Optical and electronic properties of magnetron sputtered ZrNx thin films

The optical properties of sputtered ZrNx films with 0.81≤x≤1.35 have been investigated and interpreted in terms of stoichiometry-related defects and crystal structure. The optical properties were determined by optical reflectivity, transmission and spectroscopic ellipsometry. As x increases from 0.81 to 1.35, the optical properties continuously change from metallic to semiconducting behavior. The experimental results have been fitted with a model dielectric function based on a set of Drude–Lorentz oscillators in order to separate the contributions due to free carriers and interband transitions. The effective density N* of conduction electrons decreases from N*=4.9×1022 cm−3 to N*=2.9×1021 cm−3 as x is increased from 0.81 to 1.29. The charge carrier scattering time increases from 4.9×10−16 to 2.6×10−15 s for 0.81 1.3 are poorly crystallized. In this composition range, the compounds exhibit a crystal structure close to orthorhombic Zr3N4; they are insulating with optical absorption coefficients in the range of 2×104 cm−1 below 2 eV and an optical absorption onset at 2.3 eV.