Study of Seed Layer Growth for Superconducting Fe(Se,Te) Film Deposition

Among Iron-Based Superconductors (IBS), the development of superconducting films of FeSe
_1−x
Te
_x
[Fe(Se,Te)] is looked at with increasing interest due to the high performance in high magnetic fields and low temperatures. In this work, we report on the optimization of the deposition conditions of Fe(Se,Te) films grown on single-crystal CaF
₂
substrates by pulsed laser deposition (PLD) technique. The deposition of a Fe(Se,Te) bilayer is exploited to control the stoichiometry and the epitaxy simultaneously. The Fe(Se,Te) top layer is deposited at a temperature as low as 250 °C, using a film of the same material deposited at a higher temperature as a seed layer. The seed layer's structural properties and morphology have been studied by varying the deposition temperature between 350 and 470 °C. Seed layers with sharp out-of-plane orientation and smooth surfaces have been obtained at deposition temperatures of about 400 °C. Fe(Se,Te) bilayer (top +seed layer) shows enhanced superconducting properties compared to single-layer films, with a zero-resistance critical temperature of about 19 K and a critical current density above 0.1 MAcm
⁻²
up to 9 T and 4.2 K. These results demonstrate the importance of the fine control of micro-structural and morphological properties of the seed layer to unlock high-performance Fe(Se,Te) films.