Phonon Characteristics of Polycrystalline Cubic SrTiO₃ Thin Films

Polycrystalline SrTiO₃ thin films with the cubic perovskite structure were grown on quartz substrates by pulsed laser deposition. The first-order Raman scattering processes, which were forbidden in SrTiO₃ single crystals, were observed in the films at 300 K and lower temperatures due to the structural distortion causing by strain effect and oxygen vacancies. The polar TO₂ phonon showed a typical Fano asymmetry in the entire temperature region from 95 K to 300 K. In contrast, the nonpolar TO₃ phonon and polar TO₄ phonons were mostly symmetric.