Enhanced native acceptor-related blue emission of ZnO thin films annealed in an oxygen ambient

The thermodynamic behaviors of charged point defects in unintentionally-doped ZnO thin films were investigated. The as-grown sample displayed two different types of blue-emission bands: one at ∼2.95 eV from native-donor zinc interstitial (Zni) and the other at ∼3.17 eV from native acceptor zinc vacancies (VZn). In the samples annealed at oxygen ambience, VZn-related emission was dramatically enhanced, and Zni-related emission was drastically reduced. The behavior was observed to become more apparent when the annealing temperature was increased. The results can be explained by both the increased generation probability and the lowered formation enthalpy of VZn in an oxygen-rich environment, particularly at higher temperatures.