R. Brunetti

A many-band silicon model for hot-electron transport at high energies

Abstract A new silicon model for electron transport at high electric fields is presented. The model features an original conduction-band structure consisting of three isotropic bands together with the lowest non-parabolic band in a finite spherical Brillouin zone. The bands are given by analytic expressions whose parameters are fixed by best fitting the density of states taken from band-structure calculations. Such a model is consistently used in electron dynamics and in the evaluation of the scattering probabilities. The coupling constants to the scattering agents are determined by best fitting the available experimental data on transport properties. The effect of the new model on the results is discussed for a bulk system with particular attention to the features (e.g. the detailed shape of the electron distribution function) which are important for device applications.

An improved impact‐ionization model for high‐energy electron transport in Si with Monte Carlo simulation

A new model for impact ionization in Si is presented, which goes beyond the limitations of the Keldysh formula and is based on a more realistic scheme developed starting from a first‐order perturbation theory. This scattering mechanism is modeled by an extended band structure which includes many bands for electrons and one band for holes in a finite Brillouin zone. Some processes have been identified to bring the dominant contribution to the scattering probability, in the present approach, for electron energies ranging up to 3 eV. Expressions for the differential and integrated scattering probabilities have been obtained which are consistent with the band model and can be included in a Monte Carlo simulation of the electron gas. Results for transport quantities are shown for a bulk material in presence of homogeneous and static electric fields under physical conditions where impact ionization influences the carrier dynamics. A comparison with theoretical and experimental data from the literature is also g...

Monte Carlo simulations of high energy electrons and holes in Si-n-MOSFET's

Monte Carlo simulations of high-energy electrons and holes in Si n-MOSFETs are presented. Key features of this work include the use of a suitable silicon model for carrier transport at high electric fields, an original impact ionization model, and sophisticated numerical techniques to speed up the calculation. The case of submicrometer Si n-MOSFETs is considered as a relevant application. >

Polarization Analysis of Hot-Carrier Light Emission in Silicon

In this paper a theoretical-evaluation is given of the absolute intensity and polarization of light emission from silicon devices due to conduction-conduction (c-c) and valence-valence (v-v) direct transitions. The matrix elements of the momentum operator between Bloch states have been obtained from a full band-structure calculation performed with the pseudopotential method. Results have been obtained by using both analytical model distribution functions and realistic hot-carrier distributions obtained from Monte Carlo (MC) simulations based on the same band model. They show a polarization degree of a few per cent, which should be observable for these transitions.

Monte Carlo simulation of charge transport in amorphous chalcogenides

The most peculiar feature exhibited by the I(V) characteristics of amorphous-chalcogenide materials is undoubtedly its S-shaped behavior. This type of characteristics is very important for the technological application, e.g., in the field of nanoscale solid-state memories. In this paper we give a microscopic particle description of the charge transport across a layer of amorphous Ge2Sb2Te5 sandwiched between two planar metallic contacts. A transport scheme based on the generalization of the variable-range hopping has been implemented in a current-driven Monte Carlo code. This approach allows one to investigate the aspects of the microscopic picture responsible for the electrical properties of the device. The results are compared with experimental data.

Effect of interparticle collisions on energy relaxation of carriers in semiconductors

Abstract An Ensemble Monte Carlo technique is used to simulate the dynamics of charge carriers in semiconductors in the presence of interparticle collisions with the purpose of analising the effect of such an interaction on the energy loss mechanisms. At increasing carrier concentrations, a reduction of the energy relaxation time τ ϵ due to carrier-carrier interaction is predicted by the theory. A comparison with available experimental results in p-type Ge shows qualitative agreement with the calculations. However, the theoretical results show a dependence of τ ϵ on carrier concentration not as large as that exhibited by the experiments.

Hot-carrier trap-limited transport in switching chalcogenides

Chalcogenide materials have received great attention in the last decade owing to their application in new memory systems. Recently, phase-change memories have, in fact, reached the early stages of production. In spite of the industrial exploitation of such materials, the physical processes governing the switching mechanism are still debated. In this paper, we work out a complete and consistent model for transport in amorphous chalcogenide materials based on trap-limited conduction accompanied by carrier heating. A previous model is here extended to include position-dependent carrier concentration and field, consistently linked by the Poisson equation. The results of the new model reproduce the experimental electrical characteristics and their dependences on the device length and temperature. Furthermore, the model provides a sound physical interpretation of the switching phenomenon and is able to give an estimate of the threshold condition in terms of the material parameters, a piece of information of gre...

Diffusion coefficient of holes in silicon by Monte Carlo simulation

A theoretical investigation of the diffusivity of holes in Si as a function of temperature, field strength, and field direction is reported. Calculations have been performed with the Monte Carlo procedure. The theoretical analysis explains the main features exhibited by the experimental data available from the literature. Minor discrepancies between theory and experiment are discussed in terms of microscopic mechanisms and/or reliability of the different experimental techniques used.

Wigner-function formulation for quantum transport in semiconductors: theory and Monte Carlo approach

The Wigner-function approach to the quantum theory of electron transport in mesoscopic systems is reviewed. Delta-like or “particle” contributions to the Wigner function evolve in time along “paths” formed by ballistic free flights interrupted by scattering processes as semiclassical particles. A Monte Carlo algorithm based on such Wigner paths will be presented. It extends to quantum transport the Monte Carlo procedure that proved to be very successful for the study of semiclassical transport.

A multiband Monte Carlo approach to Coulomb interaction for device analysis

This paper presents an extension of the theoretical approach for both the short‐ and long‐range components of the Coulomb interaction among carriers in semiconductors to the case of an arbitrary isotropic multiband model, devised for Monte Carlo simulation of silicon devices. The analytical and numerical aspects of the model are discussed in detail. Results for the effect of the Coulomb interaction on the carrier distribution function and on the energy‐loss properties of the carrier gas are presented for the case of electrons in homogeneous and inhomogeneous silicon structures.