title: Optoelectronic properties of valence-state-controlled amorphous niobium oxide.
abstract: In order to understand the optoelectronic properties of amorphous niobium oxide (a-NbO x ), we have investigated the valence states, local structures, electrical resistivity, and optical absorption of a-NbO x thin films with various oxygen contents. It was found that the valence states of Nb ion in a-NbO x films can be controlled from 5+  to 4+  by reducing oxygen pressure during film deposition at room temperature, together with changing the oxide-ion arrangement around Nb ion from Nb2O5-like to NbO2-like local structure. As a result, a four orders of magnitude reduction in the electrical resistivity of a-NbO x films was observed with decreasing oxygen content, due to the carrier generation caused by the appearance and increase of an oxygen-vacancy-related subgap state working as an electron donor. The tunable optoelectronic properties of a-NbO x films by valence-state-control with oxygen-vacancy formation will be useful for potential flexible optoelectronic device applications.
authors.affiliation: Graduate School of Information Science and Technology, Hokkaido University, N14W19, Kita, Sapporo 060-0814, Japan.
authors.forename: Takaki
authors.initials: T
authors.lastname: Onozato
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Katase
authors.forename: Akira
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Shota
authors.initials: S
authors.lastname: Katayama
authors.forename: Koichi
authors.initials: K
authors.lastname: Matsushima
authors.forename: Naho
authors.initials: N
authors.lastname: Itagaki
authors.forename: Hisao
authors.initials: H
authors.lastname: Yoshida
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Ohta