Growth of niobium nitride/aluminium nitride trilayers and multilayers

We examine the epitaxial growth of sputtered-deposited NbN/AlN/NbN trilayer s on A- and C-plane sapphire and MgO(001), MgO(110) and MgO(111) substrates using transmission electron microscopy. Epitaxial growth is obtained on al l 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/AlN multilayers grown on silica. In this case the NbN is p olycrystalline and untextured, and the AlN is predominantly amorphous. The layer roughness scales with the NbN grain size which is similar to the laye r thickness, and it does not significantly increase near the top of the mul tilayer stacks. The composition profiles along the layer normal as determin ed by Fresnel contrast analysis and electron-energy-loss imaging are compar ed.