Electrical conductivity in ion implanted TiO2-single crystals

Single crystals of TiO₂ (rutile) were implanted at room temperature with W- and Xe-ions applying a fluence of 10¹⁴/cm ² to 10¹⁶/cm² at 150 keV. The lattice site location together with ion range and damage distribution was measured with Rutherford backscattering and channeling (RBS-C). The electrical conductivity was measured as a function of the implanted ion fluence as well as a function of the temperature. The electrical conductivity of the implanted sample increased by about 12 orders of magnitude. A maximum value for the electrical conductivity of σ=120 Ω(-1) cm^-1 was reached for the amorphized TiO₂ single crystal at an implantation dose of 6.8×10 ¹⁶/cm². From the temperature dependence of the electrical conductivity as well as from its similar behaviour for noble-gas ions it is concluded that the carrier transport of our sample occurs by single defect state excitation at low doses and by variable-range hopping between localized defect states at high defect density. The hopping process does not seem to depend strongly on the oxidation state and on the electron charge distribution of the implanted ions