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

Abstract

High quality Nb-based superconductor-insulatorsuperconductor (SIS) junctions with Al oxide (AlOx) tunnel barriers grown from Al overlayers are widely reported in the literature. However, the thin barriers required for high critical current density (Jc) junctions exhibit defects that result in significant subgap leakage current that is detrimental for many applications. High quality, high-Jc junctions can be realized with AlNx barriers, but control of Jc is more difficult than with AlOx. It is therefore of interest to study the growth of thin AlOx barriers with the ultimate goal of achieving high quality, high-Jc AlOx junctions. In this work, 100% O2 and 2% O2 in Ar gas mixtures are used both statically and dynamically to grow AlOx tunnel barriers over a large range of oxygen exposures. In situ ellipsometry is used for the first time to extensively measure AlOx tunnel barrier growth in real time, revealing a number of unexpected patterns. Finally, a set of test junction wafers was fabricated that exhibited the well-known dependence of Jc on oxygen exposure (E) in order to further validate the experimental setup.

Microscopic Origin of Structural Disorder in $δ$-NbN: Correlation of Superconductivity and Electronic Structure

“…Formation of the Ninterstitial defect complex in δ − NbN causes strong smearing of electronic structure by creating atomic disorder in the films and thus a significant reduction in the N(ǫ F ) which strongly influencing the electronphonon coupling strength and consequently reduces the T C . Increase in the T C of vacuum annealed δ − NbN [29][30][31] and degradation of superconducting properties at N 2 atmosphere [32,33] further support our proposed mechanism. Based on above analysis we suggest that to obtain δ − NbN with high T C , films should be grown at Nb-rich conditions to avoid N interstitial defects and annealing of samples in a vacuum is recommended to eliminate residual N atoms.…”

Direct growth of crystalline SiGe nanowires on superconducting NbTiN thin films

“…We also note that there is no temperature range where the Arrhenius plot reveals linear behavior over an extended temperature range, indicating that there is no well-defined activation energy. Interestingly, figure 3 structures, strain, and alloying [18,19,30,31]. Growth of Aucatalyzed SiGe NWs on polycrystalline NbTiN could facilitate the interdiffusion of atoms (e.g.…”