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We investigate the electrical transport characteristics of graphene channel field-effect transistors (FETs) gated via ionic solid (IS), where the conventional gate insulator, such as SiO 2 , has been replaced by solid electrolytes, such as LiP 3 O 4. In this study, we focus on (i) the gate controllability of the current in comparison to conventional graphene FETs with SiO 2 as an insulating material and (ii) the transient characteristics of the drain current and time required to switch on the current. We employ the tight-binding formalism and Boltzmann equation to calculate the electronic band structure and the electronic transport in graphene, while the Nernst–Planck–Poisson equations have been employed to calculate the time-dependent charge distribution in solid electrolytes and the resulting electric double layer formation at the graphene/IS and IS/gate interfaces. Our simulations have shown that graphene FET gated via IS shows superior gate controllability more than SiO 2 -gated graphene FET with the insulator thickness of 1 nm, and the saturated drain current is insensitive to the IS thickness. Moreover, the time required to switch on the drain current is proportional to the thickness of IS, and the limited number of Li + ion vacancies in IS is preferable in obtaining faster switching than the case of unlimited vacancy cases while keeping the superior gate controllability. [ABSTRACT FROM AUTHOR]

We present a numerical study on the impact of electron–phonon scattering on the performance of a strained-graphene field-effect transistor, where the Dirac point of the channel region is shifted along the transverse momentum direction by a strain-induced vector potential and a high on-current/off-current (I on / I off ) ratio as well as a subthreshold slope (SS) steeper than 60 mV/dec have been predicted in the absence of the electron–phonon interaction previously. By using the Dirac-type effective Hamiltonian description for strained graphene and the non-equilibrium Green's function method to systematically account for the electron–phonon scattering, along with Poisson's equation, we demonstrate that the abovementioned I on / I off ratio and SS value can be maintained even in the presence of electron–phonon scattering, although the I on / I off ratio and the I D range over which the steep SS persists are reduced. [ABSTRACT FROM AUTHOR]

A self-consistent and 3-dimensional (3-D) quantum simulator is described for Si-nanowire transistors based on the Wigner function model and multidimensional Schrodinger-Poisson algorithm. The studies have shown that the source-drain tunneling is a major phenomenon related to a scaling limit of nanowire devices, and the semiclassical simulation has measurably underestimated a minimum gate length.

A comparative computational study on the strain effects in Si nanostructures including bulk, thin film and nanowire configurations is described. First principles calculation is used for identifying the bandstructure parameters such as band splitting energy and transport effective mass and it is shown that bulk Si and Si thin films have similar strain effects on the bandstructure parameters under uniaxial strain.

The linear and nonlinear characteristics of electron waveguides with respect to ionized impurity scattering are investigated through the Wigner function model. The waveguides' pertinent parameters and transition probability caused by impurity scattering are represented by using the one-dimensional Liouville equation and the transverse eigenfunctions. Results show that the waveguides' quantized steps of conductance deteriorate with the increase in the total amount of impurities.

Graphene nanomeshes (GNMs) are expected to be a high-performance channel material for metal-oxide-semiconductor field-effect-transistors (MOSFETs), since they can open up a band gap in a large sheet of graphene thin film by simply introducing two-dimensional periodical nanoscale holes. In this paper, we theoretically investigate the electronic band structures and the electron transport properties of GNMs based on a tight-binding approach. We demonstrate that GNMs have the capability of band structure engineering by controlling its neck width and furthermore the potential ability providing high current drivability when applied to a field-effect-transistor channel. [ABSTRACT FROM AUTHOR]

We have investigated the fundamental transport characteristics in carbon nanotubes (CNTs) in order to realize a high-frequency device. In the present analysis, the electron and hole densities are excited at each lead and propagate as a wave from the left contact to the right contact in the CNTs. First, we applied Green’s-function method formulation to CNTs with arbitrary chirality. We then calculated the basic conductive characteristics in the CNTs. In the metallic and intrinsic CNTs, the assumption of a linearly varying potential distribution is valid because the electron and hole densities satisfy the charge neutrality condition, and their distributions become uniform. We evaluated the I-V characteristics of semiconductive and metallic CNTs. Based on the obtained results, we can control the differential conductance from a negative value to a value of several times the conductance quantum by means of chirality, Fermi level, and bias voltage. We evaluated the GV/I-V characteristics of the zigzag CNT and found that when the group velocity of a mode with a real wave vector is comparable to that of another mode, GV/I takes a maximum at V0, which corresponds to the transition between these modes. [ABSTRACT FROM AUTHOR]

