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Self-assembled quantum dots (QDs) are highly strained heterostructures. the lattice strain significantly modifies the electronic and optical properties of these devices. A universal behavior is observed in atomistic strain simulations (in terms of both strain magnitude and profile) of QDs with different shapes and materials. In this paper, this universal behavior is investigated by atomistic as well as analytic continuum models. Atomistic strain simulations are very accurate but computationally expensive. On the other hand, analytic continuum solutions are based on assumptions that significantly reduce the accuracy of the strain calculations, but are very fast. Both techniques indicate that the strain depends on the aspect ratio (AR) of the QDs, and not on the individual dimensions. Thus simple closed form equations are introduced which directly provide the atomistic strain values inside the QD as a function of the AR and the material parameters. Moreover, the conduction and valence band edges $E_{C/V}$ and their effective masses $m^*_{C/V}$ of the QDs are dictated by the strain and AR consequently. The universal dependence of atomistic strain on the AR is useful in many ways; Not only does it reduce the computational cost of atomistic simulations significantly, but it also provides information about the optical transitions of QDs given the knowledge of $E_{C/V}$ and $m^*_{C/V}$ from AR. Finally, these expressions are used to calculate optical transition wavelengths in InAs/GaAs QDs and the results agree well with experimental measurements and atomistic simulations.

In this work, the coherent and incoherent transport simulation capabilities of the multipurpose nanodevice simulation tool NEMO5 are presented and applied on transport in tunneling field-effect transistors. The comparison with experimental resistivity data confirms the validity of NEMO5's phonon-scattering models. Common pitfalls of numerical implementations and the applicability of common approximations of scattering self-energies are discussed. The impact of phonon-assisted tunneling on the performance of TFETs is exemplified with a concrete Si nanowire device. The communication-efficient implementation of self-energies in NEMO5 is demonstrated with a scaling comparison of self-energies solved with blocking and nonblocking MPI-communication.

In recent years, alloy electronic structure calculations based on supercell Brillouin zone unfolding have become popular. There are a number of formulations of the method which on the surface might appear different. Here we show that a discrete real-space description, based on discrete Fourier transforms, is fully general. Furthermore, such an approach can more easily show the effects of alloy scattering. We present such a method for treating the random alloy problem. This treatment features straightforward mathematics and a transparent physical interpretation of the calculated effective (i.e., approximate) energy bands.

Many services, e.g., in education and research, have witnessed increased productivity and scalability, mainly because of the growing prevalence of online platforms. To accelerate this progression, a detailed understanding of user interactions with these complex systems is instrumental. Current approaches for analyzing service user behavior have two main limitations: (a) unsupervised learning methods do not discriminate behavior meaningfully and scale poorly; and (b) surveys as input data probe only intentions. We introduce a framework to analyze user behavior in complex cloud services. Our objectives are (a) a computationally lean method to cope with large data sets and (b) for the input data to be free of assumptions. We define three data-driven metrics based only on the size and volume of data, using nested arrangements of zero and infinity norms. Using threshold analysis, user behavior data is categorized over one metric and subsequently verified over the other two metrics. We apply this method to analyze the behavior of users of nanoHUB services, the world’s largest cyber-infrastructure for nanotechnology research and education. As input, actual user decisions are employed. The introduced frequency metric leads to a dispersion of usage duration. The resulting separated power and casual user categories are validated over the diversity and intensity metrics. Moreover, subcategories of previously unknown classroom users are identified. These findings allow policy makers to optimally tailor educational programs to such uncoordinated groups. Given nanoHUB’s size, its leading role in educational services, and the approach’s data-driven nature, the presented method is applicable to a wide range of cloud services.

