Relationship between the physical and structural properties of $NbzSiyNx$ thin films deposited by dc reactive magnetron sputtering

The optical and electrical properties of $NbzSiyNx$ thin films deposited by dc reactive magnetron sputtering have been investigated as a function of the Si content $(CSi)$⁠. Optical properties were studied by both specular reflectivity and spectroscopic ellipsometry. Electrical resistivity was measured by the van der Pauw method at room temperature and as a function of the temperature down to $10K$⁠. Both the optical and electrical properties of $NbzSiyNx$ films are closely related with the chemical composition and microstructure evolution caused by Si addition. For $CSi$ up to $4at.%$ the Si atoms are soluble in the lattice of the NbN crystallites. In this compositional regime, the optical and electrical properties show little dependence on the Si content. Between 4 and $7at.%$ the surplus of Si atoms segregates at the grain boundaries, builds an insulating $SiNx$ layer, and originates important modifications in the optical and electrical properties of these films. Further increase of $CSi$ leads to the formation of nanocomposite structures. The electrical properties of these films are well described by the grain-boundary scattering model with low probability for electrons to cross the grain boundary. The appearance of the intragranular-insulating $SiNx$ layer and the reduction of the grain size are noticed in the dielectric function mainly as a strong damping of the plasma oscillation.