Residual Native Shallow Donor in ZnO

Abstract

High-energy electron irradiation in ZnO produces shallow donors at about ${E}_{C}\ensuremath{-}30\mathrm{meV}$. Because the production rate is much higher for Zn-face (0001) than O-face $(000\overline{1})$ irradiation, the donor is identified as a Zn-sublattice defect, most likely the interstitial ${\mathrm{Zn}}_{I}$ or a ${\mathrm{Zn}}_{I}$-related complex. The donor energy is quite close to that of the unirradiated sample, and of other samples discussed in the literature, strongly suggesting that ${\mathrm{Zn}}_{I}$ (and not ${V}_{\mathrm{O}}$) is the dominant native shallow donor in ZnO. An exceptionally high displacement threshold energy $(\ensuremath{\sim}1.6\mathrm{MeV})$ is quantitatively explained in terms of a multiple-displacement model.