Defect formation and thermal stability of H in high dose H implanted ZnO

We studied the structural properties, defect formation, and thermal stability of H in hydrothermally grown ZnO single crystals implanted with H ^- dose ranging from 2.5 × 10¹⁶ to 1 × 10 ¹⁷ cm^-2. H implantation is found to create deformed layers with a uniaxial strain of 0.5-2.4% along the c-axis in ZnO, for the low and high dose, respectively. About 0.2-0.4% of the original implanted H concentration can still be detected in the samples by secondary ion mass spectrometry after annealing at a temperature up to 800 °C. The thermally stable H is tentatively attributed to H related defect complexes involving the substitutional H that are bound to O vacancies and/or the highly mobile interstitial H that are bound to substitutional Li occupying Zn vacancies as the samples are cooled slowly from high temperature annealing. H implantation to a dose of 1 × 10¹⁷ cm^-2 and followed by annealing at 800 °C, is found to result in the formation of vacancy clusters that evolved into faceted voids with diameter varying from 2 to 30 nm. The truncations around the voids form more favorably on the O-terminated surface than on the Zn-terminated surface, suggesting that O is a preferred surface polarity for the internal facets of the voids in the presence of H.