Semiconductor-like behavior in superconducting Nb Al films

We report here the experimental evidence of semiconductor-superconductor transitions in relatively thick Nb/Al structures. The temperature dependence of resistivity rho(T) shows a sharp superconducting transition followed by either a normal metallic behavior in low-resistivity samples, or a semiconducting behavior when the sample resistivity at 10 K is above 100 mu Omega cm. We discuss here the fabrication conditions and the electron localization regime associated with the measured rho(T) dependence.