Optical properties of metal and semiconductor SmS thin films fabricated by rf/dc dual magnetron sputtering

Optical properties of both metal and semiconductor phases of SmS thin films on Si substrate grown at a room temperature by dual targets (dc for metal Sm and rf for pressed powdered chalcogenide Sm2S3) magnetron sputtering system with the concurrent adjustment of the applied power to respective target, were evaluated by SE at the photon energy range between 0.75 to 5.0 eV. This is the first work performed on the intrinsically prepared metallic sample while the former works done for the sample transformed from semiconductor to metal phase by hard polishing. The followings are concluded: (1) in the metallic film, the refractive indices n have maximum value of 2.20 at 4.10 eV, while extinction coefficient k decreases monotonically and reaches 0.03 at 5.0 eV. The absorption coefficient derived from the obtained k and the complex dielectric constant from n and k agree satisfactorily with those cited in the preceding literatures for the bulk samples; (2) in the case of semiconductor, the refractive indices n have the maximum 3.66 at 3.93 eV, while extinction coefficient k increase monotonically from 0 at 2.31 eV to 1.633 at 5.0 eV. The optical transition mode from valence to conduction band is difficult to determine as either indirect allowed or direct forbidden mode because of the insignificant difference between the linear behavior of the curves a1/2 and that of a2/3 (a: absorption coefficient) as a function of photon energy beyond 3.5 eV. Hence the optical band gap Eg followed by indirect allowed mode and direct forbidden mode is given as 2.67 and 2.78 eV, respectively. The agreement between the derived dielectric constant and those in the preceding literatures for bulk semiconductors is not satisfactory.