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, 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. 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 H-BC was determined from the frequency shift of the E-1(LO) phonon-plasmon mode at 591 cm(-1). The H-O 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 H-O leads to the previously labeled I-4 line at 3362.8 meV. Photoconductivity spectra reveal the 1s -> 2p donor transition at 265 cm(-1).