Weak interlayer couplings at 2D van der Waals (vdW) interfaces fundamentally distinguish out-of-plane charge flow, the information carrier in vdW-assembled vertical electronic and optical devices, from the in-plane band transport processes. Here, the out-of-plane charge transport behavior in 2D vdW semiconducting transition metal dichalcogenides (SCTMD) is reported. The measurements demonstrate that, in the high electric field regime, especially at low temperatures, either electron or hole carrier Fowler–Nordheim (FN) tunneling becomes the dominant quantum transport process in ultrathin SCTMDs, down to monolayers. For few-layer SCTMDs, sequential layer-by-layer FN tunneling is observed to dominate the charge flow, thus serving as a material characterization probe for addressing the Fermi level positions and the layer numbers of the SCTMD films. Furthermore, it is shown that the physical confinement of the electron or hole carrier wave packets inside the sub-nm thick semiconducting layers reduces the vertical quantum tunneling probability, leading to an enhanced effective mass of tunneling carriers.
Bibliographical noteFunding Information:
D.H.S., D.‐H.L., and S.‐J.C. contributed equally to this work. The authors thank T.‐Y. Jeong, G. Min, and H. Kim for their support in device fabrications and measurements. The authors also thank D.‐H. Ha for his help in Raman spectroscopy measurements for SCTMD layer‐number identification. This work was supported by Basic Science Research Programs (NRF‐2017R1D1A1B03035727, 2019R1A2C2004007, 2021R1A6A1A10039823, 2022R1A2B5B01001640 and 2022R1A2C2008140) and Global Research and Development Center Program (2018K1A4A3A01064272) through the National Research Foundation of Korea. This work was also supported by Human Frontier Science Program (RGP00026/2019), the Würzburg‐Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter (EXC2147, project‐id 390858490) and by the DFG (SPP1666 and SFB1170 “ToCoTronics”).
© 2023 The Authors. Advanced Electronic Materials published by Wiley-VCH GmbH.
- 2D semiconductors
- Fowler-Nordheim tunneling
- Schottky-barrier height
- electron and hole field emission
- van der Waals vertical heterostructures