Stoichiometric and nonstoichiometric SrTiO3 (STO) films less than 50 nm were grown by molecular beam epitaxy on Si substrates for characterization with UV-Raman spectroscopy. All the films grown have first order phonon Raman scattering as the crystal symmetry has been altered due to threading dislocations and local vicinal strain at defect sites. Strong phonon scattering and hardening of the phonon modes is seen in Ti-rich films while Sr-rich films have a decrease in the phonon scattering intensity when compared with stoichiometric thin films. Excess Ti leads to a high density of planar boundaries and different chemical phases lowering the overall crystal symmetry of STO. The Sr-rich sample compensates for excess Sr by forming SrO Ruddlesden–Popper layers in the perovskite structure. © 2003 American Vacuum Society.