Abstract
The optical and electrical properties of
Nb
z
Si
y
N
x
thin films deposited by dc reactive magnetron sputtering have been investigated as a function of the Si content
(
C
Si
)
. 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
10
K
. Both the optical and electrical properties of
Nb
z
Si
y
N
x
films are closely related with the chemical composition and microstructure evolution caused by Si addition. For
C
Si
up to
4
at.
%
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
7
at.
%
the surplus of Si atoms segregates at the grain boundaries, builds an insulating
Si
N
x
layer, and originates important modifications in the optical and electrical properties of these films. Further increase of
C
Si
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
Si
N
x
layer and the reduction of the grain size are noticed in the dielectric function mainly as a strong damping of the plasma oscillation.