MC simulation of double-resonant-phonon depopulation THz QCLs for high operating temperatures

We theoretically investigate the temperature performance of GaAs-based double-resonant-phonon depopulation THz quantum cascade lasers. Based on an ensemble Monte Carlo simulation including both carrier-phonon and carrier-carrier scattering, we evaluate the temperature dependence of the different carrier transport channels and identify the detrimental factors preventing high operating temperatures. As major detrimental effects, increased leakage from the upper laser level and a deteriorating depletion efficiency of the lower laser level is found for elevated temperatures.     

Monte Carlo simulation of terahertz quantum cascade lasers: The influence of the modelling of carrier-carrier scattering

A theoretical investigation of electron-electron scattering in quantum cascade lasers is presented. The devices are studied by means of an ensemble Monte Carlo simulation that includes all relevant scattering mechanisms. The energy levels and wave functions are determined by a self-consistent resolution of the Schrödinger and Poisson equations. The influence of the modelling of carrier-carrier scattering is discussed on the example of a resonant-phonon structure operating at 3.4 THz. To demonstrate the usefulness of such a model for optimization purpose, an alternative design operating at a lower frequency is proposed. Our model predicts that a significant population inversion can be achieved at about 1 THz.     

Monte Carlo modeling of X-valley leakage in quantum cascade lasers

This paper presents the first comprehensive Monte Carlo simulation of GaAs/AlGaAs quantum cascade lasers (QCLs) that takes both Γ- and X-valley transport into account and investigates the effect of X-valley leakage on the QCL performance. Excellent agreement with experimental data is obtained for the GaAs/Al_0.45Ga_0.55As QCL at cryogenic and room temperatures. The model reveals two carrier-loss mechanisms into the X valley: coupling of the Γ continuum-like states with the X states in the same stage, and coupling between the Γ localized states in the simulated stage with the X states in the next stage. Simulation results demonstrate that the 45% Al QCL has small X-valley leakage at both 77 K and 300 K, due to the very good confinement of the Γ states, stemming from the high Al content.     

On a simple and accurate quantum correction for Monte Carlo simulation

We investigate a quantum-correction method for Monte Carlo device simulation. The method consists of reproducing quantum mechanical density-gradient simulation by classical drift-diffusion simulation with modified effective oxide thickness and work function and using these modifications subsequently in Monte Carlo simulation. This approach is found to be highly accurate and can be used fully automatically in a technology computer-aided design (TCAD) workbench project. As an example, the methodology is applied to the Monte Carlo simulation of the on-current scaling in p- and n-type MOSFETs corresponding to a 65 nm node technology. In particular, it turns out that considering only the total threshold voltage shift still involves a significant difference to a Monte Carlo simulation based on the combined correction of oxide thickness and work function. Ultimately, this quantum correction permits to consider surface scattering as a combination of specular and diffusive scattering where the conservation of energy and parallel wave vector in the specular part takes stress-induced band structure modifications and hence the corresponding surface mobility changes on a physical basis into account.     

Quantum Ensemble Monte Carlo simulation of silicon-based nanodevices

A Quantum Ensemble Monte Carlo (QEMC) simulator is used to calculate electrical characteristics and transient response of actual nanotransistors: both sub-50 nm CMOS N-MOSFETs and ultrathin double gate SOI transistors have been deeply studied. Doping profiles and oxide thickness have been selected to cope with the available specifications of the ITRS Roadmap. The Quantum corrected Ensemble Monte Carlo simulator (QEMC) has been used to self-consistently solve the Boltzmann Transport and Poisson equations in actual devices. Quantum effects are included through the Multi-Valley Effective Conduction Band Edge (MV-ECBE) technique, and adequate approaches for phonon and surface roughness scattering have been developed to include the effects of carrier quantization in pseudo-2DEG simulations.     

Monte Carlo simulation for evaluating retail wheeling effects

A Monte Carlo simulation method for evaluating retail-wheeling effects on power systems is formulated and solution methods are presented. The effects of wheeling on operating cost, transmission losses, and system security are considered. For a specific operating condition, the effects are quantified by the sensitivity of specific quantities of interest with respect to power wheeling level. Quantities of interest are total operating cost, transmission losses and security, which is quantified with several indices. This model is utilized within a Monte Carlo simulation to calculate probability distribution functions of the incremental effects of wheeling on operating cost, transmission losses, and system security. The model and solution methods are applied on an example power system and the results are presented.     

