Deposition of high Tc Nb-(Ge,Si) films at substrate temperature below 400°C by magnetron sputtering

Deposition of Si substituted A15 Nb-(Ge,Si) films has been attempted by using a magnetron sputtering apparatus. The dependence of crystal structure and superconducting critical temperature Tc of these films on sputtering conditions and film composition has been investigated. The authors have succeeded in depositing the single phase A15 Nb3(Ge,Si) films which show a small lattice constant about 5.11 Å and high Tc of 23.1K on fused silica substrate. The films with Tc above 20 K are obtained in the following region: Si substitution ratio about 0.12, (Ge+Si) content from 23 to 27 at.% and substrate temperature is much wider and 200 K lower than that for high Tc Nb3Ge binary compound. Besides, in these films, Tc does not depend on film thickness significantly and the films less than 1000 Å thick have Tc above 20 K.