Ellipsometric study on rf-plasma oxidized tunnel barriers for In/Pb/Au-alloy Josephson junctions

Abstract
Properties of oxide films formed by rf‐plasma oxidation of In/Pb/Au alloys were ellipsometrically investigated. Two types of changes in oxide properties were found during annealing or long‐term room‐temperature storage for low‐indium‐concentration alloys. One is related to excess oxygen associated with plasma oxidation, and the other is attributed to the conversion of oxide composition from a PbO‐In2O3 mixture into pure In2O3. For high‐indium‐concentration alloys, on the other hand, the oxide was revealed to be very stable because it was almost composed of pure In2O3. From these considerations it was concluded that the more stable Pb‐alloy Josephson junctions were expected with the higher‐indium‐concentration base film, such as more than 30‐wt. % alloys.