Molecular Beam Epitaxy Growth of Superconducting NdFeAs(O,F) Thin Films Using a F-Getter and a Novel F-Doping Method

NdFeAs(O,F) thin films were grown on MgO substrates by molecular beam epitaxy. The growth parameters were found to be different from those of GaAs substrates of our earlier work, and regulating the amount of fluorine was necessary to grow the target phase. The use of Ga as a getter was very effective for this purpose. We also found that doping fluorine, which had been a key challenge faced in the growth of LnFeAs(O,F) (Ln = lanthanide), is possible by growing a fluoride layer on top of NdFeAsO, resulting in a thin film with a high critical temperature.