Enhancement of Monte Carlo Simulations on Three-Dimensional Nanoscale Semiconductor Devices
Hahm, Hyung-Seok
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https://hdl.handle.net/2142/81094
Description
Title
Enhancement of Monte Carlo Simulations on Three-Dimensional Nanoscale Semiconductor Devices
Author(s)
Hahm, Hyung-Seok
Issue Date
2008
Doctoral Committee Chair(s)
Ravaioli, Umberto
Department of Study
Electrical and Computer Engineering
Discipline
Electrical and Computer Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
A full-band 3D Monte Carlo semiconductor simulator is enhanced in two ways in order to capture realistic transport properties in nanoscale device simulations. First of all, the phonon-limited multisubband scattering mechanisms have been incorporated into the 3D Monte Carlo simulator. The scattering rate for every cross section that is transverse to the transport direction is calculated and stored based on the solutions of the 2D Schrodinger equation. Then, when a carrier scatters, an appropriate scattering table is selected and utilized depending on the position of the carrier. This way, quantum effects are explicitly taken into consideration in carrier transport. The approach has been simulated for different sizes of silicon nanowires (SiNWs). When high bias applies in the longitudinal and the transverse direction of the channel and thus the multisubband scattering mechanisms are active, the simulation observables begin to be split for the above and below 10 nm groups. For SiNWs whose side length is greater than 10 nm, the scattering rate, in particular, converges due to the constant overlap integral. The multisubband scattering model has been compared with the pure quantum correction model in order to investigate the limit of the quantum correction approach. While dissimilarity is constantly observed for all the simulated cases both in electrostatic and transport properties, the differences between the two models is the most significant for the smallest device. Secondly, the multiscale technique is implemented. Because the multisubband scattering model is computationally expensive and thus should be adopted only within the user's discretion, the multiscale technique is designed to relieve this difficulty. The difference between the coulomb and the quantum potential is calculated at each grid point as a quantum criterion. If the difference is larger than the given threshold for most of the simulation region, it indicates that quantum effects are widely spread in the region and the simulator adapts itself to the multisubband mode. The quantum criterion is demonstrated to effectively perform by cross-checking it with the semiclassical potential distribution computed by Poisson solver and the quantum potential distribution by Schrodinger solver.
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