Formation and evolution of E3 centers in hydrothermally grown zinc oxide

The formation and evolution of the prominent and so-called E3 center in ZnO has been studied by in-situ deep level transient spectroscopy measurements after on-line implantation of hydrogen (H) and deuterium (D) ions at sample temperatures of ∼158K and ∼285K. The formation of E3 is shown to involve migration and subsequent trapping of interstitial hydrogen (Hi), or deuterium, and starts to occur already below 200 K. The concentration of implantation-induced E3 centers is rather unstable and decreases gradually at temperatures around 300 K by an annealing process obeying first-order kinetics. The process exhibits an activation energy of ∼0.85eV and involves presumably trapping of migrating Hi's leading to passivation of the E3 centers. A kinetics model is presented showing good agreement with the experimental data and where the E3 center is assumed to be a complex between a Zn vacancy and three hydrogen atoms (H3VZn). Further, the concentration of E3 centers is found to decrease rapidly during annealing in forming gas ambient at room temperature and then to recover gradually during subsequent annealing in vacuum, indicating a defect 'core' of the E3 center able to accommodate more than one H atom.