Gennady Mil'nikov

Simulation of the effect of arsenic discrete distribution on device characteristics in silicon nanowire transistors

We have theoretically investigated the effects of random discrete dopant (RDD) distribution on the device characteristics in silicon nanowire (NW) transistors by performing non-equilibrium Greens function simulation combined with kinetic Monte Carlo method for generating RDD distribution. We show that a small number of dopant atoms diffusing into the channel have a significant impact on the threshold voltage (Vth) variation. We examine the dependence of the Vth variation on RDD distribution and find that the fluctuation can be significantly reduced by introducing side-wall gate spacers. We also find that the on-current fluctuation is mainly caused by randomness of As dopants in the source and drain extensions and hence is inherent in ultra-small NW transistors.

Impact of Attractive Ion in Undoped Channel on Characteristics of Nanoscale Multigate Field Effect Transistors: A Three-Dimensional Nonequilibrium Green's Function Study

A rigorous simulation study of the impact of a single attractive ion in undoped channel multigate field-effect transistors is presented using a new three-dimensional nonequilibrium Greens function technique. A single donor induces threshold voltage shift, and its impact is most significant when the donor is located at the top of the potential barrier. On the other hand, on-current is not affected so much because of the electrostatic screening by the electron bound around the positively charged ion. To reduce the intrinsic device parameter fluctuation, a gate-all-around structure has better robustness than the double gate structure.

Nano-device simulation from an atomistic view

Fluctuations of device characteristics due to random discrete dopant (RDD) distribution are numerically investigated in ultra-small Si nanowire transistors. Kinetic Monte Carlo process simulation is performed to obtain realistic RDD distributions, whose effects on the transport characteristics are then analyzed by using a non-equilibrium Greens function (NEGF) method. Fluctuations due to atomic disorder near the Si/SiO2 interface are also investigated by performing molecular dynamics oxidation simulation for realistic atomic structure models and NEGF device simulation for transport characteristics.

Solution of the Poisson Equation with Coulomb Singularities

We present a new method of calculating electrostatic potential in electronic devices of complicated geometry with singular charge distribution. The method is based on analytical representation of regular and singular parts of the potential function which can be constructed independently in different parts the device. Parameters of such representation are calculated recursively and large scale N3 computer operations are avoided. The method is robust, fast, does not have limitations on the device geometry and can be readily used in statistical simulations. We illustrate the method by computing the electrostatic potential in double-gate metal–oxide–semiconductor field-effect transistor (MOSFET) with a positive impurity in the intrinsic channel.

R-matrix Theory of Quantum Transport in Nanoscale Electronic Devices

We derive continuous spectral representation of the non-equilibrium Greens function in an open system. Based on this result, we construct a theory of quantum transport and formulate a practical coarse-grain method for device simulations. As an illustration, we apply the method to quantum ballistic electron transport in model three-dimensional metal–oxide–semiconductor field-effect transistors.

Implementation of the Bloch Operator Method for Solving the Poisson Equation

A necessary ingredient of any computer simulations of charge transfer processes in nanoscale metal oxide semiconductor field-effect transistors (MOSFETs) is solution of the Poisson equation in MOS. Commonly used schemes are based on finite difference grid representation which require large number of the mesh points in order to reduce the intrinsic numerical error. In this work we present a conceptually new algorithm which is numerically cheap compared to conventional methods.

A Self-Consistent Compact Model of Ballistic Nanowire MOSFET With Rectangular Cross Section

We propose a compact model of ballistic gate-all-around metal-oxide-semiconductor field-effect transistors. In this model, the potential distribution in the wire cross section is approximated by a quadratic function. This model potential has one unknown parameter, which determines the shape of the potential. The Schrödinger equation in the wire cross section can be approximately solved using the model potential, and the electron energy levels are derived analytically. The unknown parameter is determined by numerically solving a coupled equation for charge densities derived from electrostatics and quantum statistics. We calculate the device properties using the obtained unknown parameter. A Schrödinger-Poisson solver that simulates electron states in the wire cross section is used. The results obtained using it reveal that our model exhibits good agreement for both the lowest and excited energy levels. We estimate the ballistic current using the calculated energy levels and the Landauer formula, which shows good agreement with results simulated using the nonequilibrium Greens function formalism.

Effects of phonon scattering on discrete-impurity-induced current fluctuation in silicon nanowire transistors

Effects of phonon scattering on random-dopant-induced current fluctuations are investigated in silicon nanowire transistors. Active dopant distributions obtained through kinetic Monte Carlo simulation are introduced into 10nm-gate-length n-type nanowire transistors, and the current-voltage characteristics are calculated by the non-equilibrium Greens function method. The current fluctuation is found to be suppressed by ~ 40% by phonon scatterings at the on-state, while it is very weakly affected at the off-state.

Discrete distribution of implanted and annealed arsenic atoms in silicon nanowires and its effect on device performance.

We have theoretically investigated the effects of random discrete distribution of implanted and annealed arsenic (As) atoms on device characteristics of silicon nanowire (Si NW) transistors. Kinetic Monte Carlo simulation is used for generating realistic random distribution of active As atoms in Si NWs. The active As distributions obtained through the kinetic Monte Carlo simulation are introduced into the source and drain extensions of n-type gate-all-around NW transistors. The current–voltage characteristics are calculated using the non-equilibrium Greens function method. The calculated results show significant fluctuation of the drain current. We examine the correlation between the drain current fluctuation and the factors related to random As distributions. We found that the fluctuation of the number of dopants in the source and drain extensions has little effect on the on-current fluctuation. We also found that the on-current fluctuation mainly originated from the randomness of interatomic distances of As atoms and hence is inherent in ultra-small NW transistors.

First-principles calculations of the non-equilibrium polarization in ultra-small Si nanowire devices

The paper presents a method for the first principles calculations of polarization charge in non-equilibrium states of sihcon nanowire transistor. The method combines the density-functional perturbation theory and piecewise equivalent model representation which enables us to reduce the numerical burden and eliminate erroneous contributions from the occupied electronic states. In the mean field approximation, the polarization response of the device material is taken into consideration by using appropriate dielectric constants in the Poisson solver. Our results suggest that this approximation generally fails and the electric field in the device area may give rise to a nonzero macroscopic polarization charge which is completely ignored in common device simulations.