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Three silicon nanowire (SiNW) field effect transistors (FETs) with 15-, 12.5- and 10.6-nm gate lengths are simulated using hierarchical multilevel quantum and semiclassical models verified against experimental ${I}_{D}$ – ${V}_{G}$ characteristics. The tight-binding (TB) formalism is employed to obtain the band structure in $\mathit {k}$ -space of ellipsoidal NWs to extract electron effective masses. The masses are transferred into quantum-corrected 3-D finite element (FE) drift-diffusion (DD) and ensemble Monte Carlo (MC) simulations, which accurately capture the quantum-mechanical confinement of the ellipsoidal NW cross sections. We demonstrate that the accurate parameterization of the bandstructure and the quantum-mechanical confinement has a profound impact on the computed ${I}_{D}$ – ${V}_{G}$ characteristics of nanoscaled devices. Finally, we devise a step-by-step technology computer-aided design (TCAD) methodology of simple parameterization for efficient DD device simulations. [ABSTRACT FROM AUTHOR]

Dirac-source field-effect transistors (DS-FETs) have been proposed as promising candidates for low-power switching devices by leveraging the Dirac cone of graphene as a low-pass energy filter. In particular, using 2-D materials as the channel in a DS-FET is of interest for ultimate scaling purposes. In this article, we investigate the design considerations for 2-D DS-FETs using ballistic simulations based on the Landauer formalism. We study the impact of several key device parameters on the device performance, such as graphene doping, Schottky barrier heights, and effective mass of the 2-D channel. In Part II of this article, we study the impact of nonidealities on the performance of DS-FETs and benchmark the performance of DS-FETs for different channel materials. [ABSTRACT FROM AUTHOR]

Monolayer HfS2 is promising for an all-2D CMOS platform due to its well-balanced n- and p-type transport properties, and is predicted to show high drive currents into the sub-10-nm channel length regime. However, the OFF-state performance of the ultrascaled HfS2 pMOS device is limited by direct source-drain tunneling (SDT) due to carriers in the degenerate light-hole band. Here we use full-band quantum transport simulations to show that this effect can be mitigated through the use of uniaxial tensile strain, which splits the degeneracy of the valence bands and tunes the effective mass in the transport direction to suppress SDT. Strain of 1-2% applied in the transport direction reduces the subthreshold swing by over 20 mV/dec, which can improve the ON current by over 50% at channel lengths below 7 nm. This approach can be further used to tune the HfS2 pMOS device to match the nMOS characteristics at a similar channel length. [ABSTRACT FROM AUTHOR]

We show that the coexistence of strong internal polarization and large carrier (i.e., electron and hole) effective mass accounts for ~51% of the efficiency droop under high current densities in traditional (hexagonal-phase) indium–gallium–aluminum–nitride (InGaAlN) light-emitting diodes (h-LEDs) compared to cubic-phase InGaAlN LEDs (c-LEDs). Our analysis based on variational technique on c-LEDs predicts an enhancement of the current density at the onset of the droop, inherently present in green c-LEDs. These effects are a consequence of the polarization-free nature and small carrier effective mass of c-LEDs. Our analysis indicates that, by overlooking the electron–hole wave function overlap, the well-known ABC model is suspected to overestimate the Auger coefficient, leading to questionable conclusions on the efficiency droop. In turn, it shows that the c-LED efficiency droop is much immune to the Auger electron–hole asymmetry, the increase in the Auger coefficient, and, thus, efficiency degradation mechanisms. [ABSTRACT FROM AUTHOR]

Small fission chambers manufactured by Photonis, Reuter-Stokes, CEA, and Centronic are routinely calibrated in standard neutron fields of the BR1 reactor at SCK CEN in Mol, Belgium. Two irradiation fields are available: fast spectrum in the MARK3 convertor and thermal spectrum in the Empty Cavity. In this work, for the first time the calibration procedure of larger fission chambers (Photonis CFUL01 and CFUM21 type) with the deposit length exceeding the length of the convertor is presented. Spatial energy correction factors taking into account the neutron flux shape beyond the convertor and radial gradient of the neutron flux were calculated with MCNP and experimentally validated. The combination of calibration (i.e., effective mass measurement) in fast and thermal irradiation fields allows for determination of the purity of 238U deposit. This is demonstrated on three CFUL01-type fission chambers with purity between 99.8% and 99.998%. [ABSTRACT FROM AUTHOR]

The paper presents the structural stability and electronic properties of Zigzag Gallium Nitride nano ribbons(ZGaNNR) by considering the lithium(Li) atom by employing density functional theory (DFT). Li atom has been considered as a passivating element at various symmetric sites. By using Li atoms, a significant impact has been observed on the structural and electronic characteristics of ZGaNNRs. Bare@edges_both structure emerged to be the most energetically stable among other structures. For Li-passivation@edge_Ga structures, the minimum band gap has been noticed for III-V group family of nanoribbons. Interestingly, other structures of ZGaNNRs turn metallic nature irrespective of the Li site. Further, Li-bare@edge_N structure possesses the highest Fermi velocity as compared to other structures. This is useful for designing high speed interconnect applications. Further, we investigated the effective mass of various Li-ZGaNNR structures using standard two probe models. The effective mass of H-bare@edge_N structure reveals the highest effective mass in both valence and conduction bands. The proposed work proves the high capability towards the designing of the nano-scale devices.

