Raman spectroscopy of Bi-Te thin films

The deposition of micro- and nanocrystalline bismuth telluride thin films with tailored structure and composition is of interest in view of improving the well-known material thermoelectric properties. Only a few works exist that discuss Raman scattering of Bi2Te3 crystals and films, while a Raman characterization of other phases, i.e. other lesser known compounds of the Bi-Te system, such as tsumoite (BiTe) and pilsenite (Bi4Te3), is still completely lacking. We here present a Raman investigation of Bi-Te polycrystalline thin films with controlled structure (stoichiometry and growth orientation), morphology and phase composition, produced by nanosecond pulsed laser deposition. Interpretation of Raman spectra from Bi-Te films was supported by scanning electron microscopy, energy dispersive spectroscopy (EDS) and X-Ray diffraction measurements, together with the predictions of the group theory. In this way, the first Raman characterization of Bi-rich phases (namely BiTe and Bi4Te3) has been obtained. For Bi-Te compositions characterized by a high Bi or Te content, Raman spectra reveal that segregation of elemental Bi or Te occurs.