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Introduction
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January 1983 - January 2005
January 2005 - August 2010
Education
September 1975 - June 1978
September 1970 - October 1974
Publications
Publications (327)
In this theoretical study, we compare electrostatically doped metal-transition metal dichalcogenide (TMD) edge-contacts versus substitutionally doped edge-contacts in terms of their contact resistance. Our approach involves the utilization of electrostatic doping achieved by applying back-gate bias to the metal-TMD edge contacts, where carrier inje...
Oxyhalides form a family of two-dimensional materials with a large bandgap, which makes them interesting for power electronics applications. However, significant research into oxyhalides for use in electronic devices is lacking. Using first principles calculations, we investigate the feasibility of oxyhalides for power transistors. First, we show t...
The present study is concerned with simulating the thermalization of high-energy charge carriers (electrons and/or electron–hole pairs), generated by ionizing radiation, in diamond and β-Ga2O3. Computational tools developed by the nuclear/particle physics and electronic device communities allow for accurate simulation of charge-carrier transport an...
The present study is concerned with simulating the thermalization of high-energy charge carriers (electrons and/or electron-hole pairs), generated by ionizing radiation, in diamond and β-Ga2O3. Computational tools developed by the nuclear/particle physics and electronic device communities allow for accurate simulation of charge-carrier transport an...
Since the 1960s and the first observations of radiation-induced disruption of electronic devices in space, the study of the effects of ionizing radiation on electronics has grown into an extensive field of its own. The present paper is concerned with studying accurately the energy-loss processes that control the thermalization of hot carriers (elec...
Scaling electronic devices to the nanometer scale requires, among other constrains, a reduction of the thickness of the channel. This results in quantum confinement of the carriers which, in turn, causes an unavoidable degradation of the charge-transport properties. The advent of graphene seems to have opened a new avenue to circumvent the problem:...
The present work is concerned with studying accurately the energy-loss processes that control the thermalization of hot electrons and holes that are generated by high-energy radiation in wurtzite GaN, using an ab initio approach. Current physical models of the nuclear/particle physics community cover thermalization in the high-energy range (kinetic...
Field-effect transistors (FETs) having two-dimensional (2D) materials as the channel offer superior gate control and decreased short-channel effects when compared to bulk-semiconductor channels. Here, employing ab initio band structure and scattering rates as input to Monte Carlo simulations, we investigate the electron-transport characteristics in...
The search for alternatives to Si in the VLSI technology is based on experimental and theoretical work. Here, we consider only the latter and, looking at a few two-dimensional materials of current interest, we use them as examples to emphasize the difficulties faced by theorists in assessing their potential: Silicene and germanene are examples of m...
The performance of transistors based on two-dimensional (2D) materials is affected largely by the contact resistance due to high Schottky barriers at the metal-2D-material interface. In this work, we incorporate the effect of surrounding dielectrics and image-force barrier-lowering in calculating the resistance of Schottky edge-contacts between a m...
We discuss the effect of the dielectric environment (substrate/bottom oxide, gate insulator, and metal gates) on electronic transport in two-dimensional (2D) transition metal dichalcogenides (TMD) monolayers. We employ well-known ab initio methods to calculate the low-field carrier mobility in free-standing layers and use the dielectric continuum a...
We investigate theoretically the impact of the dielectric environment on electronic transport in transition metal dichalcogenide monolayers. The low-field carrier mobility in free-standing layers is calculated using well-known ab initio methods, and the study is extended to layers in double-gate structures using the dielectric continuum approximati...
We compare the image-force barrier lowering (IFBL) and calculate the resulting contact resistance for four different metal–dielectric-two-dimensional (2D) material configurations. We analyze edge contacts in three different geometries (a homogeneous dielectric throughout, including the 2D layer; a homogeneous dielectric surrounding the 2D layer, bo...
We discuss the effect of the dielectric environment (insulators and metal gates) on electronic transport in two-dimensional (2D) transition metal dichalcogenides (TMD) monolayers. We employ well-known ab initio methods to calculate the low-field carrier mobility in free-standing layers and use the dielectric continuum approximation to extend our st...
Energetic carriers in semiconductors thermalize by impact-ionization, which generates electron–hole pairs (EHPs), and by energy losses to phonons. The average EHP creation energy is typically about three times the energy gap. In 1960, Shockley derived a simple equation for the average EHP creation energy with a single free parameter that fits exper...
The energy distributions of electrons in gate-all-around (GAA) Si MOSFETs are analyzed using full-band 3-D Monte Carlo (MC) simulations. Excellent agreement is obtained with experimental current-voltage characteristics. For these 24-nm gate length devices, the electron distribution features a smeared energy peak with an extended tail. This extensio...