The electronic properties of a field-effect transistor with two different structures of MoSi2N4 and WSi2N4 monolayers as the channel material in the presence of biaxial strain are investigated. The band structures show that these compounds are semiconductors with an indirect bandgap. Their band gaps can be adjusted by applying in- plane biaxial strain. In the following, the variation of the energies of the valleys and corresponding effective masses with respect to the strain are explored. Finally, the strained MoSi2N4 or WSi2N4 are used as the channel of a p-type FET and the corresponding current–voltage characteristic is explored. The results show that this FET has an ${I}_{ \mathrm{\scriptscriptstyle ON}} / {I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio larger than 106 and sub-threshold swing (SS) in the range of 96–98 mV/dec. The ${I}_{ \mathrm{\scriptscriptstyle ON}} / {I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio of these compounds with respect to strain are compared. [ABSTRACT FROM AUTHOR]

Conventional silicon-based transistor downscaling is approaching its physical limits, and thus additional novel solutions are urgently desired to address this issue. Herein, we show that 2-D antimonene with heavy effective mass and high density of state (DOS) via strain engineering presents reliable transistor performance with the channel length (${L}_{\text {ch}}$) shrinking below 5 nm. As the biaxial tensile strain increases to 7%, the band switching gives rise to a heavy hole effective mass of $12.6{m}_{{0}}$ and a Van Hoff singularity-like DOS. This unique electronic structure can effectively suppress the tunneling current, resulting in steep subthreshold swings (SSs) and ideal ON-current (${I}_{ \mathrm{ON}}$). Especially, as ${L}_{\text {ch}}$ downscales to 2.2 nm, the OFF-current can be easily reduced to 0.1 $\mu \text{A}/\mu \text{m}$ with SS of 120 mV/dec (310 mV/dec for pristine antimonene) and ${I}_{ \mathrm{ON}}$ exceeds 900 $\mu \text{A}/\mu \text{m}$ , fulfilling the requirements for high-performance applications. Our results provide new insights on extending the scaling limit in energy-efficient gate-controlled devices. [ABSTRACT FROM AUTHOR]

State-of-the-art Fully-Depleted Silicon-on-Insulator Transistors of different gate lengths were measured down to ${\text{L}}_{G}=20$ nm. A quasi-ballistic virtual source model was found to be in good agreement with the observed data for both NFET and PFET. The extracted injection velocity increases with decreasing channel length, as expected, reaching ${9.51}\times {10}^{{6}}\text {cm/s}$ for electrons and ${7.16}\times {10}^{{6}}\textit {cm/s}$ for holes at ${\text{L}}_{G}=20$ nm. These values are more than 80% of the thermal velocity in lightly-doped bulk silicon. Analysis shows that quantum confinement in the thin SOI channel as well as strain effects are potentially responsible for such ultra-high velocity. These results indicate that further scaling of the channel length could make it possible to approach the non-degenerate thermal velocity. [ABSTRACT FROM AUTHOR]

Design optimization of emerging nanoscale transistor technologies often requires careful design tradeoff between many objectives, including speed, power, variability, and so on. By leveraging machine learning (ML) methods, we develop a multiobjective optimization (MOO) framework for 2-D-material-based field-effect transistors (FETs) near the scaling limit. The MOO design framework performs gradient-free efficient global optimization and offers the option of using active learning. Optimum designs with a tradeoff between transistor speed, power, and variability are identified automatically for transition metal dichalcogenide (TMDC) and black phosphorene FETs by applying the MOO design framework that couples ML methods to quantum transport device simulations. The design optimization results show that the International Roadmap of Devices and Systems (IRDS) target of 2025 and 2028 technology nodes can be met by 2-D FETs. [ABSTRACT FROM AUTHOR]

Ferroelectric tunnel junction (FTJ) exploiting the switchable polarization of ferroelectric material holds great potential for the low-power non-volatile memory. Recently, two-dimensional (2D) ferroelectric material CuInP2S6 (CIPS) which can provide ferroelectricity at the ultimate atomic-scale has been successfully introduced in FTJ to achieve significantly improved TER. Here, we present a theoretical study on the performance of FTJ based on CIPS through the quantum transport simulation using kp Hamiltonian obtained from density functional theory. Benchmarking with ferroelectric HfZrO2-based FTJ reveals that much higher TER can be achieved in CIPS-based FTJ due to a lower tunneling potential barrier and a larger tunneling effective mass. [ABSTRACT FROM AUTHOR]

Ultrathin-body (UTB) (111) InAs-On-Insulator (InAs-OI) n-channel metal–oxide–semiconductor field-effect transistors (nMOSFETs) are proposed as a new technology booster using the L valley conduction in III–V channels. The performance of the conventional UTB III–V nMOSFETs is limited by the essential band features of the Γ valley conduction such as the low density of states, resulting in low inversion capacitance, and the light effective mass mz along the confinement direction, resulting in strong thickness fluctuation scattering. The strong confinement of electrons by a combination of (111) surface orientation and UTB InAs-OI structures is expected to transfer the electrons into the L valley with much heavier mz than in the Γ valley, leading to higher semiconductor capacitance and suppression of thickness fluctuation scattering. We also experimentally demonstrate the UTB (111) InAs-OI nMOSFETs operation with thinning the InAs channels down to 3 nm, realized by the smart-cut and digital etching process. Channel thickness scaling improves both the OFF- and ON-currents by expansion of the effective bandgap. It is shown that the measured mobility increases with decreasing InAs-OI thickness from 4.8 to 4.4 nm, which is attributable to the increase in the electron occupancy in the L valley. [ABSTRACT FROM AUTHOR]

