Showing papers on "Ballistic conduction published in 2008"
TL;DR: This work shows that the fluctuations are significantly reduced in suspended graphene samples and reports low-temperature mobility approaching 200,000 cm2 V-1 s-1 for carrier densities below 5 x 109 cm-2, which cannot be attained in semiconductors or non-suspended graphene.
Abstract: The discovery of graphene1,2 raises the prospect of a new class of nanoelectronic devices based on the extraordinary physical properties3,4,5,6 of this one-atom-thick layer of carbon. Unlike two-dimensional electron layers in semiconductors, where the charge carriers become immobile at low densities, the carrier mobility in graphene can remain high, even when their density vanishes at the Dirac point. However, when the graphene sample is supported on an insulating substrate, potential fluctuations induce charge puddles that obscure the Dirac point physics. Here we show that the fluctuations are significantly reduced in suspended graphene samples and we report low-temperature mobility approaching 200,000 cm2 V−1 s−1 for carrier densities below 5 × 109 cm−2. Such values cannot be attained in semiconductors or non-suspended graphene. Moreover, unlike graphene samples supported by a substrate, the conductivity of suspended graphene at the Dirac point is strongly dependent on temperature and approaches ballistic values at liquid helium temperatures. At higher temperatures, above 100 K, we observe the onset of thermally induced long-range scattering. The novel electronic properties of graphene can be compromised when it is supported on an insulating substrate. However, suspended graphene samples can display low-temperature mobility values that cannot be attained in semiconductors or non-suspended graphene, and the conductivity approaches ballistic values at liquid-helium temperatures.
2,977 citations
TL;DR: In this paper, a colloquia review of thermal transport calculations for nano-junctions connected to two semi-infinite leads served as heat-baths is presented, where the authors discuss the treatments of nonlinear effects in heat conduction, including a phenomenological expression for the transmission, NEGF for phonon-phonon interactions, molecular dynamics (generalized Langevin) with quantum heatbaths, and electronphon interactions.
Abstract: In this colloquia review we discuss methods for thermal transport calculations for nanojunctions connected to two semi-infinite leads served as heat-baths. Our emphases are on fundamental quantum theory and atomistic models. We begin with an introduction of the Landauer formula for ballistic thermal transport and give its derivation from scattering wave point of view. Several methods (scattering boundary condition, mode-matching, Piccard and Caroli formulas) of calculating the phonon transmission coefficients are given. The nonequilibrium Green's function (NEGF) method is reviewed and the Caroli formula is derived. We also give iterative methods and an algorithm based on a generalized eigenvalue problem for the calculation of surface Green's functions, which are starting point for an NEGF calculation. A systematic exposition for the NEGF method is presented, starting from the fundamental definitions of the Green's functions, and ending with equations of motion for the contour ordered Green's functions and Feynman diagrammatic expansion. In the later part, we discuss the treatments of nonlinear effects in heat conduction, including a phenomenological expression for the transmission, NEGF for phonon-phonon interactions, molecular dynamics (generalized Langevin) with quantum heat-baths, and electron-phonon interactions. Some new results are also shown. We briefly review the experimental status of the thermal transport measurements in nanostructures.
490 citations
TL;DR: In this article, the effect of induced spin splittings on the graphene transport properties was studied and it was shown that the spin polarization of the current near the Dirac point increases with the length of the barrier.
Abstract: Ferromagnetic insulators deposited on graphene can induce ferromagnetic correlations in graphene. We estimate that induced exchange splittings $\ensuremath{\Delta}\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ can be achieved by, e.g., using the magnetic insulator EuO. We study the effect of the induced spin splittings on the graphene transport properties. The exchange splittings in proximity-induced ferromagnetic graphene can be determined from the transmission resonances in the linear response conductance or, independently, by magnetoresistance measurements in a spin-valve device. The spin polarization of the current near the Dirac point increases with the length of the barrier, so that long systems are required to determine $\ensuremath{\Delta}$ experimentally.
