Monte Carlo simulation driven time resolved photon fluence analysis

In this study, time resolved (TR) Monte Carlo (MC) simulation program code was run to generate photon fluencies with increasing time steps. TR MC simulation was performed for ten time series from 4 ps to 52 ps. Generated photon fluencies were transferred to the image analysis programming platform. Imaging device geometry was created for test purpose in image reconstruction programming platform environment. Forward model weight matrix functions were calculated during each time period for 38 sources, and 38 detectors according to the back-reflected imaging geometry. A homogenous phantom, which simulated tissue, was chosen. Depending on the homogeneous tissue optical properties, such as tissue absorption coefficient μa, and tissue scattering coefficient μs, photons emitted from the laser source positions; migrated differently inside the imaging tissue. Photons migrate inside the tissue by some multiplication factor of ps depending on the tissue type for each 100-micrometer vertical distance. Superficial photons come photodetector point fast, depend on the source-detector neighborhood distances and tissue optical properties, respectively. Time resolved diffuse optic tomography (TRDOT) imaging systems are an emerging biomedical optic imaging modality due to progressive electronic technologies are helping to build the systems faster and cheap. As such, emerging microelectronic technology is giving important access to design and implement compact laser sources and photodetector units. Vertical cavity surface emitting light (VCSEL) as laser source and single photon avalanche diode (SPAD) arrays as photodetector units are becoming in common use as important hardware tools for designers and researchers in this field. TR diffuse photon analysis should be done routinely for better understanding of TRDOT devices. Hence, MC simulation driven TR photon fluence analysis was done for such a purpose in this study.     

Monte Carlo simulation of current transport in forward-biased Schottky-barrier diodes

The transport of carriers across the semiconductor space-charge region of a forward-biased Schottky-barrier diode is investigated by a Monte Carlo simulation of the transport process. The electron distribution function at the m.s. boundary turns out to be hemi-Maxwellian, but the electron concentration is about one-half of that predicted by the t.d. theory.     

蒙特卡洛法模拟半导体高场输运过程

讨论了用蒙特卡洛法模拟高电场下半导体内电子输运现象的基本过程。研究了 Ｚｎ Ｓ 中电子输运的性质,对电子数目对模拟结果的影响进行了分析。讨论了电子输运中的暂态过程,得出了稳态下的电子分布曲线     

Monte Carlo simulation of electron transport efficiency of an InGaAs/InP hot-electron transistor

Electron transport efficiency of an InGaAs/InP hot-electron transistor (HET) is determined by a Monte Carlo method including alloy scattering in an InGaAs base. Results are compared with those of a GaAs/AlGaAs HET. It is found that the InGaAs/InP HET offers a higher current gain than that of a GaAs/AlGaAs HET by an order of magnitude.     

Hydrodynamic hot-electron transport simulation based on the Monte Carlo method

A hydrodynamic hot electron model is used to study electron transport through a submicron N⁺ --- N --- N⁺ GaAs structure. This study is used to investigate improvements which the unique features of this model offer to analysis of devices operating under nonstationary transport conditions. The model is based upon semiclassical “hydrodynamic” conservation equations for the average carrier density, momentum and energy. The general model includes particle relaxation times, momentum relaxation times, energy relaxation times, electron temperature tensors and heat flow vectors as a function of average carrier energy for the Γ, X and L valleys of GaAs. For this study, we utilized a simplified single electron gas version of our model to clearly reveal the impact of the nonstationary terms in the model. Results from both a drift-diffusion model approach and a Monte Carlo analysis are used to show the relative accuracy and facility this new model offers for investigating practical submicron device structures operating under realistic conditions.     

Bootstrap, an alternative to Monte Carlo simulation

The Monte Carlo simulation is a commonly used technique for circuit analysis, but is computationally expensive. The bootstrap method can save simulation time and retain the desired accuracy     

Monte Carlo simulation of electron transport properties inextremely thin SOI MOSFET's

Electron mobility in extremely thin-film silicon-on-insulator (SOI) MOSFET's has been simulated. A quantum mechanical calculation is implemented to evaluate the spatial and energy distribution of the electrons. Once the electron distribution is known, the effect of a drift electric field parallel to the Si-SiO₂ interfaces is considered. The Boltzmann transport equation is solved by the Monte Carlo method. The contribution of phonon, surface-roughness at both interfaces, and Coulomb scattering has been considered. The mobility decrease that appears experimentally in devices with a silicon film thickness under 20 nm is satisfactorily explained by an increase in phonon scattering as a consequence of the greater confinement of the electrons in the silicon film     

Monte Carlo simulation for electron transport in MESFETs includingrealistic band structure of GaAs

A full band Monte Carlo (FBMC) simulator was developed for electron transport in GaAs MESFETs. As a result of increased scattering rate due to the complicated band structure, the average velocity in the high field region was lower than the analytical band Monte Carlo (ABMC) result. Also, the simulated energy peak was higher than the ABMC result, due to electrons populating the upper bands. Not only due to a limited number of the first conduction band states capable of ionization, but also due to a small mass of the second conduction band, more than 95% of ionization events were shown to occur in the upper bands. The simulated ionization rate lies within the range of experimental results. To our knowledge, this is the first report on the full band two-dimensional (2-D) self-consistent GaAs MESFET simulation     

Hydrodynamic transport parameters of wurtzite ZnO from analytic- and full-band Monte Carlo simulation

Analytic-band Monte Carlo simulation of electron transport in bulk wurtzite ZnO, validated against the results of a full-band code and available experimental data, is used to determine the main parameters required by drift-diffusion and hydrodynamic models. Steady-state drift velocity, carrier temperature, energy and momentum relaxation time, noise diffusivity, and electron thermal conductivity are calculated, and their dependence on temperature and electric field or average electron energy is approximated by means of a complete set of fitting models suitable for inclusion in commercial device simulation tools.     

