Preparation and Photosensitivity of Samarium Sulfide Thin Films

Abstract

Metallic SmS and Sm₃S₄ thin films, in which Sm ions possess divalent and trivalent mixed state, were prepared on Si wafer substrate at 20°C using Sm₂S₃ and Sm₂S₃/Sm mixed targets by rf magnetron sputtering. Even though only Sm₃S₄ phase was formed using a Sm₂S₃ target, both metallic SmS and Sm₃S₄ films were deposited using Sm₂S₃/Sm mixed targets depending on substrate positions. The possible formation processes of metallic SmS and Sm₃S₄ thin films were proposed. Irradiation experiments were performed using a femtosecond laser at 800 nm with a pulse duration of 120 fs and a repetition rate of 10 Hz. No macroscopic changes were observed in Sm₃S₄ thin films at a fluence <1.2×10⁴ J•m^-2 and the film ablation occurred over 1.2×10⁴ J•m^-2. On the other hand, in the case of metallic SmS films, with the fluence of 5.0×10³ J•m^-2, the metallic to semiconductor phase transition occurred, and the film ablation occurred when the fluence was over 7.0×10³ J•m^-2. X-ray photoelectron spectroscopy study revealed that Sm²⁺ (4f) peak near the Fermi energy was shifted about 0.3 eV in the irradiated metallic SmS film. The change in the electronic structure change of Sm for the films was discussed.