Spectroscopic Ellipsometry Study of Thermally Evaporated Tin Telluride (SnTe) Thin Films

In this study, SnTe thin films were successfully synthesized through thermal evaporation, and the films were characterized, with a particular emphasis on the use of spectroscopic ellipsometry (SE). The structural properties of the SnTe thin films were investigated by employing grazing incidence x-ray diffraction (GI-XRD), which indicated that the films exhibited polycrystalline growth. The thickness and density of the film were estimated to be approximately 31 nm and 6.24 g/cm(3), respectively, by analyzing the Kiessig fringe pattern obtained from x-ray reflectivity (XRR). Raman spectroscopy revealed the longitudinal optical (LO) and transverse optical (TO) modes, with a small red shift in peak positions due to the quantum confinement effect. A comparative analysis revealed that the Raman modes in the SnTe thin film were red-shifted compared to those in the bulk SnTe powder, which may be attributed to the nanometer size effect. The optical properties, studied in the wavelength range of 300-1000 nm using SE, showed that the film's refractive index (n) decreases while the extinction coefficient (k) first increases and then gradually decreases with increasing photon energy. The spectral signature of the extinction coefficient (k) indicated an increase in photon absorption in the near-infrared (NIR) region. Moreover, the optical conductivity (s(opt)) plot showed an improved optical response in the vicinity of 1.40 eV in the NIR range. The direct transition optical bandgap (E-opt(g)) obtained for the SnTe thin films was 1.20 eV, and this, along with the better optical response, suggests the potential application of the films for NIR detection.