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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Vacancy Defects in Silicon Related Materials and Gallium Nitride

Mikko Rummukainen

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 12th of January, 2007, at 13 o'clock.

Overview in PDF format (ISBN 978-951-22-8572-3)   [457 KB]
Dissertation is also available in print (ISBN 978-951-22-8571-6)

Abstract

Defects on the atomic scale strongly affect the performance of semiconductor devices and the achievable device lifetimes. Positron annihilation spectroscopy is sensitive to vacancy-type defects, which are the most common type of structural defects. In this thesis positron annihilation spectroscopy has been applied to study vacancy defects in gallium nitride and silicon related materials: silicon, silicon germanium and germanium.

Silicon related materials are dominant in current integrated circuits. Improving the channel conductivity is crucial for reducing the heat dissipation and for production of faster components. The formation of compensating defect complexes has been observed and their structure identified in highly Sb doped silicon. Native point defects in silicon germanium have been studied for Ge concentrations up to 30 per cent. Vacancies are found to form pairs with dopant P atoms reducing the free electron density and therefore the conductivity. In germanium implanted with silicon and germanium ions vacancy clustering and defect recovery during heat treatment were studied.

Gallium nitride is the most common material for blue light emitting diodes (LEDs). Blue wavelength light is required for producing e.g. high intensity white LEDs and improving the data packing density of DVDs. Bulk GaN is expensive and not readily available. Therefore GaN components are grown as thin layers on foreign substrates, the properties of which affect the GaN layer. The dislocation density was observed to decrease when using misoriented SiC substrates. The vacancy formation and impurity incorporation into GaN layers was shown to be dependent on the growth polarity. Vacancy clusters and a higher concentration of impurities are incorporated during N-polar growth.

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

  1. M. Rummukainen, I. Makkonen, V. Ranki, M. J. Puska, K. Saarinen and H.-J. L. Gossmann, Vacancy-impurity complexes in highly Sb-doped Si grown by molecular beam epitaxy, Physical Review Letters 94, 165501: 1-4 (2005). © 2005 American Physical Society. By permission.
  2. M. Rummukainen, J. Slotte, K. Saarinen, H. H. Radamson, J. Hållstedt and A. Yu. Kuznetsov, Vacancy-impurity pairs in relaxed Si1−xGex layers studied by positron annihilation spectroscopy, Physical Review B 73, 165209: 1-8 (2006). © 2006 American Physical Society. By permission.
  3. M. Rummukainen, J. Slotte, F. Tuomisto, V. Markevich and A. R. Peaker, Radiation damage in ion implanted and annealed n-type Ge studied by positron annihilation spectroscopy, Helsinki University of Technology Publications in Engineering Physics, Report TKK-F-A845 (2006). © 2006 by authors.
  4. E. Tengborn, M. Rummukainen, F. Tuomisto, K. Saarinen, M. Rudzinski, P. R. Hageman, P. K. Larsen and A. Nordlund, Effect of the misorientation of the 4H-SiC substrate on the open volume defects in GaN grown by metal-organic chemical vapor deposition, Applied Physics Letters 89, 091905: 1-3 (2006). © 2006 American Institute of Physics. By permission.
  5. M. Rummukainen, J. Oila, A. Laakso, K. Saarinen, A. J. Ptak and T. H. Myers, Vacancy defects in O-doped GaN grown by molecular-beam epitaxy: the role of growth polarity and stoichiometry, Applied Physics Letters 84, 4887-4889 (2004). © 2004 American Institute of Physics. By permission.

Keywords: positron annihilation spectroscopy, vacancy defects, gallium nitride, silicon, germanium

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© 2007 Helsinki University of Technology

Last update 2011-05-26