S. J. Wigger

Numerical challenges in particle-based approaches for the simulation of semiconductor devices

The aim of this paper is to review and discuss the most challenging aspects of the particle-based methods for simulation of charge transport in semiconductor devices. Since the early theoretical works on the Ensemble Monte Carlo (EMC) method applied to device simulation, and several successive works addressing both the physics and the numerical aspects of the EMC method, the basic algorithmic approaches have been modified to exploit the continuous improvements of both hardware and software tools. Typical examples of the algorithmic evolution are the adoption of the full band representation of the electronic structure, the so-called cellular automaton (CA), and the simulation of increasingly complex three-dimensional (3D) structures. This paper will address some of the most significant problems which are still considered open in spite of the recent technological and scientific progresses.

Overshoot velocity in ultra-broadband THz studies in GaAs and InP

We model velocity overshoot in GaAs and InP using a fullband, particle-based device simulator based on the so-called cellular automaton method. This study has been motivated by the recent availability of experimental measures of the THz radiation generated by transient acceleration of photogenerated charge carriers in pin diode structures. The fullband code used in this study includes the full energy-momentum dispersion relation of electrons and holes as well as the full dispersion for the relevant phonons. Here we use this code for the simulation of high-field transient transport in bulk GaAs, InP, and for the experimental pin structure, where favorable comparison is found with the velocities measured from the transient THz radiation after ultrafast excitation.

Cellular automata simulation of nanometre-scale MOSFETs

We present systematic theoretical cellular automata studies of vertically grown, nanometre-scale, MOSFETs. The predicted drain characteristics and output conductance are in excellent agreement with experimental data from fabricated devices. The inclusion of an inhomogeneous p-doping profiles along the channel is investigated, which is shown to improve current saturation and therefore allows the reduction of the device dimensions.

Fullband Particle-Based Simulation of High-Field Transient Transport in III–V Semiconductors

Motivated by recent experimental measurements (A. Leitenstorfer et al., 2000. Physical Review B 61(24): 16642–16652), this work presents the transient analysis of photogenerated electron-hole pairs in GaAs and InP pin diodes (S. M. Sze, 1981. Physics of Semiconductor Devices, 2nd edn., John Wiley) using a fullband particle-based simulator (M. Saraniti and S. Goodnick, 2000. IEEE Transactions on Electron Devices 47(10): 1909–1915). The fullband simulation tool is based on a particle-based technique that has been developed to reduce the computational time required for modeling charge transport phenomena in semiconductors. Excellent agreement is found between experiment and simulation of transient acceleration and velocity overshoot in GaAs and InP pin diodes due the femto-second optical excitation of carriers.

Parallel Approaches for Particle-Based Simulation of Charge Transport in Semiconductors

The aim of this contribution is to discuss possible algorithmic choices and hardware configurations for the implementation of efficient particle-based simulation programs. By using a population decomposition scheme, we modified the scalar version of the algorithm in order to improve the efficiency of our hybrid particle-based simulation engine. Using a Beowulf-class computer cluster, we measured parallel speed-up with different algorithmic configurations, and related it to the inter-process communication hardware.

Hybrid Particle-based Full-band Analysis of Ultra-small MOS

We report on the 2D and 3D modeling of ultra-small MOS structures using a newly developed full-band device simulator. The simulation tool is based on a novel approach, featuring a hybrid Ensemble Monte Carlo (EMC)-Cellular Automata (CA) simulation engine. In this hybrid approach charge transport is simulated using the CA in regions of momentum space where most scattering events occur and the EMC elsewhere, thus optimizing the trade-off between the fast, but memory consuming CA method and the slower EMC method. To account for the spatial distribution of the electric field and charge concentration, the hybrid EMC/CA simulator is self-consistently coupled with a 2D and 3D multi-grid Poisson solver. The solver is then used to simulate the performance of a 40 nm gate length n-MOSFET structure.

Hybrid particle-based full-band analysis of ultra-small MOS

We report on the 3D modeling of ultra-small MOS structures using a newly developed full-band device simulator. The simulation tool is based on a novel approach, featuring a hybrid Monte Carlo (MC)-Cellular Automata (CA) simulation engine self-consistently coupled with a 3D multi-grid Poisson solver.

Three dimensional multi-grid Poisson solver

The Newton multigrid method was shown to be an effective method for solving the nonlinear Poisson equation for semiconductor devices under thermal equilibrium conditions. This technique can also be used to solve problems involving reverse bias junctions. Assuming an insignificant concentration of minority carriers, such that no leakage current is present, and fixing the quasi-Fermi potential as a constant for majority carriers, the nonlinear Poisson equation can be used to simulate such situations.