Evaluation methods and evaporation conditions for low-resistivity contacts on high <i>T</i> <i>c</i> superconductors

Abstract

Low-resistivity contacts to bulk high Tc superconductors have been prepared by resistive evaporation with values of ρs(Ω cm2) as low as 10−10 (77 K) for Ag/YBaCuO, 10−9 (77 K) for Ag/TlPbBaCaCuO, and 10−7 (60 K) for Ag/BiCaSrCuO. ρs has been found to be improved by increasing the length of a preevaporation step. This effect has been further investigated by secondary ion-mass spectrometry analysis on several Ag/Si samples. Both three-terminal and four-terminal methods have been used to determine ρs; the three-terminal method shows less dependency on the sample/contact geometry for measurements taken above Tc.