We propose InAs/GaSb ultrathin-body tunneling field-effect transistors (TFETs) using confinement in the ( $1\bar {1}0$ ) plane and transport in the [110] direction to increase the tunneling probability by reducing the tunnel barrier energy and hole effective mass. To reduce the OFF-state leakage current, we add an InAs/In1– n Al n As1– n Sb n heterojunction to the channel, which increases the valence band barrier. The heterojunction also increases the tunneling probability and ON-current by reducing the tunneling distance through the p-n junction and introducing a resonant state. A fully atomistic non-equilibrium Green function quantum transport approach in NEMO5 is used to explore the design space. While choosing $10^{-3}$ A/m OFF-current ( $I_{\mathrm{\scriptscriptstyle OFF}}$ ) and a 0.3 V power supply, we simulate 270 A/m ON-current ( $I_{\mathrm{\scriptscriptstyle ON}}$ ) for a 30-nm gate length and 170 A/m for a 15-nm gate length $(L_{g})$ , while a conventional 15-nm $L_{g_{_{_{}}}}$ GaSb/InAs TFET under (001) confinement shows only 24 A/m $I_{\mathrm{\scriptscriptstyle ON}}$ .

A triple-heterojunction (3HJ) design is employed to improve p-type InAs/GaSb heterojunction (HJ) tunnel FETs. Atomistic quantum transport simulations show, that the added two HJs (AlInAsSb/InAs in the source and GaSb/AlSb in the channel) significantly shorten the tunnel distance and create two resonant states, greatly improving the ON state tunneling probability. Moreover, the source Fermi degeneracy is reduced by the increased source (AlInAsSb) density of states and the OFF state leakage is reduced by the heavier channel (AlSb) hole effective masses. With $V_{\mathrm{DD}}=0.3\rm {V}$ and $I_{\mathrm{OFF}}=1\rm {nA/\mu m}$ , ballistic $I_{\mathrm{ON}}$ of $606\rm {\mu A/\mu m}$ ( $492\rm {\mu A/\mu m}$ ) is obtained at $30\rm {nm}$ ( $15\rm {nm}$ ) channel length, which is comparable to n-type 3HJ counterpart and significantly exceeding p-type silicon MOSFET. Simultaneously, the nonlinear turn on and delayed saturation in the output characteristics are also greatly improved.

The main promise of tunnel FETs (TFETs) is to enable supply voltage ($V_{DD}$) scaling in conjunction with dimension scaling of transistors to reduce power consumption. However, reducing $V_{DD}$ and channel length ($L_{ch}$) typically deteriorates the ON- and OFF-state performance of TFETs, respectively. Accordingly, there is not yet any report of a high perfor]mance TFET with both low V$_{DD}$ ($\sim$0.2V) and small $L_{ch}$ ($\sim$6nm). In this work, it is shown that scaling TFETs in general requires scaling down the bandgap $E_g$ and scaling up the effective mass $m^*$ for high performance. Quantitatively, a channel material with an optimized bandgap ($E_g\sim1.2qV_{DD} [eV]$) and an engineered effective mass ($m*^{-1}\sim40 V_{DD}^{2.5} [m_0^{-1}]$) makes both $V_{DD}$ and $L_{ch}$ scaling feasible with the scaling rule of $L_{ch}/V_{DD}=30~nm/V$ for $L_{ch}$ from 15nm to 6nm and corresponding $V_{DD}$ from 0.5V to 0.2V.

In this work, the performance of Tunnel Field-Effect Transistors (TFETs) based on two-dimensional Transition Metal Dichalcogenide (TMD) materials is investigated by atomistic quantum transport simulations. One of the major challenges of TFETs is their low ON-currents. 2D material based TFETs can have tight gate control and high electric fields at the tunnel junction, and can in principle generate high ON-currents along with a sub-threshold swing smaller than 60 mV/dec. Our simulations reveal that high performance TMD TFETs, not only require good gate control, but also rely on the choice of the right channel material with optimum band gap, effective mass and source/drain doping level. Unlike previous works, a full band atomistic tight binding method is used self-consistently with 3D Poisson equation to simulate ballistic quantum transport in these devices. The effect of the choice of TMD material on the performance of the device and its transfer characteristics are discussed. Moreover, the criteria for high ON-currents are explained with a simple analytic model, showing the related fundamental factors. Finally, the subthreshold swing and energy-delay of these TFETs are compared with conventional CMOS devices., 7 pages, 8 figures. The revised version is uploaded

