Titanium Nitride as a Plasmonic Material from Near-Ultraviolet to Very-Long-Wavelength Infrared Range

Abstract

Titanium nitride is a well-known conductive ceramic material that has recently experienced resumed attention because of its plasmonic properties comparable to metallic gold and silver. Thus, TiN is an attractive alternative for modern and future photonic applications that require compatibility with the Complementary Metal-Oxide-Semiconductor (CMOS) technology or improved resistance to temperatures or radiation. This work demonstrates that polycrystalline TiNx films sputtered on silicon at room temperature can exhibit plasmonic properties continuously from 400 nm up to 30 μm. The films’ composition, expressed as nitrogen to titanium ratio x and determined in the Secondary Ion Mass Spectroscopy (SIMS) experiment to be in the range of 0.84 to 1.21, is essential for optimizing the plasmonic properties. In the visible range, the dielectric function renders the interband optical transitions. For wavelengths longer than 800 nm, the optical properties of TiNx are well described by the Drude model modified by an additional Lorentz term, which has to be included for part of the samples. The ab initio calculations support the experimental results both in the visible and infra-red ranges; particularly, the existence of a very low energy optical transition is predicted. Some other minor features in the dielectric function observed for the longest wavelengths are suspected to be of phonon origin.

Structure-dependent optical properties of Au/Ag irradiated TiN thin films

“…Similar correlation between stoichiometry and magnitude of the real part of the dielectric function of TiN was found in the study of Judek et al in Ref. [64], who investigated the plasmonic properties of nanocrystalline TiN films by changing its thicknesses and stoichiometry. In this sense, the variation in ε r magnitude could be considered as a characteristic of the structural and chemical quality of TiN films [65].…”

Transition Metal Nitrides Are Heating Up the Field of Plasmonics

“…For most nitrides, metal-rich films exhibit higher carrier concentrations (10 21 to 10 22 cm −3 ) 54 and films change from metallic to dielectric as the stoichiometry is varied from metal-rich to nitrogen-rich (Figure 1A). 34,48,55,56 Increasing the metal content has also been shown to result in a shift of the SPR frequency and zero-crossover of the real part of permittivity (i.e., when the permittivity goes from a positive to negative value) to higher energies (Figure 1B). 33,34,55 Incorporation of oxygen can lead to novel optical properties: tunable double zero-crossover (i.e., the real permittivity is equal to zero at two different frequencies) was exhibited in Ti oxynitride films (Figure 1C) and may be useful in the preparation of metasurfaces or generation of nonlinear optical devices.…”

“…34,48,55,56 Increasing the metal content has also been shown to result in a shift of the SPR frequency and zero-crossover of the real part of permittivity (i.e., when the permittivity goes from a positive to negative value) to higher energies (Figure 1B). 33,34,55 Incorporation of oxygen can lead to novel optical properties: tunable double zero-crossover (i.e., the real permittivity is equal to zero at two different frequencies) was exhibited in Ti oxynitride films (Figure 1C) and may be useful in the preparation of metasurfaces or generation of nonlinear optical devices. 57 However, increasing the oxygen content can increase the resistivity of the films and decrease the plasma frequency as the material becomes less metallic.…”

“…Along with the morphological characteristics of the thin films, the stoichiometry (i.e., ratio of metal to nitrogen) and oxygen content have been observed to strongly influence plasmonic performance metrics. For most nitrides, metal-rich films exhibit higher carrier concentrations (10 21 to 10 22 cm –3 ) and films change from metallic to dielectric as the stoichiometry is varied from metal-rich to nitrogen-rich (Figure A). ,,, Increasing the metal content has also been shown to result in a shift of the SPR frequency and zero-crossover of the real part of permittivity (i.e., when the permittivity goes from a positive to negative value) to higher energies (Figure B). ,, Incorporation of oxygen can lead to novel optical properties: tunable double zero-crossover (i.e., the real permittivity is equal to zero at two different frequencies) was exhibited in Ti oxynitride films (Figure C) and may be useful in the preparation of metasurfaces or generation of nonlinear optical devices . However, increasing the oxygen content can increase the resistivity of the films and decrease the plasma frequency as the material becomes less metallic. , Studies performed on ZrN and ZrO x N y films showed that increased oxygen content can result in a large number of interstitial defects and makes the film dielectric; however, incorporation of very low amounts of O can actually lead to a higher carrier concentration and more metallic films than ZrN .…”

“…(B) The relationship between TiN x film composition and the wavelength at which the real part of the dielectric function crosses zero. Panels A and B are reprinted from ref under the terms of the Creative Commons Attribution 4.0 International License (CC BY; ). The axes were modified from the original figure.…”