Summary: Zinc oxide (ZnO) has been intensively pursued as an
optoelectronic material, in hopes of developing it into a
wide-band-gap light emitter that would compete with GaN.
Establishing p-type doping has been most challenging.
Nitrogen has been regarded as the most promising acceptor,
but convincing demonstrations of p-type doping have been
New light has now been shed on this puzzling state of affairs.
Professor Van de Walle's Computational Materials group
has performed cutting-edge first-principles calculations that
show nitrogen acceptors to have an ionization energy of
1.3 eVmuch too large to enable p-type doping. They also
explained why the behavior of nitrogen has been
misinterpreted in so many of the previous investigations.
Does this mean that all hope for p-type ZnO has to be
abandoned? Substitutional acceptors (including Li, N, P, As,
or Sb) will not yield p-type conductivity. The computations
show, however, that interstitial doping (specifically using
fluorine) still looks promising,
J. L. Lyons, A. Janotti, and C. G. Van de Walle,