Identification of two hydrogen donors in ZnO

Abstract

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, ${\text{H}}_{\text{BC}}$, and hydrogen bound in an oxygen vacancy, ${\text{H}}_{\text{O}}$---were identified. Donor ${\text{H}}_{\text{BC}}$ has an ionization energy of 53 meV. The recombination of an exciton bound to ${\text{H}}_{\text{BC}}$ gives rise to the $3360.1\ifmmode\pm\else\textpm\fi{}0.2\text{ }\text{meV}$ photoluminescence line. A $1s\ensuremath{\rightarrow}2p$ donor transition at $330\text{ }{\text{cm}}^{\ensuremath{-}1}$ is detected in the Raman scattering and photoconductivity spectra. The stretch mode of the associated O-H bond is detected in IR absorption at $3611\text{ }{\text{cm}}^{\ensuremath{-}1}$ with an effective charge of $(0.28\ifmmode\pm\else\textpm\fi{}0.03)e$. The concentration of ${\text{H}}_{\text{BC}}$ was determined from the frequency shift of the ${E}_{1}(\text{LO})$ phonon-plasmon mode at $591\text{ }{\text{cm}}^{\ensuremath{-}1}$. The ${\text{H}}_{\text{O}}$ 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 ${\text{H}}_{\text{O}}$ leads to the previously labeled ${I}_{4}$ line at 3362.8 meV. Photoconductivity spectra reveal the $1s\ensuremath{\rightarrow}2p$ donor transition at $265\text{ }{\text{cm}}^{\ensuremath{-}1}$.