Transformation of the semi-transparent into the metallic phase of zirconium nitride compounds by implantation at controlled temperature: the evolution of the optical properties

Abstract

Zirconium nitrides reveal interesting optical and electrical properties, which strongly depend on the nitrogen stoichiometry. When preparing these compounds using dual-ion-beam sputtering, very contrasting optical film properties can be obtained: a stable ZrN metallic phase with gold-like colour and a Zr3N4 metastable phase with an insulating semi-transparent behaviour. In this paper, optical properties (complex index of refraction and colorimetric data) of these two zirconium nitride phases are presented. A colorimetric comparison between the colour of gold and that of ZrN is also reported. The Zr3N4 phase is thermodynamically unstable: this metastable character permits us to foresee a transition to the stable phase ZrN {on providing an} energy supply. Compared with other ways of providing energy, ion implantation is well suited because of its directional aspect. This work deals with the optical property evolution of Zr3N4 phase irradiated at 600 °C by 340 keV Ar2+ ions with different fluences. Ellipsometric measurements reveal a gradual evolution of the optical properties, starting from an insulating behaviour (Zr3N4 sample) and ending with a conductor-like behaviour. It is shown that a fluence of 5×1016 ions cm-2 is sufficient to transform the semi-transparent Zr3N4 film into metallic film. A study of the electrical properties of the most highly implanted samples and of ZrN films is also reported.