Thickness-Dependent Interlayer Charge Transfer in MoSe₂/MoS₂ Heterostructures Studied by Femtosecond Transient Absorption Measurements

Abstract

We report observations of a strong thickness dependence for charge transfer (CT) from MoSe 2 to MoS 2 , as evidenced by transient absorption measurements. By time-resolving CT from MoSe 2 monolayers (1Ls) to MoS 2 flakes of varying thicknesses, including 1L, bilayer (2L), and trilayer (3L), we find that the CT time is several picoseconds in the 1L-MoSe 2 /3L-MoS 2 heterostructure, which is much longer than that of 1L-MoSe 2 /1L-MoS 2 and 1L-MoSe 2 /2L-MoS 2 heterostructures. In addition, the recombination lifetime of the interlayer excitons in the 1L/3L heterostructure is several times longer than that of 1L/1L and 1L/ 2L heterostructures, reaching 800 ps. Furthermore, we show that a prepulse can reduce the CT time and enhance the interlayer exciton recombination in the 1L/3L heterostructure. These findings illustrate that layer thickness can be an important parameter to control the CT property of van der Waals heterostructures. These experimental results also provide important information for further refining the understanding of the physical mechanisms of CT in van der Waals heterostructures.

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.…”

Observation of Hole Transfer in MoS2/WS2 Van der Waals Heterostructures

“…Alternatively, electron transfer is also expected in such a II type band alignment in MoS 2 /WS 2 bilayer. As illustrated in Figure 4a, a 515 nm (2.40 eV) wavelength with a 60 μJ/cm 2 pump fluence is selected to excite the WS 2 B-excitons and a probe pulse at 41,42 The carrier life in the MoS 2 /WS 2 bilayer is about 6 times the exciton lifetime in ML MoS 2 due to the charge separation. The recombination of the carriers is suppressed.…”

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.…”

“…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 19 and increased recombination lifetimes of interlayer excitons (up to 5 orders of magnitude, ∼100 ns). 11,26 34 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.…”