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Modelling of Charge Transport in Solids


Karl-Franzens-Universität Graz, Dep. of Physics
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Ulrich Hohenester
Walter Pötz

TU Wien, Institute for Microelectronics
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Hans Kosina

Universita degli Studi di Firenze, Dip. di Matematica Applicata
Dipartimento di Matematica "Ulisse Dini"
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Giovanni Frosali
Luigi Barletti

Universite de Toulouse, Institut de Mathematiques de Toulouse
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Pierre Degond

Universita degli Studi di Catania, DMI
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Armando Majorana
Oracio Muscato
Vittorio Romano
Giovanni Russo

Universita degli Studi di Parma, Dip. di Matematica
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Gian Luca Caraffini
Maria Groppi
Giampiero Spiga

Norwegian University of Science and Technology, Dep. of Physics
Arne Brataas
Daniel Huertas-Hernando


Politecnico di Torino
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Roberto Monaco
Alberto Rossani

University of Cambridge, Dep. of Engineering
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Andrea Ferrari

UC San Diego, Dep. of Cognitive Science
Claudia Lainscsek

California State University Northridge, Dep. of Mathematics Industriale
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Jacek Polewczak

Current research activities

This page gives a short description of the different research activities, to quickly jump to a specific work use the link list below. If you are interested in a particular topic and would like to know more, please feel invited to contact the person(s) listed with this topic.
Direct Simulation of Quantum Transport in Semiconductors
Omar Morandi
Ferdinand Schürrer

Velocity distribution
The development of efficient quantum computational methods is a crucial aspect in the development of the new generation devices where the size of the charge confinement becomes comparable to the electron wavelength. We are interested in studying semiconductors where the heterostructure design induces coherent interference effects between different bands. We will investigate the contribution of interband current in a Resonant Interband Tunneling Diode by means of a multi-band Wigner transport model. Furthermore we will apply multiband quantum kinetic model to study high field effects in carbon nanotubes and in graphene structures.

FWF project No. P21326-N16
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Charge carrier transport in organic thin-film transistors
Manfred Gruber
Karin Zojer
Ferdinand Schürrer
Current distribution in an organic thin-film transistor
By means of a two-dimensional drift-diffusion approach we investigate the principle mechanisms which influence the shape of the I-V characteristic of top-contact bottom-gate pentacene thin-film transistors. Recent calculations deal with the charge carrier injection mechanisms present at the contacts, the formation of a hysteresis in the transfer characteristic due to trapping and detrapping of charge carriers, and the influence of light.

NILAustria - Project NILsimtos
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Simulation of spin-polarized currents in magnetic multilayers
Stefan Possanner
Pierre Degond
Claudia Negulescu
Ferdinand Schürrer

Since the discovery of the Giant-Magneto-Resistance (GMR)-effect by A. Fert and P. Grünberg in 1988, the spin degree of freedom has attracted a great deal of attention in the transport and the device design community. One of the open problems is to fully understand the effects of a spin-polarized current perpendicular to the planes of non-collinear magnetic multilayers. We develop a spinor-Boltzmann equation from first principles which governs the time evolution of a 2x2 distribution matrix in phase space to incorporate the spin polarization of the carriers. The crucial point is to correctly describe the different scattering behaviour of spin-up and spin-down electrons in ferrromagnetic materials. From the spinor-Boltzmann model, a drift-diffusion equation for the vector spin polarization will be derived and solved self-consistently with the Landau-Lifshitz-Gilbert equation for the magnetization of the layers to simulate the spin transfer torque in non-collinear multilayers on a mesoscopic scale. The 3D simulations focus on the effects of domain walls and vortex cores in spin valves and microwave oscillator devices.

DEASE project
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Wigner function formalism for the simulation of charge transport in graphene
Antonius Dorda
Omar Morandi
Ferdinand Schürrer

Graphene is an interesting material for future device applications not only because of its greatly enhanced mobility compared to traditional transistor materials but especially due to its unique band structure. In the proximity of the Fermi energy, the bands are well described by a biconical shape, resembling the dispersion relation of mass less Dirac fermions and thus resulting in unusual effects like the Klein paradox. Since graphene is essentially a zero band gap material, interband tunneling plays a crucial role. Therefore, the usual approach based on a semi-classical Boltzmann transport equation is of limited scope and a full quantum mechanical treatment has to be carried out. This is done in the framework of the Wigner function formalism. In this work, two different cases are examined: On the one hand, the full non-local time evolution equations for the Wigner function to study Klein tunneling and on the other hand, in the limit of larger device dimensions (submicrometer) and slowly varying electric fields, a set of approximate equations of motion is considered. The latter is in close analogy to its semi-classical counterpart with extra terms incorporating the quantum mechanical corrections.

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Investigation of the impact of built-in electric fields on the efficiency of nanocomposite solar cells
Iris Hehn
Karin Zojer
Ferdinand Schürrer

The aim of this work is to study the impact of built-in electric fields on the carrier transport and the efficiency of nanocomposite solar cells by means of numerical modeling. A two-dimensional drift-diffusion model is used to describe carrier transport in the devices. Novel strategies will be tested to incorporate electric fields due to charge rearrangements at metal-semiconductor or semiconductor-semiconductor interfaces into the model. The such developed model will be used to quantitatively study the device efficiency as a function of origin, position, and extent of such electric fields.

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