436 citations
TL;DR: In this paper, the authors review advances in chemically synthesized semiconductor nanowires as nanoelectronic devices and discuss 3-D heterogeneous integration that is uniquely enabled by multifunctional nanowire within a bottom-up approach.
Abstract: Semiconductor nanowires represent unique materials for exploring phenomena at the nanoscale. Developments in nanowire growth have led to the demonstration of a wide range of nanowire materials with precise control of composition, morphology, and electrical properties, and it is believed that this excellent control together with small channel size could yield device performance exceeding that obtained using top-down techniques. Here, we review advances in chemically synthesized semiconductor nanowires as nanoelectronic devices. We first introduce basic nanowire field-effect transistor structures and review results obtained from both p- and n-channel homogeneous composition nanowires. Second, we describe nanowire heterostructures, show that by using nanowire heterostructures, several limiting factors in homogeneous nanowire devices can be mitigated, and demonstrate that nanowire transistor performance can reach the ballistic limit and exceed state-of-the-art planar devices. Third, we discuss basic methods for organization of nanowires necessary for fabricating arrays of device and circuits. Fourth, we introduce the concept of crossbar nanowire circuits, discuss results for both transistor and nonvolatile switch devices, and describe unique approaches for multiplexing/demultiplexing enabled by synthetically coded nanowire. Fifth, we discuss the unique application of thin-film nanowire transistor arrays on low-cost substrates and illustrate this with results for relatively high-frequency ring oscillators and completely transparent device arrays. Finally, we describe 3-D heterogeneous integration that is uniquely enabled by multifunctional nanowires within a bottom-up approach.
375 citations
03 Sep 2008
TL;DR: An introduction to the nonequilibrium Green's function (NEGF) approach, which is a powerful conceptual tool and a practical analysis method to treat nanoscale electronic devices with quantum mechanical and atomistic effects.
Abstract: We aim to provide engineers with an introduction to the nonequilibrium Green's function (NEGF) approach, which is a powerful conceptual tool and a practical analysis method to treat nanoscale electronic devices with quantum mechanical and atomistic effects. We first review the basis for the traditional, semiclassical description of carriers that has served device engineers for more than 50 years. We then describe why this traditional approach loses validity at the nanoscale. Next, we describe semiclassical ballistic transport and the Landauer-Buttiker approach to phase-coherent quantum transport. Realistic devices include interactions that break quantum mechanical phase and also cause energy relaxation. As a result, transport in nanodevices is between diffusive and phase coherent. We introduce the NEGF approach, which can be used to model devices all the way from ballistic to diffusive limits. This is followed by a summary of equations that are used to model a large class of structures such as nanotransistors, carbon nanotubes, and nanowires. Applications of the NEGF method in the ballistic and scattering limits to silicon nanotransistors are discussed.
303 citations
TL;DR: In this paper, the effect of edge disorder on the conductance of the graphene nanoribbons was studied and it was shown that only very modest edge disorder is sufficient to induce the conduction energy gap.
Abstract: We study the effect of the edge disorder on the conductance of the graphene nanoribbons (GNRs).We find that only very modest edge disorder is sufficient to induce the conduction energy gap inthe ot ...
275 citations
TL;DR: A device to break the valley degeneracy in graphene and produce fully valley-polarized currents that can be either split or collimated to a high degree in a experimentally controllable way is proposed.
Abstract: We propose a device to break the valley degeneracy in graphene and produce fully valley-polarized currents that can be either split or collimated to a high degree in a experimentally controllable way. The proposal combines two recent seminal ideas: negative refraction and the concept of valleytronics in graphene. The key new ingredient lies in the use of the specular shape of the Fermi surface of the two valleys when a high electronic density is induced by a gate voltage (trigonal warping). By changing the gate voltage in a n-p-n junction of a graphene transistor, the device can be used as a valley beam splitter, where each of the beams belong to a different valley, or as a collimator. The result is demonstrated through an optical analogy with two-dimensional photonic crystals.