Two-dimensional materials with strong bandstructure anisotropy such as black phosphorus (BP) have been identified as attractive candidates for logic application due to their potential high carrier velocity and large density-of-states. However, perfectly aligning the source-to-drain axis with the desired crystal orientation remains an experimental challenge. In this letter, we use an advanced quantum transport approach from first-principle to shed light on the influence of orientation misalignments on the performance of BP-based field-effect transistors. Both ${n}$ -and ${p}$ -type configurations are investigated for six alignment angles, in the ballistic limit of transport and in the presence of electron-phonon and charged impurity scattering. It is found that up to deviations of 50° from the optimal angle, the ON-state current only decreases by 30%. This behavior is explained by considering a single bandstructure parameter, the effective mass along transport direction. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials with anisotropic electronic structures possess promising prospect for ultra-scaled field effect transistors (FETs), such as black phosphorene. Here, the quantum transport properties of anisotropic 2D group VA-VA monolayers with puckered configuration are studied in 5 nm FETs using density functional theory and nonequilibrium Green’s function. Through evaluating and comparing the transport effective mass ($\text{m}_{x}$) and density of state ($\text{m}_{\text {DOS}}$) of these 2D group VA-VA monolayers, we uncover the physical mechanism of the anisotropic electronic structures for the performances of 2D ultra-short FETs. These electronic structures can make the channel with a small $\text{m}_{x}$ hold a high $\text{m}_{\text {DOS}}$ , or the channel with heavy $\text{m}_{x}$ hold a small $\text{m}_{\text {DOS}}$ , which is beneficial to obtain high saturation current, steep sub-threshold swing, and thus a high on-current. Hence, the strong anisotropic electronic structure can be regarded as a target feature for designing high performance 2D FETs, which provides a guideline for exploring excellent 2D channels for ultra-scaled electronic devices. [ABSTRACT FROM AUTHOR]

According to quantum transport simulations, source-to-drain tunneling (SDT) has been recognized as the main cause leading to subthreshold swing (SS) saturation and degradation of short-channel MOSFETs at cryogenic temperatures. Generally, at a given low temperature, the steeper constant SS of thermionic currents may be overwhelmed by less-steep SDT currents at lower gate bias, degrading the average SS. Our simulations show that the SS of SDT currents is insensitive to temperatures for a MOSFET with a given channel length, accounting for SS saturation as lowering temperature. This work reveals the key points differentiating the possible reasons (interface traps, band tail and SDT) of SS saturation at cryogenic temperatures. We also study the impacts of carrier effective masses, gate-SD underlapping and a tunneling barrier at the source junction on SS saturation. SDT may pose a potential challenge and limit for scaling cryogenic CMOS of a quantum processor. [ABSTRACT FROM AUTHOR]

In this article, we report a physics-based compact model of drain current for InAs-on-insulator MOSFETs. The quantum confinement effect has been incorporated in the proposed model by solving the 1-D Schrödinger–Poisson equations without using any empirical model parameter. The model accurately captures the variation of surface potential, charge density in the inversion layer, and subband energy levels with gate bias inside the quantum well. The conduction-band nonparabolicity effect on modification in eigenenergy, effective mass, and density of states is derived and incorporated into the proposed model. The velocity overshoot effect that originates from the quasi-ballistic nature of carrier transport is also considered in the model. The proposed drain current model has been implemented in Verilog-A to use in the SPICE environment. The model predicted results are in good agreement with the commercial device simulator results and experimental data. [ABSTRACT FROM AUTHOR]

Si/Ge core/shell nanowires have been demonstrated to be a promising candidate for the next-generation transistor channel. The tunable electron and hole transport paths improve their mobilities significantly. Here, we comparatively investigate the electronic properties of the Si-core-Ge-shell and Ge-core-Si-shell nanowires and their pure material counterparts using the first-principles method. The effects of core/shell ratio, atom number, and cross-sectional shape are studied. The Si-core-Ge-shell nanowires show excellent transport path separation and small carrier effective mass properties when the core/shell ratios exceed 0.5. For smaller ratios, the energies of the off-&#915 valleys in the Ge shells are lowered and become the conduction band minimum (CBM) because of the intrinsic strains along the radial direction, enlarging the electron effective masses significantly. To restrain this effect, the uniaxial strain engineering is adopted and the best performance is exhibited when 2%–3% tensile strains are applied. In the Ge-core-Si-shell nanowires, both electrons and holes are easily confined to the core region. Compared with the Si-core-Ge-shell nanowires, their energy gaps and electron effective masses are smaller and larger, indicating poor transportability. The above discoveries are further validated by changing the cross-sectional shapes of the nanowires and device performance simulations, confirming that the Si-core-Ge-shell nanowires can outperform their pure material counterparts in high-speed transistor designs. [ABSTRACT FROM AUTHOR]

In this paper, we report a novel honeycomb-like disk resonator gyroscope (HDRG) and its comprehensive test results. HDRG inherits many advantages from traditional nested-ring disk resonator such as axisymmetric structure and huge capacitive area. In addition, HDRG owns unique characteristics and potentials due to its topology structure, namely, higher immunity to fabrication errors, better resonant mode consistency and better inner electrode arrangement. This new design of HDRG is based on a tradeoff between performance parameters including quality factor, decaying time constant, effective mass, effective capacitive area, transducer sensitivity and mechanical noise. The characteristics and potentials of HDRG are investigated firstly. Afterwards, the parameter optimization and frame structure optimization of HDRG are investigated. Based on the investigation, a novel HDRG is proposed. A prototype of this design is fabricated and its overall performance is tested. Results show that the quality factor of HDRG increases from 81.1k to 171.6k and the decaying time constant increases from 1.507 s to 6.973 s. The bias instability of the gyroscope reaches 0.11 °/h at room temperature without any compensation, more than eighty times smaller than the former design, exhibiting significant performance improvement. Moreover, ranging from −40 °C to 60 °C, the temperature coefficient of scale factor is 0.188%/ °C, and the maximum variations of zero offset and bias instability over temperature are 40 °/h and 0.12 °/h respectively, showing good robustness to environment disturbance. This new gyroscope has the potential to operate steadily under variable temperature conditions, offering as a new type of MEMS gyroscope with high performance and good robustness. [ABSTRACT FROM AUTHOR]