Over the last few years, ab initio methods have become an increasingly popular tool to evaluate intrinsic carrier transport properties in 2D semiconductors.
The lack of experimental information, and the progress made in the development of DFT tools to evaluate electronic band structures, phonon dispersions, and electron–phonon scattering matrix-ele...
We present a theoretical study of the effect of defects on the charge-transport properties of gate-all-around graphene nanoribbons field-effect transistors. Electronic transport is treated atomistically using an efficient method we have recently proposed that makes use of a Bloch-wave basis obtained from empirical pseudopotentials and solves the Sc...
Experimental studies on two-dimensional (2D) materials are still in the early stages, and most of the theoretical studies performed to screen these materials are limited to the room-temperature carrier mobility in the free-standing 2D layers. With the dimensions of devices moving toward nanometer-scale lengths, the room-temperature carrier mobility...
We find a fundamental limit of channel-length scaling for Laterally Diffused Metal-Oxide-Semiconductor (LDMOS) FETs. We optimize a set of devices with different channel lengths, from 10 nm to 100 nm, through an optimization algorithm to meet a predetermined criterion for drain-to-source subthreshold leakage-current and breakdown voltage. We identif...
Experimental studies on two-dimensional (2D) materials are still in the early stages, and most of the theoretical studies performed to screen these materials are limited to the room-temperature carrier-mobility in the free standing 2D layers. With the dimensions of devices moving towards nanometer-scale lengths, the room-temperature carrier-mobilit...
To investigate inelastic electron scattering, which is ubiquitous in various fields of study, we carry out ab initio study of the real-time dynamics of a one-dimensional electron wave packet scattered by a hydrogen atom using different methods: the exact solution, the solution provided by time-dependent density functional theory (TDDFT), and the so...
To investigate inelastic electron scattering, which is ubiquitous in various fields of study, we carry out ab initio study of the real-time dynamics of a one-dimensional electron wave packet scattered by a hydrogen atom using different methods: the exact solution, the solution provided by time-dependent density functional theory (TDDFT), and the so...
We study ballistic and dissipative quantum transport of electrons in realistic semiconductor devices. Ballistic electron transport is modeled by solving self-consistently the Schrödinger and Poisson equations in the two-dimensional plane of the device using the effective-mass approximation. The quantum transmitting boundary method (QTBM) is used to...
The absence of a band gap in graphene makes it of minor interest for field-effect transistors. Layered metal chalcogenides have shown great potential in device applications thanks to their wide bandgap and high carrier mobility. Interestingly, in the ever-growing library of two-dimensional (2D) materials, monolayer InSe appears as one of the new pr...
Over the last few years, $ab~initio$ methods have become an increasingly popular tool to evaluate intrinsic carrier transport properties in 2D materials. The lack of experimental information, and the progress made in the development of DFT tools to evaluate electronic band structures, phonon dispersions, and electron-phonon scattering matrix-elemen...
The simulation of charge transport in ultra-scaled electronic devices requires the knowledge of the atomic configuration and the associated potential. Such “atomistic” device simulation is most commonly handled using a tight-binding approach based on a basis-set of localized orbitals. Here, in contrast to this widely-used tight-binding approach, we...
Using first-principles calculations we have previously shown that placing graphene on a (111)-oriented perovskite SrTiO3 (STO) surface provides a possible doping mechanism [D. Shin and A. A. Demkov, Phys. Rev. B 97, 075423 (2018)]. Further theoretical analysis presented here suggests that coupling of electrons in graphene to interfacial hybrid plas...
Silicane, a hydrogenated monolayer of hexagonal silicon, is a candidate material for future complementary metal-oxide-semiconductor technology. We determined the phonon-limited mobility and the velocity-field characteristics for electrons and holes in silicane from first principles, relying on density functional theory. Transport calculations were...
Theoretical studies of heat generation and diffusion in Si devices generally assume that hot electrons in Si lose their energy mainly to optical phonons. Here, we briefly review the history of this assumption, and using full-band Monte Carlo simulations—with electron-phonon scattering rates calculated using the rigid-ion approximation and both empir...
High-electron-mobility transistors (HEMTs) based on AlxGa1−xN/GaN heterostructures have great potential for applications in power electronics and radio frequency applications. Operating under large bias and electric fields, hot electrons are present in the channel where they can activate preexisting benign defects that cause scattering or carrier t...
The simulation of charge transport in ultra-scaled electronic devices requires the knowledge of the atomic configuration and the associated potential. Such "atomistic" device simulation is most commonly handled using a tight-binding approach based on a basis-set of localized orbitals. Here, in contrast to this widely used tight-binding approach, we...
