Hydrogen is readily incorporated into bulk, single-crystal ZnO during exposure to plasmas at moderate (100-300degreesC) temperatures. Incorporation depths of >25 mum were obtained in 0.5 h at 300degreesC, producing a diffusivity of similar to8 x 10(-10) cm(2)/V s at this temperature. The activation energy for diffusion is 0.17 +/- 0.12 eV, indicating an interstitial mechanism. Subsequent annealing at 500-600 degreesC is sufficient to evolve all of the hydrogen out of the ZnO, at least to the sensitivity of Secondary Ion Mass Spectrometry (<5 x 10(15) cm(-3)). The thermal stability of hydrogen retention is slightly greater when the hydrogen is incorporated by direct implantation relative to plasma exposure, due to trapping at residual damage. (C) 2003 Elsevier Ltd. All rights reserved.