EPR spectra of electron-irradiated ZnO, taken at 30 K and 9.48 GHz, with the magnetic field perpendicular to the axis. (a) In the dark. (b) After illumination with 325 nm light. The Zn vacancies are in the 1– charge state and the O vacancies are in the charge state. Reprinted with permission from L. A. Kappers, O. R. Gilliam, S. M. Evans, L. E. Halliburton and N. C. Giles, Nucl. Instrum. Methods Phys. Res. B, 266, 2953 (2008). Copyright © 2008, Elsevier.
PL spectrum of ZnO, showing exciton lines (3.3–3.4 eV), donor-acceptor pair transitions , and their phonon replicas ( and ). The broad “green luminescence” is centered at . Reprinted with permission from B. K. Meyer, H. Alves, D. M. Hoffman, W. Kriegseis, D. Forster, F. Bertram, J. Christen, A. Hoffman, M. Strassburg, M. Dworzak, U. Haboeck, and A. V. Rodina, Phys. Status Solidi B, 241, 231 (2009). Copyright © 2009, Wiley-VCH Verlag GmbH & Co. KgaA.
PL spectrum of donor-bound excitons in ZnO at 4.2 K. Reprinted with permission from B. K. Meyer, H. Alves, D. M. Hoffman, W. Kriegseis, D. Forster, F. Bertram, J. Christen, A. Hoffman, M. Strassburg, M. Dworzak, U. Haboeck, and A. V. Rodina, Phys. Status Solidi B, 241, 231 (2009). Copyright © 2009, Wiley-VCH Verlag GmbH & Co. KgaA.
Schematic of Cu energy levels in ZnO (see Ref. 148). Intra- transitions of result in IR absorption peaks at 10 K, shown in the top spectrum. The transition of a hole from the () state to the state produces a no-phonon emission line at 2.86 eV, shown in the expanded spectrum (shifted to the left). Phonon replicas result in the structured green luminescence band centered around 510 nm. Reprinted with permission from R. Dingle, Phys. Rev. Lett. 23, 579 (1969). Copyright © 1969, American Physical Society.
Models for interstitial H donors in ZnO. Left: antibonding configuration. Right: bond-centered configuration. The dashed lines indicate broken Zn–O bonds. See Ref. 161.
IR absorption spectra (4.2 K) of O–H complexes in three different ZnO samples. The Eagle-Picher and Cermet samples were -cut crystals tilted at 45° to the IR beam (inset). The Erlangen sample was -cut and was perpendicular to the IR beam. All samples contained the 3326 and peaks, but the intensities of the peaks varied from sample to sample. Reprinted with permission from G. Alvin Shi, M. Stavola, S. J. Pearton, M. Thieme, E. V. Lavrov, and J. Weber, Phys. Rev. B, 72, 195211 (2008). Copyright © 2005, American Physical Society.
IR spectrum (10 K) of ZnO grown in a mixture of (90%) and (10%); see Ref. 191. Absorption peaks from N–H bond-stretching vibrational modes are indicated by the arrows. The ball-and-stick model is from first-principles calculations (Ref. 193).
EPR parameters for donors in ZnO, where and refer to directions parallel and perpendicular to the axis, respectively. The electron spins are .
EPR parameters for acceptors in ZnO. For centers with axial symmetry, and refer to directions parallel and perpendicular to the axis, respectively. Deep acceptors can have their holes localized on axial or nonaxial O atoms. is the angle between the and axes. For Li and the singly ionized Zn vacancy, points roughly along the Zn–O bond direction. For the neutral Zn vacancy, lies in the basal plane and points from one O atom to an adjacent O atom.
Local vibrational modes of H complexes in ZnO, determined by IR spectroscopy at liquid-helium temperatures. Frequencies correspond to O–H or N–H bond-stretching vibrations.
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