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(degree)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 ( (Delta)=~2.5 meV). The resultant 2(Delta)/k/sub B/T/sub c/ was significantly smaller than the predicted BCS value of 3.52.