A first-principles investigation, based on density functional theory, showed that native defects were unlikely to be the cause of the unintentional n-type conductivity. Detailed results for the O vacancy showed that it was a deep donor, and that its paramagnetic state was metastable. An investigation of likely donor impurities reveals that H acts as a shallow donor.

Defect Analysis and Engineering in ZnO. C.G.Van de Walle: Physica B, 2001, 308-310, 899-903