High-energy electron irradiation produced shallow donors at about Ec - 0.03eV. Because the production rate was much higher for Zn-face (00•1) than for O-face (00•¯1) irradiation, the donor was identified as being a Zn sub-lattice defect; probably interstitial Zni, or a Zni-related complex. The donor energy was quite close to that of the unirradiated sample. This strongly suggested that Zni, and not VO, was the predominant native shallow donor. The exceptionally high displacement threshold energy (about 1.6MeV) was explained in terms of a multiple-displacement model.

Residual Native Shallow Donor in ZnO. D.C.Look, J.W.Hemsky, J.R.Sizelove: Physical Review Letters, 1999, 82[12], 2552-5