194 citations
TL;DR: It is found that for graphene samples with a large width over length ratio W/L, the Fano factor F reaches a maximum F ~ 1/3 at the Dirac point and that it decreases strongly with increasing charge density.
Abstract: We have investigated shot noise in graphene field effect devices in the temperature range of 42-30 K at low frequency (f=600-850 MHz) We find that for our graphene samples with a large width over length ratio W/L, the Fano factor F reaches a maximum F ~ 1/3 at the Dirac point and that it decreases strongly with increasing charge density For smaller W/L, the Fano factor at Dirac point is significantly lower Our results are in good agreement with the theory describing that transport at the Dirac point in clean graphene arises from evanescent electronic states
194 citations
TL;DR: In this article, a 10-band sp3d5s* semi-empirical atomistic tight-binding model coupled to a self-consistent Poisson solver is used for the dispersion calculation.
Abstract: Bandstructure effects in the electronic transport of strongly quantized silicon nanowire field-effect-transistors (FET) in various transport orientations are examined. A 10-band sp3d5s* semiempirical atomistic tight-binding model coupled to a self-consistent Poisson solver is used for the dispersion calculation. A semi-classical, ballistic FET model is used to evaluate the current-voltage characteristics. It is found that the total gate capacitance is degraded from the oxide capacitance value by 30% for wires in all the considered transport orientations ([100], [110], [111]). Different wire directions primarily influence the carrier velocities, which mainly determine the relative performance differences, while the total charge difference is weakly affected. The velocities depend on the effective mass and degeneracy of the dispersions. The [110] and secondly the [100] oriented 3 nm thick nanowires examined, indicate the best ON-current performance compared to [111] wires. The dispersion features are strong functions of quantization. Effects such as valley splitting can lift the degeneracies particularly for wires with cross section sides below 3 nm. The effective masses also change significantly with quantization, and change differently for different transport orientations. For the cases of [100] and [111] wires the masses increase with quantization, however, in the [110] case, the mass decreases. The mass variations can be explained from the non-parabolicities and anisotropies that reside in the first Brillouin zone of silicon.
192 citations
TL;DR: In this article, the scaling of nanowire transistors to 10-nm gate lengths and below is considered and compared with the published experimental data of nan-wire transistors, and the performance limit of a nan-ire transistor is assessed by applying a ballistic current model.
Abstract: This paper considers the scaling of nanowire transistors to 10-nm gate lengths and below. The 2-D scale length theory for a cylindrical surrounding-gate MOSFET is reviewed first, yielding a general guideline between the gate length and the nanowire size for acceptable short-channel effects. Quantum confinement of electrons in the nanowire is discussed next. It gives rise to a ground-state energy and, therefore, a threshold voltage dependent on the radius of the nanowire. The scaling limit of nanowire transistors hinges on how precise the nanowire size can be controlled. The performance limit of a nanowire transistor is then assessed by applying a ballistic current model. Key issues such as the density of states of the nanowire material are discussed. Comparisons are made between the model results and the published experimental data of nanowire devices.
138 citations
TL;DR: In this article, the charge density distribution, the electric field profile, and the resistance of an electrostatically created lateral p-n junction in graphene were studied, and it was shown that the voltage at the interface of the electron and hole regions is strongly enhanced due to limited screening capacity of Dirac quasiparticles.
Abstract: We study the charge density distribution, the electric field profile, and the resistance of an electrostatically created lateral p-n junction in graphene. We show that the electric field at the interface of the electron and hole regions is strongly enhanced due to limited screening capacity of Dirac quasiparticles. Accordingly, the junction resistance is lower than estimated in previous literature.
TL;DR: In a clean system the two-terminal conductance of the sample is reduced below the ballistic limit and is almost totally suppressed at low carrier concentrations in samples under tension, but residue disorder restores a small finite conductivity.
