Recent progress in pulsed laser deposition of iron based superconductors

Pulsed laser deposition (PLD) is the most commonly used deposition technique for Fe-based superconductor thin films today. The number of grown compounds using PLD is still quite limited to so-called 11 compounds (FeTe_xS_y, FeSe_1−xTe_x) and 122 compounds (primarily Co-and P-substituted BaFe₂As₂). Especially in the growth of Fe-chalcogenides, PLD is challenged by the strong volatility of the elements and their non-negligible vapour pressure. In addition, in situ PLD of the high-temperature superconducting F-doped iron oxypnictides seemed to be feasible only under reactive deposition and stayed disregarded for some time. Here, we summarise the progress that was recently made in the growth of Fe-based superconducting thin films towards an improved control of thin film stoichiometry and the in situ growth of F-doped iron oxypnictides. The presented new ideas deviate from the standard approach of an adjustment of target composition. We first focus on the growth of FeSe_1−xTe_x films, where the introduction of a buffer layer of same composition decreased surface roughness and allowed epitaxial film growth at reduced deposition temperatures with enhanced reproducibility. Second, we illustrate how F-doping in iron oxypnictide thin films can be obtained during in situ PLD using a diffusive reaction between substrate and the growing film.