Introduction Given that the nanoscale regime has been reached, atomistic simulations are being used as predictive tools on a nanoscopic scale in nanoelectronics, materials science, and computational fluid dynamics. These simulations are generally supported by complex and specific simulation engines that require a deep knowledge of the engine as well as the field. The inputs required by these engines are usually described in long-text files, and their composition is error prone. These files contain details about the corresponding materials, geometries, algorithms, initial values, etc. The introduction of visualizations to the simulation creation process could alleviate some common user issues with simulation creation, in particular regarding the input-text files. In other fields, visual analytics have been used to facilitate user interaction with complex data. This work features a case study on the creation of a nanoelectronic device simulation and provides evidence of how the use of visual analytics reduces the cognitive complexity of defining an atomistic simulation. Case description NEMO5 is a tool designed to simulate the electronic properties of nanoelectronic devices on an atomistic level. In this work we introduce NemoViz, an interactive visualization tool that enables users to define the simulation inputs required by NEMO5. Regular NEMO5 users were exposed to NemoViz, and users’ effectiveness and efficiency was measured while debugging the input for a simulation. Discussion and Evaluation The results of this work show that NemoViz reduced the time that users spent defining the inputs of a NEMO5 simulation. When using NemoViz, Expert NEMO5 users detected errors twice as fast as when NemoViz was not used, and non-expert NEMO5 users were able to detect errors as effectively and efficiently as expert users. Conclusions These results suggest that the use of visual analytics as a simulation design process tool reduces the cognitive load of complex simulators such as NEMO5. Users’ interaction with visualization facilitates their understanding of output results and input descriptors, which may lead to new research codes from their widespread user base.

State of the art quantum transport models for semi-conductor nanodevices attribute negative (positive) unit charges to states of the conduction (valence) band. Hybrid states that enable band-to-band tunneling are subject to interpolation that yield model dependent charge contributions. In any nanodevice structure, these models rely on device and physics specific input for the dielectric constants. This work exemplifies the large variability of different charge interpretation models when applied to ultrathin body transistor performance predictions. To solve this modeling challenge, an electron-only band structure model is extended to atomistic quantum transport. Performance predictions of MOSFETs and tunneling FETs confirm the generality of the new model and its independence of additional screening models.

New designs for vertical 2D-materials-based TFETs are proposed in this paper adopting asymmetric layer numbers for the top and bottom layer with undoped source/drain using Black Phosphorus as an example. The results show that abrupt turn-on and I on /I off > 105 can be sustained when the channel length is down to sub-5 nm. The results are benchmarked against other TFETs based on promising 2D materials homo-/hetero-structures, meanwhile, the limitations, as well as guidelines, are presented.

As interconnects become smaller, their conductivity increases along with the parasitic effects in MOSFET technologies [1] Therefore, investigating how to model the scattering effects on the nanoscale is important to determine how to engineer interconnects toreduce those parasitic effects. In this work, a fully atomistic method is studied to model the electronic transport properties of copper thin films. For this purpose, a tight binding basis previously benchmarked against first principles calculations [2] is used todescribe surface roughness and grain boundary effects on comparablepper thin films with a thickness comparable to the values suggested by ITRS roadmap [3]. In contrast with traditional models, the results show that the tight binding method can quantify those scattering effects at low temperature without fitting any experimental parameters [4], [5].

We identify the presence of monoatomic steps at the Si/SiGe or Si/SiO$_2$ interface as a dominant source of variations in the dephasing time of Si quantum dot (QD) spin qubits. First, using atomistc tight-binding calculations we show that the g-factors and their Stark shifts undergo variations due to these steps. We compare our theoretical predictions with experiments on QDs at a Si/SiO$_2$ interface, in which we observe significant differences in Stark shifts between QDs in two different samples. We also experimentally observe variations in the $g$-factors of one-electron and three-electron spin qubits realized in three neighboring QDs on the same sample, at a level consistent with our calculations. The dephasing times of these qubits also vary, most likely due to their varying sensitivity to charge noise, resulting from different interface conditions. More importantly, from our calculations we show that by employing the anisotropic nature of the spin-orbit interaction (SOI) in a Si QD, we can minimize and control these variations. Ultimately, we predict that the dephasing times of the Si QD spin qubits will be anisotropic and can be improved by at least an order of magnitude, by aligning the external DC magnetic field towards specific crystal directions., 5 pages, 3 figures, Supplemental Material (3 pages, 2 figures)