We report experimental demonstration of a right-angle black phosphorus (BP) tunneling field effect transistor (TFET). This device utilizes the effective mass anisotropy between the armchair (AC) and zigzag (ZZ) crystal orientations in BP as a means of inducing asymmetry between source and drain tunneling. As a result of this asymmetry, the BP TFET displays a higher ${I}_{ \mathrm{\scriptscriptstyle ON}} / {I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio by 2 orders of magnitude and steeper SS than BP TFETs oriented along either the AC or ZZ direction only. [ABSTRACT FROM AUTHOR]

We have studied the impact of the cross-sectional shape on the electron mobility of n-type silicon nanowire transistors (NWTs). We have considered circular and elliptical cross-section NWTs including the most relevant multisubband scattering processes involving phonon, surface roughness, and impurity scattering. For this purpose, we use a flexible simulation framework, coupling 3D Poisson and 2D Schrödinger solvers with the semi-classical Kubo-Greenwood formalism. Moreover, we consider cross-section dependent effective masses calculated from tight binding simulations. Our results show significant mobility improvement in the elliptic NWTs in comparison to the circular one for both [100] and [110] transport directions. [ABSTRACT FROM AUTHOR]

A novel micro shell resonator gyroscope (MSRG) with 16 T-shape masses using out-of-plane electrodes is proposed in this paper. The T-shape masses are designed for high transduction efficiency. Out-of-plane electrodes are used to drive and detect the spatial deformation of the resonator. The finite element method (FEM) is applied to evaluate the influence of the T-shape mass on transduction efficiency. Compared with the MSRG without the T-shape masses, the FEM results reveal that the MSRG with T-shape masses has shown an increase of 42% on effective mass (${M}_{ {eff}}$) and a decrease of 8% on ${f}_{ {n=2}}$. For the MSRG without T-shape mass, spherical–cylindrical, spherical, and out-of-plane electrodes have been applied to drive and sense n = 2 wineglass modes. Compared with the MSRG without T-shape using out-of-plane electrodes, the MSRG with T-shape masses has showed the improvement of 334%, 522%, and 598% on driving efficiency (${S}_{ {d}}$), detection efficiency (${S}_{ {s}}$), and mechanical sensitivity (${S}_{ {mech}}$) due to large ${M}_{\text {eff}}$ and electrode area. In addition, the improvement of 15% in the thermal noise of a gyroscope (ARW $_{\text {mech}}$) is dominated by a large effective mass, contributing to the improvement of signal-to-noise ratio. The process of micro blow torching with the whirling platform and femtosecond ablation is presented to fabricate the MSRG with T-shape masses. The performance of MSRG is demonstrated experimentally with out-of-plane capacitive transduction. The MSRG is operated in the force-rebalance mode, which demonstrates a scale factor of 0.107V/(°/s), an angle random walk of 0.099°/ $\text{h}^{{1/2}}$ , and a bias instability of 0.46°/h, showing a great potential for high-performance gyroscopic application. [ABSTRACT FROM AUTHOR]

We investigate the performance of 5-nm gate length GaN nMOS nanowire field effect transistor (GaN-NW-nFET) of various geometrical shapes, around the limits of cross-sectional scalability, using atomistic quantum transport simulations. For square cross-sections, the benchmarking results with the simulated Si-NW-nFET reveal over 30% enhancement in GaN drive current in both low standby power (LP − $I_{ \mathrm{\scriptscriptstyle OFF}}=1$ nA/ $\mu \text{m}$) and high performance (HP − $I_{ \mathrm{\scriptscriptstyle OFF}}=100$ nA/ $\mu \text{m}$) applications. Further performance enhancement is observed with the use of non-square geometries that are akin to GaN’s wurtzite crystal structure. Particularly, for ${T}_{\text {nw}}=2.4 $ mn, triangular cross-section GaN-NW-nFETs exhibit the smallest subthreshold swing, down to 62 mv/decade, excellent drive current, ${I}_{\text {DSAT}} > 2\times 10^{6}\,\, \mu \text {A}/ \mu \text {m}^{2}$ and superior energy-delay product compared to simulated Si-NW-nFET. [ABSTRACT FROM AUTHOR]

In nanoscale MOSFETs with sub-10 nm channels, the source-to-drain tunneling is expected to be a critical bottleneck, especially in III-V devices on account of their extremely low effective masses. Also, to maintain electrostatic integrity at extremely small gate lengths, the channels need to be made ultrathin. In such devices, the bandstructure of the channel material becomes thickness dependent due to quantum confinement effects, and deviates remarkably from that of the bulk material. In this paper, we use first principle density functional theory calculations to evaluate the variation of the effective mass and bandgap with channel thickness. Then, we perform semi-classical ballistic and full quantum non-equilibrium Green's function transport simulations to study the impact on source-to-drain tunneling in III-V nMOSFETs. We demonstrate that the severity of the expected degradation due to source-to-drain leakage is reduced significantly, when the beneficial impacts of change in bandstructure, and multi-valley transport are taken into account.

