Anomalous interface resistance of low temperature sputtered Au/In bilayers

Abstract

Au/In and In/Au bilayers are prepared at T = 86 K by ion beam sputtering and the corresponding electrical resistances are monitored in situ during film growth. For both preparation sequences (gold on a thick indium film and vice versa) an anomalous resistance increase is observed for thin top layers (1.5 nm off gold and 1.1 nm of indium respectively.) For larger thickness d, the expected 1/d behaviour is found. The above resistance increase can be consistently described by the formation of a thin amorphous interface layer of the nominal composition AuIn2 in the case of gold on top of indium and AuIn in the case of indium on top of gold. Heat treatments of In/Au multilayers (layer thicknesses dIn = 8.4 nm and dAu= 2.7 nm) prepared at 86 K lead to an interdiffusion starting at approximately 170 K and the formation of the crystalline AuIn2 phase. A thermally driven amorphization of In/Au multilayers (with modulation lengths above 6 nm) can definitely be excluded.