Examination of the Properties of Superconducting Nb–Ge Films Prepared by DC Magnetron Sputtering

The superconductivity and film structure of A15 Nb–Ge were extensively examined through film preparation utilizing the characteristic features of dc magnetron sputtering. T co 22.9 K and Δ T c 0.5 K films of 2400 Å thickness were obtained. Films of T co>22 K and Δ T c<1 K could be prepared with good reproducibility. As a result of Auger analysis, it was concluded that impurities, especially oxygen, were unnecessary for metastable high-T c Nb3Ge phase growth. Impurity oxygen was concentrated into a depositing film from surface impurity-rich layer and tended to make a hexagonal Nb5Ge3 phase formed. In order to control this and to attain high-T c, film fabrication with a high deposition rate over short sputtering time was effective. A high-T c Nb3Ge phase grew on a base layer 1000–1500 Å thick. The layer was found to contain no impurities and rather to be rich in anti-site defects.