Pulsed laser deposition and characterisation of perovskite-type LaTiO3−xNx thin films

Abstract LaTiO 3− x N x films with high nitrogen contents ( x ≈ 0.4–0.8) have been grown on (0 0 1)-oriented MgO and LaAlO 3 substrates by pulsed reactive crossed-beam laser ablation from a La 2 Ti 2 O 7 target in a one-step process. These films have a perovskite-type structure, similar to bulk polycrystalline LaTiO 2 N. The nitrogen content in the films can be changed by selecting the nitriding source, i.e. NH 3 or N 2 gas pulse, and by varying the substrate temperature. Films deposited on MgO show a preferential (0 0 1) and (1 1 2) orientation, whereas films on LaAlO 3 are predominantly (0 0 1) oriented. N(2 p ) orbitals contribute to the top of the valence band, leading to a considerable decrease in the band gap energy from ∼4.0 eV for the parent LaTiO 3.5 to ∼2.4–2.9 eV for LaTiO 3− x N x ( x ≈ 0.4–0.8) films. This results in a strong visible light absorption at wavelengths below ∼500 nm. The band gap energies in LaTiO 3− x N x films decrease with increasing nitrogen content. The values of the band gap energies for LaTiO 3− x N x as a function of the N content agree well with other titanate-based perovskite-type oxynitrides, which confirms the proposed band gap model.