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Summary: Binary oxides such as SnO2 display a host of interesting
properties: they can be highly conductive, they are
transparent, and they can be used as sensors. Improved
control over conductivity would enable new applications,
including optical detectors and light emitters.
Unintentional conductivity in oxides has conventionally
been attributed to point defects such as oxygen
vacancies or tin interstitials. Using state-of-the-art first-
principles calculations, the group of Prof. Van de Walle
has shown that this hypothesis is incorrect. Instead, the
conductivity must be attributed to unintentional impurities,
with hydrogen being a prime candidate. Both interstitial
hydrogen (Hi) and substitutional hydrogen on an oxygen
site act as shallow donors (HO).
Furthermore, in work published in Physical Review
Letters, they have shown that p-type doping of SnO2 can
be achieved by incorporating group-III elements such as
Al, Ga, or In. These acceptors have adequate solubilities
and low ionization energies, offering the prospect of
ambipolar doping.
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