One-dimensional multi-subband Monte Carlo simulation of charge transport in Si nanowire transistors (original) (raw)
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Physical Review B, 2009
An atomistic full-band quantum transport simulator has been developed to study three-dimensional Si nanowire field-effect transistors in the presence of electron-phonon scattering. The nonequilibrium Green's function ͑NEGF͒ formalism is solved in a nearest-neighbor sp 3 d 5 s ء tight-binding basis. The scattering selfenergies are derived in the self-consistent Born approximation to inelastically couple the full electron and phonon energy spectra. The band dispersion and the eigenmodes of the confined phonons are calculated using a dynamical matrix that includes the bond and the angle deformations of the nanowires. The optimization of the numerical algorithms and the parallelization of the NEGF scheme enable the investigation of nanowire structures with diameters up to 3 nm and lengths over 40 nm. It is found that the reduction in the device drain current, caused by electron-phonon scattering, is more important in the ON state than in the OFF state of the transistor. Ballistic transport simulations considerably overestimate the device ON currents by artificially increasing the charge injection mechanism at the source contact.
Atomistic Full-Band Simulations of Si Nanowire Transistors: Effects of Electron-Phonon Scattering
An atomistic full-band quantum transport simulator has been developed to study threedimensional Si nanowire field-effect transistors (FETs) in the presence of electron-phonon scattering. The Non-equilibrium Green’s Function (NEGF) formalism is solved in a nearest-neighbor sp3d5s∗ tight-binding basis. The scattering self-energies are derived in the self-consistent Born approximation to inelastically couple the full electron and phonon energy spectra. The band dispersion and the eigenmodes of the confined phonons are calculated using a dynamical matrix that includes the bond and the angle deformations of the nanowires. The optimization of the numerical algorithms and the parallelization of the NEGF scheme enable the investigation of nanowire structures with diameters up to 3 nm and lengths over 40 nm. It is found that the reduction of the device drain current, caused by electron-phonon scattering, is more important in the ON-state than in the OFF-state of the transistor. Ballistic transport simulations considerably overestimate the device ON-currents by artificially increasing the charge injection mechanism at the source contact. 1
Hierarchical simulation of transport in silicon nanowire transistors
Journal of Computational Electronics, 2008
We propose a very fast hierarchical simulator to study the transport properties of silicon nanowire FETs. We obtain the transverse wave functions and the longitudinal effective masses and band-edges of the lowest conduction bands from a nearest-neighbor sp 3 d 5 s * tight-binding study of an infinite nanowire with null external potential. Then we plug these parameters into a self-consistent Poisson-Schrödinger solver, using an effective mass approach and considering the bands decoupled. We apply this method, which gives quantitatively correct results with notable time savings, for the simulation of transport in two different silicon nanowire FETs.
Three-dimensional simulation of one-dimensional transport in silicon nanowire transistors
IEEE Transactions on Nanotechnology, 2007
We present a simulation study of silicon nanowire transistors, based on an in-house code providing the self-consistent solution of Poisson, Schrödinger, and continuity equations on a generic three-dimensional domain. The main assumption, based on the very small nanowire cross section considered, is that an adiabatic approximation can be applied to the Schrödinger equation, so that transport occurs along one-dimensional subbands. Different subband transport models are considered, such as ballistic transport, either including quantum tunneling or not, and drift-diffusion. We show that nanowire transistors exhibit good control of short channel effects, and that barrier tunneling is significant in the strong inversion regime even for longer devices, while it is significant in subthreshold only for the shortest channel lengths. Finally, we show that a subband-based transport model allows to reach a very good trade off between physical accuracy of the simulation and computing time.
Electron dynamics in silicon nanowire using a Monte-Carlo method
Journal of Physics: Conference Series, 2009
We present a theoretical study of electron transport in silicon nanowire (SNW). A self-consistent 2D-Poisson-Schrödinger solver provides the band structure. Then, both electron velocity and low-field electron mobility along the SNW axis are computed with an ensemble Monte-Carlo method. Scattering mechanisms due to phonons (acoustic phonons, zero-order and first-order intervalley phonons) and surface roughness are taken into account. We investigate the effect of cross section size and transverse electric field on electron mobility in SNW.
Multi-Subband Ensemble Monte Carlo simulation of Si nanowire MOSFETs
2015
The need for an accurate simulation of non-planar devices such as FinFETs and nanowire based FETs, including a full quantun treatment of transversal two-dimensional confinement, motivated the development of a three-dimensional Multi-Subband Ensemble Monte Carlo (MS-EMC) simulator. Here we describe the last improvements of such simulator including better convergence properties and statistical improvements for the computation of the drain current. The simulator is employed to study MOS devices based on Si nanowires with lateral sizes of a few nanometers. The results show the importance of a proper two-dimensional treatment of quantum confinement, which can be achieved with our simulator.
Simulation of one-dimensional subband transport in ultra-short silicon nanowire transistors
6th International Conference on the Ultimate Integration of Silicon, 2005
In this paper we present three-dimensional (3D) simulations of nanowire transistors (SNWTs), based on the self-consistent solution of the Poisson and Schrödinger equations, in which two dimensional confinement and one-dimensional (1D) transport of electrons in the channel have been considered. In particular, the continuity equation has been solved in 1D subbands for both the semiclassical and quantum ballistic regime, and in the drift-diffusion regime, in order to consider both limiting cases.
Electron mobility in gate all around cylindrical silicon nanowires: A Monte Carlo study
International Conference on Microelectronics, 2010
Electron mobility in gated silicon nanowires is calculated using a Monte Carlo simulation that considers phonon and surface roughness scattering. Surface roughness scattering rates are calculated using Ando's model. The eigenenergies and eigenfunctions required for scattering rate calculation are determined by self-consistent solution of the Schrödinger and Poisson equations. The effects of size quantization and transverse electric field on electron
In this work we investigate the correlation between channel strain and device performance in various n-type Si-NWTs. We establish a correlation between strain, gate length and cross-section dimension of the transistors. For the purpose of this paper we simulate Si NWTs with a <110> channel orientation, four different ellipsoidal channel cross-sections and five gate lengths: 4nm, 6nm, 8nm, 10nm and 12nm. We have also analyzed the impact of strain on drain-induced barrier lowering (DIBL) and the subthreshold slope (SS). All simulations are based on a quantum mechanical description of the mobile charge distribution in the channel obtained from a 2D solution of the Schrödinger equation in multiple cross sections along the current path, which is mandatory for nanowires with such ultra-scale dimensions. The current transport along the channel is simulated using 3D Monte Carlo (MC) and drift-diffusion (DD) approaches.