Enhancement of Electrical Properties of TiO2−x Oxide Semiconductor by d-Orbital Ordering Using Swift Heavy Ni-Ion Irradiation at Room Temperature
The electrical properties of radiofrequency (RF)-sputtered TiO2−x films have been investigated as a function of Ni-ion irradiation dose at room temperature. The prepared TiO2−x films were irradiated with 130-MeV swift heavy Ni ions in the range from 5 × 1011 ions/cm2 to 1 × 1013 ions/cm2. Increasing the Ni-ion irradiation dose dramatically enhanced the mobility in the TiO2−x films from 2.2 cm2/V s to 1.24 × 102 cm2/V s, while the carrier concentration did not vary. To explain this change in the electrical properties of the TiO2−x films, we investigated various physical properties, namely the physical structure, molecular orbital ordering in the conduction band, and shallow/deep trap states in the band-edge area below the conduction band. We suggest that the improvement in mobility originates from the ordering of the Ti 3d orbital in the conduction band. In addition, increase of the Ni-ion irradiation dose changed two distinct band-edge states below the conduction band.