Influence of substrates and buffer layers on the quality of NbN ultra thin film for THz HEB

In order to improve the crystalline quality of NbN ultra thin film for THz HEB applications, several buffer layers have been selected and investigated. The influence of the buffer layers on thermal boundary resistance of membrane-type Hot Electron Bolometer (HEB) devices and on their IF bandwidth is discussed. The influence of substrates and buffer layers on the quality of NbN ultra thin film has been studied by performing Atomic Force Microscopy (AFM) and low reflectometry measurements on NbN films on different substrates (3 μm SOI substrate and MgO buffered 3 μm SOI substrate). In particular, the physical properties (roughness and thickness) of NbN film layers have been carefully measured.