Polaritonic Nitrides for Near-UV-to-Far-Infrared Nanophotonics

Polaritons, the hybrid quasiparticles of photons and electric dipoles (plasmons, polar phonon modes, excitons, etc.), have attracted significant interest in numerous nano-photonic applications. Due to their sub-diffraction mode confinement and field enhancement, plasmon- and phonon-polaritons are researched extensively to overcome the fundamental resistance-capacitance delay in electronics and the diffraction limit in photonic devices. However, applications of polaritons in practical devices are limited primarily due to the significant optical losses arising from the scattering of the free electrons and optical phonon modes. Therefore, materials exhibiting low-loss and high-quality plasmon and phonon-polaritons in the ultraviolet (UV)-visible and infrared (IR) spectral range are in great demand. Titanium nitride (TiN), an archetypal refractory transition metal nitride, has been studied extensively as an alternative plasmonic material to gold for visible spectral range applications. However, as the epsilon-near-zero wavelength of TiN cannot be varied readily, there is a pressing demand to develop new polaritonic materials that lead to strong light-matter interactions in near-UV to far-IR spectral range.<br/><br/>In this talk, we will present low-loss and high-quality plasmon and phonon-polariton resonances in epitaxial transition metal nitrides and group III-nitride semiconductors spanning from the near-UV to far-IR spectral ranges. Epitaxial hafnium nitride (HfN) heterostructures are developed as an alternative plasmonic material to silver for near-UV applications, such as solar mirrors. Similarly, with tuneable carrier concentration, polar semiconducting scandium nitride (ScN) thin films are designed to exhibit IR plasmon-polaritons with low optical loss and high propagation lengths. Polar phonon modes of ScN and gallium nitride (GaN) are further utilized to achieve surface phonon-polaritons and Reststrahlen band nanophotonics. Additionally, the optical properties of the nitride heterostructures are tuned by accessing their transdimensional regime, designing hyperbolic metamaterials, Ferrell-Berreman mode engineering, and activating surface-polaritons with nanostructure formation. Our recent findings also show an electron confinement-induced plasmonic breakdown in epitaxial ultrathin nitride metals that originate due to the strong Coulomb interaction among electrons. Our work elucidates that nitride thin films and heterostructures are excellent hosts for polaritonic resonances for a wide array of near-UV to far-IR spectral range applications.<br/><br/><br/>References:<br/><br/>1. K. C. Maurya, D. Rao, S. Acharya, P. Rao, A. I. K. Pillai, S. K. Selvaraja, M. Garbrecht and B. Saha, <b><i>Nano Letters, 22, 13, 5182-5190 (2022).</i></b><br/>2. K. C. Maurya, A. Chatterjee, S. M. Shivaprasad and B. Saha, <b><i>Nano Letters, 22, 23, 9606–9613 (2022).</i></b><br/>3. P. Das, B. Biswas K. C. Maurya, M. Garbrecht and B. Saha, <b><i>ACS Appl. Mater. Interfaces, 14, 41, 46708-46715(2022).</i></b><br/>4. P. Das, S. Rudra, D. Rao, S. Banerjee, A. I. K. Pillai, M. Garbrecht, A. Boltasseva, I. V. Bondarev, V. M. Shalaev and B. Saha, “Electron Confinement-Induced Plasmonic Breakdown in Metals”, <b><i>arXiv: 2406.03226 (2024)</i></b>