Fabrication and characterization of metal and semiconductor SmS thin films by rf/dc dual magnetron sputtering

SmS thin films have been individually fabricated on either a-SiO/Si or NaCl substrates at a room temperature by dual targets (dc for metal Sm and rf for pressed powdered chalcogenide Sm ₂ S ₃ ) magnetron sputtering of concurrent power control. The fabricated films were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE), respectively, to identify phase formation, structure, and optical band gap. The followings are summarized: (1) polycrystalline metal, intermedium, or semiconductor SmS thin films were identified by XRD, TEM and the phase formation was achieved by controlling the ratio of dc to rf power; (2) the obtained lattice constant of intermedium phase was 5.85 Å from electron diffraction (ED) and 5.91 Å from lattice image. The former value is contraction by 2% compared with bulk semiconductor (5.97 Å), while the later one is contraction by 1% compared with semiconducting one, although this being probably semiconductor which is suggested by the dominated Sm ²⁺ valence state in Sm 3d of XPS; (3) XPS depth profile result confirm that metal Sm and samarium oxide exist near the film-substrate boundary in intermedium case, while stoichiometric SmS is dominant at the surface layer; (4) in semiconductor case, optical band gap is 2.67eV obtained by Tauc plot from SE results.