扫描电子显微学中二次电子发射过程的蒙特卡洛模拟

利用蒙特卡洛模拟固体中电子散射轨迹的计算方法，系统地研究了扫描电镜中二次电子信号的发射过程。该模拟电子与固体相互作用的蒙特卡洛模型包含了级联二次电子产生的过程，并且采用光学介电函数方法描述电子的能量损失和相伴的二次电子激发。由于模拟计算可以给出背散射电子和二次电子的绝对产额，以及它们随加速电压和样品的原子序数的变化关系，因此可以用于模拟元素衬度和形貌衬度像。还计算得到了关于二次电子产生和发射的其它分布，并与实验结果作了比较。     

Monte Carlo simulation of bipolar transistors

A new approach is proposed to investigate, the limits of validity of the conventional drift-diffusion equation analysis for modeling bipolar transistor structures containing submicrometer dimensions. The single-particle Monte Carlo method is used for the solution of the Boltzmann equation. An electron velocity overshoot of 1.8 times the static saturation velocity has been found for electrons near the base-collector junction of a silicon device. The effect of this velocity overshoot was calculated to enhance the output collector current and reduce the electron transit time by 5 percent for the device structure considered in this work.     

FPGA-based Monte Carlo simulation for fault tree analysis

The reliability analysis of critical systems is often performed using fault-tree analysis. Fault trees are analyzed using analytic approaches or Monte Carlo simulation. The usage of the analytic approaches is limited in few models and certain kinds of distributions. In contrast to the analytic approaches, Monte Carlo simulation can be broadly used. However, Monte Carlo simulation is time-consuming because of the intensive computations. This is because an extremely large number of simulated samples may be needed to estimate the reliability parameters at a high level of confidence.In this paper, a tree model, called Time-to-Failure tree, has been presented, which can be used to accelerate the Monte Carlo simulation of fault trees. The time-to-failure tree of a system shows the relationship between the time to failure of the system and the times to failures of its components. Static and dynamic fault trees can be easily transformed into time-to-failure trees. Each time-to-failure tree can be implemented as a pipelined digital circuit, which can be synthesized to a field programmable gate array (FPGA). In this way, Monte Carlo simulation can be significantly accelerated. The performance analysis of the method shows that the speed-up grows with the size of the fault trees. Experimental results for some benchmark fault trees show that this method can be about 471 times faster than software-based Monte Carlo simulation.     

A Monte Carlo simulation algorithm for finding MTBF

Prediction of mean time between failures (MTBF) is an important aspect of the initial stage of system development. It is often difficult to predict system MTBF during a given time since the component failure processes are extremely complex. The authors present a Monte Carlo simulation algorithm to calculate the MTBF during a given time of a binary coherent system. The algorithm requires the lifetime distributions of the components and the minimal path sets of the system. The MTBF for a specific time interval, e.g. a month or a year, can be estimated. If the component lifetime distributions are unknown, then a lower bound of system MTBF can be estimated by using known constant failure rates for each component     

Improved sequential stopping rule for Monte Carlo simulation

This letter presents an improved result on the negative-binomial Monte Carlo technique analyzed in a previous paper1 for the estimation of an unknown probability p. Specifically, the confidence level associated to a relative interval [p/?2, p?1], with ?1, ?2 > 1, is proved to exceed its asymptotic value for a broader range of intervals than that given in the referred paper, and for any value of p. This extends the applicability of the estimator, relaxing the conditions that guarantee a given confidence level.     

Trajectory split method for Monte Carlo simulation of ionimplantation

A new method for the acceleration of two- and three-dimensional Monte Carlo simulation of ion implantation into crystalline targets is presented. The trajectory split method ensures a much better statistical representation in regions with a dopant concentration several orders of magnitudes smaller than the maximum. As a result, the time required to perform a simulation with comparable statistical accuracy is drastically reduced. The advantages of the new approach have been confirmed by a thorough statistical analysis     

Monte Carlo simulation of growth of nanowhiskers

The growth of silicon nanowhiskers on the Si (111) surface activated with Au is studied by Monte Carlo simulation. The dependences of the rate of growth of whiskers on the temperature, deposition rate, and catalyst droplet diameter are obtained, and the morphological properties of the growing wirelike nanocrystal are studied. In addition to the growth of nanowhiskers, a number of experimentally observed effects, such as migration of the droplet from the whisker top, faceting of the whisker sidewalls, and branching are established for the model system. It is shown that, under certain conditions of wetting of the whisker material with the catalyst, formation of hollow nanowhiskers is possible.     

