Growth of niobium nitride/aluminium nitride trilayers and multilayers

We examine the epitaxial growth of sputtered-deposited NbN/AIN/NbN trilayers on A- and C-plane sapphire and MgO(001), MgO(110) and MgO(111) substrates using transmission electron microscopy. Epitaxial growth is obtained on all the substrates, but columnar growth associated with the presence of more than one variant in at least one of the layers leads to a rough surface on which it is difficult to grow further layers uniformly. We also report the structure of NbN/AIN multilayers grown on silica. In this case the NbN is polycrystalline and untextured, and the AIN is predominantly amorphous. The layer roughness scales with the NbN grain size which is similar to the layer thickness, and it does not significantly increase near the top of the multilayer stacks. The composition profiles along the layer normal as determined by Fresnel contrast analysis and electron-energy-loss imaging are compared.