Fabrication and characterization of superconducting MgB₂ thin films grown by rf sputtering and thermal evaporation method

We have grown MgB₂ thin films by co-deposition method. Magnesium (Mg) and Boron (B) were simultaneously deposited on the substrates using the radio frequency (rf) sputtering and thermal evaporation. The deposition conditions were varied by changing Mg evaporation rate, B sputtering rate, substrate temperature, deposition time, and types of substrates (c-Al₂O₃, r-Al₂O₃, LaAlO₃, MgO). The MgB₂ layers had 400-500 nm in thickness and occasionally MgB₁₂ was formed as a second phase. Superconducting transition temperatures have been measured around 20-37 K depend on the types of substrates and growth conditions. The relative deposition rate of Mg and B was important to maintain the stoichiometry of MgB₂. The structural features such as second phases, crystal orientation across the interface, and defects in the cross-sectional direction were characterized with XRD, SEM, and EDS.