It is well known that there is a critical Sn content for a GeSn alloy, at which the conduction band edges at ${L}$ and $\Gamma$ symmetry points are aligned in energy. For GeSn tunnel FET (TFET) simulations, with a given donor concentration, this paper reveals that simulations neglecting the multivalley and nonparabolic band structure would incorrectly predict the subthreshold slope (SS) and the off-currents. We highlight the indispensability of the consideration of the multivalley band structure of GeSn for TFET simulations. This paper provides the required parameters, which may be useful for numerical simulations of other optoelectronic and electronic GeSn devices. [ABSTRACT FROM AUTHOR]

The metal-semiconductor contact resistivity has started to play a critical role for the overall device performance as Si is reaching 10-nm size ranges. The International Technology Roadmap for Semiconductors (ITRS) target predicts a requirement of $\text{10}^{-9} \; \Omega {\cdot} \text{cm}^{2}$ by 2023 which has been a challenging target to achieve. This paper explores the impact of doping concentration, Schottky barrier height, strain, and SiGe mole fraction on the resistivity of Si/SiGe p-type metal-oxide semiconductor (PMOS) contacts with 20-band atomistic tight binding quantum transport simulations. Commonly used simple effective mass approximation models are shown to overestimate the resistivity values. The predicted model results are compared with experimental data and the device parameters needed to achieve $\text{10}^{-9} \; \Omega {\cdot} \text{cm}^{2}$ are identified. [ABSTRACT FROM AUTHOR]

The electron mobility in strained ultra-thin InGaAs-on-InP MOSFETs is investigated combining band-structure and physics-based modeling including all relevant scattering mechanisms and effects. The most important effect is Fermi-level pinning which occurs due to high density of interface states at InGaAs/oxide interface. Different interface states densities are considered in order to investigate impact of interface states on electron mobility in biaxially strained ultra-thin InGaAs-on-InP structures. We report the tensile biaxial strain values that can alleviate the unfavorable impact of interface states charge on electron transport. [ABSTRACT FROM AUTHOR]

We explore the performance limits of monolayer InSe n -type and p -type FETs by means of first-principle simulations of carrier transport in nanoscale devices. We evaluate the impact on device performance of different device parameters, such as channel length, oxide thickness, and gate underlap. Finally, we assess the operation of a 32-bit CMOS ALU, based on InSe FETs with 10-nm channel length, for both high-performance and low-power applications, and find promising figures of merit with respect to CMOS and other beyond-CMOS proposals. [ABSTRACT FROM AUTHOR]

We model the effects of cross-sectional radius scaling on C-V and I-V characteristics of gate-all-around FETs (GAAFETs), capturing the continuous transition from a 3-D electron system to a 1-D electron system. We have obtained computationally efficient models for effective mass, bandgap, and subband energies as functions of the cross-sectional radius and gate voltage based on simple approximate analytic expressions. Together, they provide a compact model for VLSI circuit simulation, especially for analog and RF circuits that will be seriously affected by the new humps and peaks in C-V and I-V introduced by the subbands. The model has been validated with k · p-based technology computer aided design simulations as well as measured data. To the best of our knowledge, this is the first compact model capturing cross-sectional size-dependent dimensional crossover (3-D to 1-D) in I-V and C-V for GAAFETs. [ABSTRACT FROM AUTHOR]

A complete description of physical models for fabricated asymmetric spacer tunnel layer (ASPAT) diodes is reported in this paper. A novel In0.53Ga0.47As/AlAs design is presented and compared to the conventional GaAs/AlAs material system. For both material schemes, physical models were developed based on experimental measurements. Simulated dc characteristics of the devices are given for both planar- and back-contacted structures to highlight the impact of spreading resistance on device behavior. Furthermore, full S-parameter derivations from numerical simulation for tunnel diodes are demonstrated for the first time on the basis of quantum-mechanical ac modeling of the capacitance–voltage and conductance–voltage performances of these ASPAT diodes. A negligibly small difference between measured and simulated zero-biased intrinsic capacitances is observed (i.e., ≤ 0.2 fF). These are beneficial for accurate predictive models for device characteristics. In addition, key parameters which can be extracted from simulation results are obtained to aid in the development of millimeter-wave/terahertz applications of these types of heterostructure tunnel devices. [ABSTRACT FROM PUBLISHER]

Feasible device architectures for ultrascaled carbon nanotubes field-effect transistors (CNTFETs) are studied down to 5.9 nm using a multiscale simulation approach covering electronic quantum transport simulations and numerical device simulations. Schottky-like and ohmiclike contacts are considered. The simplified approach employed in the numerical device simulator is critically evaluated and verified by means of comparing the results with electronic quantum simulation results of an identical device. Different performance indicators, such as the switching speed, switching energy, the subthreshold slope, Ion/Ioff -ratio, among others, are extracted for different device architectures. These values guide the evaluation of the technology for different application scenarios. For high-performance logic applications, the buried gate CNTFET is claimed to be the most suitable structure. [ABSTRACT FROM PUBLISHER]

PtSe2, a new family of transition metal dichalcogenides, has been explored for electronic device applications using density functional theory and non-equilibrium Green’s function within the third nearest neighbor tight-binding approximation. Interestingly, despite its small effective mass ( me^{\ast } as low as 0.21\mathrm m\text {0} ; \mathrm m\text {0} being electron rest mass), PtSe2 has large density of states due to its unique six-valley conduction band within the first Brillouin zone, unlike MoX2 family. This has direct impacts on the device characteristics of PtSe2 field-effect transistors, resulting in superior on-state performance (30% higher on current and transconductance) as compared with the MoSe2 counterpart. Our simulation shows that the PtSe2 device with a channel longer than 15 nm exhibits near-ideal subthreshold swing, and sub-100 mV/V of drain-induced barrier lowering can be achieved with an aggressively scaled gate oxide, demonstrating new opportunities for electronic devices with novel PtSe2. [ABSTRACT FROM AUTHOR]

We investigate the channel material dependence of wave function deformation scattering (WDS), a phenomenon that occurs when the shape of the carrier wave function is forced to change as the channel is traversed. Line-edge roughness (LER) is one nonideality that can induce WDS in confined device geometries. We perform nonequilibrium Green's function simulations of ensembles of ultrascaled Fin Field Effect Transistors that exhibit correlated LER to determine the resulting on-current distributions. By considering various channel materials, we demonstrate two trends. First, WDS has a greater impact when the transport effective mass of the channel material is low, due to stronger coupling between conducting subbands. Second, WDS has a greater impact when the confinement effective mass of the channel material is high, due to the presence of more conducting subbands, which further enhances coupling. [ABSTRACT FROM AUTHOR]