We have studied the basic conductive characteristics in carbon nanotubes (CNTs) for the purpose of application to a high-frequency device. In the analysis, the current flow in the CNTs is viewed as the quantum transport of electronic waves. First, we analyzed the dispersion relations of electronic waves in the CNTs based on the linear combination of atomic orbitals expansion method. In addition, we investigated the current-density distributions around the circumference of the CNTs and the current-voltage characteristics by using the transfer-matrix method. As a result, the current distributions were found to be significantly controlled by both the chirality of the CNTs and the position of the current sources around the circumference. Based on these results, we propose herein a ferrite device that acts as a filter in the terahertz frequency domain. In this device, the high-frequency current flowing on the CNTs may excite and receive directly the spin waves in the ferrite film beneath them, and the operating wavelength may be controlled by means of the chirality via the current-density distributions on the CNTs. In addition, we found that the performance of the device can be improved by using the p-type CNTs as the excitation electrodes rather than the intrinsic CNTs. [ABSTRACT FROM AUTHOR]

Electron transport in Si double-gate junctionless transistors (JLTs) is simulated on the basis of the multisubband Monte Carlo method, considering acoustic phonons, intervalley phonons, ionized impurities (IIs), and surface roughness (SR) scattering. It is demonstrated that JLTs can actually minimize the mobility degradation caused by SR scattering and improve the current drivability. On the other hand, II scattering is confirmed to degrade the current drivability compared with conventional MOSFETs with an intrinsic channel. However, the performance degradation in JLTs due to II scattering is shown to be insignificant, owing to the screening effect of free carriers and the forward scattering properties of high-speed carriers. Furthermore, by extracting a backscattering coefficient, the screening effect and the forward scattering properties are shown to more mitigate II scattering as the gate voltage increases. [ABSTRACT FROM AUTHOR]

We evaluate drive currents and consumption powers of InAs and Si nanowire metal–oxide–semiconductor field-effect transistors (MOSFETs) with various crystal orientations, by using a ballistic MOSFET model coupled with tight-binding band structure calculation. We demonstrate that performance dependence on the wire orientation is not significant in InAs NWFETs compared to Si NWFETs, due to an isotropic nature of the \Gamma valley, and furthermore, a lower power switching is expected in InAs NWFETs even if the gate oxide thickness reduces down to a quantum capacitance limit. The present results suggest that InAs NWFETs have the advantage over the Si counterpart in terms of lower power operation and flexibility in layout design of integrated circuits. [ABSTRACT FROM AUTHOR]

Abstract: We predict an anomalous 0-π transition in Josephson junctions with a ferromagnetic-insulator (FI) barrier. Previously it wasfoundthattheground stateofsuch junctions alternates between0and π states when the thickness of FI is increasing by a single atomic layer. By solving the Bogoliubov de-Gennes equation and using the Furusaki-Tsukada formula, we show that similar 0-π transition canbe also inducedby increasing temperature T. Therefore the existence of π state can beexperimentally confirmedby simply observing the nonmonotonic T dependence of the Josephson critical current. [Copyright &y& Elsevier]

In this paper, we study the band structures of Si and InAs nanowires based on a first-principles calculation and project performance potentials of Si and InAs nanowire field-effect-transistors (NWFETs) by using a semiclassical ballistic transport model. We demonstrate that the device performance of InAs NWFETs strongly depends on its cross-sectional dimension and gate oxide thickness. In particular, InAs NWFETs unexpectedly indicate lower current drivability than Si NWFETs as the gate oxide thickness is extremely scaled down to 0.5 nm in the ballistic limit. We discuss the mechanism in terms of operation in quantum capacitance limit (QCL). We also demonstrate that the advantage in the lower power operation with InAs NWFETs reduces when the devices operate in the QCL or higher subbands with a heavier transport effective mass participate in the transport. [ABSTRACT FROM PUBLISHER]