Abstract: We study a suspended graphene sheet subject to the electric field of a gate underneath. We compute the elastic deformation of the sheet and the corresponding effective gauge field, which modifies the electronic transport. In a clean system the two-terminal conductance of the sample is reduced below the ballistic limit and is almost totally suppressed at low carrier concentrations in samples under tension. Residual disorder restores a small finite conductivity.
TL;DR: In this article, the non-equilibrium green function (NEGF) method was used to provide a quantitative description of the conductance of graphene pn junctions, which is an important building block for graphene electronics devices.
Abstract: We use the non-equilibrium Green function (NEGF) method in the ballistic limit to provide a quantitative description of the conductance of graphene pn junctions - an important building block for graphene electronics devices. In this paper, recent experiments on graphene junctions are explained by a ballistic transport model, but only if the finite junction transition width, Dw, is accounted for. In particular, the experimentally observed anamolous increase in the resistance asymmetry between nn and np junctions under low source/drain charge density conditions is also quantitatively captured by our model. In light of the requirement for sharp junctions in applications such as electron focusing, we also examine the pn junction conductance in the regime where Dw is small and find that wavefunction mismatch (so-called pseudo-spin) plays a major role in sharp pn junctions.
Journal Article•
TL;DR: It is shown that the electric field at the interface of the electron and hole regions is strongly enhanced due to limited screening capacity of Dirac quasiparticles, and the junction resistance is lower than estimated in previous literature.
Abstract: We study the charge density distribution, the electric field profile, and the resistance of an electrostatically created lateral p-n junction in graphene. We show that the electric field at the interface of the electron and hole regions is strongly enhanced due to limited screening capacity of Dirac quasiparticles. Accordingly, the junction resistance is lower than estimated in previous literature.
TL;DR: In this paper, the inelastic scattering rate and the carrier mean free path for energetic hot electrons in graphene, including both electron-electron and electron-phonon interactions, were theoretically studied.
Abstract: We theoretically study the inelastic scattering rate and the carrier mean free path for energetic hot electrons in graphene, including both electron-electron and electron-phonon interactions. Taking account of optical phonon emission and electron-electron scattering, we find that the inelastic scattering time τ∼10−2–10−1ps and the mean free path l∼10–102nm for electron densities n=1012–1013cm−2. In particular, we find that the mean free path exhibits a finite jump at the phonon energy 200meV due to electron-phonon interaction. Our results are directly applicable to device structures where ballistic transport is relevant with inelastic scattering dominating over elastic scattering.
TL;DR: In this paper, the lateral displacements for ballistic electron beams in a two-dimensional electron gas modulated by metallic ferromagnetic (FM) stripes with parallel and antiparallel (AP) magnetization configurations were investigated.
Abstract: We investigate the lateral displacements for ballistic electron beams in a two-dimensional electron gas modulated by metallic ferromagnetic (FM) stripes with parallel and antiparallel (AP) magnetization configurations. It is shown that the displacements are negative as well as positive, which can be controlled by adjusting the electric potential induced by the applied voltage and the magnetic field strength of FM stripes. Based on these phenomena, we propose an efficient way to realize a spin beam splitter, which can completely separate spin-up and spin-down electron beams in the AP configuration by their corresponding spatial positions.
TL;DR: In this article, an efficient approach for the simulation of electronic transport in nanoscale transistors is presented based on the multi-subband Boltzmann transport equation under the relaxation time approximation, which takes into account the effects of quantum confinement and quasi-ballistic transport.
Abstract: An efficient approach for the simulation of electronic transport in nanoscale transistors is presented based on the multi-subband Boltzmann transport equation under the relaxation time approximation, which takes into account the effects of quantum confinement and quasi-ballistic transport. This approach is applied to the study of electronic transport in circular gate-all-around silicon nanowire transistors. Comparison with the nonequilibrium Green's function method shows that the new method gives reasonably accurate terminal characteristics. We study the influence of silicon body diameter and gate length on the terminal current and subthreshold slope (SS). We have found that the calculated ON current is inversely proportional to the gate length to the power 1/2, and that the silicon body diameter should be smaller than roughly 2/3 of the channel length in order to maintain the SS within 80 mV/dec.