Orientation effects on the resistivity of copper grain boundaries are studied systematically with two different atomistic tight binding methods. A methodology is developed to model the resistivity of grain boundaries using the Embedded Atom Model, tight binding methods and non-equilibrum Green's functions (NEGF). The methodology is validated against first principles calculations for small, ultra-thin body grain boundaries (, 18 pages, 12 figures

The 2-D material-based TFETs are among the most promising candidates for low-power electronics applications since they offer ultimate gate control and high-current drives that are achievable through small tunneling distances ( $\Lambda $ ) during the device operation. The ideal device is characterized by a minimized $\Lambda $ . However, devices with the thinnest possible body do not necessarily provide the best performance. For example, reducing the channel thickness ( ${T}_{\text {ch}}$ ) increases the depletion width in the source, which can be a significant part of the total $\Lambda $ . Hence, it is important to determine the optimum ${T}_{\text {ch}}$ for each channel material individually. In this paper, we study the optimum ${T}_{\text {ch}}$ for three channel materials: WSe2, black phosphorus, and InAs using full-band self-consistent quantum transport simulations. To identify the ideal ${T}_{\text {ch}}$ for each material at a specific doping density, a new analytic model is proposed and benchmarked against the numerical simulations.

State of the art quantum transport models for semiconductor nanodevices attribute negative (positive) unit charges to states of the conduction (valence) band. Hybrid states that enable band-to-band tunneling are subject to interpolation that yield model dependent charge contributions. In any nanodevice structure, these models rely on device and physics specific input for the dielectric constants. This paper exemplifies the large variability of different charge interpretation models when applied to ultrathin body transistor performance predictions. To solve this modeling challenge, an electron-only band structure model is extended to atomistic quantum transport. Performance predictions of MOSFETs and tunneling FETs confirm the generality of the new model and its independence of additional screening models., Comment: 8 pages, 8 figures

Artificial semiconductors with manufactured band structures have opened up many new applications in the field of optoelectronics. The emerging two-dimensional (2D) semiconductor materials, transition metal dichalcogenides (TMDs), cover a large range of bandgaps and have shown potential in high performance device applications. Interestingly, the ultrathin body and anisotropic material properties of the layered TMDs allow a wide range modification of their band structures by electric field, which is obviously desirable for many nanoelectronic and nanophotonic applications. Here, we demonstrate a continuous bandgap tuning in bilayer MoS2 using a dual-gated field-effect transistor (FET) and photoluminescence (PL) spectroscopy. Density functional theory (DFT) is employed to calculate the field dependent band structures, attributing the widely tunable bandgap to an interlayer direct bandgap transition. This unique electric field controlled spontaneous bandgap modulation approaching the limit of semiconductor-to...

The k.p perturbation method for determination of electronic structure first pioneered by Kohn and Luttinger continues to provide valuable insight to several band structure features. This method has been adapted to heterostructures confined in up to three directions. In this paper, numerical details of setting up a k.p Hamiltonian using the finite difference approximation for such confined nanostructures is explicitly demonstrated. Nanostructures belonging to two different symmetry classes, namely, the cubic zincblende and rhombohedral crystals are considered. Rhombohedral crystals, of late, have gained prominence as candidates for the recently discovered topological insulator (TI) class of materials. Lastly, the incorporation of a strain field to the k.p Hamiltonian and the corresponding matrix equations for computing the intrinsic and an externally applied strain in heterostructures within a continuum approximation is shown. Two applications are considered (1) Computation of the eigen states of a multi-million zincblende InAs quantum dot with a stress-reducing InGaAs layer of varying Indium composition embedded in a GaAs matrix and (2) Dispersion of a rhombohedral TI $$\hbox {Bi}_{2}\hbox {Se}_{3}$$Bi2Se3 film and the necessary alteration in presence of proximity-induced superconductivity.

Quantum transport simulations are performed in tunneling FETs (TFETs) with the gate electric field in-line with the tunneling junction direction (in-line TFETs). Charge self-consistency and thermalization effects are included in a semiclassical Poisson solution to compute the electrostatic potential. The obtained potential is then used for current calculation with the ballistic nonequilibrium Green’s function method (NEGF) in the tight binding basis. It is shown that the NEGF method predicts a higher subthreshold swing than the often-used dynamic nonlocal (DNL) path band-to-band method. The NEGF method accounts for the direct source–drain tunneling, which is underestimated in the DNL path approach in the studied geometries. Undercut is shown to be essential to obtain switching slope below 60 mV/decade in the in-line TFETs.

