As mentioned above, there are three primary different approaches that have been investigated to generate appreciable hole conduction in ZnO at room temperature: substitution of Group IA impurities on the Zn sublattice, codoping of donors and acceptors, and substitution of Group VA impurities on the O sublattice.
Such weak p-type behavior is not anticipated to yield substantial hole conduction at room temperature.
Ionization energies of 0.33 , ~0.4 [37, 46], and 1.3 eV  have been predicted, none of which would be compatible with appreciable hole conduction at room temperature.
The observation of hole conduction in As-doped ZnO however is contrary to the predictions of Park et al.
The acceptor ionization energy assigned (using the method described by Wang and Giles ) to the [V.sub.Zn]-[N.sub.O]-[H.sup.+] complex is 134 meV, which is sufficiently low to allow appreciable room temperature hole conduction as we reported.