Reactively sputtered V3Si and Nb3Ge films

We have investigated the reactive sputtering of V-Si and Nb-Ge films in a dc diode and in a magnetron sputtering system toward the possible use of such films in high (
\simg 10K
) operating temperature Josephson devices. Large differences in the dependence of T
c
on deposition temperature and on average film composition were found. Above 700°C maximum T
c
's of 16.8K in V
3
Si and 21K in Nb
3
Ge were obtained in the dc diode sputtered films. Below this temperature T
c
's degraded, however at 500 °C values of close to 12K were still found in both sets of films. Transmission electron microscopy studies indicate that a growth mechanism operates during both sputtering processes which can produce adjacent grains which have greatly different compositions. As a result, high T
c
's in both Nb-Ge and V-Si can be obtained in films which have average compositions very far removed from ideal 3/1 stoichiometry.