Optical Properties of Nitrogen-Substituted Strontium Titanate Thin Films Prepared by Pulsed Laser Deposition

Perovskite-type N‑substituted SrTiO(3) thin films with a preferential (001) orientation were grown by pulsed laser deposition on (001)-oriented MgO and LaAlO(3) substrates. Application of N(2) or ammonia using a synchronized reactive gas pulse produces SrTiO(3-x):N(x) films with a nitrogen content of up to 4.1 at.% if prepared with the NH(3) gas pulse at a substrate temperature of 720 °C. Incorporating nitrogen in SrTiO(3) results in an optical absorption at 370‑460 nm associated with localized N(2p) orbitals. The estimated energy of these levels is ≈2.7 eV below the conduction band. In addition, the optical absorption increases gradually with increasing nitrogen content.