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

Perovskite-type N-substituted SrTiO3 thin films with a preferential (001) orientation were grown by pulsed laser deposition on (001)-oriented MgO and LaAlO3 substrates. Application of N-2 or ammonia using a synchronized reactive gas pulse produces SrTiO3-x:N-x films with a nitrogen content of up to 4.1 at.% if prepared with the NH3 gas pulse at a substrate temperature of 720 degrees C. Incorporating nitrogen in SrTiO3 results in an optical absorption at 370-460 nm associated with localized N(2p) orbitals. The estimated energy of these levels is approximate to 2.7 eV below the conduction band. In addition, the optical absorption increases gradually with increasing nitrogen content.