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An emission–diffusion theory that describes MOSFETs from the ballistic to diffusive limits is developed. The approach extends the Crowell–Sze treatment of metal–semiconductor junctions to MOSFETs and is equivalent to the scattering/transmission model of the MOSFET. This paper demonstrates that the results of the transmission model can be obtained from a traditional, drift–diffusion analysis when the boundary conditions are properly specified, which suggests that the traditional drift–diffusion MOSFET models can also be extended to comprehend ballistic limits. [ABSTRACT FROM PUBLISHER]

We constructed the Hamiltonian of spin–orbit splitting for carriers of a tubular electron gas in InAs nanowires. The spectral problem is solved using an exact numerical diagonalization. It is shown that the contribution of k -linear Dresselhaus-like spin–orbit (SO) coupling leads to renormalization of the so-called SO-gaps and appearance of anticrossings in subband spectrum. These features can be detected in ballistic transport. [ABSTRACT FROM AUTHOR]

In this paper, we attempt the theoretical modeling of the magnetic tunnel junctions with embedded magnetic and nonmagnetic nanoparticles (NPs). A few abnormal tunnel magnetoresistance (TMR) effects, observed in related experiments, can be easily simulated within our model: we found, that the suppressed TMR magnitudes and the TMR sign-reversing effect at small voltages are related to the electron momentum states of the NP located inside the insulating layer. All these TMR behaviors can be explained within the tunneling model, where NP is simulated as a quantum well (QW). The coherent double barrier tunneling is dominating over the single barrier one. The origin of the TMR suppression is the quantized angle transparency for spin polarized electrons being in one of the lowest QW states. The phenomenon was classified as the quantized conductance regime due to restricted geometry. [ABSTRACT FROM AUTHOR]

In this paper, we report the observation of random telegraph noise (RTN) in highly scaled InGaAs gate-all-around (GAA) MOSFETs fabricated by a top-down approach. RTN and low-frequency noise were systematically studied for devices with various gate dielectrics, channel lengths, and nanowire diameters. Mobility fluctuation is identified to be the source of 1/f noise. The 1/f noise was found to decrease as the channel length scaled down from 80 to 20 nm comparing with classical theory, indicating the near-ballistic transport in highly scaled InGaAs GAA MOSFET. Low-frequency noise in ballistic transistors is discussed theoretically. [ABSTRACT FROM AUTHOR]

The spin wave (SW) ballistic transport properties are investigated for nanojunction systems composed of thin [ Co 1 − c Gd c ] ℓ ′ [ Co ] ℓ [ Co 1 − c Gd c ] ℓ ′ layered nanostructures between cobalt leads. The nanojunction is considered as a homogeneous random alloy of concentrations c on an hcp crystal lattice. ℓ corresponds to the numbers of the hcp (0001) atomic planes per given layer. The phase field matching theory (PFMT) is used to investigate the spin dynamics of the nanojunction system in the virtual crystal approximation (VCA), valid in particular for submicroscopic SW wavelengths. The model calculations yield the spin modes localized on the nanojunction, normal to its plane, in their propagating and resonant forms. The eigenvectors of these modes are calculated for certain cases to illustrate the spin precession configurations on the nanojunction. The VCA-PFMT approach yields a general model, and is used to calculate the SW ballistic scattering and transport across the nanojunction for spin waves incident from the Co leads onto the nanojunction. The results demonstrate resonance Fano assisted maxima in the SW transmission spectra due to interactions between incident lead spin waves and localized spin resonances on the nanojunction. It is shown that these maxima change with nanojunction thickness and alloy concentration. The spectral transmission results for low frequency SWs are of specific interest, in particular they correspond to submicroscopic wavelengths which present an interest for current research of magnonic devices. [ABSTRACT FROM AUTHOR]

We investigate ballistic transport phenomena through a region containing a cavity in a quasi-one-dimensional quantum wire. Conductance curve calculated as a function of a structure parameter shows very narrow periodic dips, which are due to anti-resonances. The nature of the virtual bound state appearing around the cavity is studied in detail. Transport phenomena through a small dilute magnetic semiconductor are also investigated. [ABSTRACT FROM AUTHOR]

Here, we report the effect of channel thickness on the performance of a InGaSb-on-insulator FET with 15-nm gate length. The ballistic current-voltage characteristic is computed by nonequilibrium Green’s function method using thickness-dependent effective mass, which is extracted from tight binding dispersion. Simulation result reveals that the threshold voltage and subthreshold slope decrease with decreasing channel thickness. Nearly three times enhancement in the ON-state current is observed for 3 nm compared with a 5-nm channel when the OFF-state current is made equal in each case by tuning the gate metal work function (WF). The drain-induced barrier lowering is found to decrease with decreasing channel thickness. However, interface states and roughness greatly affect the performance of such ultrathin-body device. Nevertheless, impact of interface states can be compensated by engineering the gate metal WF. [ABSTRACT FROM AUTHOR]

