Unambiguous identification of an OH-Li center in ZnO: Experiment

Theory has found that isolated H is always a donor in ZnO [1] and has led to a number of studies of the properties of H in this promising wide bandgap semiconductor. Of interest here is an OH vibrational line at 3577.3 cm$^{-1}$ that is dominant in ZnO grown by the hydrothermal method [2,3]. We show that the two naturally abundant isotopes of Li [$^{6}$Li (7.5{\%}) and $^{7}$Li (92.5{\%})] cause the D-stretching counterpart of the 3577.3 cm$^{-1}$ IR line to be split into two components that can be separately resolved, even though the 3577.3 cm$^{-1}$ line itself shows no Li-related splitting. This unexpected result establishes unambiguously that the 3577.3 cm$^{-1}$ IR line is due to an OH-Li complex. Overtone and oxygen isotope data for the OH-Li center provide an unusually complete picture of the vibrational properties of this defect. Because isotope splittings for elements heavier than Li will be more difficult to detect, this OH-Li center may be considered a model system for H trapped by impurities in ZnO. \newline \newline [1] C. G. Van de Walle, Phys. Rev. Lett. \textbf{85}, 1012 (2000). \newline [2] L. E. Halliburton \textit{et al.}, J. Appl. Phys. \textbf{96}, 7168 (2004). \newline [3] E. V. Lavrov \textit{et al.}, Phys. Rev. B \textbf{71}, 035205 (2005).