Different bound states of impurity hydrogen atoms in hydrothermally grown ZnO detected with nuclear reaction analysis

The concentration of hydrogen impurities (H) incorporated in hydrothermally grown ZnO single crystals and their thermal behaviors were investigated by means of 1H(15N,αγ)12C nuclear reaction analysis (NRA) and positron annihilation lifetime spectroscopy (PALS). The H concentration measurements with NRA suggest that H exist in three different bound states in as-grown ZnO: two types of loosely bound H (LBH) and a strongly bound H (SBH). The LBH are removed out of the reaction site by heat treatment up to 773 K but SBH remain even at 1373 K. The PALS measurements demonstrate the presence of (zinc vacancy)-H complexes (VZn + H) which also remain at 1373 K. Comparison with earlier theoretical calculations suggests that the SBH exist as VZn + H at a concentration of 0.10(4) at.%.