A quasi-analytical model bas been developed for predicting the current–voltage characteristics of a cylindrical surrounding gate metal-oxide-semiconductor field-effect-transistor (MOSFET) by taking ballistic transport and quantum confinement effects into consideration. Quantum effect was incorporated in the Poisson’s equation in a self-consistent way together with the calculated subband energy levels. The model was validated with numerical simulation. Better agreements were obtained as compared with several previous models. Our results further revealed that the top of barrier (ToB) approximation is not accurate enough at large gate and drain biases; tunneling current and better electrostatic model have to be taken into account. [ABSTRACT FROM AUTHOR]

We investigated the effect of body thickness on the electrical performance of GaSb double-gate ultrathin-body (DG-UTB) MOSFET by examining the band structure of the 12- ( $\sim 2$ nm), 24- ( $\sim 4$ nm), 36- ( $\sim 6$ nm), and 48- ( $\sim 8$ nm) atomic-layer (AL) thick GaSb. Two different surface orientations, namely, (100) and (111), were studied. sp3d5s* tight-binding model is used to calculate the band structures of GaSb MOSFET. Ballistic transport was studied using the semiclassical top-of-barrier model with applied self-consistent real-space potential across the body. First, we found that for (100) surface orientation, GaSb DG-UTB FET with body thickness of 24 ALs offered relatively larger ON-state current for various gate dielectric materials studied. However, for (111) surface orientation, 12 ALs GaSb DG-UTB FET showed the best performance due to its reasonably higher injection velocity and larger electron density. Furthermore, for the FET with a body thickness of 48 ALs and HfO2 dielectric, it was observed that the charge occupations shift toward the surface, unlike the cases of FETs with thinner body, leading to the formation of inversion charge on the surface. Finally, we compared the ON-state current of GaSb DG-UTB FET with different channel surface orientations and found that (100) surface generally outperforms (111) surface in terms of ON-state current. [ABSTRACT FROM AUTHOR]

Magnetotransport measurements of a ballistic quantum wire exposed to two magnetic barriers of opposite polarity in series are reported. We find two types of conductance resonances with quite different characteristic magnetic fields. Numerical simulations show that the first type, characterized by a larger fluctuation period of the magnetoconductance, originates from bound states localized at the magnetic barrier oriented in the same direction with the perpendicular component of the external magnetic field, and the second type of conductance fluctuation can be traced back to states that reside close to the second magnetic barrier with antiparallel alignment. The simulations furthermore show that the confinement mechanism for these states can be understood in terms of spatially varying diamagnetic shifts of the one-dimensional wire modes. [ABSTRACT FROM AUTHOR]

The effective thermal conductivity of nanofilms is size dependent due to the diffusive–ballistic transport of phonons. In this paper, we investigate the cross-plane phonon transport from the viewpoint of the phonon Boltzmann equation. A predictive model for the size dependent thermal conductivity is proposed and agrees well with the results of molecular dynamics simulation for silicon nanofilms. The ballistic transport has different effects on the heat conduction in the in-plane or cross-plane directions, which causes the anisotropy of thermal conductivity of nanofilms. Such anisotropy is also size dependent and vanishes with the increase of film thickness. [ABSTRACT FROM AUTHOR]

After Vesta, the NASA Dawn spacecraft will visit the dwarf planet Ceres to carry out in-depth observations of its surface morphology and mineralogical composition in 2015. One of the important questions is whether Ceres has any outgassing activity that would lead to the formation of a thin atmosphere. The recent detection of water vapor emitted from localized source regions by Herschel ( Küppers et al., 2014 ) has only underscored this point. If the localized outgassing activity observed by Herschel is totally switched off, could a sizable surface-bounded exosphere still be maintained by other source mechanisms? Our preliminary assessment is that chemical sputtering via solar wind interaction and meteoroid impact are probably not adequate because of the large injection speed of the gas at production relative to the surface escape velocity of Ceres. One potential source is a low-level outgassing effect from its subsurface due to thermal sublimation with a production rate of the order of 10 24 molecules s −1 as first considered by Fanale and Salvail (1989) . If the water plumes are active, the fall-back of some of the water vapor onto Ceres’ surface would provide an additional global source of water molecules on the surface with a production rate of about 10 25 molecules s −1 . In this work, different scenarios of building up a tenuous exosphere by ballistic transport and the eventual recycling of the water molecules to the polar cold trap are described. It turns out that a large fraction of the exospheric water could be transferred to the polar caps area as originally envisaged for the lunar polar ice storage. [ABSTRACT FROM AUTHOR]

