F. Dessenne

Modeling of electron–electron scattering in Monte Carlo simulation of quantum cascade lasers

A theoretical model of electron–electron scattering in multisubband systems is proposed and used to set up a Monte Carlo simulator of quantum cascade lasers. Special features of the electron–electron scattering model are the following: (i) A fast and accurate computation of bare potential matrix elements by means of Fourier analysis is developed. (ii) A screening model is proposed that allows us to describe intersubband matrix elements. (iii) Nonequilibrium screening factors, defined through an effective subband temperature for each subband, are periodically reevaluated. (iv) The developed algorithm makes use of rejection procedures in order to determine the correct number of scattering events as well as the distribution of the final states. Other characteristics of the model are the following: the energy levels and the wave functions are determined in a self-consistent way, the Pauli exclusion principle is included, and the periodicity of the structure is accounted for. This model is applied to the study...

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. >

Comparison of wurtzite and zinc blende III-V nitrides field effect transistors : a 2D Monte Carlo device simulation

Abstract An ensemble Monte Carlo method is used to compare the potentialities of zinc blende and wurtzite GaN for field effect transistor applications. First, bulk material electron transport properties are compared and we find that mobility, steady state velocity and velocity overshoot are at the advantage of zinc blende GaN. Then, zinc blende GaN and wurtzite GaN MESFET with very short gate length (Lg=0.12 μm) are investigated using a 2D Monte Carlo device simulation. A 50% gain in performance is obtained for the zinc blende GaN MESFET as compared with the wurtzite one. A zinc blende AlGaN/GaN HEMT is also simulated and exhibits a current density of 900 mA mm−1, a transconductance of 480 mS mm−1 and a cut-off frequency of 180 GHz.

Monte Carlo modeling of high‐field transport in III‐V heterostructures

A Monte Carlo model of parallel high‐field transport in III‐V heterostructures is presented. Special features of the model are the following: only two‐dimensional electron states are considered, the possible existence of secondary wells inside the barriers is accounted for, and nonparabolicity effect and quantization of satellite valleys are included. The wave functions and eigenenergies are calculated by self‐consistent resolution of Poisson and Schrodinger equations. The effect of nonparabolicity on dispersion relations is determined at first order by a perturbation method. First, the simple case of an infinite GaAs square well is investigated as a test for the model, then more realistic heterostructures are considered. A study of a modulation‐doped pseudomorphic AlxGa1−xAs/In0.15Ga0.85As structure shows that the electric field induces a significant repopulation of the doped AlGaAs layer. When x=0.32, this real‐space transfer is strongly correlated with the intervalley transitions toward X valley states...

Three-dimensional Monte Carlo study of three-terminal junctions based on InGaAs/InAlAs heterostructures

We apply a three-dimensional (3D) semiclassical ensemble Monte Carlo simulation method to study T-branch junctions based on InGaAs/InAlAs heterostructures and obtain an accurate insight into the physics behind the operation of such structures. Electron transport in these devices is investigated and their rectifying behavior is demonstrated at 77 and 300 K and for different branch sizes. Detailed device analysis is performed to establish the relationship between the extent of ballistic transport and the rectifying behavior of the junctions and show the influence of surface charge effects, which are carefully included in the model. Results from the simulation of a T-branch junction with a Schottky gate terminal are presented, demonstrating the necessity of using 3D simulation models to study the physics of semiconductor junctions.

Self-consistent electrothermal Monte Carlo simulation of single InAs nanowire channel metal-insulator field-effect transistors

Electron transport and self-heating effects are investigated in metal-insulator field-effect transistors with a single InAs nanowire channel, using a three-dimensional electrothermal Monte Carlo simulator based on finite-element meshing. The model, coupling an ensemble Monte Carlo simulation with the solution of the heat diffusion equation, is carefully calibrated with data from experimental work on these devices. This paper includes an electrothermal analysis of the device basic output characteristics as well the microscopic properties of transport, including current-voltage curves, heat generation and temperature distributions, and electron velocity profiles. Despite the low power dissipation, results predict significant peak temperatures, due to the high power density levels and the poor thermal management in these structures. The extent of device self-heating is shown to be strongly dependent on both device biasing configuration as well as geometry.

InP HEMT downscaling for power applications at W band

We have developed new solutions for InP high-electron mobility transistor (HEMT) scaling for power applications at W band. We have shown that the use of a small barrier thickness in order to respect the aspect ratio for a 70-nm gate length results in a significant kink effect and high gate source capacitances. We have also shown through a theoretical study that a structure containing an InP layer between the cap layer and the barrier would support both the frequency performances and the breakdown voltage. Thus, we propose an HEMT structure containing a thick InP/AlInAs composite barrier and where the gate is buried into the barrier. This enables us to respect the aspect ratio and simultaneously to obtain an important drain current density without observing any kink effect. Moreover, we have applied this process to structures containing innovative large band-gap InP and InAsP channels. We have achieved the best frequency performances ever reached for an InP channel HEMT structure. Power measurements at 94 GHz were performed on these devices. The InAsP channel HEMT demonstrated a maximum output power of 260 mW/mm at 3 V of drain voltage with 5.9-dB power gain and a power-added efficiency of 11%. These results are favorably comparable to the state-of-the-art of InP-based HEMT at this frequency.

Monte Carlo simulation of electron transport in narrow gap heterostructures

A Monte Carlo method is proposed for the study of in-plane electron transport in narrow gap heterostructures. Special attention is paid to the consequences of the strong nonparabolicity of the conduction band. The electron states are calculated within the framework of envelope function theory, which leads to a Schrodinger equation with an energy-dependent effective mass. This equation is solved in a numerically efficient way by including a standard eigenvalue solver in an iterative method. The mixing between conduction and valence band states is taken into account, at an approximate level, through a “Bloch overlap factor,” defined by analogy with the case of three-dimensional transport. This model was applied to a typical AlSb/InAs single well structure, and realistic results were obtained. The important role played by the Bloch overlap factor is demonstrated. When it is neglected, the mobility is strongly underestimated. A more sophisticated double well structure was also investigated. It is intended to reduce impact ionization, thanks to transfer toward the thinner well. This transfer is found to depend strongly on the potential profile.

MONTE CARLO STUDY OF ELECTRON TRANSPORT IN III-V HETEROSTRUCTURES WITH DOPED QUANTUM WELLS

The transport properties of AlGaAs/GaAs/AlGaAs heterostructures with doped GaAs quantum well have been investigated by means of an ensemble Monte Carlo method. The model accounts for nonparabolicity, size quantization in all valleys, and degeneracy. The influence of doping profile, density of donors and electrons, well width, and temperature are discussed. Both steady state and transient transport have been studied, and the possibility of strong velocity overshoot has been demonstrated. The electron velocity may be strongly influenced by the spatial distribution of impurities. The choice of a doping plane located at one edge of the well allows for obtaining the highest values of mobility, static peak velocity, and maximum transient velocity. At high fields, some parasitic conduction takes place in the barriers and the transport properties are strongly affected by the characteristics of the AlGaAs layers.

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.