Introducing energy broadening in semiclassical Monte Carlo simulations

Combining an insight on the quantum transport given by the Wigner function formalism and the classical perturbation theory, an algorithm has been developed that allows the introduction of collisional broadening in semiclassical electron transport Monte Carlo (MC) simulations. In the proposed algorithm, electron energy and momentum are treated as independent variables; the laws of energy and momentum conservation are fulfilled at each scattering event, but the relationship between energy and momentum is not given by the traditional expression, since Bloch states are not eigenstates of the total Hamiltonian. The results obtained for a simple model semiconductor demonstrate that the non-physical instabilities observed in previous attempts to introduce collisional broadening in semiclassical MC simulations have been removed. The algorithm is suitable for application in MC simulations of realistic device models.     

Monte Carlo simulation of 2D TASER

A possibility to develop the so called TASER (Terahertz-Amplification-by-the-Stimulated-Emission-of- Radiation) by using two-dimensional (2D) electron transport in quantum well (QW) structures is investigated by Monte Carlo simulation of the optical-phonon-emission assisted transit-time resonance (OPTTR) of 2D electrons in momentum space under the low lattice temperature. A considerable extension of the frequency region for THz radiation generation (upto 5 times) when going from 3D- to 2D-case is predicted.     

Non-equilibrium quantum transport theory: current and gain in quantum cascade lasers

We have developed a self-consistent non-equilibrium Green’s function theory (NEGF) for charge transport and optical gain in THz quantum cascade lasers (QCL) and present quantitative results for the I-V characteristics, optical gain, as well as the temperature dependence of the current density for a concrete GaAs/Al_.15Ga_.85As QCL structure. Phonon scattering, impurity, Hartree electron-electron and interface roughness scattering within the self-consistent Born approximation are taken into account. We show that the characteristic QCL device properties can be successfully modeled by taking into account a single period of the structure, provided the system is consistently treated as open quantum system. In order to support this finding, we have developed two different numerically efficient contact models and compare single-period results with a quasi-periodic NEGF calculation. Both approaches show good agreement with experiment as well as with one another.     

马尔可夫跳变系统的蒙特卡罗仿真

针对跳变系统理论研究中缺少有效的仿真方法,提出了一种适用于跳变系统的蒙特卡罗法.跳变系统蒙特卡罗仿真的关键是马尔可夫链的仿真实现,研究了两种生成马尔可夫链的方法,即利用MATLAB函数randsrc和基于unifrnd函数产生均匀分布的随机数,提出了根据转移概率矩阵P对随机数设置不同的阈值来形成马尔可夫链的算法.根据仿真的结果对转移概率进行了验证,该方法概念清晰,简单易行,可用于切换系统等一般随机系统的研究.     

基于蒙特卡罗仿真的校准结论风险分析

针对已有的单次校准结论风险,计量实验室更加需要总体校准结论风险来分析测量仪器的校准状态,提出将蒙特卡罗仿真方法应用于校准结论的风险分析中。通过对单次校准结论的风险分析得出影响误判率的参数;进而通过蒙特卡罗仿真法分析总体校准结论,结果显示,提高测量不确定度比一倍,误判率下降120%。最后,结合仿真过程建立总体校准风险的模型,通过分析总体校准结论的风险,提出可以降低错误判断风险的概率的方法,对校准工作具有一定的理论指导价值。     

Monte Carlo simulation of double gate MOSFET including multi sub-band description

A new two-dimensional self-consistent Monte-Carlo simulator including the multi sub-band transport in a 2D electron gas is described and applied to an ultra-thin Double Gate MOSFET. This approach takes into account both out of equilibrium transport and quantization effects. This method improves significantly microscopic insight into the operation of deep sub-100 nm CMOS devices. We analyze the ballistic, quantization and roughness effects in a 12 nm-long DGMOS transistor. In particular, we focus on the link between non-stationary transport and the evolution of sub-band occupancy along the channel.     

Scattering and space-charge effects in Wigner Monte Carlo simulations of single and double barrier devices

Transport in single and double barrier devices is studied using a Monte Carlo solver for the Wigner transport equation. This approach allows the effects of tunneling and scattering to be included. Several numerical methods have been improved to render the Wigner Monte Carlo technique more robust, including a newly developed particle annihilation algorithm. A self-consistent iteration scheme with the Poisson equation was introduced. The role of scattering and space charge effects on the electrical characteristics of n-i-n nanostructures, ultra-scaled double gate MOSFETs, and GaAs resonant tunneling diodes is demonstrated. An erratum to this article can be found at     

Monte Carlo simulation of polaron transport in DNA

Charge transport characteristics in a double-stranded DNA are discussed. Based on the polaron drift model, DNA was modeled as a 1D quantum wire. The phonon scattering rates were calculated by deformation potential theory, and the carrier dynamics in DNA were simulated by the Monte Carlo technique. The simulation result shows a rapid charge transport from the initial point. Lastly, the validity of the modeling is discussed.     

