Ion-beam-assisted deposition of textured NbN thin films

Abstract

Ion-beam-assisted deposition (IBAD) offers the opportunity to prepare thin textured films on non-textured substrates. The approach was used to study if superconducting NbN can be textured in this way. Therefore, a reactive process using pulsed laser deposition of pure Nb in combination with a nitrogen-containing ion beam was utilized for the preparation of textured NbN on amorphous seed layers. It is shown that NbN reveals a textured nucleation similar to IBAD-MgO or IBAD-TiN. The biaxial texture was stabilized in thicker layers using homoepitaxial growth leading to highly textured NbN layers with an in-plane alignment below 5°. The dependence of the lattice parameter as well as of the superconducting transition temperature Tc on the deposition conditions, such as, for example, the N2 partial pressure during the homoepitaxial growth, was studied in detail. A clear correlation between structural and superconducting properties was found for the deposited NbN thin films. As a result, highly textured NbN layers were prepared showing a Tc up to 14 K.