Optical and electronic properties of magnetron sputtered ZrN x thin films

Abstract

The optical properties of sputtered ZrN x 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*=4.9×10 22 cm −3 to N*=2.9×10 21 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< x≤0.98, and decreases from 2.6×10 −15 to 3.3×10 −16 s for 0.98< x≤1.29. The ZrN x films with x>1.3 are poorly crystallized. In this composition range, the compounds exhibit a crystal structure close to orthorhombic Zr 3N 4; they are insulating with optical absorption coefficients in the range of 2×10 4 cm −1 below 2 eV and an optical absorption onset at 2.3 eV.