A TCAD-oriented mobility model, whose main features are: 1) inclusion of ballistic effects in the linear region and 2) smooth transition between the linear and saturation regions, is presented. It is applied to short-channel double-gate thin-body InGaAs MOSFETs. The bases of the model are the concept of ballistic mobility and Matthiessen's rule in the linear regime, and the saturation velocity within a modified Canali model at high-longitudinal fields. Comparisons with accurate semiclassical multivalley multisubband Monte Carlo transport simulations indicate that TCAD simulations making use of the proposed model are able to correctly predict the terminal currents and the internal device quantities in the linear regime in a 15-nm device with no need of fitting parameters. In the saturation region, an empirical adjustment of the saturation velocity is needed, after which currents are accurately predicted for a wide range of gate lengths and bias conditions. [ABSTRACT FROM AUTHOR]

Tunnel FETs (TFETs) have attracted a great deal of attention due to their steep subthreshold swing (SS) of less than 60 mV/dec, which overcomes the theoretical constraint imposed by the thermal limit in a conventional inversion-mode (IM) FET. Based on its advantages as a short-channel device with low stand-by power consumption, TFETs shows promise to replace IM-FETs. As the channel length is shortened to minimize the total gate pitch; however, the gate sidewall spacer is miniaturized as well. In this paper, the influence of junction extension length (Lext) on TFET behavior is discussed where the length of the gate spacer is assumed to be the gap between the source and drain (S/D) electrodes and the gate edge. It was found that, when Lext is aggressively scaled down, having S/D electrodes (silicide or metal) with identical work functions (WFs) leads to a severely high OFF-current (IOFF) and high SS. By adopting separate asymmetric WFs for the p-type and n-type S/D electrodes, the on/off characteristics were improved with suppressed IOFF and steeper slopes. It was also shown that the device performance of a TFET with higher source-side doping concentrations (~5 × 1020 cm-3) can be further improved even at the aggressively scaleddown Lext by boosting the on-current. [ABSTRACT FROM AUTHOR]

Two-dimensional semiconductors provide excellent electrostatic control that is critical for scaled nodes. However, due to their lower dimensionality, contact resistance can be a limiting factor for performance of devices based on these materials. In this letter, we examine the intrinsic limits to contact resistance in 2-D semiconductors based on their band structure. It is found that for large enough doping concentration, contact resistance as outlined in the International Technology Road-map for Semiconductors road-map for high performance transistors can indeed be achieved. [ABSTRACT FROM AUTHOR]

High quality ultrathin body (UTB)-Ge-oninsulator (GeOI) substrates have been fabricated with advanced layer transfer technology called HEtero-LayerLift-Off. With precise control of interfacial qualities, Ge crystallinity and thickness fluctuation in GeOI substrates, electron mobility of UTB-GeOI nMOSFETs with body thickness (Tbody) from 20 to 3 nm has been systematically investigated. A significant electron mobility enhancement as Tbody scaling below 13 nm has been observed. This newly found mobility enhancement induced by channel thickness scaling could be attributed to the modulation of energy band structure in (001) confined UTB GeOI, where electron effective mass reduction is predicted by first-principle calculation. [ABSTRACT FROM AUTHOR]

A new numerical approach is presented for the determination of the statistical density matrix as a solution of the Liouville-von Neumann equation in center-mass coordinates. The numerical discretization is performed by utilizing a finite volume method, which leads to a discretized drift and diffusion operator. The solution is based on the eigenvector basis of the discretized diffusion operator with its corresponding eigenvalues and on the introduction of the self-energy concept. More specifically, the self-energy concept is essential to describe open-boundary problems adequately. Furthermore, this approach allows the definition of inflow and outflow conditions. The method presented is investigated with regard to the conventional Wigner transport equation and the quantum transmitting boundary method, when investigating coherent effects. [ABSTRACT FROM PUBLISHER]

We present a self-consistent and three-dimensional quantum simulation for nanowire resonant tunneling diodes (RTDs) based on the Wigner transport equation with spatially dependent effective masses (SDEM), which is discretized by a third-order upwind difference scheme for high-accuracy calculation. Our calculation shows that the current density/voltage (J\text--V) characteristics of nanowire RTDs with a radius ($R$) $<$ 5 nm largely deviate from those of the one-dimensional RTDs. As $R$ decreases below 5 nm, the peak-to-valley ratio (PVR) of the low-$V$ negative differential resistance (NDR) decreases rapidly, and the high- $V$ NDR peak shifts sensitively to lower $V$ and becomes sharper. In this study, these results are shown to be closely related to the SDEM. According to our analysis, the SDEM along the transport direction contributes to the formation of an ‘effective double barrier’ in the energy subbands that is higher than the double barrier expected by the band offset, and the SDEM along the confinement direction reduces the height of the effective double barrier. The performance of nanowire RTDs with $R<$ 5 nm was proven to be highly dependent on $R$ because of the SDEM along the confinement direction. [ABSTRACT FROM PUBLISHER]

The physical influence of temperature down to the cryogenic regime is analyzed in a comprehensive study and the comparison of IV and III–V Schottky barrier (SB) double-gate MOSFETs. The exploration is done using the Synopsys TCAD Sentaurus device simulator and first benchmarked with experimental data. The important device physics of both SB-MOSFETs and conventional MOSFETs are reviewed. The impact of temperature on device performance down to the liquid-nitrogen regime is then explored. We find reduced drive currents in SB-MOSFETs fabricated on small effective mass materials and that SB lowering can significantly improve SB-MOSFETs, especially at low temperatures. [ABSTRACT FROM PUBLISHER]

