Polarized Raman spectroscopy on epitaxial barium titanate thin films on silicon

Silicon (Si)-integrated thin barium titanate (BTO) films can be used in the design of CMOS compatible ferroelectric (FE) nano-electronic building blocks for future information technology. Material properties as well as the orientation of the FE domains in the BTO films are key for the functionality of the targeted devices. In addition to assessing material properties like crystal structure, composition and strain, Raman spectroscopy permits to investigate the FE domain orientation in BTO thin films. However, except when using a deep UV laser source, Raman spectra from thin oxides on Si are superimposed by strong Raman scattering from the Si substrate. Here we show, how a proper alignment of sample axis, polarizers and analyzers permits to fully suppress Raman scattering from the Si substrate and enables the recording of polarized Raman spectra from thin BTO films on Si. Raman spectra were collected for 5-20 nm BTO films grown on Si by molecular beam epitaxy under various processing conditions and will be discussed in comparison to the Raman response of a bulk, unstrained and stoichiometric BTO single crystal. The crystal structure and FE domain orientation of the BTO films are investigated and correlated to the information gained from scanning transmission electron microscopy.