Direct Monte Carlo simulation of hot-carrier conductivity

We present a Monte Carlo procedure which, by including the mechanism of generation and recombination from impurity centers, enables us to calculate directly from the simulation the field dependent conductivity for the first time. The reliability of the theoretical model has been checked by comparing numerical results with experiments provided by the Montpellier group and performed on p-Si at different acceptor concentrations and temperatures.     

红外光源辐射特性的蒙特卡洛模拟

为满足红外跟踪仿真的高精度、高稳定性设计要求,本文基于蒙特卡洛算法针对红外光源的辐射特性进行了模拟仿真研究。首先,介绍了系统结构和工作原理。接着,以蒙特卡洛方法为基础,对钨丝灯圆柱体光源进行建模,给出光阑处的辐照度精确分布,为建立光阑通光口径的非线性控制函数提供依据。然后,分析了不同条件下蒙特卡洛算法的准确度,并研究了装配位置对系统光能利用率的影响。仿真结果表明:在旋转抛物面反射镜的焦点外存在一个最佳的光源装配位置;在装配过程中,允许的轴向偏移为0.1 mm,垂轴偏移为0.1 mm,角度偏移为2°。该系统满足了红外跟踪仿真的稳定可靠、高精度要求。同时,本文所采用的分析方法对其他红外光源的优化设计也有借鉴作用。     

鲜红斑痣数值计算模型的构建及其蒙特卡罗模拟

基于人体皮肤的组织结构以及鲜红斑痣(PWS)皮肤的病理特征,光在皮肤组织中的传输特性以及皮肤各层的组织光学参数,建立了一种具有多层组织结构的鲜红斑痣皮肤数值模拟计算模型,介绍了该模型中组织光学参数的确定方法.利用蒙特卡罗(MC)方法结合临床数据对模型进行了验汪,同时计算了光能量在PWS皮肤中随深度的分布,结果可为临床上如何选择最佳光剂量提供部分参考依据.利用本模型做进一步的详细完整的计算可以为光动力学治疗PWS提供理论支持.     

Monte Carlo simulation of the GaAs permeable base transistor

A two-dimensional multiparticle Monte Carlo (MC) method for the solution of the Boltzmann transport equation has been implemented and the results compared with the conventional drift-diffusion equation solution obtained for both a uniformly doped and an n⁺-n-n⁺GaAs permeable base transistor structure. Improved high-frequency performance is predicted by the MC simulation. Two-dimensional boundary conditions for a "regional" MC analysis have been applied to reduce the computer time that would be spent largely in analyzing the device retarding field region and the neutral regions of the device. The dc parameters, I-V characteristics, and unity current gain-frequency (fT) are discussed. In the n⁺-n-n⁺doped structure, a cooling effect was found that significantly enhances the device frequency performance by reducing the satellite valley population of electrons.     

Monte Carlo simulation of the CHISEL flash memory cell

This work shows how physically-based hot carrier simulation was used to understand the importance of CHannel Initiated Secondary ELectron (CHISEL) injection in scaled MOSFETs, and how it was used to develop a powerful CHISEL-based technique for low voltage flash programming. Furthermore, it is shown how CHISEL flash addresses many of the disadvantages of CHE programming techniques, making it an ideal candidate for low-voltage, low-power Gigabit flash memories     

Monte Carlo simulation of threshold bandwidth for high-order harmonic extraction

The feasibility of bulk semiconductors subjected to strong periodic electric fields for terahertz radiation generation due to the high-order harmonic extraction is analyzed by using Monte Carlo simulations. The high-order harmonic intensity and the spectral density of velocity fluctuations are calculated for GaAs, InP, and InN. By comparing the harmonic intensity with the noise level the threshold bandwidth for high-order harmonic extraction determined by their ratio is introduced and evaluated for the above materials. The results show that semiconductor materials with a high value of the threshold field for the Gunn-effect are characterized by a high value of the threshold bandwidth under high-order harmonic generation and, hence, they are promising materials for microwave generation in the THz frequency range by high-order harmonic extraction.     