We investigate the diffusive electron-transport properties of charge-doped graphene ribbons and nanoribbons with imperfect edges. We consider different regimes of edge scattering, ranging from wide graphene ribbons with (partially) diffusive edge scattering to ribbons with large width variations and nanoribbons with atomistic edge roughness. For th...
The thermalization process of sub-10 eV charge carriers is examined with treating carrier transport with full-band Monte Carlo simulations. The average energy loss (3.69 eV in Si and 2.62 eV in Ge) required to create a thermalized electron-hole pair, obtained from the simulations, is very close to the experimentally measured radiation-ionization en...
Recent ab initio theoretical calculations of the electrical performance of several two-dimensional materials
predict a low-field carrier mobility that spans several orders of magnitude (from 26 000 to 35 cm2 V−1 s−1, for
example, for the hole mobility in monolayer phosphorene) depending on the physical approximations used.
Given this state of uncer...
The critical role of silicon and germanium in the semiconductor industry, combined with the need for extremely thin channels for scaled electronic devices, has motivated research towards monolayer silicon (silicene) and monolayer germanium (germanene). The lack of horizontal mirror (σh) symmetry in these two-dimensional crystals results in a very s...
We investigate the diffusive electron-transport properties of graphene ribbons and nanoribbons with imperfect edges. We treat different regimes of edge scattering, ranging from wide graphene ribbons with (partially) diffusive edge scattering, to ribbons with large width-variations, and nanoribbons with atomistic edge roughness. For the latter, we c...
In two-dimensional crystals that lack symmetry under reflections on the horizontal plane of the lattice (non-$\sigma_{\rm h}$-symmetric), electrons can couple to flexural modes (ZA phonons) at first order. We show that in materials of this type that also exhibit a Dirac-like electron dispersion, the strong coupling can result in electron pairing me...
In two-dimensional crystals that lack symmetry under reflections on the horizontal plane of the lattice (non-$\sigma_{\rm h}$-symmetric), electrons can couple to flexural modes (ZA phonons) at first order. We show that in materials of this type that also exhibit a Dirac-like electron dispersion, the strong coupling can result in electron pairing me...
Recent $\textit{ab initio}$ theoretical calculations of the electrical performance of several two-dimensional materials predict a low-field carrier mobility that spans several orders of magnitude (from 26,000 to 35 cm$^{2}$ V$^{-1}$ s$^{-1}$, for example, for the hole mobility in monolayer phosphorene) depending on the physical approximations used....
In the past couple of decades, the theoretical study of two-dimensional (2D) materials that could (hopefully) extend the miniaturization of semiconductor devices beyond the perceived limits of the Si CMOS technology has been affected by two major changes. On the one hand, these new materials are poorly known, so that one must rely almost exclusivel...
We present a theoretical study of the ballistic performance of gate-all-around field-effect transistors (FETs) with channels consisting of armchair-edge graphene nanoribbons (aGNRs) of various widths and silicon nanowires (SiNWs) with square cross sections. We apply an atomistic quantum transport formalism based on empirical pseudopotentials. Our r...
We present a theoretical study of the negative differential transconductance (NDT) recently observed in lateral-quantum-well Si n-channel field-effect transistors [J. Appl. Phys. 118, 124505 (2015)]. In these devices, p+ doping 'pockets' are introduced at the source-channel and drain-channel junctions, thus creating two potential barriers that defi...
Two-dimensional topological insulators (2D TIs) host topologically protected edge-states with excellent transport properties even in the presence of large amounts of imperfections, such as edge roughness or defects. To overcome the challenge of using two-dimensional materials for nanoelectronic devices, we propose 2D TI field-effect transistors (FE...
We discuss some basic physical properties of electron transport in two-dimensional materials. First, we discuss how the predicted thermodynamic instability of 2D crystals may influence charge transport via the coupling of electrons with acoustic flexural modes. We then review the properties of suspended and supported graphene and its ribbons and co...
We present first-principles analytical and Monte Carlo simulations of electron transport in silicene and germanene, assuming a long-wavelength cutoff for the acoustic flexural modes (ZA) to control the divergence of the electron/ZA-phonons coupling at small wavevectors. We also consider the electron mobility in phosphorene as an example illustratin...
We model a field-effect transistor making use of the spin-polarized edge states of two-dimensional topological insulators. To account for scattering while respecting Pauli's exclusion principle and the ballistic limit, we employ the Boltzmann equation. We account for phonon-assisted scattering processes and show that the current can be modulated ov...