Traditional thinking assumes that a light effective mass ( $m^*$ ), high mobility material will result in better transistor characteristics. However, sub-12-nm metal-oxide-semiconductor field effect transistors (MOSFETs) with light $m^*$ may underperform compared to standard Si, as a result of source to drain (S/D) tunneling. An optimum heavier mass can decrease tunneling leakage current, and at the same time, improve gate to channel capacitance because of an increased quantum capacitance ( $C_q$ ). A single band effective mass model has been used to provide the performance trends independent of material, orientation and strain. This paper provides guidelines for achieving optimum $m^*$ for sub-12-nm nanowire down to channel length of 3 nm. Optimum $m^*$ are found to range between 0.2–1.0 $m_0$ and more interestingly, these masses can be engineered within Si for both p-type and n-type MOSFETs. $m^*$ is no longer a material constant, but a geometry and strain dependent property of the channel material.

Full-band quantum transport simulations are performed to study the scaling of InGaAs MOSFETs. Short-channel effects evoke severe performance degradation in InGaAs MOSFETs and the tunneling leakage further deteriorates their performances. Reducing the body width is shown to suppress the short channel effects. Doping densities show big impacts on device performances. With inhomogeneous doping InGaAs could outperform Si at gate lengths below 15 nm with 5-nm body width. The density of state bottleneck does not affect InGaAs in simulated devices at 0.5 V supply voltage. At the ultrascaled dimensions the full band simulations are essential to capture strong nonparabolic dispersion. Comparison with a multivalley effective mass model shows that the population of higher conduction band valleys contributes to the total current at thin body widths.

The concept and simulated device characteristics of tunneling field-effect transistors (TFETs) based on III-nitride heterojunctions are presented for the first time. Through polarization engineering, interband tunneling can become significant in III-nitride heterojunctions, leading to the potential for a viable TFET technology. Two prototype device designs, inline and sidewall-gated TFETs, are discussed. Polarization-assisted p-type doping is used in the source region to mitigate the effect of the deep Mg acceptor level in p-type GaN. Simulations indicate that TFETs based on III-nitride heterojunctions can be expected to achieve ON/ OFF ratios of $10^{6}$ or more, with switching slopes well below 60 mV/decade, ON-current densities approaching 100 $\mu \text{A}/\mu \text{m}$ , and energy delay products as low as 67 aJ-ps/ $\mu \text{m}$ .

Atomistic quantum transport simulation of realistically large devices is computationally very demanding. The widely used mode space (MS) approach can significantly reduce the numerical cost but good MS basis is usually very hard to obtain for atomistic full-band models. In this work, a robust and parallel algorithm is developed to optimize the MS basis for atomistic nanowires. This enables tight binding non-equilibrium Green's function (NEGF) simulation of nanowire MOSFET with realistic cross section of $\rm 10nm\times10nm$ using a small computer cluster. This approach is applied to compare the performance of InGaAs and Si nanowire nMOSFETs with various channel lengths and cross sections. Simulation results with full-band accuracy indicate that InGaAs nanowire nMOSFETs have no drive current advantage over their Si counterparts for cross sections up to about $\rm 10nm\times10nm$., 8 pages (double column), 13 figures, 1 table

With continuous shrinking of devices in accordance with Moore's law, metal-semiconductor resistivity starts playing an important role for device performance. To meet ITRS target of 10−9 Ω·cm2 by 2023, it is important to evaluate the effect of different device parameters such as doping concentration, Schottky barrier height, strain and SiGe mole fraction on contact resistivity. In this work, such a resistivity study has been done on Si/SiGe PMOS contacts through 10-band atomistic tight binding quantum transport simulations. Optimum target values for barrier height as a function of doping concentration are obtained.