A drain current model of 2-D monolayer (ML) transition-metal dichalcogenide (TMD) tunnel FETs (TFETs) is proposed. For better accuracy, the proposed model features the following two points: 1) the accurate lateral energy profiles considering the extension of the depletion width ( Wd ) owing to the reduced dimensionality and 2) the spin- and valley-dependent complex band structure considering the spin-orbit coupling effect. The proposed model is validated by the tight-binding nonequilibrium green function simulation, in the case of ML MoS2 double-gate TFETs. By using the proposed model, the design guideline of ML TMD TFETs is presented. [ABSTRACT FROM PUBLISHER]

Using high-order vibration mode has been regarded as an effective way to improve the sensitivity of piezoelectric resonant cantilever mass sensors. To further improve the high-order mode sensitivity without reducing the overall dimension, a new shape design method was proposed to improve the sensitivity at the desired high-order vibration mode by optimizing the multi-stepped thickness along the cantilever axis. With the proposed method, a new fourth-order mode mass sensor is proposed incorporating a three-stepped piezoelectric-elastic composite cantilever. The effect of structural parameters on the vibration modes and also the sensitivity is analyzed. With the optimized three-stepped cantilever, the sensitivity can be at least 3.0 times that of the uniformed cantilever sensor also operated in the fourth-order vibration mode. Then, a piezoelectric mass sensor is fabricated with the step thickness ratio and step length ratio of 0.5 and 0.29. The experimental results show that the fourth-order mode sensitivity can achieve 185.41\times 10^4 Hz/g, which is nearly 19.5 times and 3.0 times greater than those of the custom uniform cantilever sensor working in the first and fourth vibration modes. Meanwhile, the quality factor is 82.65 about 3.5 times as great as that of the rectangular uniform cantilever sensor. The nearly consistency between simulation and experiments fully validates the feasibility and effectiveness of the newly proposed sensitivity improving method. [ABSTRACT FROM PUBLISHER]

We investigate the impact of uniaxial tensile stress on the performance of germanium–tin (GeSn) fin tunneling field-effect transistor (FinTFET) with fin rotating within (001) plane by numerical simulation. The uniaxial tensile stress with a magnitude of 1 GPa is always along the fin direction. Nonlocal empirical pseudopotential method and k \cdot p method were utilized to calculate the energy band structure of GeSn. Dynamic nonlocal band-to-band tunneling (BTBT) algorithm was used to analyze the electrical characteristics of the strained GeSn FinTFETs with point and line tunneling modes. The substantial improvement of BTBT generation rate {G}_{\text {BTBT}} and on-state current {I}_{ \mathrm{\scriptscriptstyle ON}} achieved in tensile-strained FinTFETs compared to the relaxed devices is attributed to the reduced direct bandgap EG in strained GeSn. The device performance enhancement induced by the stress demonstrates the obvious dependence on the fin direction and tunneling mode. Under 1 GPa uniaxial tensile stress, GeSn point-FinTFETs with \langle 100\rangle fin directions demonstrate an 11.7% I \mathrm{\scriptscriptstyle ON} enhancement as compared with the relaxed devices. For the strained GeSn line-FinTFETs, the devices with \langle 110\rangle fin directions obtain a 96.7% I \mathrm{\scriptscriptstyle ON} improvement, in comparison with the relaxed devices at {V}_{\text {DD}}$ of −0.3 V. [ABSTRACT FROM AUTHOR]

Within the framework of the coherent quantum-mechanical model, which is based on the solution of the time-dependent Schrödinger equation with exact open boundary conditions, we have numerically analyzed the behavior of the InGaAs/AlAs resonant-tunneling diode (RTD) in an alternating-current electric field in the presence of spacer layers. It is shown that the interaction of the energy levels in a quantum well of the RTD, and the same in a quantum well of the emitter spacer, leads to splitting of these levels, which sharply increases the active current of RTD. In this case, the value of the active current at the finite frequencies may exceed the active current within the low-frequency limits. For RTD, heterostructure considered active current at frequency 1.77 THz takes its maximum value at the thickness of the emitter spacer equals to 6.5 nm exceeding the corresponding value in the absence of the spacer by the factor of 32. The results obtained in this paper may be useful to improve the frequency characteristics of resonant-tunneling nanostructures. [ABSTRACT FROM PUBLISHER]

We study the performance of GaN nanowire n-MOSFETs (GaN-NW-nFETs) with a channel length, Lg = 5 nm based on fully ballistic quantum transport simulations. Our simulation results show high I ${} _{\textsf {ON}} = 1137 \mu \text{A}/\mu \text{m} and excellent on-off characteristics with Q = \,\, \textg\textsf {m} /SS = \,\, 188\mu \text{S} -decade/ \mu \textm -mV calculated for I ${} _{\mathrm{\scriptscriptstyle OFF}} = 1$ nA/ \mu \textm and V ${} _{\textsf {GS}} = \textsf {V}_{\textsf {DS}} = \textsf {V}_{\textsf {CC}} = 0.5$ V. These results represent: 1) ~ 15% higher \text{I}_{\mathrm{\scriptscriptstyle ON}} than Si-NW-nFET and 2) ~ 17% better Q than Si-NW-nFET, all with Lg = 5 nm, thus suggesting the GaN n-channel, an intriguing option for application in logic at sub-10-nm channel length. The superior performance of the GaN channel compared with Si and other semiconductors at this scaled dimension can be attributed to its relatively higher effective mass of electron and lower permittivity. [ABSTRACT FROM AUTHOR]

