Structural characterization of H plasma-doped ZnO single crystals by positron annihilation spectroscopies

Nominally undoped, hydrothermally grown ZnO single crystals have been investigated after doping in remote H plasma. Characterizations have been made by positron annihilation (slow positron implantation spectroscopy, lifetime, coincidence Doppler broadening), temperature-dependent Hall and photoluminescence measurements. The H content before and after the doping has been determined using nuclear reaction analysis. In addition, changes of the polished surface of the crystals have been monitored by atomic force microscopy.
H plasma doping produced a metallic conducting near-surface layer. It is discussed if this is due to an increased H and zinc incorporation into pre-existing zinc vacancy – H complexes, as this also could explain the occurrence of a second positron lifetime component in the volume of the crystals, from which a bulk positron lifetime of (153 +/- 2) ps for ZnO is derived in very good agreement with previous experiments and theoretical calculations.