VLSI devices are constrained by CF dd 2/2 power dissipation. Low power dissipation requires low V dd , yet reducing V dd increases I off . Tunnel FETs (TFETs) have steep subthreshold swings (S.S.) and can operate at low V dd , yet their I on is limited by low tunneling probability. This low I on results in large CV dd /I delay and slow logic operation. For greatly increased Ion, we had proposed a triple-heterojunction (3HJ) TFET design incorporating source and channel heterojunctions (HJ) [1, 2]. The designs of [1, 2] have an InAlAsSb channel, yet no low-trap-density dielectric interfaces to InAlAsSb have been reported. In contrast, low-trap-density dielectric interfaces have been demonstrated to InAs, InGaAs, and InP [3, 4, 5]. Here we propose an InGaAs/GaAsSb/InAs/InP 3HJ TFET design, with growth lattice-matched to InP. The gated channel surface is InAs and InP, and thus can have low trap density. The p-type side of the tunnel junction is GaAsSb, instead of strained GaSb [6], as compressive strain increases the hole transport effective mass, reducing the tunneling probability. In ballistic simulations, with I off = 10 3 μA/μm and V dd =0.3V, I on is an extremely high 540μA/μm. Even when simulated assuming incoherent quantum transport, with acoustic and optical phonon scattering modelled, I on remains very high at 250μA/μm.

The design and optimization of realistically extended multi-quantum-well GaN-based light emitting diodes requires a quantitative understanding of the quantum mechanics-dominated carrier flow. Typical devices can be characterized by spatial regions of extremely high carrier densities such as n-GaN/p-GaN layers and quantum wells coupled to each other by tunneling and thermionic emission-based quantum transport. This work develops a multi-scale model that partitions the device into different spatial regions where the high carrier domains are treated as reservoirs in local equilibrium and serve as injectors and receptors of carriers into the neighboring reservoirs through tunneling and thermionic emission. The nonequilibrium Green's function (NEGF) formalism is used to compute the dynamics (states) and the kinetics (filling of states) in the entire extended complex device. The local density of states in the whole device is computed quantum mechanically within a multi-band tight binding Hamiltonian. The model results agree with experimental I-V curves quantitatively. Our results indicate tunneling to be a major contributor to the total charge current in LEDs.

In the present paper, we propose an extension of the Sakurai-Sugiura projection method (SSPM) for a circumference region on the complex plane. The SSPM finds eigenvalues in a specified region on the complex plane and the corresponding eigenvectors by using numerical quadrature. The original SSPM has also been extended to compute the eigenpairs near the circumference of a circle on the complex plane. However these extensions can result in division by zero, if the eigenvalues are located at the quadrature points set on the circumference. Here, we propose a new extension of the SSPM, in order to avoid a decrease in the computational accuracy of the eigenpairs resulting from locating the quadrature points near the eigenvalues. We implement the proposed method in the SLEPc library, and examine its performance on a supercomputer cluster with many-core architecture.

Observation of interference in the quantum Hall regime may be hampered by a small edge state velocity due to finite phase coherence time. Therefore designing two quantum point contact (QPCs) interferometers having a high edge state velocity is desirable. Here, we present a new simulation method for realistically modeling edge states near QPCs in the integer quantum Hall effect (IQHE) regime. We calculate the filling fraction in the center of the QPC and the velocity of the edge states, and predict structures with high edge state velocity. The 3D Schr��dinger equation is split into 1D and 2D parts. Quasi-1D Schr��dinger and Poisson equations are solved self-consistently in the IQHE regime to obtain the potential profile near the edges, and quantum transport is used to solve for the edge state wavefunctions. The velocity of edge states is found to be $\left< E \right> / B$, where $\left< E \right>$ is the expectation value of the electric field for the edge state. Anisotropically etched trench gated heterostructures with double sided delta doping have the highest edge state velocity among the structures considered., 12 pages, 11 figures

Two-electron states bound to donors in silicon are important for both two qubit gates and spin readout. We present a full configuration interaction technique in the atomistic tight-binding basis to capture multi-electron exchange and correlation effects taking into account the full bandstructure of silicon and the atomic scale granularity of a nanoscale device. Excited $s$-like states of $A_1$-symmetry are found to strongly influence the charging energy of a negative donor centre. We apply the technique on sub-surface dopants subjected to gate electric fields, and show that bound triplet states appear in the spectrum as a result of decreased charging energy. The exchange energy, obtained for the two-electron states in various confinement regimes, may enable engineering electrical control of spins in donor-dot hybrid qubits., Comment: 7 pages, 4 figures

