R. Fauquembergue

A comparison of numerical solutions of the Boltzmann transport equation for high-energy electron transport silicon

In this work we have undertaken a comparison of several previously reported computer codes which solve the semiclassical Boltzmann equation for electron transport in silicon. Most of the codes are based on the Monte Carlo particle technique, and have been used here to calculate a relatively simple set of transport characteristics, such as the average electron energy. The results have been contributed by researchers from Japan, Europe, and the United States, and the results were subsequently collected by an independent observer. Although the computed data vary widely, depending on the models and input parameters which are used, they provide for the first time a quantitative (though not comprehensive) comparison of Boltzmann Equation solutions. >

Dynamics of molecular reorientational motion and vibrational relaxation for symmetric top molecules in the liquid phase

Detailed studies of the molecular relaxation processes in pure liquid t‐butyl chloride (TBC) and t‐butyl bromide (TBB) and in solutions in carbon tetrachloride and in n‐hexane have been made using several experimental techniques. Single particle reorientational motions perpendicular to the symmetry axis were studied using Raman scattering and a comparison of these results with those obtained from depolarized Rayleigh scattering allowed an evaluation of the importance of correlations in orientation between pairs of molecules in the two systems, also, collision induced scattering was not found to be significant. Additional cross comparisons of related data obtained using infrared absorption and dipolar absorption were made. In all cases, the original experimental data were subjected to Fourier transform analyses so that the time evolution of the resulting correlation functions could be studied. In general, at short times the reorientational motions are inertial, but at long times exponential decay of the co...

MONTE CARLO SIMULATION OF HIGH-FIELD ELECTRON TRANSPORT IN GAAS USING AN ANALYTICAL BAND-STRUCTURE MODEL

We present a study of high energy electron transport in GaAs using an analytical model of the band structure. This model is based on piecewise polynomial approximation of the dispersion relation in different regions of the Brillouin zone. It accounts for the first two conduction bands and reproduces all important features of the full band structure. We have used this model to set up a Monte Carlo simulation of electron transport accounting for impact ionization. It has been shown that this “extended valley” model yields essentially the same results as the most rigorous full band Monte Carlo calculations. We have found a large influence of high energy anisotropy on electron transport. Another important result is that most impact ionization events are due to electrons in the second conduction band.

Determination of diffusion coefficients in degenerate electron gas using Monte Carlo simulation

We propose a method for determining diffusion coefficients in degenerate semiconductors from an ensemble Monte Carlo simulation. The basic idea is that what is relevant for this problem is not the whole electron distribution function, but its perturbation in response to an addition of “excess carriers.” Starting from the Boltzmann transport equation, we derive the equation of evolution for this “excess electron distribution function.” We propose an interpretation in terms of scattering events suffered by particles, allowing one to solve the problem by Monte Carlo simulation. We simulate two sets of carriers, coupled by an “exchange scattering” mechanism which is properly defined. The first set represents the uniform background density in the semiconductor, whereas the second one represents the excess carriers. Only the latter is used for calculating diffusion coefficients. This method is applied to a highly degenerate two-dimensional electron gas in a doped GaAs quantum well. The diffusivity-field charact...

III–V photoconductive detectors : Gain and noise studies

Abstract The steady-state gains, the dynamical gains and the noise properties of N-type GaAs planar photoconductive detectors have been extensively investigated and it has been found that, in the gigahertz range, the noise due to the illumination of the photodetectors is lower than that of an avalanche photodiode. Planar photoconductive detectors using GaInAs materials, GaAlAs-GaAs and InP-GaInAs heterojunction layers have also been studied. A monolithic integrated photoreceiver in GaAs, constituted of an intedigitated photoconductive detector and a FET is presented.

Computational and experimental study of vibrational relaxation in liquids: Symmetric top molecules

Detailed studies of vibrational relaxation in pure liquid CH3I, t‐butyl chloride (CH3)3CCl, t‐butyl bromide (CH3)3CBr and in solutions in carbon tetrachloride and in n‐hexane, over the −90 to 50°C temperature range, have been made using Raman scattering. Assuming that only phase relaxation contributes to the isotropic band shapes, the mechanism of vibrational relaxation in these liquids was first studied by investigating the characteristics of the fluctuations of the vibrational frequencies, which are caused by the intermolecular interactions. A first study allowed us to determine the correlation time of these fluctuations. The obtained values are between 0.1 and 0.5 ps and are consistent with a binary collision model. This model has been used to develop an efficient computational model to describe the experimental data relative to vibrational relaxation and orientational motions as well.

HEMT Models and Simulations

The paper presents a series of modeling tools for pseudomorphic High Electron Mobility Transistors, discussing their physical content and presenting specific applications. The presented results will show the most peculiar features of electronic transport in such device.

Theoretical investigation of impurity scattering limited mobility in quantum wells: The influence of wave‐function modeling

A theoretical investigation of the impurity scattering limited mobility in quantum wells is presented. Emphasis is put on the influence of wave‐function modeling, since the literature about this topic is contradictory. For an infinite square well, Dirac and sine wave functions yield the same evolutions of the mobility with temperature, carrier density, and well width. These results contradict those published by Lee [J. Appl. Phys. 54, 6995 (1983)], which are shown to be wrong. Self‐consistent wave functions have also been used to compute the mobility in finite barrier height quantum wells. A strong influence of the presence of electrons inside the doped barrier has been demonstrated. It is suggested that, although simple models are useful for qualitative discussions, accurate evaluation of mobility requires a reasonably realistic description of wave functions.

Implementation of a Bi-Parallel Monte Carlo Device Simulation on Two Architectures

This paper describes two implementations of a semiconductor device simulator on two different architectures. The simulation process is based on the Monte Carlo method, a particle-in-cell algorithm. It simulates the motion of particles under the influence of electric fields, that have to be periodically updated with the Poisson equation solution. We present a parallelization using a bi-parallelism scheme, to avoid load imbalance that can be encountered with the domain decomposition. The parallelization of the Monte Carlo part gives optimal speed-up. However the poor efficiency of the implemented Poisson solution damaged this result.

Monte Carlo study of diffusion phenomena in III - V modulation doped heterostructures

This paper presents a Monte Carlo study of diffusion coefficients in two-dimensional electron gas (TDEG) in III - V heterostructures. The model accounts for the quantization of all valleys and for non-parabolicity. The diffusion coefficients are determined by the spreading of a narrow pulse of carriers drifting along the interface. Two kinds of heterostructures have been considered: AlGaAs/InGaAs/AlGaAs and the AlInAs/InGaAs/AlInAs lattice matched on InP. The diffusion coefficient - field characteristics at 77 K temperature have been extensively studied. Large deviations from the Einstein relation have been observed, even at low-fields. The longitudinal diffusion coefficient is shown to be strongly field dependent and may reach high values for fields around . Its evolution is explained by the behaviour of scattering rates, especially for impurity and phonon scattering.