSe2 layer is selectively populated with the holes, which then tunnel to the third MoSe2 layer. By monitoring decay of the hole population with an ultrashort probe pulse, we measure a hole tunneling time of about 20 ps, which is found to slightly increase with the injected carrier density. Besides the fundamental interests of real-time observation of the quantum-mechanical tunneling effect across a nanometer barrier, these results provide quantitative understanding on tunneling mechanisms of charge transfer in van der Waals heterostructures, which is useful for designing sophisticated van der Waals multilayer heterostructures.

Polarity-Tunable Photocurrent through Band Alignment Engineering in a High-Speed WSe2/SnSe2 Diode with Large Negative Responsivity

“…It is well-known that a tunnel device can switch in the GHz limit . Interlayer charge carrier tunneling time is reported to be on the order of picoseconds for vdW heterostructures . Therefore, the speed of the device used in this study is likely limited by the lateral transport of carriers (electrons) from the (i) WSe 2 (source) contact to the heterointerface, due to bound state electron transport through WSe 2 VB or (ii) from heterointerface to the SnSe 2 (drain) contact via the SnSe 2 CB, which contributes to the series resistance in the diode current.…”

“…53 Interlayer charge carrier tunneling time is reported to be on the order of picoseconds for vdW heterostructures. 54 Therefore, the speed of the device used in this study is likely limited by the lateral transport of carriers (electrons) from the (i) WSe 2 (source) contact to the heterointerface, due to bound state electron transport through WSe 2 VB or (ii) from heterointerface to the SnSe 2 (drain) contact via the SnSe 2 CB, which contributes to the series resistance in the diode current. Hence, the speed can be improved further by narrowing the distance between the source/drain contacts from the heterointerface and by reducing the contact resistance.…”

Ultrafast Interlayer Charge Transfer between Bilayer PtSe2 and Monolayer WS2

“…Next, CT in the heterostructure is studied by transient absorption measurements using a homemade experimental setup, for which details have been described previously. , A 3.02 eV and 1 μJ cm –2 pump pulse excites electrons (−) and holes (+) in both layers, as schematically shown in Figure a. Using absorption coefficients , of 2 × 10 8 and 3.6 × 10 7 m –1 for WS 2 and PtSe 2 , respectively, the pump pulse excites peak carrier densities of 3.2 and 1.1 × 10 11 cm –2 in the WS 2 and PtSe 2 layers, accordingly.…”

“…Interlayer charge transfer (CT) is a critical process to achieve superior electronic and optical properties of van der Waals heterostructures. For example, ultrafast CT in several heterobilayers formed by TMDs has been observed. − However, CT between PtSe 2 and other 2D materials has been less studied.…”

Multilayered Vertical Heterostructures Comprised of MoS2 and WS2 Nanosheets for Optoelectronics

“…It is well-known that the physical properties of 2D TMDCs can be manipulated through tuning of the compositions, layer number, stacking sequence, and relative stacking angles. Therefore, abundant research enthusiasm had been devoted to the fabrication and fantastic properties of three-layer or multilayered 2D TMDC vdW HSs, which exhibits enhanced light absorption ranging from the UV-light to near-infrared region and increased recombination lifetimes of interlayer excitons (up to 5 orders of magnitude, ∼100 ns). , To date, multitudinous three- or four-layer TMDC vdW HSs, for example, MoSe 2 /WS 2 /MoSe 2 , MoS 2 /MoSe 2 /MoS 2 , ,, MoS 2 /WS 2 /MoSe 2 , MoSe 2 /WS 2 /MoS 2 , , WSe 2 /MoSe 2 /WS 2 , WSe 2 /MoSe 2 /WS 2 /MoS 2 , and 1L-MoSe 2 / n L-MoS 2 , have been prepared via multiple mechanical exfoliations and transfer processes. For the widely adopted mechanical transfer approach, it is extremely difficult to avoid the existence of undesired impurities and organic residues, inducing degradation of the device performance.…”