TL;DR: In this paper, a detailed heat generation and transport mechanism in silicon devices with a focus on the nonequilibrium behavior of electrons and phonons is discussed, and fully coupled and self-consistent ballistic phonon and electron simulations are developed in order to examine the departure from equilibrium within the phonon system and its relevance for properly simulating the electrical behavior of devices.
Abstract: Heat conduction from transistors and interconnects is a critical design consideration for computing below the 20-nm milestone. This paper reviews detailed heat generation and transport mechanisms in silicon devices with a focus on the nonequilibrium behavior of electrons and phonons. Fully coupled and self-consistent ballistic phonon and electron simulations are developed in order to examine the departure from equilibrium within the phonon system and its relevance for properly simulating the electrical behavior of devices. We illustrate the manner in which nanoscale-transport phenomena are critically important for a broad variety of low-dimensional silicon-based devices, including FinFETs and depleted substrate transistors.
TL;DR: In this paper, the authors theoretically study the inelastic scattering rate and the carrier mean free path for energetic hot electrons in graphene, including both electron-electron and electron-phonon interactions.
Abstract: We theoretically study the inelastic scattering rate and the carrier mean free path for energetic hot electrons in graphene, including both electron-electron and electron-phonon interactions. Taking account of optical phonon emission and electron-electron scattering, we find that the inelastic scattering time $\tau \sim 10^{-2}-10^{-1} \mathrm{ps}$ and the mean free path $l \sim 10-10^2 \mathrm{nm}$ for electron densities $n = 10^{12}-10^{13} \mathrm{cm}^{-2}$. In particular, we find that the mean free path exhibits a finite jump at the phonon energy $200 \mathrm{meV}$ due to electron-phonon interaction. Our results are directly applicable to device structures where ballistic transport is relevant with inelastic scattering dominating over elastic scattering.
TL;DR: In this article, the authors investigated the electrical characteristics of cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field effect transistors with 4nm radius and the gate length ranging from 22to408nm.
Abstract: We have investigated the electrical characteristics of cylindrical gate-all-around twin silicon nanowire metal-oxide-semiconductor field effect-transistors with 4nm radius and the gate length ranging from 22to408nm. We observed strong transconductance overshoot in the linear source-drain bias regime in the devices with channel length shorter than 46nm. The mean free path estimated from the slope of the zero-field one dimensional ballistic resistance measured as a function of device length was almost the same as this length.
TL;DR: In this article, the surface roughness effects on surface-roughness-limited mobility in silicon-nanowire FETs were analyzed by means of a full-quantum 3D self-consistent simulation.
Abstract: Lateral size effects on surface-roughness-limited mobility in silicon-nanowire FETs are analyzed by means of a full- quantum 3-D self-consistent simulation. A statistical analysis is carried out by considering different realizations of the potential roughness at the Si-SiO2 interfaces. Nanowires with lateral section varying from 3 times 3 to 7 times 7 nm2 are considered. Effective mobility is computed by evaluating the electron density in a reduced channel region to eliminate parasitic effects from contacts. It is found that transport in wires with the smallest section is dominated by scattering due to potential fluctuations, resulting in a larger standard deviation of the effective mobility, whereas it is dominated by transverse-mode coupling in wires with larger section, resulting in a stronger influence of surface roughness at high gate voltages.
TL;DR: In this paper, the authors propose the theory of transport in a gate-tunable graphene junction, in which the gradient of the carrier density is controlled by the gate voltage, and find the conditions for observing ballistic transport and show that in existing devices they are satisfied only marginally.
Abstract: We propose the theory of transport in a gate-tunable graphene $p\text{\ensuremath{-}}n$ junction, in which the gradient of the carrier density is controlled by the gate voltage. Depending on this gradient and on the density of charged impurities, the junction resistance is dominated by either diffusive or ballistic contribution. We find the conditions for observing ballistic transport and show that in existing devices they are satisfied only marginally. We also simulate numerically the trajectories of charge carriers and illustrate challenges in realizing more delicate ballistic effects, such as Veselago lensing.