We derive a microscopic Poisson equation using the density-density response function. This equation is valid for any realistic potential perturbation and permits the study of dielectric response in nanostructures, especially in 1D nanostructures and quantum dots. We apply this equation to simulate a nanoscale parallel-plate capacitor (nanocapacitor...
This textbook is aimed at second-year graduate students in Physics, Electrical Engineering, or Materials Science. It presents a rigorous introduction to electronic transport in solids, especially at the nanometer scale. Understanding electronic transport in solids requires some basic knowledge of Hamiltonian Classical Mechanics, Quantum Mechanics...
In this chapter we present the basic definition of lattices, crystals, their symmetries, and the concept of reciprocal lattice, on which studies of electronic structure and transport are based. We also give a brief review of how group theory can be used to understand the physical properties of crystals.
We set the foundations of the formalism used in following chapters: We first discuss why we need a formulation of Quantum Mechanics that goes beyond the simple single-particle Schrödinger equation. We then review the Lagrangian and Hamiltonian formulation of Classical Mechanics, since this leads to the formal Canonical Quantization, that is, the fo...
Going beyond the Hartree and Hartree–Fock approximations, this chapter deals with fluctuations of an electron gas away from the mean-field approximation. Having introduced the basic distinction between collective effects at long wavelength (plasmons) and single-particle interactions at short range, we derive the short-range interparticle scattering...
In this chapter, we review in some detail the solutions of Schrödinger’s equation for a single particle in three dimensions. We treat the case of a free particle, a particle in a box, and a particle in the presence of a Coulomb potential, that is, the hydrogen atom. This first part of the chapter is presented using mathematical details that will be...
We present various methods used to calculate the band structure of solids: Plane-wave methods; orthogonalized plane waves, which leads to the concept of model potentials and/or pseudopotentials, self-consistent, and empirical; linear combination of atomic orbitals—LCAO or tight-binding; and k ⋅ p perturbation theory. We also present some significan...
We present the formal procedure to quantize fields—the many-body problem—starting from the Lagrangian and Hamiltonian formulation of fields and performing the procedure of canonical quantization of systems with an infinite number of degrees of freedom. We apply this procedure to the significant examples of electrons (the Schrödinger field), plasmon...
We illustrate the use of empirical pseudopotentials to study the electronic structure of low-dimensional structures. We consider two-dimensional systems, such as thin Si films, hetero-structures, and graphene, and one-dimensional structures, such as carbon nanotubes and Si nanowires.
We discuss the dielectric response of a crystal. We consider separately the ionic response and the electronic response in the Random Phase Approximation. We then consider explicitly the interesting limits of the response of an electron gas in three and two dimensions at low temperature, and in the static- and long-wavelength limits.
First-order perturbation theory (Fermi’s Golden Rule or the Born approximation) is used to discuss how to calculate the rate at which electrons in a crystal scatter with space- and/or time-dependent perturbations.The case of electrons in three, two, and one dimension(s) is considered in the general case in which the band structure is known from num...
Impurity scattering in semiconductors is discussed presenting the Brooks–Herring and Conwell–Weisskopf models. More advanced treatments, such as Ridley’s statistical screening and partial-wave analysis, are also briefly discussed.
The electron–phonon interaction is presented in detail starting from its most general formulation, considering nonpolar (deformation potential) and polar (Fröhlich) interactions. The possible way to calculate the nonpolar electron–phonon matrix elements using DFT is discussed and the rigid-ion approximation is developed in detail. The general form...
Starting from the Liouville–von Neumann equation of motion for the density matrix of a system of electrons and phonons, we derive a Master Equation valid over short length-scales by treating the phonons as first-order perturbations. In so doing, we show how elusive is the Ansatz required to introduce irreversibility. We then show how the Boltzmann...
We present various methods used to solve numerically the Boltzmann transport equation. The moments methods (drift diffusion, hydrodynamic model, energy transport) are first considered. Particle-based methods (Monte Carlo, cellular automata, scattering matrices, and weighted particles method) are then discussed and we conclude with an overview of di...
We formulate the problem of understanding the electronic structure of crystals starting from the “exact” Schrödinger equation for the ions and the electrons and introducing the main approximations—namely, the adiabatic and Hartree–Fock approximations—required to reach a single-electron picture. We then discuss qualitatively the main features of the...
Electron dynamics in crystals is presented, starting from the envelope approximation of Luttinger and Kohn. We present the acceleration theorem and apply these results to some interesting cases: Si inversion layers, Stark-ladder quantization and Bloch oscillations, Landau levels, and shallow impurity states.
