Tunable Infrared Plasmonic Properties of Epitaxial TiMgN(001) Layers.

Optical transmission and reflection spectra in combination with ellipsometry and transport measurements on epitaxial rocksalt structure TiMgN(001) layers with 0.00 ≤ ≤ 0.49 are employed to explore their potential as refractory infrared plasmonic materials. A red shift in the reflection edge ℏω from 2.0 to 0.8 eV and the corresponding unscreened plasma energy ℏω from 7.6 to 4.7 eV indicate a linear reduction in the free carrier density with increasing . However, nitrogen vacancies in Mg-rich samples act as donors, resulting in a minimum = 1.6 × 10 cm for = 0.49. Photoelectron valence band spectra confirm the diminishing conduction band density of states and indicate a 0.9 eV decrease in the Fermi level as increases from 0 to 0.49. The dielectric function ε = ε + iε can be divided into a low-energy spectral region where intraband transitions result in large negative and positive ε and ε, respectively, and a higher energy interband transition region with both ε and ε > 0. The screened plasma energy that separates these two regions red-shifts from 2.6 to 1.3 eV for = 0-0.39, indicating a tunable plasmonic activity that extends from the visible to the infrared (470-930 nm). Electron transport measurements indicate a metallic temperature coefficient of resistivity (TCR) for TiN-rich alloys with ≤ 0.26 but weak carrier localization and a negative TCR <60 K for = 0.39 and <300 K for = 0.49, attributed to Mg alloying-induced disorder. The plasmonic quality factor is approximately an order of magnitude larger than what was previously reported for polycrystalline TiMgN, making TiMgN(001) layers competitive with TiScN(001).