Effects of Te- and Fe-doping on the superconducting properties in Fe(y)Se(1−)(x)Te(x) thin films

High quality Fe(y)Se(1−x)Te(x) epitaxial thin films have been fabricated on TiO(2)-buffered SrTiO(3) substrates by pulsed laser deposition technology. There is a significant composition deviation between the nominal target and the thin film. Te doping can affect the Se/Te ratio and Fe content in chemical composition. The superconducting transition temperature T(c) is closely related to the chemical composition. Fe vacancies are beneficial for the Fe(y)Se(1−x)Te(x) films to exhibit the higher T(c). A 3D phase diagram is given that the optimize range is x = 0.13–0.15 and y = 0.73–0.78 for Fe(y)Se(1−x)Te(x) films. The anisotropic, effective pining energy, and critical current density for the Fe(0.72)Se(0.94)Te(0.06), Fe(0.76)Se(0.87)Te(0.13) and Fe(0.91)Se(0.77)Te(0.23) films were studied in detail. The scanning transmission electron microscopy images display a regular atomic arrangement at the interfacial structure.