Ultraviolet Raman spectroscopy characterization of epitaxial SrTiO₃ films grown with substrate temperature gradient

Low temperature ultraviolet Raman spectroscopy was applied to characterize SrTiO₃ films grown by absorption-controlled molecular beam epitaxy at very high substrate temperatures. CO₂ laser substrate heating was utilized to grow the films on the LaAlO₃ substrates with temperature gradient during the growth, 1370–1530°C within the same substrate. Bulk SrTiO₃ has a a cubic perovskite structure with all phonon modes being symmetry forbidden in the 1^st order Raman spectra. Therefore, the defect-induced activation of the Raman peaks can be used to characterize the structural quality of the films. Normalized Raman intensity ratio of the 1^st order SrTiO₃ phonon peaks to the substrate features has been used to study the effect of the growth temperature on the crystalline quality of the films and compared with other structural characterization data (reflection high energy electron diffraction, atomic force microscopy).