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.     

Monte Carlo calculation of noise transport in a two-dimensional diode

The noise transport phenomena in a two-dimensional diode operated under space-charge-limited conditions are investigated by means of the statistical Monte Carlo method. Effects on the transport characteristics of an electron beam by the multi-dimensional nature of the potential distribution in the vicinity of the potential minimum are evaluated. Contrary to both the single velocity and multivelocity linear small-signal noise theories, the noise parametersS, II,S-- II andS+ II are found to be nonconservative. A reduction in the equivalent noise figure from 6.96 db corresponding to full-shot noise input at the cathode to approximately 2 db is observed at the anode of the two-dimensional diode for a wide range of frequencies. A substantial amount of correlation between the kinetic potential and the current fluctuations is developed in the multivelocity region beyond the potential minimum. It is believed that the improvement in noise performance of the two-dimensional diode over the one-dimensional model is directly attributable to the space-charge potential-depression effects by which an additional amount of velocity spread is introduced in the electron beam, creating an extension of the multivelocity non-linear region. The theoretical minimum-noise figures obtained indicate that possibly two-dimensional dc effects are more important than two-dimensional ac effects in essentially hollow-beam low-noise devices.     

多隧道结单电子动态存储器的Monte Carlo模拟

本文采用Monte Carlo方法模拟了多隧道结单电子动态存储器的存储特性，考察了隧道结的个数、隧道结电容、隧道结电阻、脉冲电压幅度等参数对存储器的存储时间和饱和充电电荷的影响，并与宏观RC电路进行了比较。     

Monte Carlo simulation of a millimeter-wave Gunn-effect relaxation oscillator

A large-signal computer simulation of a GaAs millimeter-wave Gunn-effect relaxation oscillator has been developed. This computer simulation utilizes a Monte Carlo computation of the electron distribution behavior rather than relying on an analytical expression for the velocity-field characteristic now known to be inaccurate at millimeter-wave frequencies. Results of this simulation are presented for a 70-GHz fundamental oscillator. The device simulated is consistent with currently produced millimeter-wave designs with an active length of 2.0 µm and doping density of 1 × 10¹⁶cm³. A peak efficiency of 2.4 percent with an output power of 144 mW was determined. The device can be characterized as operating in an accumulation transit mode, but with the proverbial "dead-zone" at the cathode.     

Monte Carlo particle simulation of a GaAs short-channel MESFET

A Monte Carlo particle simulation of a 0.25 ?m-long gate (and 0.25 ?m-long channel) GaAs MESFET having a practical doping density and sitting on a substrate is carried out. Extremely high values of gm and Idss of 643 mS/mm and 5.35 mA/20 ?m were obtained. The near-ballistic nature of the electron transport in the FET was confirmed.     

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     

Monte Carlo simulation of electron transport in the III-nitridewurtzite phase materials system: binaries and ternaries

We present a comprehensive study of the transport dynamics of electrons in the ternary compounds, Al_xGa_1-xN and In_xGa_1-xN. Calculations are made using a nonparabolic effective mass energy band model. Monte Carlo simulation that includes all of the major scattering mechanisms. The band parameters used in the simulation are extracted from optimized pseudopotential band calculations to ensure excellent agreement with experimental information and ab initio band models. The effects of alloy scattering on the electron transport physics are examined. The steady state velocity field curves and low field mobilities are calculated for representative compositions of these alloys at different temperatures and ionized impurity concentrations. A field dependent mobility model is provided for both ternary compounds AlGaN and InGaN. The parameters for the low and high field mobility models for these ternary compounds are extracted and presented. The mobility models can be employed in simulations of devices that incorporate the ternary III-nitrides     

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.     

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.     

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.     

Monte Carlo simulation of scattering from a layer of verticalcylinders

Electromagnetic scattering by a collection of randomly distributed vertical cylinders over a half-space dielectric is considered, using two approaches. In the first approach, a Monte Carlo simulation that takes into account scattering terms up to second order is used. Closed-form expressions for the second-order scattering terms are derived for cylinders that are in each other's near field. The second approach is based on the radiative transfer equations, which are solved by an iterative method up to and including the second-order terms. Radar backscatter measurements at X-band for a collection of metallic cylinders over a conducting ground plane are compared with the Monte Carlo and radiative transfer solutions. The data were acquired polarimetrically from 144 independent spots of the cylinder layer at incidence angles ranging from 20° to 60°. The simulation results agree well with the measured data and are used to check the validity of the radiative transfer results for a medium with large particles. It is shown that both the phase function computed for the cylinders and the extinction matrix of the layer are overestimated in the radiative transfer solution