Composite system well-being evaluation based on non-sequential Monte Carlo simulation

The reliability evaluation of composite power systems has historically been assessed using deterministic and probabilistic criteria and methods. The well-being approach was recently proposed in order to combine deterministic criteria with probabilistic methods and evaluates the system by healthy, marginal and risky states. This paper presents an efficient method for composite system well-being evaluation based on non-sequential Monte Carlo simulation. It is assumed that the system is coherent, and the frequency and duration indices are calculated by the conditional probability method. The system adequacy is evaluated by a non-linear power flow solved by the Newton–Raphson method and by an optimal power flow solved by the Interior Points method. Results are presented for the IEEE-RTS system with a constant load and with a variable load curve. It is demonstrated that the proposed method, as well as the assumed hypothesis, are valid and provide an efficient alternative for the well-being analysis of large scale power systems.     

Monte Carlo simulation of harmonic generation in GaAs structures operating under large-signal conditions

By using a multiparticles Monte Carlo technique, with a self-consistently coupled one-dimensional Poisson solver, we investigate the dependence of the nonlinear carrier dynamics in GaAs n⁺nn⁺ micro e submicro-structures operating under very intense sub-terahertz signals by: (i) the frequency and the intensity of the excitation signal and (ii) the length of the n region.     

Parallel Monte Carlo simulation for reliability and cost evaluation of equipment and systems

An algorithm for reliability simulation of equipment and systems using a parallel computing environment is developed. A sequential Monte Carlo simulation-based method is applied for generating reliability and maintainability history charts for equipment, from which the reliability indices, as well as their probability distributions, are calculated. A parallel methodology is developed to discretize the simulation into periods, and the simulation of individual periods is dispatched to different processors for efficient computing. Case studies utilizing the proposed method for reliability evaluation of equipment and simple systems are presented. Simulation results are compared with the analytical approach results for the same cases. The study provides the basis for using a parallel computing environment in power system reliability and cost evaluations. The environment used in this paper is Rock-131 from the San Diego Supercomputer Center in La Jolla, CA.     

A three‐dimensional Monte Carlo model for the simulation of nanoelectronic devices

We present a three‐dimensional (3D) semi‐classical ensemble Monte Carlo model newly developed to simulate a variety of nanoelectronic devices. The characteristics of the 3D model are compared with the widely used two‐dimensional (2D) models. The advantages of our model, in terms of accuracy in modelling the physics behind the operation of nanodevices, are presented by applying it to T‐branch junctions based on InGaAs/InAlAs heterostructures. Simulation of a T‐branch junction with a Schottky gate terminal is presented, using both 2D and 3D models, demonstrating the necessity of using 3D simulation models to study the physics of complex‐geometry nanostructures. Copyright © 2009 John Wiley & Sons, Ltd.     

Business scenario evaluation using Monte Carlo simulation on qualitative and quantitative hybrid model

We propose a business scenario evaluation method using a qualitative/quantitative hybrid model. In order to evaluate business factors with qualitative causal relations, we introduce statistical values based on propagation and combination of effects of business factors by Monte Carlo simulation. In propagating an effect, we divide a range of each factor by landmarks and decide an effect to a destination node based on the divided ranges. In combining effects, we determine an effect of each arc using contribution degree and sum all effects. Through applied results to practical models, it is confirmed that there are no differences between results obtained by quantitative relations and results obtained by the proposed method at the risk rate of 5%. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(3): 9–18, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20950     

Monte Carlo simulation of microparticle motion in vacuum gap

Breakdown voltages of vacuum gaps become lower when the gaps are contaminated by metallic and ceramic microparticles. In this paper, the motion of the microparticles in the gap is simulated using Monte Carlo method in order to evaluate the effect of parameters upon motion and the removal time of the microparticles. As the parameters, we focused on the material of the microparticle, the frequency, the peak value of the applied voltage, the gap length, and the diameter of the lower and upper electrodes. It turned out that the maximum time needed to remove all microparticles could be expressed as multiple regression function. It is suggested that the reliability of the microparticle removal can be increased by spark conditioning with opening/closing operation.