Electron Spin Resonance Studies of Donors and Acceptors in ZnO

Electron spin resonance of acceptors due to substitutional Li, and the resonance of certain donors previously reported at $g\cong 1.96$ were examined using polycrystalline samples of ZnO. It was found that the latter signal could actually be a superposition of two independent signals, one arising from the oxygen vacancy and the other from the substitutional halogen. The analysis of the resonance spectra gave for the Li acceptor $g_{\mathrm{II}}=2.0026\mathrm{}\pm 0.0005$, $g_{\perp }=2.0254\mathrm{}\pm 0.0005$, $A_{\mathrm{II}} \left(\mathrm{with} {\mathrm{Li}}^7 \mathrm{nucleus}\right)\leqq 0.1\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and $A_{\perp } \left(\mathrm{with} {\mathrm{Li}}^7 \mathrm{nucleus}\right)=(1.73\mathrm{}\pm 0.02)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$; for the donor due to oxygen vacancy $g_{\mathrm{II}}=1.957\mathrm{}\pm 0.001$, and $g_{\perp }=1.956\mathrm{}\pm 0.001$; and for the halogen donor $g=1.960\mathrm{}\pm 0.001$. These $g$ values are interpreted in terms of a picture in which a hole associated with the Li acceptor is localized in the valence orbital of one of the four adjacent oxygen, while the electrons trapped by the donor levels due to oxygen vacancies or substitutional halogen are shared more or less equally among the valence orbitals of the surrounding zinc ions.