Physics-based transistor models are important for technology projections and circuit simulations. To date, there has been little discussion on the incorporation of ballistic effects in transistor models. Recent experimental studies have revealed the significance of ballistic transport in the electrical characteristics of nanometer-scale InGaAs MOSFETs with ultra-low external resistance. Without proper accounting for the ballistic resistance and its gate voltage dependence, the access resistance to the intrinsic device cannot be accurately determined, and any physics-based transistor modeling is bound to fail. In this letter, we show that the MIT Virtual Source model, which natively captures ballistic transport physics, correctly incorporates the impact of ballistic resistance. As a result, it accurately models the electrical characteristics of self-aligned nanoscale InGaAs MOSFETs, an excellent model system for near-ballistic transistors, over a broad operational range. We also show that the success of the model development effort crucially relies on the correct extraction of the external source and drain resistance, R{\text {sd}} , from experimental measurements. [ABSTRACT FROM AUTHOR]

Here we explore the performance limit of monolayer germanane (GeH) field-effect transistors (FETs). We first plotted an electronic band structure of GeH using density functional theory and then tight-binding parameters were extracted. Device characteristics of GeH FETs are investigated using rigorous self-consistent atomistic quantum transport simulations within tight-binding approximations. Our simulation results indicate that GeH FETs can exhibit exceptional on-state device characteristics, such as high \textI\textit {on} (>2 mA/ \mu \textm ) and large \textgm (~7 mS/ \mu \textm ) with \textV\textit {DD} = 0.5 V due to the very light effective mass of GeH (0.07m0), while maintaining excellent switching characteristics (SS ~64 mV/dec). We have also performed a scaling study by varying the channel length, and it turned out that GeH FET can be scaled down to ~14-nm channel without facing significant short channel effects but it may suffer from large leakage current at the channel length shorter than 10 nm. Finally, we have benchmarked GeH FET against MoS2 counterpart, exhibiting better suitability of GeH device for high-performance applications compared with MoS2 transistors. [ABSTRACT FROM AUTHOR]

Formulation of accurate yet computationally efficient surface potential equation (SPE) is the fundamental step toward developing compact models for low effective mass channel quantum well MOSFETs. In this paper, we propose a new SPE for such devices considering multisubband electron occupancy and oxide thickness asymmetry. Unlike the previous attempts, here, we adopt purely physical modeling approaches (such as without mixing the solutions from finite and infinite potential wells or using any empirical model parameter), while preserving the mathematical complexity almost at the same level. Gate capacitances calculated from the proposed SPE are shown to be in good agreement with numerical device simulation for wide range of channel thickness, effective mass, oxide thickness asymmetry, and bias voltages. [ABSTRACT FROM AUTHOR]

Theoretical calculations of the hydrostatic pressure influence on the electronic band structure and the optical gain of N-containing InAs0.98N0.02/GaSb quantum wells laser diodes are presented. A \mathbf k\cdot \mathbf p model, taking into account, the p-like valence band, the s-like and p-like conduction band, and the nitrogen resonant level is introduced. We have used a unitary transformation that block diagonalizes the 16\times16 Hamiltonian into two 8\times8 blocks that are real symmetric in the finite difference formulation. Numerical results have been determined over a pressure range from 0 to 30 kbar. It has been shown that the hydrostatic pressure changes the electronic band structure and as a result the optical gain decreases with the hydrostatic pressure by about 80% and 50% for [111] and [001] growth directions, respectively for transverse electric modes. Hence, the emission spectrum is shifted to shorter wavelength (i.e., for [111] direction, from 2.65~\mu \textm to 1.16~\mu \textm ). [ABSTRACT FROM AUTHOR]

An improved band-to-band tunneling (BTBT) model for SiGe random alloy is presented. The model takes into account the coherent transition through the direct band gap as well as the phonon and alloy scattering induced transitions to the indirect conduction band valleys. The complex valence and conduction band structures obtained from the 6-band k\cdot p and from the multi-valley effective mass models are combined to compute the non-parabolic imaginary dispersions for the direct and indirect BTBT transitions, which agree well with the full band calculations. The present model is validated against the atomistic quantum simulation based on the empirical tight binding method. Simulation results show that the alloy scattering plays an important role in the indirect BTBT of SiGe alloy and should not be neglected. [ABSTRACT FROM AUTHOR]

GaSb/InAs heterojunction tunnel FETs are strong candidates in building future low-power ICs, as they could provide both steep subthreshold swing and large ON-state current ( I\mathrm{\scriptscriptstyle ON} ). However, at short-channel lengths, they suffer from large tunneling leakage originating from the small bandgap and small effective masses of the InAs channel. As proposed in this paper, this problem can be significantly mitigated by reducing the channel thickness, meanwhile retaining a thick source-channel tunnel junction, thus forming a design with a nonuniform body thickness. Because of the quantum confinement, the thin InAs channel offers a large bandgap and large effective masses, reducing the ambipolar and source-to-drain tunneling leakage at OFF-state. The thick GaSb/InAs tunnel junction, instead, offers a low tunnel barrier and small effective masses, allowing a large tunnel probability at ON-state. In addition, the confinement-induced band discontinuity enhances the tunnel electric field and creates a resonant state, further improving I\mathrm{\scriptscriptstyle ON} . Atomistic quantum transport simulations show that ballistic I\mathrm{\scriptscriptstyle ON}=284 A/m is obtained at 15-nm channel length, I\mathrm{\scriptscriptstyle OFF}=1\times 10^{-3} A/m, and V\mathrm{DD}=0.3 V, while with uniform body thickness, the largest achievable I\mathrm{\scriptscriptstyle ON} is only 25 A/m. Simulations also indicate that this design is scalable to sub-10-nm channel length. [ABSTRACT FROM AUTHOR]