TL;DR: In this paper, the authors investigate energy transport in several two-level atom or spin-1∕2$ models by a direct coupling to heat baths of different temperatures, based on a recently derived quantum master equation which describes the nonequilibrium properties of internally weakly coupled systems appropriately.
Abstract: We investigate energy transport in several two-level atom or spin-$1∕2$ models by a direct coupling to heat baths of different temperatures. The analysis is carried out on the basis of a recently derived quantum master equation which describes the nonequilibrium properties of internally weakly coupled systems appropriately. For the computation of the stationary state of the dynamical equations, we employ a Monte Carlo wave-function approach. The analysis directly indicates normal diffusive or ballistic transport in finite models and hints toward an extrapolation of the transport behavior of infinite models.
TL;DR: In this article, experimental studies on the carrier transport in gate-all-around (GAA) silicon nanowire transistors (SNWTs) are reported, demonstrating their great potential as an alternative device structure for near-ballistic transport from top-down approach.
Abstract: As devices continue scaling down into nanometer regime, carrier transport becomes critically important. In this paper, experimental studies on the carrier transport in gate-all-around (GAA) silicon nanowire transistors (SNWTs) are reported, demonstrating their great potential as an alternative device structure for near-ballistic transport from top-down approach. Both ballistic efficiency and apparent mobility were characterized. A modified experimental extraction methodology for SNWTs is adopted, which takes into account the impact of temperature dependence of parasitic source resistance in SNWTs. The highest ballistic efficiency at room temperature is observed in sub-40-nm n-channel SNWTs due to their quasi-1-D carrier transport. The apparent mobility of GAA SNWTs are also extracted, showing their close proximity to the ballistic limit as shrinking the gate length, which can be explained by Shur's model. The physical understanding of the apparent mobility in SNWTs is also discussed using flux's scattering matrix method.
TL;DR: In this article, a theoretical study of the transport properties of zigzag and armchair graphene nanoribbons with a magnetic barrier on top is presented, and a method based on the Green's function technique is presented for the calculation of the magnetosubband structure, Bloch states and magnetoconductance of the graphene in a perpendicular magnetic field.
Abstract: A theoretical study of the transport properties of zigzag and armchair graphene nanoribbons with a magnetic barrier on top is presented. The magnetic barrier modifies the energy spectrum of the nanoribbons locally, which results in an energy shift of the conductance steps toward higher energies. The magnetic barrier also induces Fabry--P\'erot-type oscillations, provided the edges of the barrier are sufficiently sharp. The lowest propagating state present in zigzag and metallic armchair nanoribbons prevents confinement of the charge carriers by the magnetic barrier. Disordered edges in nanoribbons tend to localize the lowest propagating state, which get delocalized in the magnetic barrier region. Thus, in sharp contrast to the case of two-dimensional graphene, the charge carriers in graphene nanoribbons cannot be confined by magnetic barriers. We also present a method based on the Green's function technique for the calculation of the magnetosubband structure, Bloch states and magnetoconductance of the graphene nanoribbons in a perpendicular magnetic field. Utilization of this method greatly facilitates the conductance calculations, because, in contrast to existing methods, the present method does not require self-consistent calculations for the surface Green's function.
TL;DR: In this paper, the impact of band structure on deeply scaled III-V devices by using a self-consistent 20-band -SO semiempirical atomistic tight-binding model was examined.
Abstract: This paper examines the impact of band structure on deeply scaled III-V devices by using a self-consistent 20-band -SO semiempirical atomistic tight-binding model. The density of states and the ballistic transport for both GaAs and InAs ultrathin-body n-MOSFETs are calculated and compared with the commonly used bulk effective mass approximation, including all the valleys (, , and ). Our results show that for III-V semiconductors under strong quantum confinement, the conduction band nonparabolicity affects the confinement effective masses and, therefore, changes the relative importance of different valleys. A parabolic effective mass model with bulk effective masses fails to capture these effects and leads to significant errors, and therefore, a rigorous treatment of the full band structure is required.
