Kosuke Nagashio

The mobility of graphene transferred on a SiO2/Si substrate is limited to ∼10 000 cm2V−1s−1. Without understanding the graphene/SiO2 interaction, it is difficult to improve the electrical transport properties. Although surface structures on SiO2 such as silanol and siloxane groups are recognized, the relation between the surface treatment of SiO2 and graphene characteristics has not yet been elucidated. This paper discusses the electrical transport properties of graphene on specific surface stru

The electric properties of mono- and multi-layer graphene films were systematically studied with the layer number determined by their optical contrast. The current modulation increased monotonically with a decrease in the layer number due to the reduction of the interlayer scattering. Carrier mobility in the monolayer was significantly greater than that in the multilayer due to linear dispersion relation. On the other hand, in the monolayer, carrier transport was extremely sensitive to charged i

The key to achieve high-quality van der Waals heterostructure devices made of stacking various two-dimensional (2D) layered materials lies in the clean interface without bubbles and wrinkles. Although polymethylmethacrylate (PMMA) is generally used as a sacrificial transfer film due to its strong adhesion property, it is always dissolved in the solvent after the transfer, resulting in the unavoidable PMMA residue on the top surface. This makes it difficult to locate clean interface areas. In thi

Graphene with a high carrier mobility of more than 10,000 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has attracted much attention as a promising candidate of future high-speed transistor materials. The contact resistance (RC) between graphene and metal electrodes is crucially important for achieving potentially high perfo

Graphene has attracted much attention as one of promising candidates of future high-speed transistor materials because of its high carrier mobility of more than 10,000 cm2 V-1 s-1. Up to this point, we have focused on the contact properties as performance killers, as a very small density of states in graphene might suppress the current injection from metal to graphene. This paper systematically reviews the metal/graphene contact properties and discusses the present status and future requirements

Graphene has attracted much attention as one of promising candidates of future high-speed transistor materials because of its high carrier mobility of more than 10,000 cm 2 V -1 s -1 . Up to this point, we have focused on the contact properties as performance killers, as a very small density of states in graphene might suppress the current injection from metal to graphene. This paper systematically reviews the metal/graphene contact properties and discusses the present status and future requirem

Van der Waals heterostructures are the ideal material platform for tunnel field-effect transistors (TFETs) because a band-to-band tunneling (BTBT) dominant current is feasible at room temperature (RT) because of ideal, dangling bond-free heterointerfaces. However, achieving subthreshold swing (SS) values lower than 60 mV dec^-1 of the Boltzmann limit is still challenging. In this work, we systematically studied the band alignment and heterointerface quality in n-MoS₂ channel

Remarkable optical/electrical features are expected in two-dimensional group-IV monochalcogenides (MXs; M = Sn/Ge and X = S/Se) with a uniquely distorted layered structure. The lone pair electrons in the group-IV atoms are the origin of this structural distortion, while they also cause a strong interlayer force and high chemical reactivity. The fabrication of chemically stable few-to-monolayer MX has been a significant challenge. We have observed that, once the SnS surface is oxidized, the SnO<s

Understanding the operation mode of a two-dimensional (2D) material-based field-effect transistor (FET) is one of the most essential issues in the study of electronics and physics. The existing Schottky barrier FET model for devices with global back gate and metallic contacts overemphasizes the metal/2D contact effect, and the widely observed residual conductance cannot be explained by this model. Here, an accumulation-mode (ACCU) FET model, which directly reveals 2D channel transport properties

Abstract 2D materials are highly promising for tunnel field effect transistors (TFETs) with low subthreshold swing and high drive current because the shorter tunnel distance and strong gate controllability can be expected from the van der Waals gap distance and the atomically sharp heterointerface formed independently of lattice matching. However, the common problem for 2D–2D TFETs is the lack of highly doped 2D materials with the high process stability as the sources. In this study, it is found

Although MoS2 field-effect transistors (FETs) with high-k dielectrics are promising for electron device applications, the underlying physical origin of interface degradation remains largely unexplored. Here, we present a systematic analysis of the energy distribution of the interface state density (Dit) and the quantum capacitance (CQ) in a dual-gate monolayer exfoliated MoS2 FET. The CQ analysis enabled us to construct a Dit extraction method as a function of EF. A band tail distribution of Dit

High‐speed digital imaging was conducted during the containerless solidification of rare‐earth orthoferrites (RE = La, Sm, Dy, Y, Yb, and Lu) with the perovskite structure to determine the metastable phase and elucidate its growth behavior. Observation using a high‐speed video camera revealed that the formation of the metastable phase became pronounced, and double recalescence from the metastable phase to a stable phase occurred, as the ionic radius of the rare‐earth element decreased. In the pr

Hexagonal boron nitride (h-BN) is an important insulating substrate for two-dimensional (2D) heterostructure devices and possesses high dielectric strength comparable to SiO₂. Here, we report two clear differences in their physical properties. The first one is the occurrence of Fermi level pinning at the metal/h-BN interface, unlike that at the metal/SiO₂ interface. The second one is that the carrier of Fowler-Nordheim (F-N) tunneling through h-BN is a hole, which is opposi