This chapter presents the basic elements of Quantum Statistical Mechanics, starting from the definition of the density matrix. Some examples of density matrices are given, before discussing the grand canonical ensemble, the concept of distribution function, and concluding by deriving the Liouville–von Neumann equations of motion for the density mat...
Perturbation theory and the dipole approximation are used to derive the electron–photon Hamiltonian, its matrix elements between Bloch states, and the transition rates for electrons absorbing or emitting a photon. The calculation of the absorption spectrum is presented using these results. As an example, we show the energy distribution of carriers...
In this chapter we discuss how to treat electronic transport in small structures with a full quantum-mechanical formulation; that is, we introduce the problem of “quantum transport.” We introduce the concept of Green’s functions and see how they are related to the density matrix. In order to find a solution of the transport problem, we consider fir...
We present an introduction to Density Functional Theory. We discuss briefly the Kohn–Sham functional, the local density approximation, and some more sophisticated implementations of the theory. We present some computational examples and show how the theory can be used to provide information needed to study electron transport, focusing on the calcul...
We show that the electron mobility in ideal, free-standing two-dimensional
`buckled' crystals with broken horizontal mirror ($\sigma_{\rm h}$) symmetry
and Dirac-like dispersion (such as silicene and germanene) is dramatically
affected by scattering with the acoustic flexural modes (ZA phonons). This is
caused both by the broken $\sigma_{\rm h}$ sy...
Following investigations into monolayer silicon (silicene) and germanium (germanene), interest has recently been raised towards monolayer tin (“stanene”). In this chapter, we will discuss the interesting features that can be found in monolayer tin compared to the other hexagonal lattices of the group IV elements. Currently, no experimental results...
The scaling of electronic devices has continued unabated for the past 5 decades, despite repeated predictions of the "end of scaling". The "more than Moore" slogan has been, and still is, viewed by industry as a need to explore realistic low-to-medium-risk avenues, some already in production -- such as strained Si/Ge or high-κ dielectrics, some yet...
Several theoretical electronic structure methods are applied to study the relative energies of the minima of the X- and L-conduction-band satellite valleys of InxGa1−xAs with x = 0.53. This III-V semiconductor is a contender as a replacement for silicon in high-performance n-type metal-oxide-semiconductor transistors. The energy of the low-lying va...
We present a formalism to treat quantum electronic transport at the nanometer scale based on empirical pseudopotentials. This formalism offers explicit atomistic wavefunctions and an accurate band structure, enabling a detailed study of the characteristics of devices with a nanometer-scale channel and body. Assuming externally applied potentials th...
A weakly coupled system of two crossed graphene
nanoribbons exhibits direct tunneling due to the overlap of the wavefunctions of both ribbons. We apply the Bardeen transfer Hamiltonian formalism, using atomistic band structure calculations to account for the effect of the atomic structure on the tunneling process. The strong quantum-size confineme...
The tunneling current between two crossed graphene ribbons is described
invoking the empirical pseudopotential approximation and the Bardeen transfer
Hamiltonian method. Results indicate that the density of states is the most
important factor determining the tunneling current between small (nm) ribbons.
The quasi-one dimensional nature of graphene...
After performing one-dimensional simulation of electron transport in narrow quantum wires without gate control in Ref [1], [2] using the open boundary-conditions full-band plane-wave transport formalism derived in Ref [3], we now extend the work to simulate three-dimensionally field-effect transistors (FETs) with a gate bias applied and obtain thei...
The tunneling current between two crossed graphene ribbons is described invoking the empirical pseudopotential approximation and the Bardeen transfer Hamiltonian method. Results indicate that the density of states is the most important factor determining the tunneling current between small (˜nm) ribbons. The quasi-one dimensional nature of graphene...
An open boundary-conditions full-band quantum transport formalism with a plane-wave basis based on empirical pseudopotentials is used to self-consistently simulate transistors in the sub-1 nm technology node, with one-dimensional silicon nanowires, armchair-edge graphene nanoribbons, and zigzag-edge carbon nanotubes as the channel. The electrostati...
The empirical pseudopotential band-structure of Ge, Si, GaAs, InAs, and In(0.53)Ga(0.47)As is used to compute the impact ionization (pair production) rate for electrons and holes. The constant-matrix-element and Kane's random-k approximations are also employed, to assess the importance of the energy-dependence of the Coulomb matrix element, of mome...
We discuss why low-dimensionality materials are needed to scale logic devices to the 5 nm gate-length. We discuss the advantages and disadvantages of graphene and graphene nanoribbons, the feasibility of Bose-Einstein condensation in bilayer graphene, and the use of 2D topological insulators, such as halogen-functionalized monolayer tin.