RF-plasma assisted pulsed laser deposition of nitrogen-doped SrTiO_3 thin films

摘要

Perovskite-type nitrogen substituted SrTiO_3 thin films were deposited with a one-step process by RF-plasma assisted pulsed laser deposition from a SrTiO_3 target using a N_2 plasma, while deposition with a NH3 plasma yields films with almost no incorporated nitrogen. The deposited films exhibit a cubic perovskite-type crystal structure and reveal oriented growth on MgO(100) substrates. The unit cell parameters of the studied N-doped SrTiO_3 films range within 3.905 < a < 3.918 A, which is slightly larger than for SrTiO_3 (a = 3.905 A). The nitrogen content in the deposited films varies from 0.2 to 0.7 atom%. The amount of incorporated nitrogen in the films decreases with increasing RF-power, while the N_2 flow rate does not have any pronounced influence on the N content. Nitrogen incorporation results in an increased optical absorption at 400-600 nm, which is associated with N(2p) energy states that have a higher energy level than the valence band in strontium titanate. The optical band gap energies in the studied N-doped SrTiO_3 films are at 3.2-3.3 eV, which is very similar to that of pure strontium titanate (～3.2 eV). Films deposited with NH3 for the RF-plasma exhibit a lower degree of crystallinity and reveal almost no nitrogen incorporation into the crystal lattice.