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.
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Multiscale Modeling of Effects Due to Impurity Clustering in Semiconductor Systems

Teemu Hynninen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium K at Helsinki University of Technology (Espoo, Finland) on the 19th of December, 2008, at 13 o'clock.

Overview in PDF format (ISBN 978-951-22-9682-8)   [2579 KB]
Dissertation is also available in print (ISBN 978-951-22-9681-1)

Abstract

The properties of materials visible to us at the macroscopic scale are due to the microscopic behavior of the atoms in the material. In many cases, small disturbances from an ideal microstructure can lead to completely different behavior at the macroscale. In order to exploit or prevent such phenomena, it is important to understand both the microscopic interactions governing the individual atoms and the mechanisms which lead to the observed collective behavior of the particles at the macroscale. Computational methods can offer insight to such problems, since in a computational scheme it is possible to manipulate the systems at will and without unwanted disturbances. On the other hand, these methods necessarily contain approximations and care must be taken in choosing and combining the methods used for examining the different physically relevant length and time scales.

This dissertation presents computational simulations of the role of impurities and impurity clusters in two types of semiconductor systems. The influence of the microstructure of Mn dopants in the diluted magnetic semiconductors (Ga,Mn)N and (Ga,Mn)As is examined. Also, the effect of metal impurities, such as Cu and Pb, on the surface morphologies of wet etched Si surfaces is studied. In both cases, density-functional calculations are used for studying the microscopic interactions and models based on Monte Carlo schemes are developed for simulating the macroscopic behavior. In the presented work, a direct correspondence between the microstructures of the magnetic semiconductors and their magnetic properties is found, explaining the experimentally observed variations in Curie temperatures. The dependence of the roughness of etched surfaces on the types of impurities present during etching is also explained by different adsorption and cluster formation tendencies of the various impurities on the Si surface.

This thesis consists of an overview and of the following 7 publications:

  1. Teemu Hynninen, Hannes Raebiger, J. von Boehm, and Andrés Ayuela. 2006. High Curie temperatures in (Ga,Mn)N from Mn clustering. Applied Physics Letters, volume 88, 122501.
  2. Teemu Hynninen, Hannes Raebiger, and Juhani von Boehm. 2006. A multiscale study of ferromagnetism in clustered (Ga,Mn)N. Journal of Physics: Condensed Matter, volume 18, pages 1561-1567. © 2006 Institute of Physics Publishing. By permission.
  3. Teemu Hynninen, Hannes Raebiger, and Juhani von Boehm. 2007. Structural and magnetic properties of (Ga,Mn)N from first principles. Physical Review B, volume 75, 125208.
  4. Teemu Hynninen, Maria Ganchenkova, Hannes Raebiger, and Juhani von Boehm. 2006. Ferromagnetism and its evolution during long-term annealing in (Ga,Mn)As. Physical Review B, volume 74, 195337.
  5. A. S. Foster, M. A. Gosálvez, T. Hynninen, R. M. Nieminen, and K. Sato. 2007. First-principles calculations of Cu adsorption on an H-terminated Si surface. Physical Review B, volume 76, 075315.
  6. Teemu Hynninen, Miguel A. Gosálvez, Adam S. Foster, Hiroshi Tanaka, Kazuo Sato, Makio Uwaha, and Risto M. Nieminen. 2008. Effect of Cu impurities on wet etching of Si(110): formation of trapezoidal hillocks. New Journal of Physics, volume 10, 013033. © 2008 Institute of Physics Publishing. By permission.
  7. Teemu Hynninen, Adam S. Foster, Miguel A. Gosálvez, Kazuo Sato, and Risto M. Nieminen. 2008. Adsorption of metal impurities on H-terminated Si surfaces and their influence on the wet chemical etching of Si. Journal of Physics: Condensed Matter, volume 20, 485005. © 2008 Institute of Physics Publishing. By permission.

Keywords: impurities, clusters, magnetic semiconductors, Curie temperature, etching, surface morphology

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© 2008 Helsinki University of Technology

Last update 2011-05-26