Dominant hydrogen-oxygen complex in hydrothermally grown ZnO

A hydrogen-related defect labeled as $\mathrm{H}\text{−}\mathrm{I}*$, observed in as-grown hydrothermal ZnO, is studied by means of infrared absorption spectroscopy. The defect possesses a stretch local vibrational mode at $3577.3{\mathrm{cm}}^{-1}$ that is associated with a single hydrogen atom bound to oxygen with the $\mathrm{O}-\mathrm{H}$ bond oriented along the $c$ axis of the crystal. $\mathrm{H}\text{−}\mathrm{I}*$ can be destroyed only after anneal for several hours at $1200°\mathrm{C}$. Possible microscopic models of $\mathrm{H}\text{−}\mathrm{I}*$ are discussed.