Local structure analysis of an optically active center in Er-doped ZnO thin film

Abstract

The local structure of an optically active center in erbium-doped zinc oxide (ZnO:Er) thin film produced by a laser ablation technique and its optical activation process are investigated by Er LIII-edge x-ray absorption fine structure analysis using a synchrotron radiation as an x-ray source. In as-ablated ZnO:Er thin film, Er has an approximately five-fold coordination of O surrounded by eight other O atoms as second-nearest neighbors. The high-order coordination of O decreases the Er-related photoluminescence (PL) intensity due to an undesirable crystal field for 4f radiation transition. After annealing in O2 ambient, the local structure of Er changes to a pseudo-octahedral structure with C4v symmetry, similar to the optically activated Er-doped Si (Si:Er), resulting in strong PL. The bond lengths of Er–O are evaluated, and differences in the optical activation processes between ZnO:Er and Si:Er thin films are discussed.