Steep transistors are crucial in lowering power consumption of the integrated circuits. However, the difficulties in achieving steepness beyond the Boltzmann limit experimentally have hindered the fundamental challenges in application of these devices in integrated circuits. From a sensitivity perspective, an ideal switch should have a high sensitivity to the gate voltage and lower sensitivity to the device design parameters like oxide and body thicknesses. In this work, conventional tunnel-FET (TFET) and negative capacitance FET are shown to suffer from high sensitivity to device design parameters using full-band atomistic quantum transport simulations and analytical analysis. Although Dielectric Engineered (DE-) TFETs based on 2D materials show smaller sensitivity compared with the conventional TFETs, they have leakage issue. To mitigate this challenge, a novel DE-TFET design has been proposed and studied.

Electron spins confined to phosphorus donors in silicon are promising candidates as qubits because of their long coherence times, exceeding seconds in isotopically purified bulk silicon. With the recent demonstrations of initialization, readout and coherent manipulation of individual donor electron spins, the next challenge towards the realization of a Si:P donor-based quantum computer is the demonstration of exchange coupling in two tunnel-coupled phosphorus donors. Spin-to-charge conversion via Pauli spin blockade, an essential ingredient for reading out individual spin states, is challenging in donor-based systems due to the inherently large donor charging energies (∼45 meV), requiring large electric fields (>1 MV m(-1)) to transfer both electron spins onto the same donor. Here, in a carefully characterized double donor-dot device, we directly observe spin blockade of the first few electrons and measure the effective exchange interaction between electron spins in coupled Coulomb-confined systems.

We report simulations of logic transistor operation at supply voltages V dd between 0.08–0.18V. Tunnel FETs (TFETs) can operate at low voltage with low off-currents I off , but on-currents I on are greatly reduced by low tunneling probability. The minimum feasible Vdd is constrained not only by the transistor subthreshold swing (SS) given a target /on//off ratio, but also by the reduction of the drain current as the drain Fermi level approaches the channel conduction-band energy. This output conductance reduces the TFET voltage gain and impairs the logic gate noise margin; increasing the TFET threshold voltage Vh increases the noise margin while reducing both I on and I off . In ballistic simulations with 10−3A/m I off , triple-heterojunction tunnel FETs (3HJ-TFETs) show >50% tunneling probability and a high 265A/m I on at V dd = 0.18V and 195A/m at V dd =0.12V. In simulations with an optical deformation constant (proportional to scattering strength) of 220meV/nm, consistent with μ=1.1×105 cm2V−1s−1, reduces I on by 31% given fixed I off and V dd . In ballistic simulations, increasing Vth by 0.02 V above that required for 10−3A/m I off , a noise margin of 24% of V dd is obtained at V dd =0. 12 V.

In this paper, electrostatically configurable 2D tungsten diselenide (WSe2 ) electronic devices are demonstrated. Utilizing a novel triple-gate design, a WSe2 device is able to operate as a tunneling field-effect transistor (TFET), a metal-oxide-semiconductor field-effect transistor (MOSFET) as well as a diode, by electrostatically tuning the channel doping to the desired profile. The implementation of scaled gate dielectric and gate electrode spacing enables higher band-to-band tunneling transmission with the best observed subthreshold swing (SS) among all reported homojunction TFETs on 2D materials. Self-consistent full-band atomistic quantum transport simulations quantitatively agree with electrical measurements of both the MOSFET and TFET and suggest that scaling gate oxide below 3 nm is necessary to achieve sub-60 mV dec-1 SS, while further improvement can be obtained by optimizing the spacers. Diode operation is also demonstrated with the best ideality factor of 1.5, owing to the enhanced electrostatic control compared to previous reports. This research sheds light on the potential of utilizing electrostatic doping scheme for low-power electronics and opens a path toward novel designs of field programmable mixed analog/digital circuitry for reconfigurable computing.

