Hydrogen in ZnO

The results of a combined study of Raman scattering, IR absorption, photoluminescence, and photoconductivity on ZnO are presented. Two shallow donors hydrogen at the bond-centered lattice site, H(BC), and hydrogen bound in an oxygen vacancy, H(O)-were identified. Donor H(BC) has an ionization energy of 53 meV. The recombination of an exciton bound to H(BC) gives rise to the 3360.1 +/- 0.2 meV photoluminescence line. The 1s -> 2p donor transition at 330 cm(-1) is detected in the Raman scattering and photoconductivity spectra. The stretch mode of the associated O-H bond is detected in IR absorption at 3611 cm(-1). The Ho donor in ZnO has an ionization energy of 47 meV. The excitonic recombination at H(O) leads to the previously labeled I(4) line at 3362.8 meV. Photoconductivity and Raman spectra reveal the 1s -> 2p donor transition at 265 cm(-1). It is shown that H(BC) migrating through the ZnO lattice forms electrically inactive interstitial H(2). Vibrational modes of H(2), HD, and D(2) were identified at 4145, 3628, and 2985 cm(-1), respectively. These results suggest that interstitial H(2) is responsible for the "hidden" hydrogen in ZnO. (C) 2009 Elsevier B.V. All rights reserved.