Although a graphene is a zero-gap semiconductor, band-gap energy values up to several hundred millielectronvolts have been introduced by utilizing quantum–mechanical confinement in nanoribbon structures or symmetry breaking between two carbon layers in bilayer graphenes (BLGs). However, the opening of a band gap causes a significant reduction in carrier velocity due to the modulation of band structures in their low-energy spectra. In this paper, we study intrinsic effects of the band-gap opening on ballistic electron transport in graphene nanoribbons (GNRs) and BLGs based on a computational approach, and discuss the ultimate device performances of FETs with those semiconducting graphene channels. We have shown that an increase in the external electric field in BLG-FETs to obtain a larger band-gap energy degrades substantially its electrical characteristics because of deacceleration of electrons due to a Mexican hat structure; therefore, GNR-FETs outperform in principle BLG-FETs. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the performance potentials of silicon nanowire (SNW) and semiconducting graphene nanoribbon (GNR) MOSFETs by using first-principles bandstructures and ballistic current estimation based on the "top-of-the-barrier" model. As a result, we found that SNW-MOSFETs display a strong orientation dependence via the atomistic bandstructure effects, and [110]-oriented SNW-MOSFETs provide smaller intrinsic device delays than Si ultrathin-body MOSFETs when the wire size is scaled smaller than 3 nm. Furthermore, GNR-MOSFETs are found to exhibit promising device performance if the ribbon width is designed to be larger than a few nanometers and a finite band gap can be established. [ABSTRACT FROM AUTHOR]

Abstract: We present a study on the atomistic simulation of the spin-polarized transmissions through InAs/AlSb double barrier resonant tunneling heterostructures. By making use of the atomistic sp3s* tight binding Hamiltonian including the intra-atomic spin-orbit interaction and the recursive Green’s function method, we obtain the significant anisotropic zero-magnetic-field spinsplitting of the resonant transmission peak in the absence of the external electric field, demonstrating the importance of the barrier material and the atomic scale detail of the hetero interfaces on the spin-splitting. [Copyright &y& Elsevier]

By inserting a strain into the active layer of quantum-well lasers, the functionality of the laser can be improved. Regarding the valence band structure of the strained quantum-well laser with an external electric field applied, a multiband-effective-mass theory is developed in which the band-mixing effect of the valence band including the spin-split off interaction is taken into account herein. Further, the present method is applied to the gain calculation of the TE and TM modes in a strained quantum well laser. As a result, it is found that the switching operation from the TE mode to the TM mode of the induced emission is possible with an external electric field. [ABSTRACT FROM AUTHOR]

We study computationally the electronic transport properties through mechanically squashed zigzag carbon nanotubes (CNTs) under the uniform electric field perpendicular to the tube axis, based on the tight-binding molecular dynamics method for the structural analysis and the Landauer-Büttiker's formalism for the transport analysis. Our simulations show that the band gaps of the zigzag carbon nanotubes exhibit nonlinear decrease as increasing the deformation ratio in the presence of the external perpendicular electric field, in contrast to the case of zero electric field, where the band gap decreases linearly as increasing the deformation ratio. Such properties allow us to tune the sensitivity of the electromechanical response in CNT devices by applying the external electric field. [ABSTRACT FROM AUTHOR]

The difference in the impact of source–drain (SD) direct tunneling in In0.53Ga0.47As and InP metal–oxide–semiconductor field-effect transistors (MOSFETs) was investigated by a quantum Wigner Monte Carlo simulation. It was found that the subthreshold current increase due to SD direct tunneling is more marked in In0.53Ga0.47As MOSFETs owing to their lower effective mass. In addition, the critical channel length at which a drastic increase in subthreshold current occurs owing to SD direct tunneling was found to be about 20 nm for both In0.53Ga0.47As and InP MOSFETs. Since this value is significantly larger than that for Si MOSFETs, SD direct tunneling can be a major obstacle in downscaling III–V MOSFETs into Lch < 20 nm. Hence, to go beyond the end of the roadmap, we will need a selection of materials to suppress SD direct tunneling. [ABSTRACT FROM AUTHOR]

