Identification of substitutional Li in n-type ZnO and its role as an acceptor

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School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Physical Review B, Volume 83, Issue 24
Monocrystalline n-type zinc oxide (ZnO) samples prepared by different techniques and containing various amounts of lithium (Li) have been studied by positron annihilation spectroscopy (PAS) and secondary ion mass spectrometry. A distinct PAS signature of negatively charged Li atoms occupying a Zn-site (Li−Zn), so-called substitutional Li, is identified and thus enables a quantitative determination of the content of LiZn. In hydrothermally grown samples with a total Li concentration of ~2×10 exp 17 cm exp −3,LiZn is found to prevail strongly, with only minor influence, by other possible configurations of Li. Also in melt grown samples doped with Li to a total concentration as high as 1.5×10 exp 19 cm exp −3, a considerable fraction of the Li atoms (at least 20%) is shown to reside on the Zn-site, but despite the corresponding absolute acceptor concentration of ⩾(2–3)×10 exp 18 cm exp −3, the samples did not exhibit any detectable p-type conductivity. The presence of LiZn is demonstrated to account for the systematic difference in positron lifetime of 10–15 ps between Li-rich and Li-lean ZnO materials as found in the literature, but further work is needed to fully elucidate the role of residual hydrogen impurities and intrinsic open volume defects.
ZnO, Li, vacancies, positron annihilation
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Johansen, K. M. & Zubiaga, A. & Makkonen, I. & Tuomisto, Filip & Neuvonen, P. T. & Knutsen, K. E. & Monakhov, E. V. & Kuznetsov, A. Yu. & Svensson, B. G. 2011. Identification of substitutional Li in n-type ZnO and its role as an acceptor. Physical Review B. Volume 83, Issue 24. 245208/1-7. ISSN 1098-0121 (printed). DOI: 10.1103/physrevb.83.245208