Thermal conductance in helically coiled carbon nanotubes (HCCNTs) is calculated out of phonon dispersion relations: anharmonicity is included through Brenner interatomic potential and scattering rates of the three-phonon Umklapp processes are calculated exactly, for all allowed transport channels. Highlighted are the universal features of the quantized thermal conductance and crossover from the ballistic to the diffusive transport regime is studied in detail. Correlation between the geometrical parameters of HCCNTs and thermal conductance is investigated. Finally, the specific heat is calculated and compared to that of the other carbon materials. [ABSTRACT FROM AUTHOR]

Basic topics of spintronics such as spin valve, interface resistance due to the mismatch of conduction modes, spin potentials, non-local spin voltage, spin moment and its transport, Landau-Lifshitz-Gilbert equation, and explanation on its basis why a magnet has an "easy axis", nanomagnet dynamics by spin current, polarizers and analyzers of spin current, diffusion equation for ballistic transport and current in terms of non-equilibrium potentials are discussed in the frame of the "bottom-up" approach of modern nanoelectronics. [ABSTRACT FROM AUTHOR]

Two-dimensional group-IV lattices silicene and germanene are known to share many of graphene's remarkable mechanical and electronic properties. Due to the out-of-plane buckling of the former materials, there are more means of electronic funtionalization, e.g. by applying uniaxial strain or an out-of-plane electric field. We consider monolayer hexagonal Sn (stanene) as an ideal candidate to feasibly implement and exploit graphene physics for nanoelectronic applications: with increased out-of-plane buckling and sizable spin-orbit coupling it lends itself to improved Dirac cone engineering. We investigate the ballistic charge transport regime of armchair Sn nanoribbons, classified according to the ribbon width W = {3 m - 1, 3 m, 3 m + 1} with integer m. We study transport through (non-magnetic) armchair ribbons using a combination of density functional theory and non-equilibrium Green's functions. Sn ribbons have earlier current onsets and carry currents 20% larger than C/Si/Ge-nanoribbons as the contact resistance of these ribbons is found to be comparable. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: Calculations are presented for the scattering and ballistic transport of spin waves (SW) incident from cobalt leads, on ultrathin ferrimagnetic cobalt–gadolinium nanojunction systems. The nanojunction itself is a randomly disordered alloy of thickness ℓ hcp lattice planes between matching hcp planes of the Co leads, at known stable concentrations for this alloy system. To compute the spin dynamics, and the SW scattering and ballistic transport, this alloy nanojunction is modeled in the virtual crystal approximation (VCA), valid in particular at the length scale of the nanojunction for submicroscopic SW wavelengths. The phase field matching theory (PFMT) is applied to compute the localized and resonant magnons on the nanojunction. These magnons, characteristic of the embedded nanostructure, propagate in its symmetry plane with spin precession amplitudes that decay or match the spin wave states in the semi-infinite leads. The eigenvectors of these magnon modes are calculated for certain cases to illustrate the spin precession configurations on the nanojunction. The VCA-PFMT approach is also used to calculate the reflection and transmission spectra for the spin waves incident from the Co leads on the nanojunction. The results demonstrate resonance assisted maxima for the ballistic SW transmission spectra due to interactions between the incident spin waves and the nanojunction magnon modes. These properties are general for variable nanojunction thicknesses and alloy stable concentrations . In particular, the positions of the resonance assisted maxima of spin wave transmission can be modified with nanojunction thickness and alloy concentration. [Copyright &y& Elsevier]

We show that a discrete tight-binding model representing either a random or a quasiperiodic array of bonds can have the entire energy spectrum or a substantial part of it absolutely continuous, populated by extended eigenfunctions only, when atomic sites are coupled to the lattice locally, or non-locally from one side. The event can be fine-tuned by controlling only the host–adatom coupling in one case, while in two other cases cited here an additional external magnetic field is necessary. The delocalization of electronic states for the group of systems presented here is sensitive to a subtle correlation between the numerical values of the Hamiltonian parameters – a fact that is not common in the conventional cases of Anderson localization. Our results are analytically exact, and supported by numerical evaluation of the density of states and electronic transmission coefficient. [ABSTRACT FROM AUTHOR]

Theoretical models are adapted to describe the hysteresis effects seen in the electrical characteristics of carbon nanotube field-effect transistors. The ballistic transport model describes the contributions of conduction energy sub-bands over carbon nanotube field-effect transistor drain current as a function of drain-source and gate-source voltages as well as other physical parameters of the device. The limiting-loop proximity model, originally developed to understand magnetic hysteresis, is also utilized in this work. The curves obtained from our developed model corroborate well with the experimentally derived hysteretic behavior of the transistors. Modeling the hysteresis behavior will enable designers to reliably use these effects in both analog and memory applications. [ABSTRACT FROM AUTHOR]