Monte Carlo simulation and random number generation

Methods of generating pseudorandom number sequences that might have predetermined spectral and probability distribution functions are discussed. Such sequences are of potential value in Monte Carlo simulation of communication, radar, and allied systems. The methods described are particularly suited to implementation on microcomputers, are machine portable, and have been subjected to exhaustive investigation by means of both statistical and theoretical tests     

火灾探测器可靠性的Monte Carlo仿真

从“人-机-环境”的角度对导致火灾探测器误报、漏报的原因进行了分析，利用Monte Cario系统仿真方法对火灾探测器的可靠性进行了模拟分析，得到的探测器可靠度、故障率曲线与理论和工程实际情况相符。正确地描述了火灾探测器的故障率随时间变化的规律，为进一步应用该方法来分析整个火灾探测报警系统的可靠性提供了理论基础。     

Monte Carlo simulation of GaAs Schottky barrier behaviour

The transport of carriers through the space-charge region (SCR) of a GaAs Schottky barrier is studied by the Monte Carlo simulation technique. Simulation results indicate that the carrier distribution is significantly perturbed from a Max-wellian near the metal-semiconductor boundary, limiting the validity of the commonly used thermionic diffusion model. Phenomena related to the disturbed distribution include increased recombination velocity at the interface and reduced carrier concentration near the junction. The interface recombination velocity is found to be constant with applied bias and the Bethe condition is shown to be more than sufficient to ensure the validity of the thermionic emission model.     

Monte Carlo simulation and measurement of nanoscale n-MOSFETs

The output characteristics of state-of-the-art n-MOSFETs with effective channel lengths of 40 and 60 nm have been measured and compared with full-band Monte Carlo simulations. The device structures are obtained by process simulation based on comprehensive secondary ion mass spectroscopy and capacitance-voltage measurements. Good agreement between the measured output characteristics and the full-band Monte Carlo simulations is found without any fitting of parameters and the on-currents are reproduced within 4%. The analysis of the velocity profiles along the channel confirms that the on-current is determined by the drift velocity in the source side of the channel. Analytic-band Monte Carlo simulations are found to involve an overestimation of the drain current in the nonlinear regime which becomes larger for increasing drain voltage and decreasing gate length. The discrepancy originates from a higher nonlinear drift velocity and a higher overshoot peak in bulk silicon which is due to differences in the band structures above 100 meV. The comparison between analytic-band and full-band Monte Carlo simulation therefore shows that the source-side velocity in the on-state is influenced by nonlinear and quasiballistic transport.     

Monte Carlo simulation of boron implantation into single-crystalsilicon

An improved Monte Carlo simulation model has been developed for boron implantation into single-crystal silicon. This model is based on the Marlowe Monte Carlo code and contains significant improvements for the modeling of ion implantation, including a newly developed local electron concentration-dependent electronic stopping model and a newly developed cumulative damage model. These improvements allow the model to reliably predict boron implant profiles not only as a function of energy, but also as a function of other important implant parameters such as tilt angle, rotation angle, and dose. In addition, profiles of implant generated point defects (silicon interstitials and vacancies) can be calculated     

Sequential Monte Carlo methods for multiple target tracking anddata fusion

The classical particle filter deals with the estimation of one state process conditioned on a realization of one observation process. We extend it here to the estimation of multiple state processes given realizations of several kinds of observation processes. The new algorithm is used to track with success multiple targets in a bearings-only context, whereas a JPDAF diverges. Making use of the ability of the particle filter to mix different types of observations, we then investigate how to join passive and active measurements for improved tracking