Browsing by Subject "Monte Carlo method--Computer programs"
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Item Production of [beta-gamma] coincidence spectra of individual radioxenon isotopes for improved analysis of nuclear explosion monitoring data(2008-08) Haas, Derek Anderson, 1981-; Biegalski, Steven R.Radioactive xenon gas is a fission product released in the detonation of nuclear devices that can be detected in atmospheric samples far from the detonation site. In order to improve the capabilities of radioxenon detection systems, this work produces [beta-gamma] coincidence spectra of individual isotopes of radioxenon. Previous methods of radioxenon production consisted of the removal of mixed isotope samples of radioxenon gas released from fission of contained fissile materials such as ²³⁵U. In order to produce individual samples of the gas, isotopically enriched stable xenon gas is irradiated with neutrons. The detection of the individual isotopes is also modeled using Monte Carlo simulations to produce spectra. The experiment shows that samples of [superscript 131m]Xe, ¹³³Xe, and ¹³⁵Xe with a purity greater than 99% can be produced, and that a sample of [superscript 133m]Xe can be produced with a relatively low amount of ¹³³Xe background. These spectra are compared to models and used as essential library data for the Spectral Deconvolution Analysis Tool (SDAT) to analyze atmospheric samples of radioxenon for evidence of nuclear events.Item Quantum corrected full-band semiclassical Monte Carlo simulation research of charge transport in Si, stressed-Si, and SiGe MOSFETs(2006) Fan, Xiaofeng, 1978-; Banerjee, Sanjay; Register, Leonard F.This Ph.D. research is centered around a full-band Monte Carlo device simulator (“Monte Carlo at the University of Texas”, MCUT) with quantum corrections (based on one-dimensional Schrödinger equation solver). The code itself was based on a solid infrastructure of a Monte Carlo simulator, “MoCa” from the University of Illinois at Urbana-Champaign. To that there were added new methods and features during my Ph.D. program, including strained band structures, alternative (to conventional 100 ) surface orientations, full-band scattering mechanisms, and valley-dependent quantum correction. These features enable “MCUT” to be used to model various strained and/or alloyed silicon MOSFETs, as well as the MOSFETs composed of alternative materials such as Ge, in sub-100 nm regime. Monte Carlo simulation, itself, handles short channel effects and hot carriers in ultra small device well; full-band structure replaces the inaccurate and unknown (for new/strained materials) analytical formulae; and the quantum corrections approximate quantum-confinement effects on device performance. The goal is to understand and predict the device behavior of the so called “non-classical” CMOS ― beyond bulk Si based CMOS ― in the sub-100 nm regime.Item Schrödinger equation Monte Carlo simulation of nano-scaled semiconductor devices(2004) Chen, Wanqiang; Register, Leonard F.Semiconductor devices have been continuously scaled into the deep submicron regime. As a result, quantum effects which were neglected in semiclassical models become more and more important. Meanwhile, scattering still remains important down to the gate length around 10 nm. Accurate quantum transport simulators with scattering will be needed to explore the essential device physics. The work of this dissertation project is aimed at developing an accurate quantum transport simulation tool for deep submicron device modeling, as well as utilizing this newly developed simulation tool to study the quantum transport and scattering effects in ultra-scaled semiconductor devices. The quantum transport simulator “Schrödinger Equation Monte Carlo” (SEMC) provides a physically rigorous treatment of quantum transport and phasebreaking inelastic scattering (in 3D) via real (actual) scattering processes such as optical and acoustic phonon scattering. SEMC has been used to simulate carrier transport in nano-scaled devices in order to gauge the potential reliability of semiclassical models, phase-coherent quantum transport, and other limiting models as the transition from classical to quantum transport is approached. SEMC has also been successfully applied to study the carrier capture and transport in tunnel injection lasers. In this work, a 2D version of SEMC − SEMC-2D − has been developed. The quantum transport equations are solved self-consistently with Poisson equation. SEMC-2D has been used to simulate quantum transport in nano-scaled double gate MOSFETs. Simulation results serve not only to demonstrate the capability of this new quantum transport simulator, but also to illuminate the importance of physically accurate simulation of scattering for predictive modeling of transport in nano-scaled MOSFETs.Item Schrödinger equation Monte Carlo simulation of nanoscale devices(2007-12) Zheng, Xin, 1975-; Register, Leonard F.Some semiconductor devices such as lasers have long had critical dimensions on the nanoscale where quantum effects are critical. Others such as MOSFETs are now being scaled to within this regime. Quantum effects neglected in semiclassical models become increasing important at the nanoscale. Meanwhile, scattering remains important even in MOSFETs of 10 nm and below. Therefore, accurate quantum transport simulators with scattering are needed to explore the essential device physics at the nanoscale. The work of this dissertation is aimed at developing accurate quantum transport simulation tools for deep submicron device modeling, as well as utilizing these simulation tools to study the quantum transport and scattering effects in the nano-scale semiconductor devices. The basic quantum transport method "Schrödinger Equation Monte Carlo" (SEMC) provides a physically rigorous treatment of quantum transport and phasebreaking inelastic scattering (in 3D) via real (actual) scattering processes such as optical and acoustic phonon scattering. The SEMC method has been used previously to simulate carrier transport in nano-scaled devices in order to gauge the potential reliability of semiclassical models, phase-coherent quantum transport, and other limiting models as the transition from classical to quantum transport is approached. In this work, SEMC-1D and SEMC-2D versions with long range polar optical scattering processes have been developed and used to simulate quantum transport in tunnel injection lasers and nanoscaled III-V MOSFETs. Simulation results serve not only to demonstrate the capabilities of the developed quantum transport simulators, but also to illuminate the importance of physically accurate simulation of scattering for the predictive modeling of transport in nano-scaled devices.Item Schrödinger equation Monte Carlo-3D for simulation of nanoscale MOSFETs(2008-08) Liu, Keng-ming; Register, Leonard F.A new quantum transport simulator -- Schrödinger Equation Monte Carlo in Three Dimensions (SEMC-3D) -- has been developed for simulating the carrier transport in nanoscale 3D MOSFET geometries. SEMC-3D self-consistently solves: (1) the 1D quantum transport equations derived from the SEMC method with open boundary conditions and rigorous treatment of various scattering processes including phonon and surface roughness scattering, (2) the 2D Schrödinger equations of the device cross sections with close boundary conditions to obtain the spatially varying subband structure along the conduction channel, and (3) the 3D Poisson equation of the whole device. Therefore, SEMC-3D can provide a physically accurate and electrostatically selfconsistent approach to the quantum transport in the subbands of 3D nanoscale MOSFETs. SEMC-3D has been used to simulate Si nanowire (NW) nMOSFETs to both demonstrate the capabilities of SEMC-3D, itself, and to provide new insight into transport phenomena in nanoscale MOSFETs, particularly with regards to interplay among scattering, quantum confinement and transport, and strain.