Correlation between optical and structural properties of nitrogen doped anatase TiO2 thin films
Résumé
Raman spectroscopy, grazing incidence X-ray diffractometer (GIXRD), X-ray photoelectron spectroscopy (XPS),
spectroscopic ellipsometry (SE), atomic force microscopy (AFM) and photoluminescence spectroscopy (PL) were
performed on TiO2 thin films exposed to a nitrogen N+2 ion beam at different temperatures from 45 ◦C to 585 ◦C.
The crystalline structure, the thickness, the dielectric functions, the band gap and the Urbach energies were
studied. The obtained results show a strong change of physical properties of TiO2 after exposing to N+2 ion beam.
Raman modes and diffracted peaks show the anatase structure for all the deposited N-doped films. The presence
of nitrogen doping into the TiO2 layer is confirmed by XPS measurements. The substitutional nitrogen defects
promote a decrease of the band gap for N-doped TiO2 by 150 meV at the doping temperature 585 ◦C. This
reduction was explained by the increase in valence band extremity caused by the hybridization of the N 2p states
and the O 2p states of the valence band of TiO2. The Raman, GIXRD, XPS, SE, AFM, and PL results are consistent
and provide an invaluable complementary information about the nitrogen diffusion within the TiO2 lattice at
different temperatures.