The ballistic transport performance of field-effect transistor (FET) based on hydrogenated silicene and germanene, i.e., silicane and germanane, respectively, is examined. The electronic band structures of silicane and germanane are investigated using the first-principles density functional theory. Subsequently, the ballistic performance of FETs is evaluated via the semiclassical ballistic transport model. We find that silicane n-MOSFET offers a relatively better ON-current performance than transistors made of germanane and 2-D transition metal dichalcogenides (2-D-TMDs) ( MoS{2} , MoSe{2} , WS{2} , and WSe{2} ). Germanane n-MOSFET suffers from the issue of low density of states due to its smaller electron effective mass. P-FETs based on germanane and silicane have higher ON-current than those of 2-D-TMDs p-FETs. Further investigation on other aspects of silicane and germanane MOSFETs, such as gate leakage and contact resistance, is needed to comprehensively assess their overall performance metrics. [ABSTRACT FROM PUBLISHER]

Electron transport through the quantized L valley of (111) surface orientation is a possible solution to density-of-states bottleneck of GaAs. Quantization splits the L valley into L[111] valley pair and remote L valley pairs, L[\overline111] , L[1\overline11] , and L[11\overline1] . The L[111] valley pair projects to the 2-D Brillouin zone center above the \Gamma valley and its population enhances the drive current. However, for a typical 5-nm thin body, the \Gamma{-}L[111] energy separation is still {\approx}{\rm 0.17}~{\rm eV} and the \Gamma valley primarily governs the electron transport. We analyze the compressive biaxial strain effects on the energy levels and effective masses of \Gamma , L[111] , and remote L valleys of a 5-nm (111) GaAs ultrathin body using a orbital basis tight binding model. We then evaluate the ballistic performance of a 10-nm double-gate device using an effective mass Schrodinger's equation with the extracted masses and band energies from sp^3s^\astd^5 model. Compressive strain promotes the L[111] and remote L valleys transport by reducing the \Gamma-L[111] and $\Gamma$ -remote L valleys energy offsets. This results in a significant improvement in charge density and drive current. A compressive stress larger than 2.5 GPa brings the remote L valleys even below the L[111] valley. Under this stress condition, the remote L[\overline111] and L[1\overline11] valleys govern the ON-state transport. The different wavefunction symmetries of L[111] and remote L valleys are the physics behind the stress modulated enhanced L valley transport. [ABSTRACT FROM AUTHOR]

Abstract: Ballistic thermoelectric properties in double-bend graphene nanoribbons (GNRs) are investigated by using the nonequilibrium Green's function. We find that due to the elastic scattering caused by the interface mismatching, the thermal conductance contributed by phonons is greatly reduced, while ballistic transport behaviors for electrons are dramatically demolished, and even some gaps can be opened at antiresonance energies. Near these antiresonance gaps, the maximum value of ZT ( ) can be observed, much larger than that for straight GNRs. Moreover, this can be effectively tuned by modulating the length or width of double-bend GNRs. [Copyright &y& Elsevier]

In this work, we present a new theoretical framework to model the transport and surface chemistry under molecular (Knudsen) flow. Our approach is based on casting the transport inside nanostructures as a single-particle discrete Markov chain process. One of the advantages of this approach is that it allows us to decouple the complexity of the surface chemistry from the transport model, thus allowing its application under general surface chemistry conditions, including atomic layer deposition (ALD) and chemical vapor deposition (CVD). Our model also allows us to determine statistical information of the trajectory of individual molecules, such as the average interaction time or the number of wall collisions for molecules entering the nanostructures as well as to track the relative contributions to thin-film growth of different independent reaction pathways at each point of the feature. This offers a straightforward way of incorporating into ALD simulations non-ideal surface processes, such as parasitic CVD or surface recombination. By studying the asymptotic behavior of the Markov chain process, we were also able to establish a direct link between ballistic models, kinetic Monte Carlo simulations, and continuous models based on the use of the diffusion equation under Knudsen conditions. Finally, we show that, under certain approximations, the coverage profile inside a nanostructure under ALD conditions is controlled by the total exposure, and not by the details of the surface flux dependence with time during the exposure, as long as the reaction probabilities are pressure independent. [ABSTRACT FROM AUTHOR]

A ballistic-electron transport-based semiconductor nanorectifier, also known as a ballistic rectifier, has been demonstrated to have an intrinsic zero threshold voltage. In this paper, we characterize its low-frequency noise properties and show that the zero-threshold property enables elimination of the flicker noise. As a potential terahertz detector, the ballistic rectifier exhibits a noise equivalent power in the range of commercially available, uncooled thermal terahertz detectors. The observed noise in the device at finite biases is modeled quantitatively. The derived simple formula reveals that the narrowest part of the electron channels has a dominant role in the device noise properties. [ABSTRACT FROM PUBLISHER]