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

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Journal Title
Journal ISSN
Volume Title
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2011
Major/Subject
Mcode
Degree programme
Language
en
Pages
245208/1-7
Series
Physical Review B, Volume 83, Issue 24
Abstract
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.
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Keywords
ZnO, Li, vacancies, positron annihilation
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Citation
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