抄録
We study nitrogen-doping effects on the energetics and electronic properties of titanium dioxide (TiO2) at high doping concentrations using the first-principles electronic-structure study. From the defect formation energies obtained, it is confirmed that nitrogen atoms should tend to be clustered in the heavily-doped system. This clustering should occur because dopants share the surrounding distorted region and then the lattice-distortion energy per dopant become smaller if dopants are located at shorter distances. We also find that the impurity-induced states seem to be sufficiently hybridized with the original valence band in all the cases studied. The system would show the photoabsorption spectrum expanding to the longer-wavelength region down to around 620 nm in rutile and 730 nm in anatase if nitrogen atoms are sufficiently doped.
