NbN ultra-thin films for HEB-based THz systems

Abstract

The key technology for low-noise THz receivers operating above 1 THz, lies inevitably in the employment niobium nitride superconductors with critical bulk temperature of 16-17K. The enhancement of HEB’s limited IF bandwidth has been a relevant topic for two decades and is associated with the quality, hence critical temperature, Tc, of the 3.5-6nm thin NbN films. This thesis revisits the concept of employing buffer-layers which have not been utilized yet to deposit NbN onto. As a result, state-of-the-art 5.5nm thin NbN films have been successfully deposited exhibiting Tc as high as 13.2K and RRR-figure-of-merit close to unity. These films show considerable potential for highly-integrated THz electronics.