Solid Phase Epitaxial Growth of Fe(Te, S) Thin Films and Their Superconducting Properties

We have studied a fabrication of Fe(Te, S) epitaxial thin films by means of second harmonic Nd:YAG pulsed laser deposition method on various substrates. However, these films had off-stoichiometric composition because of re-evaporations of Te and S. In order to prevent the re-evaporations, we developed a face-to-face solid phase epitaxy (SPE) for the fabrication of Fe(Te, S) epitaxial thin films. In the face-to-face SPE method, amorphous Fe(Te, S) films were fabricated by the second harmonic Nd:YAG pulsed laser deposition method at room temperature. The surface of an amorphous film was covered by that of another film and the sample was sandwiched by two stainless plates and uniformly fixed. Then, the sandwiched sample was heat-treated in Ar gas flow. As a result, the face-to-face SPE method enabled to maintain the stoichiometric composition and to obtain Fe(Te, S) epitaxial films with good crystallinity. Maximum zero resistance temperature and critical current density at 2 K were 8.0 K and 6600 A/cm², respectively. Certain precipitates grown at the grain boundaries might lower the superconducting properties of our films. Although the superconducting properties are not sufficient, the face-to-face SPE method is an easy way to obtain the stoichiometric epitaxial films of 11-type superconductors.