Tunnel junctions on as-grown superconducting MgB2 thin films

We demonstrate that good superconductor/insulator/normal-metal tunnel junctions can be fabricated on as-grown superconducting MgB2 thin films. The as-grown films were prepared by coevaporation at low growth temperatures of around 280deg. The insulating barrier was formed by an Mg overlayer, which is subsequently oxidized in air. The tunneling spectra for Au/MgOx/MgB2 junctions showed a reproducible and well-defined superconducting gap (delta= ~ 2.5 meV). The resultant 2delta/ kBTc was significantly smaller than the predicted BCS value of 3.52.