Characterization of native vacancies in epitaxial GaN and ZnSe semiconductor layers by positron annihilation spectroscopy

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Doctoral thesis (article-based)
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31, [38]
Dissertations / Laboratory of Physics, Helsinki University of Technology, 117
Point defects in epitaxial GaN and ZnSe semiconductor layers have been studied using a low-energy positron beam. Ga vacancies are found to be present in n-type GaN grown by metal organic chemical vapor deposition, where the conductivity is due to residual oxygen. When n-type silicon impurity doping is done, clearly less vacancies are observed. In Mg-doped p-type and semi-insulating materials the vacancies are not observed. In GaN layers grown by molecular-beam epitaxy also bigger vacancy clusters are detected. The formation of Ga vacancies is found to depend strongly on the stoichiometry during the growth, and much less on the structural quality of the layers. In GaN layers positrons are trapped also at edge-type dislocations, which are shown to be negatively charged but not to contain open-volume defects. Undoped Znse layers are found to contain negative Zn vacancies. In nitrogen doped ZnSe and ZnS0.06Se0.94 layers Se vacancies are detected. These are most likely part of a defect complex with N impurity. Positron trapping at negative N acceptors is also observed. By combining the results of positron annihilation, secondary ion mass spectrometry, and capacitance-voltage measurements, a detailed picture of the deactivation of N impurities in ZnSe is obtained.
GaN, ZnSe, Ga vacancy, compensation, positron annihilation spectroscopy
Other note
  • K. Saarinen, P. Seppälä, J. Oila, P. Hautojärvi, C. Corbel, O. Briot, and R. L. Aulombard, Gallium vacancies and the growth stoichiometry of GaN studied by positron annihilation spectroscopy, Applied Physics Letters 73, 3253-3255 (1998).
  • J. Oila, V. Ranki, J. Kivioja, K. Saarinen, P. Hautojärvi, J. Likonen, J. M. Baranowski, K. Pakula, T. Suski, M. Leszczynski, and I. Grzegory, Influence of dopants and substrate material on the formation of Ga vacancies in epitaxial GaN layers, Physical Review B 63, 045205:1-8 (2001). [article2.pdf] © 2001 American Physical Society. By permission.
  • P. Laukkanen, S. Lehkonen, P. Uusimaa, M. Pessa, J. Oila, S. Hautakangas, K. Saarinen, J. Likonen, and J. Keränen, 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, 786-792 (2002).
  • J. Oila, K. Saarinen, A. E. Wickenden, D. D. Koleske, R. L. Henry, and M. E. Twigg, Ga vacancies and grain boundaries in GaN, submitted for publication in Applied Physics Letters.
  • P. Desgardin, J. Oila, K. Saarinen, P. Hautojärvi, E. Tournié, J.-P. Faurie, and C. Corbel, Native vacancies in nitrogen-doped and undoped ZnSe layers studied by positron annihilation, Physical Review B 62, 15711-15717 (2000). [article5.pdf] © 2000 American Physical Society. By permission.
  • J. Oila, K. Saarinen, T. Laine, P. Hautojärvi, P. Uusimaa, M. Pessa, and J. Likonen, Experimental identification of the doping deactivation mechanism in semiconductors: Application to nitrogen in ZnS<sub>0.06</sub>Se<sub>0.94</sub>, Physical Review B: Rapid communication 59, 12736-12739 (1999). [article6.pdf] © 1999 American Physical Society. By permission.
  • J. Oila, V. Ranki, J. Kivioja, K. Saarinen, and P. Hautojärvi, Target chamber for a slow positron beam: optimization of count rate and minimization of backscattering effects, Applied Surface Science 194, 38-42 (2002). [article7.pdf] © 2002 Elsevier Science. By permission.
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