Correlation between optical and structural properties of nitrogen doped anatase TiO2 thin films

Abstract

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 N2+ 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 N2+ 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.