Optical Spectroscopic Study of AlN-Based SIS Devices Grown by Inductively Coupled Plasma

High-quality Nb-based superconductor-insulator-superconductor (SIS) junctions with aluminum oxide tunnel barriers grown from Al overlayers are broadly reported in the literature. However, as the current density increases, aluminum oxide tunnel barriers yield significant leakage current due to the pinholes and defects in the tunnel barrier. In this work, the growth dynamics of AlN are studied through the inductively coupled plasma (ICP) nitridation of an Al overlayer at an increased sample-to-ICP distance with the modification of the University of Virginia (UVA) trilayer deposition system. The new ICP geometry follows the previous UVA optical spectroscopy investigation of the plasma at the wafer, but now, it also allows spectroscopy measurement in the vicinity of the ICP source via an additional quartz window. We report a significantly slower nitridation growth rate, while maintaining the relative dissociation, at a larger growth distance. High-quality, low leakage SIS I(V) characteristics with current densities exceeding 30 kA/cm
²
and better control of R
_n
A are obtained.