Experimental confirmation of the predicted shallow donor hydrogen state inzinc oxide

We confirm the recent prediction that interstitial protium may act as a sha llow donor in zinc oxide, by direct spectroscopic observation of its muoniu m counterpart. On implantation into ZnO, positive muons -chemically analogo us to protons in this context - form paramagnetic centers below about 40 K. The muon-electron contact hyperfine interaction, as well as the temperatur e and activation energy for ionization, imply a shallow level. Similar resu lts for the cadmium chalcogenides suggest that such shallow donor states ar e generic to the II-VI compounds. The donor level depths should serve as a guide for the electrical activity of interstitial hydrogen.