The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Modeling of Electronic Transport in Nanostructures

Paula Havu

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium K at Helsinki University of Technology (Espoo, Finland) on the 28th of October, 2005, at 13 o'clock noon.

Overview in PDF format (ISBN 951-22-7859-6)   [1673 KB]
Dissertation is also available in print (ISBN 951-22-7858-8)

Abstract

Nanometer-scale electronic devices are building blocks of future electronics. The function of these components is based on quantum-mechanical phenomena and therefore new modeling methods has to be developed to model properties of nano-devices. In this thesis one solution and implementation is presented.

In this thesis transport properties of the nano-devices are modeled using the density-functional theory. In the main part of the work electron densities and currents calculated using the Green's function method. The method enables the connection of the nanostructure to the semi-infinite leads by the open boundary conditions making finite-size effects small. Electron currents under finite bias conditions can also be calculated.

The use of the Green's function method is computationally heavy in comparison to the explicit wave-function methods. An important part of this thesis work is to choose efficient numerical methods and their implementation. The computer code created has one-, two- and three-dimensional versions so that different types of nanostructures can be modeled. The one- and two-dimensional versions use the effective mass approximation while the three-dimensional one uses nonlocal pseudopotential operators. The numerical implementation is done using the finite-element method with the so-called hp-elements.

The codes implemented are used to model magnetic resonance tunneling diodes, two-dimensional quantum wires, Na-atom chains and thin HfO2 layers.

This thesis consists of an overview and of the following 5 publications:

  1. P. Havu, T. Torsti, M. J. Puska, and R. M. Nieminen, Conductance oscillations in metallic nanocontacts, Physical Review B 66, 075401 (2002) (5 pages). © 2002 American Physical Society. By permission.
  2. P. Havu, V. Havu, M. J. Puska, and R. M. Nieminen, Nonequilibrium electron transport in two-dimensional nanostructures modeled using Green's functions and the finite-element method, Physical Review B 69, 115325 (2004) (13 pages). © 2004 American Physical Society. By permission.
  3. P. Havu, M. J. Puska, R. M. Nieminen, and V. Havu, Electron transport through quantum wires and point contacts, Physical Review B 70, 233308 (2004) (4 pages). © 2004 American Physical Society. By permission.
  4. P. Havu, N. Tuomisto, R. Väänänen, M. J. Puska, and R. M. Nieminen, Spin-dependent electron transport through a magnetic resonant tunneling diode, Physical Review B 71, 235301 (2005) (12 pages). © 2005 American Physical Society. By permission.
  5. P. Havu, V. Havu, M. J. Puska, M. H. Hakala, A. Foster, and R. M. Nieminen, Finite-element implementation for electron transport in nanostructures, Journal of Chemical Physics, submitted for publication (9 pages). © 2005 by authors and © 2005 American Institute of Physics. By permission.

Keywords: nanostructure, electron transport, density-functional theory, finite-element method

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© 2005 Helsinki University of Technology

Last update 2011-05-26