Impact of phonon scattering in Si/GaAs/InGaAs nanowires and FinFets: a NEGF perspective

Martı́nez, Antonio; Price, A.; Valin, R.; Aldegunde, Manuel; Barker, John R.

doi:10.1007/s10825-016-0851-0

Cited by 11 publications

(16 citation statements)

References 41 publications

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“…The source potential is given by the N=0 in the first series of equation (24). The image locations along the y-axis and charge assignments are: For a separation of source charge and field point ρ=10d (where here d=2b is the distance between the two conducting slabs) and an accuracy in the potential of the order of 1% requires ~ 10 8 image charges, a result first observed in reference [6]. This slow convergence disappears for shorter distances between the source charge and the field point, precisely the localised regime where the self-energy is defined.…”

Section: Dielectric Sandwiched Between Two Conducting Slabsmentioning

confidence: 83%

“…For dielectric heterostructures with regions with nanometer dimensions the electrostatic self-energies of carriers and charged impurities may be high (meV to a few eV, [1]). Here we focus on semiconductor nanostructures including wrapround-gate field effect nanowire transistors [2][3][4][5][6] but the following is applicable also to biological systems such as ion channels and to molecular heterostructures including carbon nanostructures. For semiconductor nanostructures the electrostatic self-energy (when considered at all) is generally pre-computed numerically along with a tight-binding evaluation of nanostructure energy band structure [7].…”

Section: Introductionmentioning

confidence: 99%

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Image charge models for accurate construction of the electrostatic self-energy of 3D layered nanostructure devices

Barker

Martı́nez

2018

J. Phys.: Condens. Matter

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Efficient analytical image charge models are derived for the full spatial variation of the electrostatic self-energy of electrons in semiconductor nanostructures that arises from dielectric mismatch using semi-classical analysis. The methodology provides a fast, compact and physically transparent computation for advanced device modeling. The underlying semi-classical model for the self-energy has been established and validated during recent years and depends on a slight modification of the macroscopic static dielectric constants for individual homogeneous dielectric regions. The model has been validated for point charges as close as one interatomic spacing to a sharp interface. A brief introduction to image charge methodology is followed by a discussion and demonstration of the traditional failure of the methodology to derive the electrostatic potential at arbitrary distances from a source charge. However, the self-energy involves the local limit of the difference between the electrostatic Green functions for the full dielectric heterostructure and the homogeneous equivalent. It is shown that high convergence may be achieved for the image charge method for this local limit. A simple re-normalisation technique is introduced to reduce the number of image terms to a minimum. A number of progressively complex 3D models are evaluated analytically and compared with high precision numerical computations. Accuracies of 1% are demonstrated. Introducing a simple technique for modeling the transition of the self-energy between disparate dielectric structures we generate an analytical model that describes the self-energy as a function of position within the source, drain and gated channel of a silicon wrap round gate field effect transistor on a scale of a few nanometers cross-section. At such scales the self-energies become large (typically up to ~100 meV) close to the interfaces as well as along the channel. The screening of a gated structure is shown to reduce the self-energy relative to un-gated nanowires.

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Section: Dielectric Sandwiched Between Two Conducting Slabsmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Image charge models for accurate construction of the electrostatic self-energy of 3D layered nanostructure devices

Barker

Martı́nez

2018

J. Phys.: Condens. Matter

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“…We have considered the acoustic and optical (for f-type and g-type) intervalley scattering mechanisms, as well as the intra-valley elastic acoustic phonons scattering mechanism. The specific parameters and models used can be found in references [85,86]. The electrostatic potential is calculated from the Poisson equation in the mean field approximation.…”

Section: Device Structure and The 1d Representationmentioning

confidence: 99%

“…The calculation of phonon modes in confined nanostructures is also a challenge, as they strongly depend on the boundary conditions used [99]. In our study, the acoustic deformation potential has been parameterised to partially take care of the decrease in mobility for narrow nanowire following [86,98]. Using a heat equation has the advantage of extending thermal simulations in larger regions surrounding the device and interconnects.…”

Section: Perspectives and Challengesmentioning

confidence: 99%

Quantum Transport in a Silicon Nanowire FET Transistor: Hot Electrons and Local Power Dissipation

