Two-dimensional semiconductors are structurally ideal channel materials for the ultimate atomic electronics after silicon era. A long-standing puzzle is the low carrier mobility (μ) in them as compared with corresponding bulk structures, which constitutes the main hurdle for realizing high-performance devices. To address this issue, we perform a combined experimental and theoretical study on atomically thin MoS2 field effect transistors with varying the number of MoS2 layers (NLs). Experimentally, an intimate μ-NL relation is observed with a 10-fold degradation in μ for extremely thinned monolayer channels. To accurately describe the carrier scattering process and shed light on the origin of the thinning-induced mobility degradation, a generalized Coulomb scattering model is developed with strictly considering device configurative conditions, that is, asymmetric dielectric environments and lopsided carrier distribution. We reveal that the carrier scattering from interfacial Coulomb impurities (e.g., chemical residues, gaseous adsorbates, and surface dangling bonds) is greatly intensified in extremely thinned channels, resulting from shortened interaction distance between impurities and carriers. Such a pronounced factor may surpass lattice phonons and serve as dominant scatterers. This understanding offers new insight into the thickness induced scattering intensity, highlights the critical role of surface quality in electrical transport, and would lead to rational performance improvement strategies for future atomic electronics.
We investigate the organized formation of strain, ripples, and suspended features in macroscopic graphene sheets transferred onto corrugated substrates made of an ordered array of silica pillars with variable geometries. Depending on the pitch and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lie fully suspended between pillars in a fakir-like fashion over tens of micrometers. With increasing pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to organized domains of parallel ripples linking pillars, eventually leading to suspended tent-like features. Spatially resolved Raman spectroscopy, atomic force microscopy, and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the structural transition between fully suspended and collapsed graphene. For the arrays of high density pillars, graphene membranes stay suspended over macroscopic distances with minimal interaction with the pillars' apexes. It offers a platform to tailor stress in graphene layers and opens perspectives for electron transport and nanomechanical applications.
This manuscript has been published as ACS Nano, 8 (2014) ABSTRACTUnderstanding the interfacial electrical properties between metallic electrodes and low dimensional semiconductors is essential for both fundamental science and practical applications. Here we report the observation of thickness reduction induced crossover of electrical contact at Au/MoS 2 interfaces. For MoS 2 thicker than 5 layers, the contact resistivity slightly decreases with reducing MoS 2 thickness. By contrast, the contact resistivity sharply increases with reducing MoS 2 thickness below 5 layers, mainly governed by the quantum confinement effect. It is found that the interfacial potential barrier can be finely tailored from 0.3 to 0.6 eV by merely varying MoS 2 thickness. A full evolution diagram of energy level alignment is also drawn to elucidate the thickness scaling effect. The finding of tailoring interfacial properties with channel thickness represents a useful approach controlling the metal/semiconductor interfaces which may result in conceptually innovative functionalities. KEYWORDS: two-dimensional material, chalcogenide, field-effect transistor, electrical contact, Schottky barrier, quantum confinementThis manuscript has been published as ACS Nano, 8 (2014) 12836-12842 3 Modern microelectronics roots in a fine control with gate bias on the height of potential barriers and the flow of charges at the interfaces between metallic contacts and active semiconductor channels, 1 which led to a great success of the semiconductor industry and revolutionized our life. The formation of ohmic contacts and high-efficient carrier transfer is the first step to construct high-performance devices. 2 Recently, layered transition-metal dichalcogenides (TMDs) 3-5 have attracted great interest not only for post-silicon electronics, 6-8 but also for optoelectronic 9-14 and photovoltaic 15,16 applications. The concurrence of atomic thickness and sizable bandgap promises them next-generation transistor channels after silicon. In addition, the exotic symmetry breaking in band structure, high optical absorption and mechanical flexibility can be exploited for valleytronic and photovoltaic devices. Undoubtedly, all the electrical systems begin with carrier transfer from electrodes to semiconductor channels; a profound understanding on the interfacial behavior between them is truly essential. 2In conventional bulk materials, the interfacial properties are basically independent on their dimensions. However, the physical scenario totally changes in the low dimensional systems. Generally speaking, the reduced material dimension increases bandgap (E g ) due to quantum confinement, a ubiquitous phenomenon in low-dimensional systems, such as quantum dots 17 and carbon nanotubes (E g ∝1/diameter). 18 The abnormal E g variation was extensively investigated in optical studies 19 but seldom studied in electrical experiments, although it is very important for contact design because an expanded E g may increase interfacial barrier height and suppress charge trans...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.