Molecular Beam Epitaxy Growth of Superconducting Sr1-xKxFe2As2 and Ba1-xKxFe2As2

We report on the molecular beam epitaxy growth of nonsuperconducting SrFe2As2 and BaFe2As2 and superconducting Sr1-xKxFe2As2 and Ba1-xKxFe2As2 thin films. SrFe2As2 and BaFe2As2 films were obtained rather easily at the growth temperatures of 540-600 degrees C, which are not much different from those for GaAs growth. However, superconducting Sr1-xKxFe2As2 and Ba1-xKxFe2As2 films cannot be obtained at the same growth temperatures as elemental K is highly volatile. The key to incorporating K into films is low-temperature growth (<= 350 degrees C) in reduced As flux. The resultant films showed good superconducting properties: T-c(on) (T-c(end)) = 33.2 K (30.0 K) and 38.3 K (35.5 K) for Sr1-xKxFe2As2 and Ba1-xKxFe2As2 thin films respectively. (c) 2010 The Japan Society of Applied Physics