Hydrogen local modes and shallow donors in ZnO

Abstract

The annealing behavior of the free-carrier absorption, O-H vibrational absorption, and photoluminescence lines previously associated with H-related donors in ZnO has been studied. One set of H-related defects gives rise to O-H local vibrational mode absorption at either 3326 or $3611\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, with the relative intensities of these lines depending on the source of the ZnO starting material. These O-H lines anneal away together at 150 \ifmmode^\circ\else\textdegree\fi{}C along with $\ensuremath{\sim}80%$ of the free carriers introduced by H. The common annealing behavior of the O-H ir lines suggests that they are closely related. An additional defect produced by hydrogenation is thermally stable up to an annealing temperature of 500 \ifmmode^\circ\else\textdegree\fi{}C where a bound-exciton photoluminescence line often associated with H in ZnO is also annealed away. This more thermally stable donor accounts for $\ensuremath{\sim}20%$ of the free carriers introduced by H. These experiments on H in ZnO reveal a complex behavior with several defects being introduced and with properties that depend strongly on the source of the ZnO starting material.