Synthesis of a Nitrogen-Doped TiO2 (Rutile) Single Crystal and Its p-Type Behaviors

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We have synthesized nitrogen-doped (N-doped) TiO2 (rutile) single crystals by annealing in a 1.0 MPa N2 atmosphere after reduction treatment. Transmittance, electrical resistivity, and sample weight decreased with the reduction treatment, but recovered after the subsequent N-doping process. The N 1s X-ray photoelectron spectroscopy (XPS) signal disappeared after 8 min of Ar sputtering. Diodelike behaviors were observed in the voltage--current ($V$--$I$) characteristics of the TiO2--metal contact for the as-received TiO2 and N-doped TiO2. They demonstrated that the as-received TiO2 is an n-type semiconductor and the N-doped TiO2 is a p-type semiconductor. Photoinduced voltage was measured under irradiation with a Xe lamp. The sign of the photoinduced voltage in the N-doped TiO2 was found to be opposite to that of the as-received or reduced TiO2, which also indicates that the N-doped TiO2 is a p-type semiconductor. We discuss the electronic states of dopant nitrogen atoms.
2011-02-25