Graphene is very popular because of its many fascinating properties, but its lack of an electronic bandgap has stimulated the search for 2D materials with semiconducting character. Transition metal dichalcogenides (TMDCs), which are semiconductors of the type MX2, where M is a transition metal atom (such as Mo or W) and X is a chalcogen atom (such as S, Se or Te), provide a promising alternative. Because of its robustness, MoS2 is the most studied material in this family. TMDCs exhibit a unique combination of atomic-scale thickness, direct bandgap, strong spin–orbit coupling and favourable electronic and mechanical properties, which make them interesting for fundamental studies and for applications in high-end electronics, spintronics, optoelectronics, energy harvesting, flexible electronics, DNA sequencing and personalized medicine. In this Review, the methods used to synthesize TMDCs are examined and their properties are discussed, with particular attention to their charge density wave, superconductive and topological phases. The use of TMCDs in nanoelectronic devices is also explored, along with strategies to improve charge carrier mobility, high frequency operation and the use of strain engineering to tailor their properties. Two-dimensional transition metal dichalcogenides (TMDCs) exhibit attractive electronic and mechanical properties. In this Review, the charge density wave, superconductive and topological phases of TMCDs are discussed, along with their synthesis and applications in devices with enhanced mobility and with the use of strain engineering to improve their properties.

2D transition metal dichalcogenides

The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.

Electronics based on two-dimensional materials

Physical Review B

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

In the quest for higher performance, the dimensions of field-effect transistors (FETs) continue to decrease. However, the reduction in size of FETs comprising 3D semiconductors is limited by the rate at which heat, generated from static power, is dissipated. The increase in static power and the leakage of current between the source and drain electrodes that causes this increase, are referred to as short-channel effects. In FETs with channels made from 2D semiconductors, leakage current is almost eliminated because all electrons are confined in atomically thin channels and, hence, are uniformly influenced by the gate voltage. In this Review, we provide a mathematical framework to evaluate the performance of FETs and describe the challenges for improving the performances of short-channel FETs in relation to the properties of 2D materials, including graphene, transition metal dichalcogenides, phosphorene and silicene. We also describe tunnelling FETs that possess extremely low-power switching behaviour and explain how they can be realized using heterostructures of 2D semiconductors. Field-effect transistors (FETs) with semiconducting channels made from 2D materials are known to have fewer problems with short-channel effects than devices comprising 3D semiconductors. In this Review, a mathematical framework to evaluate the performance of FETs is outlined with a focus on the properties of 2D materials, such as graphene, transition metal dichalcogenides, phosphorene and silicene.

Two-dimensional semiconductors for transistors

This paper presents both analytical models and Monte Carlo simulations concerning strain engineering in n-type silicon FinFETs. Our analysis identifies the stress configurations and the physical mechanisms able to produce a significant stress-induced mobility enhancement and provides the insight necessary for device optimization. We first derive analytical expressions for the stress-induced changes of the subband minima and of the transport masses, which clearly identify the stress components leading to mobility improvements. Then, we present multisubband Monte Carlo mobility simulations, which confirm the potentials for remarkable stress-induced mobility enhancements in n-FinFETs.

Mobility Enhancement in Strained $n$ -FinFETs: Basic Insight and Stress Engineering

Here, we propose a strain gauge based on single-layer MoSe2 and WSe2 and show that, in these materials, the strain induced modulation of inter-valley phonon scattering leads to large mobility changes, which in turn result in highly sensitive strain gauges. By employing density-functional theory bandstructure calculations, comprehensive scattering models, and the linearized Boltzmann equation, we explain the physical mechanisms for the high sensitivity to strain of the resistivity in single-layer MoSe2 and WSe2, discuss the reduction of the gauge factor produced by extrinsic scattering sources (e.g., chemical impurities), and propose ways to mitigate such sensitivity degradation.

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Very large strain gauges based on single layer MoSe2 and WSe2 for sensing applications

Reports, for the first time, an extensive experimental characterization of effective mobility (/spl mu//sub eff/) in ultra-thin SOI transistors operated in double gate mode To this purpose we devised an experimental technique to determine the inversion density (N/sub inv/) and hence /spl mu//sub eff/ in SOI devices biased with arbitrary front- and back-gate voltages Using this technique, we compared /spl mu//sub eff/ of the same samples biased either in single or double gate mode For silicon thicknesses (T/sub SI/) of 10 nm and below a modest but unambiguous /spl mu//sub eff/ improvement in the double-gate mode is observed

An experimental study of low field electron mobility in double-gate, ultra-thin SOI MOSFETs

A simple analytic model based on the Kane-Sze formula is proposed to describe the current-voltage characteristics of tunnel field-effect transistors (TFETs). This model captures the unique features of the TFET including the decrease in subthreshold swing with drain current and the superlinear onset of the output characteristic. The model has fairly general validity and is not specific to a particular TFET geometry. Good agreement is shown with published atomistic simulations of an InAs double-gate TFET with gate perpendicular to the tunnel junction and with numerical simulations of a broken-gap AlGaSb/InAs TFET with gate in parallel with the tunnel junction.

Continuous semiempirical model for the current-voltage characteristics of tunnel fets

This paper presents a new self-consistent MC simulator for the 2D electron gas of nano-MOSFETs The simulator is two-dimensional in real space and in k-space, and accounts for the electron gas degeneracy in the k-plane Simulations of thin-film SOI MOSFETs show that the subband structure and the carrier degeneracy strongly affect the transport properties particularly the injection velocity Our results also point-out the strong anisotropy of the occupation function, which seriously hampers the use of simulators based on the momentum of the BTE

David Esseni

Papers

Mobility Enhancement in Strained $n$ -FinFETs: Basic Insight and Stress Engineering

Very large strain gauges based on single layer MoSe2 and WSe2 for sensing applications

An experimental study of low field electron mobility in double-gate, ultra-thin SOI MOSFETs

Continuous semiempirical model for the current-voltage characteristics of tunnel fets

Multi-subband monte carlo modeling of nano-mosfets with strong vertical quantization and electron gas degeneration