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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Defect Complexes in Silicon: Electronic Structures and Positron Annihilation

Mikko Hakala

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 E at Helsinki University of Technology (Espoo, Finland) on the 9th of February, 2001, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-5311-9)   [273 KB]
Dissertation is also available in print (ISBN 951-22-5310-0)

Abstract

In silicon processing technology one of the most important current objectives is to achieve a controlled impurity doping in the crystal. Point defects and defect complexes present in the crystal influence in an important way the electrical activity and the diffusion properties of the dopants. In this thesis, defect complexes in silicon are studied by using quantum-mechanical electronic-structure calculations and by modeling positron annihilation experiments.

The electronic-structure calculations are based on the density-functional theory and its state-of-the-art implementations, such as a plane-wave pseudopotential computer code. For the calculation of the momentum density of annihilating electron-positron pairs a new method is presented and tested. It is based on a two-particle description of the correlated pair so that the contact density depends explicitly on the whole spatial distribution of the electron state in question. The new method is found to be superior to the state-independent methods for the momentum density and provides a basis for identifying defect complexes with different chemical surroundings from their momentum distribution fingerprint.

In this work, the computational methods are used to study the positron annihilation characteristics at small vacancy clusters in silicon and the properties of typical dopant atoms, which include arsenic and boron. In highly arsenic-doped silicon an electrically inactive defect complex consisting of a vacancy decorated by three arsenic atoms is identified. In boron-doped silicon the defect structures containing one boron atom are analyzed and an estimate is given for the activation energy of boron diffusion.

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

  1. M. Alatalo, B. Barbiellini, M. Hakala, H. Kauppinen, T. Korhonen, M. J. Puska, K. Saarinen, P. Hautojärvi, and R. M. Nieminen, Theoretical and experimental study of positron annihilation with core electrons in solids, Physical Review B 54, 2397-2409 (1996). © 1996 American Physical Society. By permission.
  2. B. Barbiellini, M. Hakala, M. J. Puska, R. M. Nieminen, and A. A. Manuel, Correlation effects for electron-positron momentum density in solids, Physical Review B 56, 7136-7142 (1997). © 1997 American Physical Society. By permission.
  3. M. Hakala, M. J. Puska, and R. M. Nieminen, Momentum distributions of electron-positron pairs annihilating at vacancy clusters in Si, Physical Review B 57, 7621-7627 (1998). © 1998 American Physical Society. By permission.
  4. K. Saarinen, J. Nissilä, H. Kauppinen, M. Hakala, M. J. Puska, P. Hautojärvi, and C. Corbel, Identification of vacancy-impurity complexes in highly n-type Si, Physical Review Letters 82, 1883-1886 (1999). © 1999 American Physical Society. By permission.
  5. M. Hakala, M. J. Puska, and R. M. Nieminen, First-principles calculations of interstitial boron in silicon, Physical Review B 61, 8155-8161 (2000). © 2000 American Physical Society. By permission.

Keywords: point defects, density-functional theory, ab initio calculations

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© 2001 Helsinki University of Technology

Last update 2011-05-26