Properties and local environment of p-type and photoluminescent rare earths implanted into ZnO single crystals

This thesis presents an experimental study of the local environment of p-type and Rare- Earth dopants implanted in ZnO single-crystals (SCs). Various nuclear and bulk property techniques were combined in the following evaluations: Implantation damage annealing was evaluated in ZnO SCs implanted with Fe, Sr and Ca. P-type dopants Cu and Ag implanted ZnO SCs were studied revealing that the solubility of Cu in substituting Zn is considerably higher than that of Ag. These results are discussed within the scope of the ZnO p-type doping problematic with these elements. Experimental proofs of the As “anti-site” behavior in ZnO were for the first time attained, i.e., the majority of As atoms are substitutional at the Zn site (SZn), possibly surrounded by two Zn vacancies (VZn). This reinforces the theoretical prediction that As acts as an acceptor in ZnO via the AsZn-2VZn complex formation. The co-doping of ZnO SC with In (donor) and As (acceptor) was addressed. The most striking result is the possible In-As “pair” formation. Two configurations are proposed for this “pair”, both with In and As at SZn. A purely In-related defect is also identified. These are preliminary experiments that can serve as guidelines for future and deeper studies. Rare-earths (RE) RE lattice site location, RE surface segregation and optical activation were investigated in Er and Tm implanted ZnO SCs, as a function of annealing temperature, implantation doses and implantation conditions. RE surface segregation and lattice recovery occur for high annealing temperatures, being more pronounced in the low dose implanted crystals. The RE-O clusters formation is suggested for the higher dose implanted samples. Er and Tm optical activation occurs at different annealing temperatures depending on the implantation doses, suggesting that the RE-related emission is associated with defects/impurities in the RE close vicinity that change with the annealings