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Regensburg 2000 – scientific programme

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DS: Dünne Schichten

DS 38: Postersitzung

DS 38.4: Poster

Tuesday, March 28, 2000, 09:30–17:30, Poster B

Electrical Conductivity and Current Transport Mechanism in Ion Implanted TiO2-Single Crystals — •R. Fromknecht1, O. Meyer2, I. Khubeis2, S. Massing1, R.C. da Silva3, and E. Alves31Forschungszentrum Karlsruhe, IFP, 76021 Karlsruhe — 2Al-Balqa Appl. Univ., Al-Salt, Jordan — 3Dep. Fisica, ITN-E.N.10, 2685 Sacavem

TiO2 single crystals, implanted at low and elevated temperatures, with 15 different ions using fluences from 1014/cm2 to 1017/cm2 at Ei = 260 keV. Lattice site location, ion range and damage distribution were measured by Rutherford Backscattering Channeling. The electrical conductivity of those samples, measured between 5 and 300 K, with the ion dose, the implantation temperature and the annealing conditions (air, vacuum) as parameter, increased by about 12 orders of magnitude with increasing ion dose. Samples implanted at 300 K and below, their resistivity was thermally activated over the whole temperature region, indicating carrier hopping. The T−1 dependence observed at low doses implies localized defect states. With increasing defect density, states with different energy levels, localized in the gap, are formed and the electron transport is due to variable range hopping (VRH), as indicated by the T−1/4 dependence at high doses. The T−1/2 dependence observed at medium doses, attributed to VRH with a pseudogap near the Fermi energy, due to long range Coulomb interaction between carriers. Samples implanted at high temperatures or annealed in vacuum, showed metallic behaviour between about 30 K and 100 K. Concluded from annealing experiments in air, oxygen vacancies seem to be the main defect causing this behaviour.

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