TL;DR: Based on the Landauer-Buttiker formula and the tight binding model, the rectifying behavior can be achieved by applying an external gate voltage in the heterjunction region as mentioned in this paper.
Abstract: In this paper, we focus on a graphene heterojunction device: a Z-shaped graphene nanoribbon, which consists of two armchair leads and a zigzag junction. Based on the Landauer–Buttiker formula and the tight binding model, we found that the rectifying behavior can be achieved by applying an external gate voltage in the heterjunction region. We also found that the rectification effect is independent of junction width and length, it is an intrinsic property of the Z-junction graphene nanoribbon. This platform can be used to design and study functional graphene nanoscale devices.
TL;DR: In this paper, a 20-band sp3d5s* spin-orbit (SO) coupled atomistic tight-binding model coupled to a self-consistent Poisson solver is used for the valence-band dispersion calculation.
Abstract: Bandstructure effects in p-channel MOS (PMOS) transport of strongly quantized silicon nanowire FETs in various transport orientations are examined. A 20-band sp3d5s* spin-orbit (SO) coupled atomistic tight-binding model coupled to a self-consistent Poisson solver is used for the valence-band dispersion calculation. A ballistic FET model is used to evaluate the capacitance and current-voltage characteristics. The dispersion shapes and curvatures are strong functions of device size, lattice orientation, and bias, and cannot be described within the effective mass approximation. The anisotropy of the confinement mass in the different quantization directions can cause the charge to preferably accumulate in the (110) and then on the (112) rather than on (100) surfaces, leading to significant differences in the charge distributions for different wire orientations. The total gate capacitance of the nanowire FET devices is, however, very similar for all wires in all the investigated transport orientations ([100], [110], [111]), and is degraded from the oxide capacitance by ~30%. The [111] and then the [110] oriented nanowires indicate highest carrier velocities and better on-current performance compared to [100] wires. The dispersion features and quantization behavior, although a complicated function of physical and electrostatic confinement, can be explained at first order by looking at the anisotropic shape of the heavy-hole valence band.
TL;DR: It is demonstrated that the self-assembled three-terminal nanowire junctions can be used to implement the functions of frequency mixing, multiplication, and phase-difference detection of input electrical signals at room temperature.
Abstract: We investigate electrical properties of self-assembled branched InAs nanowires. The branched nanowires are catalytically grown using chemical beam epitaxy, and three-terminal nanoelectronic devices are fabricated from the branched nanowires using electron-beam lithography. We demonstrate that, in difference from conventional macroscopic junctions, the fabricated self-assembled nanowire junction devices exhibit tunable nonlinear electrical characteristics and a signature of ballistic electron transport. As an example of applications, we demonstrate that the self-assembled three-terminal nanowire junctions can be used to implement the functions of frequency mixing, multiplication, and phase-difference detection of input electrical signals at room temperature. Our results suggest a wide range of potential applications of branched semiconductor nanostructures in nanoelectronics.
TL;DR: In this paper, the authors developed a fully analytical ballistic theory of carbon nanotube field effect transistors enabled by the development of an analytical surface potential capturing the temperature dependence and gate and quantum capacitance electrostatics.
Abstract: We developed a fully analytical ballistic theory of carbon nanotube field effect transistors enabled by the development of an analytical surface potential capturing the temperature dependence and gate and quantum capacitance electrostatics. The analytical ballistic theory is compared to the experimental results of a ballistic transistor with good agreement. The validated analytical theory enables intuitive circuit design, provides techniques for parameter extraction of the bandgap and surface potential, and elucidates on the device physics of drain optical phonon scattering and its role in reducing the linear conductance and intrinsic gain of the transistor. Furthermore, a threshold voltage definition is proposed reflecting the bandgap-diameter dependence. Projections for key analog and digital performances are discussed.