Optical and electronic properties of magnetron sputtered ZrNx thin films

The optical properties of sputtered ZrNx films with 0.81less than or equal toxless than or equal to1.35 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 x 10(22) cm(-3) to N* = 2.9 x 10(21) cm(-3) as x is increased from 0.81 to 1.29. The charge carrier scattering time increases from 4.9 x 10(-16) to 2.6 x 10(-15) s for 0.81<xless than or equal to0.98, and decreases from 2.6 x 10(-15) to 3.3 x 10(-16) s for 0.98<xless than or equal to1.29. The ZrNx films with x>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 x 10(4) cm(-1) below 2 eV and an optical absorption onset at 2.3 eV. (C) 2003 Elsevier B.V. All rights reserved.