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, HBC, and hydrogen bound in an oxygen vacancy, HO-were identified. Donor HBC has an ionization energy of 53 meV. The recombination of an exciton bound to HBC gives rise to the 3360.1±0.2meV photoluminescence line. The 1s→2p donor transition at 330cm-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 3611cm-1. The HO donor in ZnO has an ionization energy of 47 meV. The excitonic recombination at HO leads to the previously labeled I4 line at 3362.8 meV. Photoconductivity and Raman spectra reveal the 1s→2p donor transition at 265cm-1. It is shown that HBC migrating through the ZnO lattice forms electrically inactive interstitial H2. Vibrational modes of H2, HD, and D2 were identified at 4145, 3628, and 2985cm-1, respectively. These results suggest that interstitial H2 is responsible for the 'hidden' hydrogen in ZnO.