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 Studies in n-Type Indium Nitride

Christian Rauch

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the School of Science for public examination and debate in Auditorium F at the Aalto University School of Science (Espoo, Finland) on the 4th of May 2012 at 13 o'clock.

Overview in PDF format (ISBN 978-952-60-4607-5)   [1870 KB]
Dissertation is also available in print (ISBN 978-952-60-4606-8)

Abstract

Sparked by the discovery of its narrow bandgap, indium nitride (InN) has recently attracted major scientific interest as a promising material in opto- and high-speed electronics. Industrial application, however, is hampered by the material's strong propensity for n-type conductivity and high defect concentrations. Despite major research efforts in that area, relatively little is known about the properties of defects in InN. The main goal of this thesis was to study the formation and characteristics of native point defects in n-type InN and investigate their role for the material's electrical properties. Positron annihilation spectroscopy was used as the main experimental technique for defect characterization. By combining density functional theory calculations with experimental positron annihilation methods, the dominant vacancy-type positron traps in common InN material were identified. As-grown and n-doped InN layers that were deposited by different growth methods, as well as irradiated and annealed material with varying carrier concentrations, were analyzed to investigate the formation and evolution of point defects in different environments. The data were compared to results from complementary techniques in order to study the interplay of point and extended defects, and their role in limiting the conductivity in n-type InN.

It is found that isolated indium (In) vacancies and their complexes are the dominant vacancy-type positron traps in InN. Isolated In vacancies are introduced in high-energy particle irradiation of InN, and anneal out at moderate temperatures if not stabilized by one or more nitrogen (N) vacancies. In-N vacancy complexes are the dominant vacancy-type positron traps in as-grown InN. In state-of-the-art material with low free electron concentrations, their concentration is at or below the detection limit of positron annihilation methods. For increasing free electron concentration, an enhanced formation of these vacancy complexes is observed, which act as significant source of compensation and scattering centers in highly n-type material. Additionally, a high density of negatively charged defects with only small effective open-volume is found that is tentatively attributed to negatively charged N vacancies. Estimated defect densities are significantly higher than what is expected from thermodynamic considerations, which suggests that alternative defect formation mechanisms determine the point defect densities in the material.

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

  1. C. Rauch, F. Reurings, F. Tuomisto, T. D. Veal, C. F. McConville, H. Lu, W. J. Schaff, C. S. Gallinat, G. Koblmüller, J. S. Speck, W. Egger, B. Löwe, L. Ravelli, and S. Sojak. In-vacancies in Si-doped InN. Physica Status Solidi A, 207, 1083, pages 1-4, November 2010. © 2010 Wiley-VCH Verlag. By permission.
  2. F. Reurings, C. Rauch, F. Tuomisto, R. E. Jones, K. M. Yu, W. Walukiewicz, and W. J. Schaff. Defect redistribution in postirradiation rapid-thermal-annealed InN. Physical Review B, 82, 153202, pages 1-4, October 2010. © 2010 American Physical Society (APS). By permission.
  3. C. Rauch, I. Makkonen, and F. Tuomisto. Identifying vacancy complexes in compound semiconductors with positron annihilation spectroscopy: a case study of InN. Physical Review B, 84, 125201, pages 1-9, September 2011. © 2011 American Physical Society (APS). By permission.
  4. C. Rauch, Ö. Tuna, C. Giesen, M. Heuken, and F. Tuomisto. Point defect evolution in low-temperature MOCVD growth of InN. Physica Status Solidi A, 209, 87, pages 1-4, November 2011. © 2011 Wiley-VCH Verlag. By permission.
  5. C. Rauch, F. Tuomisto, A. Vilalta-Clemente, B. Lacroix, P. Ruterana, S. Kraeusel, B. Hourahine, and W. J. Schaff. Defect evolution and interplay in n-type InN. Applied Physics Letters, 100, 091907, pages 1-3, March 2012. © 2012 American Institute of Physics (AIP). By permission.
  6. C. Rauch, F. Tuomisto, P. D. C. King, T. Veal, H. Lu, and W. J. Schaff. Self-compensation in highly n-type InN. arXiv:1204.3299v1 [cond-mat.mtrl-sci], pages 1-5, April 2012. © 2012 by authors.

Errata of publications 3 and 4

Keywords: indium nitride, n-type, defects, vacancies, positron annihilation, density functional theory

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© 2012 Aalto University

Last update 2012-10-31