Optical reactivity of epitaxially grown nitrogen-doped titanium oxide (TiO2) films

Abstract

We investigated the optical-response properties of nitrogen(N)-doped titanium dioxide (TiO2) film by using a ultraviolet-visible absorption spectra. The TiO2 films were epitaxially grown on the sapphire substrate by using pulsed laser deposition (PLD) with and without oxygen gas introduction into the deposition chamber. The doping of N atoms was done by using 70-keV of N+ ion implantation, followed by post-irradiation heat treatment at 550 degrees C for 2 hrs. Our experiment shows not only that N-ion doping causes the absorption edge of the epitaxially grown TiO2 film to be quite reproducibly shifted to lower energy by about 0.07 (0.09) eV when 5 x 10(16)(l X 10(17)) N ions/cm(2) are implanted, but also that a significant optical absorption extends into the visible-light region. The redshift of the oxygen deficient TiO2 film prepared in the absence of oxygen was about 0.23 eV, and N ion implantation into this under-stoichiometric film at 70 keV and an ion dose of I X 10(17) ions/cm(2) resulted in an additional band-edge shift.