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

Spin-Dependent Transport in Mn Doped GaAs and GaN Diodes

Heikki Holmberg

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Electronics, Communications and Automation for public examination and debate in Large Seminar Hall (2190) of Micronova at Helsinki University of Technology (Espoo, Finland) on the 14th of March, 2008, at 12 noon.

Overview in PDF format (ISBN 978-951-22-9260-8)   [1210 KB]
Dissertation is also available in print (ISBN 978-951-22-9259-2)

Abstract

The main idea of the thesis was to study experimentally the potential and the possibilities of semiconductor spintronic devices. Spin dependent magnetotransport was studied in different Mn doped GaAs and GaN thin films and diode structures. The ferromagnetic thin films and pn, spin Esaki-Zener tunnel and resonant tunnelling diodes were fabricated from Mn doped GaAs and GaN using the Molecule Beam Epitaxy technique. The magnetotransport measurements consist of, e.g., I-V, resistance and Hall measurements as a function of magnetic field and temperature. In this study also the magnetic field dependence of the current of the ferromagnetic diodes were modeled. In addition, the material studies were carried out using Secondary Ion Mass Spectroscopy and X-ray Diffraction techniques and the magnetization measurements using a magnetometer.

The main result of this study was the observation of the tunnelling anisotropic magnetoresistance effect (TAMR) in Mn doped GaAs spin Esaki-Zener tunnel and resonant tunnelling diodes. In the Mn doped GaAs Esaki-Zener diode the TAMR effect was observed at low bias voltages, which makes it possible to fabricate ultra low power spintronic devices. Another important result was that a room temperature ferromagnet of Mn doped GaN can be fabricated by a solid state diffusion method. The effect of Mn doping on the resonant tunnelling diodes with magnetic Mn doped GaAs emitters was also characterized. In addition, the reason why the current of a pn-diode having a lightly doped region is independent of magnetic field, even when some part of the device is magnetic, is given. Also the negative magnetoresistance due to the spin disorder scattering was observed and modeled in Mn doped GaAs and GaN thin films.

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

  1. H. Holmberg, N. Lebedeva, S. Novikov, J. Ikonen, P. Kuivalainen, M. Malfait, and V. V. Moshchalkov, Large magnetoresistance in a ferromagnetic GaMnAs/GaAs Zener diode, Europhysics Letters 71 (5), 811-816 (2005). © 2005 EDP Sciences. By permission.
  2. H. Holmberg, N. Lebedeva, S. Novikov, P. Kuivalainen, M. Malfait, V. V. Moshchalkov, and P. Kostamo, Magnetotransport properties of a room-temperature ferromagnet (Ga, Mn)N, IEEE Transactions on Magnetics 41 (10), 2736-2738 (2005). © 2005 IEEE. By permission.
  3. H. Holmberg, N. Lebedeva, S. Novikov, P. Kuivalainen, M. Malfait, and V. V. Moshchalkov, Magnetotransport in ferromagnetic (Ga, Mn)As and (Ga, Mn)N pn-diodes, IEEE Transactions on Magnetics 42 (10), 2712-2714 (2006). © 2006 IEEE. By permission.
  4. H. Holmberg, N. Lebedeva, S. Novikov, P. Kuivalainen, M. Malfait, and V. V. Moshchalkov, Electrical transport in Mn-doped GaAs pn-diodes, physica status solidi (a) 204 (3), 791-804 (2007).
  5. H. Holmberg, N. Lebedeva, S. Novikov, M. Mattila, P. Kuivalainen, G. Du, X. Han, M. Malfait, and V. V. Moshchalkov, Magnetotransport of holes through an AlAs/GaAs/AlAs resonant tunnelling quantum well with a ferromagnetic Ga1−xMnxAs emitter, physica status solidi (a) 204 (10), 3463-3477 (2007).

Keywords: semiconductor, spintronics, tunneling, diode, magnetotransport, manganese, gallium arsenide, gallium nitride

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© 2008 Helsinki University of Technology

Last update 2011-05-26