Tunnel junctions on as-grown superconducting MgB/sub 2/ thin films
We demonstrate that good superconductor/insulator/normal-metal tunnel junctions can be fabricated on as-grown superconducting MgB/sub 2/ thin films. The as-grown films were prepared by coevaporation at low growth temperatures of around 280/spl deg/C. The insulating barrier was formed by an Mg overlayer, which is subsequently oxidized in air. The tunneling spectra for Au/MgO/sub x//MgB/sub 2/ junctions showed a reproducible and well-defined superconducting gap (/spl Delta/=/spl sim/2.5 meV). The resultant 2/spl Delta//k/sub B/T/sub c/ was significantly smaller than the predicted BCS value of 3.52.