Properties of tunneling junctions on the superconducting transition metals Nb, Ta, and V

Well-developed phonon-structures are observed on Ta/Ta-Oxid/Ag and Nb/Nb-Oxid/Ag tunneling junctions, if the conditions of oxidation are suitably choosen. These structures are analyzed according to McMillan's numerical program and the results are discussed. From the nonlinear current-voltage characteristics in the normal state, informations are obtained on the electronic structure of the semiconducting oxid presenting the barrier. Impurity concentration leading to a nonideal semiconductor gap in the oxid, seems to be largely reduced if oxidation is performed with low oxygen pressure. (orig.)