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A Study of Co and Mn in ZnO Varistors

Published online by Cambridge University Press:  28 February 2011

G. E. Pike ,
C. H. Seager  and
R. G. Dosch
G. E. Pike
Affiliation:
Sandia National Laboratories, Albuquerque, NM 87185
C. H. Seager
Affiliation:
Sandia National Laboratories, Albuquerque, NM 87185
R. G. Dosch
Affiliation:
Sandia National Laboratories, Albuquerque, NM 87185
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Abstract

ZnO varistors are polycrystalline materials which have highly non—linear current/voltage characteristics controlled by depletion regions around the grain boundaries. Dissolved transition metals at concentrations of about 1 at.% are required to achieve this large nonlinearity, but their role is unclear. To address this issue we have usedthe technique of photothermal deflection spectroscopy to measure the optical absorption of varistors containing Co or Mn, both common dopants. Prominent peaks and edges appear in the spectra, and are associated with substitutional Co2+and Mn2+ ions whose ground states are deep within the ZnO bandgap. Electro— and photoluminescence spectra show Stokes shifted peaks for some of these transitions. The spectral dependence of the photoconductivity shows that some of the absorption features correspond to ionization of the impurities. This result is used to show how the dark impact ionization of these impurities due to a high applied voltage can contribute to the current/voltage nonlinearity.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 46: Symposium B – Microscopic Identification of Electronic Defects in Semiconductors , 1985 , 409
Copyright
Copyright © Materials Research Society 1985

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