Characterization of Non-Polar ZnO Layers with Positron Annihilation Spectroscopy
A. Zubiaga a, F. Tuomisto a, J. Zúñiga-Pérez b and V. Muñoz-San José c
a Department of Engineering Physics, Helsinki University of Technology, P.O. Box 1100, 02015 TKK Espoo, Finland
b Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications (CRHEA), Centre National de la Recherche Scientifique (CNRS), 06560 Valbonne, France
c Universitat de Valncia, Departamento de Fisica Aplicada i Electromagnetisme, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain
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Received: 7 06 2008;
We applied positron annihilation spectroscopy to study the effect of growth polarity on the vacancy defects in ZnO grown by metal-organic vapor phase deposition on sapphire. Both c-plane and a-plane ZnO layers were measured, and Zn vacancies were identified as the dominant defects detected by positrons. The results are qualitatively similar to those of earlier experiments in GaN. The Zn vacancy concentration decreases in c-plane ZnO by almost one order of magnitude (from high 1017 cm-3 to low 1017 cm-3) when the layer thickness is increased from 0.5 to 2 μm. Interestingly, in a-plane ZnO the Zn vacancy concentration is constant at a level of about 2×1017 cm-3 in all the samples with thicknesses varying from 0.6 to 2.4 μm. The anisotropy of the Doppler broadening of the annihilation radiation parallel and perpendicular to the hexagonal c-axis was also measured.
DOI: 10.12693/APhysPolA.114.1257
PACS numbers: 61.72.uj, 68.55.Ln, 68.37.-d, 78.70.Bj