| 초록 |
Strontium titanate is a typical perovskite oxide with a wide range of electrical properties upon various doping. Various dopants such as La, Nb, and oxygen vacancies lead to the change from insulator to an n-type semiconductor and finally to a metallic behavior. Among them, the self-doping by oxygen vacancies is essential since the oxygen vacancy is one of the fundamental and intrinsic defects in perovskite oxides and gives a critical impact on their properties, such as magneto-resistance and super conductivity. In our previous study, we report that oxygen vacancies in SrTiO3-δ tend to order in a linear way. Simultaneously, electrical conduction decreases via electron localization. In this study, we verified oxygen vacancy clustering and electron localization in SrTiO3-δ thin films by measuring transport properties and electronic structure. In the result, we found the reduction of the carrier density of annealed SrTiO3-δ thin films at below 400℃. The photoemission spectroscopy (PES) result showed that electrons are localized at defect states in band gap. The defect states are generated by the oxygen vacancy leading to the Ti oxidation state Ti(II). The corresponding electronic configuration of defect state is Ti 3d2, which is good agreement with the localization state in our previous study. This phenomenon is understood by oxygen vacancy clustering and electron localization. |