Magnetotransport measurements on electron bilayer systems under low frequency continuous microwave irradiation reveal an anomalous magnetoresistance behavior. At low total imbalanced carrier densities, pronounced features in the longitudinal and Hall resistance emerge that show a surprisingly strong sensitivity to frequency, microwave power, and density. We suggest its origin to be related to resonantly induced capacitance oscillations of the two-layer system.Magnetotransport measurements on electron bilayer systems under low frequency continuous microwave irradiation reveal an anomalous magnetoresistance behavior. At low total imbalanced carrier densities, pronounced features in the longitudinal and Hall resistance emerge that show a surprisingly strong sensitivity to frequency, microwave power, and density. We suggest its origin to be related to resonantly induced capacitance oscillations of the two-layer system.

Due to recent improvements in computing power, non-orthogonal tight-binding models have moved beyond their traditional applications in molecular electronics to nanoelectronics. These models are appealing due to their physical chemistry content and the availability of tabulated material parameterizations. There are, however, problems with them, related to their non-orthogonality, which are more serious in nanoelectronic vs molecular applications. First, the non-orthogonal basis leads to an inherent ambiguity in the charge density. More importantly, there are problems with the position matrix in a non-orthogonal basis. The position matrix must be compatible with the underlying translationally symmetric system, which is not guaranteed if it is calculated with explicit wavefunctions. In an orthogonal basis, the only way to guarantee compatibility and gauge invariance is to use diagonal position matrices, but transforming them to a non-orthogonal basis requires major computational effort in a device consisting of 103–105 atoms. We study the charge density, position matrix, and optical absorption using a non-orthogonal two-band one-dimensional model, comparing correct and approximate calculations. We find that a typical naive calculation produces highly inaccurate results, while in contrast a first-order orthogonalized basis can represent a reasonable accuracy-efficiency trade-off.

We report design of double-gate metal-oxide-semiconductor field-effect-transistors having InGaAs/InAlAs superlattices between the N+ source and a planar InGaAs channel. As with nanowire superlattice transistors, the 2-D superlattice bandgap reduces injection into the channel of electrons having energy above the source Fermi energy. Simulated ballistic transport characteristics of FETs using a three-well superlattice show 29-37.5-mV/decade minimum subthreshold swing and 390-A/m ON-current given 0.1-A/m OFF-current and a 0.2 V power supply.

Research and teaching in nanoscience can, and should, be thought as one joint endeavour. nanoHUB, a cyberinfrastructure that aims to use interactive cloud-based software to meet the needs of both code developers and end-users, is redefining research and education in nanoscience and engineering.

As semiconductor devices scale to new dimensions, the materials and designs become more dependent on atomic details. NEMO5 is a nanoelectronics modeling package designed for comprehending the critical multi-scale, multi-physics phenomena through efficient computational approaches and quantitatively modeling new generations of nanoelectronic devices as well as predicting novel device architectures and phenomena. This article seeks to provide updates on the current status of the tool and new functionality, including advances in quantum transport simulations and with materials such as metals, topological insulators, and piezoelectrics., 10 pages, 12 figures

A new capability of our well-known NEMO 3-D simulator (Ref. Klimeck et al., 2007 [10]) is introduced by carefully investigating the utility of III-V semiconductor quantum dots as infrared photodetectors at a wavelength of 1.2-1.5 mu m. We not only present a detailed description of the simulation methodology coupled to the atomistic sp(3)d(5)s* tight-binding band model, but also validate the suggested methodology with a focus on a proof of principle on small GaAs quantum dots (QDs). Then, we move the simulation scope to optical properties of realistically sized dome-shaped InAs/GaAs QDs that are grown by self-assembly and typically contain a few million atoms. Performing numerical experiments with a variation in QD size, we not only show that the strength of ground state inter-band light transitions can be optimized via QD size-engineering, but also find that the hole ground state wavefunction serves as a control factor of transition strengths. Finally, we briefly introduce the web-based cyber infrastructure that is developed as a government-funded project to support online education and research via TCAD simulations. This work not only serves as a useful guideline to experimentalists for potential device designs and other modelers for the self-development of optical TCAD, but also provides a good chance to learn about the science gateway project ongoing in the Republic of Korea. (C) 2012 Elsevier Ltd. All rights reserved.

As metal-oxide-semiconductor field-effect transistors (MOSFET) channel lengths (Lg) are scaled to lengths shorter than Lg