In situ spectroscopic ellipsometry of SIS barrier formation

First reported by our research group in 2007, AlN tunnel barriers grown by ICP nitridation of thin Al overlayers offer a promising alternative to Al oxide barriers for high current density SIS junctions used in quantum limited THz heterodyne receivers [1]. However, the growth rate of AlN is heavily dependent on ICP operating conditions and as new uncharacterized nitridation processes are investigated, knowledge of the barrier thickness is integral to realizing SIS junctions of desired current density, which is exponentially dependent upon barrier thickness. An in situ method for real time monitoring of ICP AlN growth on thin Al overlayers through the use of spectroscopic ellipsometry and a correlation of the determined AlN thickness to the normal resistance area product (R_NA) of the resulting trilayer is reported.