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 Sm2S3) 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 Sm2+ 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 2.67 eV obtained by Tauc plot from SE results.