Silicene or germanene is a monolayer honeycomb lattice made of Si or Ge, similar to graphene made of C. In this work, we have assessed the performance potentials of silicene nanoribbon (SiNR), germanene nanoribbon (GeNR), and graphene nanoribbon (GNR), which all have a sufficient band gap to switch off, as field-effect transistor (FET) channel materials. We have demonstrated that, by comparing at the same band gap of ∼0.5 eV, the GNR FET maintains an advantage over SiNR or GeNR FETs under an ideal transport situation, but SiNR and GeNR are attractive channel materials for high-performance FETs as well. [ABSTRACT FROM AUTHOR]

The influence of quantum transport effects in ultrashort-channel InP metal–oxide–semiconductor field-effect transistors (MOSFETs) was investigated using a Wigner Monte Carlo method, in which both quantum transport and carrier scattering effects can be fully incorporated. It was found that source–drain (SD) direct tunneling becomes evident for channel lengths of less than about 20 nm. Since this critical channel length is approximately three times larger than that in Si-MOSFETs, countermeasures should be taken to suppress SD direct tunneling in order to aggressively downscale III–V channel MOSFETs. In contrast, quantum reflection effects were found to have a negligible influence on the on-state drain current. [ABSTRACT FROM AUTHOR]

We study channel length scaling effects on the device performance of junctionless field-effect transistors, based on a Monte Carlo approach. We found that impurity scattering due to ionized donors in the channel significantly decreases the drain current at a small gate overdrive for a long channel device, but the influence of impurity scattering gradually disappears on reducing the channel length. We discuss the mechanism behind these behaviors in terms of an increasing importance of the forward-scattering nature of ionized impurities in accordance with the channel length scaling. [ABSTRACT FROM AUTHOR]

Ballistic performances of InAs, InSb, and GaSb nanowire field-effect transistors (NWFETs) were theoretically investigated. We found that InAs and InSb NWFETs exhibit similar device performances due to 1D band structure effects. Furthermore, although these In-based NWFETs suffer from the density-of-states (DOS) bottleneck, a lower power switching is expected. On the other hand, GaSb NWs have multiple energy subbands at conduction band minima, as a result of the projection of L-valleys which thus improves the DOS. In particular, a <110>-oriented GaSb NW has an improved DOS and a high electron velocity simultaneously, and thus, it could be a strong competitor to In-based NWFETs. [ABSTRACT FROM AUTHOR]

A junctionless (JL) transistor has no pn junctions and has a number of advantages to fabricate ultrashort-channel metal–oxide–semiconductor field-effect transistors. In this paper, we study the electron transport in JL transistors based on a Monte Carlo simulation. We demonstrate that high channel doping will not degrade the drive current seriously, because ionized impurities scatter electrons mostly forward, and thus there is less chance for scattered electrons to return back to the source. We also find that smaller parasitic resistance in the source of a JL transistor also contributes to achieve high drive current. [ABSTRACT FROM AUTHOR]

In this paper, we present a theoretical evaluation of ballistic electron transport in field-effect transistors (FETs) with semiconducting graphehe channels; bilayer graphenes (BLGs), monolayer graphene nanoribbons (MLGNRs), and bilayer graphene nanoribbons (BLGNRs). We found that the use of BLGNRs produces little advantage in either increasing the band gap energy or improving the device performance, as compared with a pristine BLG device. We also demonstrated that BLG-based FETs exhibit quite different behavior in the drain current versus gate voltage characteristics from that of MLGNR-FETs, since a distorted dispersion relation around the conduction band minima significantly affects the drain current property. [ABSTRACT FROM AUTHOR]

The influence of source/drain (S/D) parasitic resistance in ultrathin body (UTB) III–V channel metal–oxide–semiconductor field-effect transistor (MOSFET) was investigated based on Monte Carlo simulation. We found that heavily doped S/D improves source starvation and suppresses carrier's backscattering from drain to channel, owing to increased electron–electron scattering. As a result, the heavily doped S/D was shown to be effective to enhance the current drive and transconductance of UTB III–V channel MOSFET. In addition, we demonstrated that the heavily doped S/D has the advantage to provide unsaturated drain current characteristics. [ABSTRACT FROM AUTHOR]