Martı́nez

Barker

2020

Materials

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A review and perspective is presented of the classical, semiclassical and fully quantum routes to the simulation of electrothermal phenomena in ultrascaled silicon nanowire fieldeffect transistors. It is shown that the physics of ultrascaled devices requires at least a coupled electron quantum transport semiclassical heat equation model outlined here. The importance of the local density of states (LDOS) is discussed from classical to fully quantum versions. It is shown that the minimal quantum approach requires selfconsistency with the Poisson equation and that the electronic LDOS must be determined within at least the selfconsistent Born approximation. To bring in this description and to provide the energy resolved local carrier distributions it is necessary to adopt the nonequilibrium Green function (NEGF) formalism, briefly surveyed here. The NEGF approach describes quantum coherent and dissipative transport, Pauli exclusion and nonequilibrium conditions inside the device. There are two extremes of NEGF used in the community. The most fundamental is based on coupled equations for the Green functions electrons and phonons that are computed at the atomically resolved level within the nanowire channel and into the surrounding device structure using a tight binding Hamiltonian. It has the advantage of treating both the nonequilibrium heat flow within the electron and phonon systems even when the phonon energy distributions are not described by a temperature model. The disadvantage is the grand challenge level of computational complexity. The second approach, that we focus on here, is more useful for fast multiple simulations of devices important for TCAD (Technology Computer Aided Design). It retains the fundamental quantum transport model for the electrons but subsumes the description of the energy distribution of the local phonon subsystem statistics into a semiclassical Fourier heat equation that is sourced by the local heat dissipation from the electron system. It is shown that this selfconsistent approach retains the salient features of the fullscale approach. For focus, we outline our electrothermal simulations for a typical narrow Si nanowire gate allaround fieldeffect transistor. The selfconsistent Born approximation is used to describe electronphonon scattering as the source of heat dissipation to the lattice. We calculated the effect of the device selfheating on the current voltage characteristics. Our fast and simpler methodology closely reproduces the results of a more fundamental computeintensive calculations in which the phonon system is treated on the same footing as the electron system. We computed the local power dissipation and “local lattice temperature” profiles. We compared the selfheating using hot electron heating and the Joule heating, i.e., assuming the electron system was in local equilibrium with the potential. Our simulations show that at low bias the source region of the device has a tendency to cool down for the case of the hot electron heating but not for the case of Joule heating. Our methodology opens the possibility of studying thermoelectricity at nanoscales in an accurate and computationally efficient way. At nanoscales, coherence and hot electrons play a major role. It was found that the overall behaviour of the electron system is dominated by the local density of states and the scattering rate. Electrons leaving the simulated drain region were found to be far from equilibrium.

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“…In fact, instead of the recondite mathematical language, the governing equation in NEGF formalism can be regarded as a modified Schrödinger equation with an appropriate boundary condition. To make the simulation more practical, the solver has considered multiple scattering mechanisms including electron‐phonon, ionized impurity (IMP), and surface roughness (SR) scattering.…”

Section: Introductionmentioning

confidence: 99%

3D Self-Consistent Quantum Transport Simulation for GaAs Gate-All-Around Nanowire Field-Effect Transistor with Elastic and Inelastic Scattering Effects

Hsiao

2018

Phys. Status Solidi A

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As the gate length of metal-oxide-semiconductor-field-effect transistor has been scaled down to the sub-10 nm regime, semi-classical Boltzmann transport theory can no longer satisfactorily describe the behavior of carrier transport since the quantum mechanical effects start to play a dominant role. Non-equilibrium Green's function formalism (NEGF) is a fully quantum mechanical approach which can take the wave nature of electron into account, and it provides a flexible framework for including the incoherent and dissipative transport processes. In this work, the authors develope an efficient three-dimensional quantum transport simulator based on solving the NEGF and Poisson equations self-consistently to investigate the electron transport in GaAs gate-all-around (GAA) nanowire field-effect transistor (NWFET) with considering electron-phonon scattering, ionized impurity (IMP) scattering, and surface roughness (SR) scattering. Several transport properties and device characteristics can be captured by the proposed solver, such as current spectrum broadening, electron relaxation, and the role of scattering effects. It allows to think the underlying physics in a different way, which will be useful for designing and predicting the performance of transistors in nanoscale.

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Impact of phonon scattering in Si/GaAs/InGaAs nanowires and FinFets: a NEGF perspective

Cited by 11 publications

References 41 publications

Image charge models for accurate construction of the electrostatic self-energy of 3D layered nanostructure devices

Image charge models for accurate construction of the electrostatic self-energy of 3D layered nanostructure devices

Quantum Transport in a Silicon Nanowire FET Transistor: Hot Electrons and Local Power Dissipation

3D Self-Consistent Quantum Transport Simulation for GaAs Gate-All-Around Nanowire Field-Effect Transistor with Elastic and Inelastic Scattering Effects

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