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.

Impurity Decoration of Native Vacancies in Ga and N Sublattices of Gallium Nitride

Sami Hautakangas

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 20th of May, 2005, at 12 noon.

Overview in PDF format (ISBN 951-22-7667-4)   [396 KB]
Dissertation is also available in print (ISBN 951-22-7666-6)


The effects of impurity atoms as well as various growth methods to the formation of vacancy type defects in gallium nitride (GaN) have been studied by positron annihilation spectroscopy. It is shown that vacancy defects are formed in Ga or N sublattices depending on the doping of the material. Vacancies are decorated with impurity atoms leading to the compensation of the free carriers of the samples. In addition, the vacancy clusters are found to be present in significant concentrations in n-type as well as in p-type GaN.

Nitrogen vacancies compensate Mg impurities in magnesium doped GaN. The high Mg content creates a defect profile with a low vacancy concentration near the surface. Post-growth annealing dissociates Vn-related complexes activating the p-type conductivity. Also the vacancy profile is made homogeneous by thermal treatment in highly Mg-doped GaN.

The direct experimental evidence of oxygen decorated Ga vacancy is obtained in O-doped n-type GaN. The present study shows that VGa-ON is distinguishable from an isolated Ga vacancy by positron annihilation spectroscopy. Yellow luminescence (YL) is common in n-type GaN, which is usually related to Ga vacancy defects. However, carbon doped semi-insulating GaN is exhibiting strong YL emission, but without the presence of Ga vacancies. The YL is attributed to C interstitials. The investigations concerning silicon doped GaN and GaN grown by the mass-transport method reveal vacancy type defects, which were identified as vacancy clusters.

This thesis consists of an overview and of the following 6 publications:

  1. S. Hautakangas, J. Oila, M. Alatalo, K. Saarinen, L. Liszkay, D. Seghier, and H. P. Gislason. 2003. Vacancy defects as compensating centers in Mg-doped GaN. Physical Review Letters 90, 137402. © 2003 American Physical Society. By permission.
  2. S. Hautakangas, K. Saarinen, L. Liszkay, J. A. Freitas, and R. L. Henry. The role of open volume defects in Mg-doped GaN studied by positron annihilation spectroscopy. Physical Review B, submitted for publication. © 2005 by authors and © 2005 American Physical Society. By permission.
  3. P. Laukkanen, S. Lehkonen, P. Uusimaa, M. Pessa, J. Oila, S. Hautakangas, K. Saarinen, J. Likonen, and J. Keränen. 2002. Structural, electrical, and optical properties of defects in Si-doped GaN grown by molecular-beam epitaxy on hydride vapor phase epitaxy GaN on sapphire. Journal of Applied Physics 92, pages 786-792.
  4. R. Armitage, W. Hong, Q. Yang, H. Feick, J. Gebauer, E. R. Weber, S. Hautakangas, and K. Saarinen. 2003. Contributions from gallium vacancies and carbon-related defects to the "yellow luminescence" in GaN. Applied Physics Letters 82, pages 3457-3459.
  5. S. Hautakangas, V. Ranki, I. Makkonen, M. J. Puska, K. Saarinen, X. Xu, and D. C. Look. Direct experimental evidence of impurity decoration of Ga vacancies in GaN. Physical Review Letters, submitted for publication. © 2005 by authors and © 2005 American Physical Society. By permission.
  6. T. Paskova, P. P. Paskov, E. M. Goldys, E. Valcheva, V. Darakchieva, U. Södervall, M. Godlewski, M. Zielinski, S. Hautakangas, K. Saarinen, C. F. Carlström, Q. Wahab, and B. Monemar. 2004. Characterization of mass-transport grown GaN by hydride vapour-phase epitaxy. Journal of Crystal Growth 273, pages 118-128.

Keywords: gallium nitride, positron annihilation, vacancy

This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

© 2005 Helsinki University of Technology

Last update 2011-05-26