In situ deposition of MgB2 thin films by magnetron cosputtering and sputtering combined with thermal evaporation

We report on two approaches to the in situ synthesis of superconducting MgB2 thin films. In the first approach, Mg and B were simultaneously sputtered from two separate planar targets. The substrate temperature Ts was limited to a small range of 290-320 °C. The resulting films on sapphire substrates were c-axis textured with low growth quality. Their transition temperature Tc reached a maximum of 24 K with a transition width of 0.6 K. A short-time in situ annealing at 600 °C improved Tc to 28 K. In the second approach, the Mg sputter source was replaced by a specially designed Mg evaporator. Due to this intense Mg source Ts could be increased to 440 °C, and Tc of the “as-grown” films rose to 33 K. Short-time in situ annealing after the film deposition enhanced Tc to 36 K. For these films we also measured a high critical current density of 15 MA/cm2 at 6 K.