Laurent Baudry

Electron transport properties of strained InxGa1−xAs

As a first approach to the study of strained pseudomorphic materials, we have used a Monte Carlo method to calculate the effect of strain on electron transport properties of bulk InGaAs. Strain‐induced velocity reduction is found to be much more pronounced for InGaAs grown on GaAs substrate than for InGaAs grown on InP substrate.

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. >

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...

Model for ferroelectric semiconductors thin films accounting for the space varying permittivity

Reducing thickness of ferroelectric films typically comes with an apparent degradation of their ferroelectric and dielectric properties. The existence of low-dielectric interfacial layers is often invoked to explain such behaviors. Much work has been done on modeling ferroelectric thin films by considering a ferroelectric layer between two layers with low dielectric constant. In these models it is necessary to introduce extrinsic parameters; the dielectric constant and the polarization are step functions of the depth inside the film. We have developed a model for ferroelectric semiconductors based on the inhomogeneous Landau–Devonshire theory, including surface effects. The local electric field is determined by solving Poisson’s equation in which a differential permittivity replaces the dielectric constant. We have found that the hysteresis loops were strongly influenced by the correlation length. That point is discussed by examining the electric field, polarization, and differential permittivity profile ...

Polarization vortex domains induced by switching electric field in ferroelectric films with circular electrodes

We describe ferroelectric thin films with circular electrodes and develop a thermodynamic theory that explains exotic experimental results previously reported. It is found to be especially useful for restricted geometries such as microstructures for which boundary conditions are well known to play an important role in ferroelectric properties. We have explored a switching mechanism that consists of an inhomogeneous rotational motion of the polarization and leads to a vortex state. The vortex appearance exhibits characteristic properties of a first-order field-induced phase transition with three critical electric fields and the possibility of hysteresis behavior.

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.

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.

Dynamics of field-induced polarization reversal in thin strained perovskite ferroelectric films withc-oriented polarization

The field-induced polarization reversal in

Ferroelectric symmetry-protected multibit memory cell

c

Influence of the screening model and wave‐function shape on impurity scattering mobility in quantum wire

-oriented ferroelectric phase of strained perovskite film has been studied. We show that in additional to the conventional longitudinal switching mechanism, when c-oriented polarization vector changes its modulus, the longitudinal-transversal and transversal mechanisms when the perpendicular component of polarization is dynamically admixed are possible. The later process can occurs either via the straight-abrupt or initially-continues polarization turnover scenario. We specified the obtained results for the case of PbTiO