Identification of two hydrogen donors in ZnO

A combined study of Raman scattering, IR absorption, photoluminescence, and photoconductivity was performed in ZnO. 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±0.2 meV photoluminescence line. A 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 with an effective charge of (0.28±0.03)e. The concentration of HBC was determined from the frequency shift of the E₁(LO) phonon-plasmon mode at 591 cm^-1. The HO donor in ZnO [A. Janotti and C. G. Van de Walle, Nat. Mater. 6, 44 (2007)] has an ionization energy of 47 meV. The excitonic recombination at HO leads to the previously labeled I₄ line at 3362.8 meV. Photoconductivity spectra reveal the 1s→2p donor transition at 265 cm^-1.