Temperature-dependent infrared dielectric function and localized surface phonon polaritons in polar AlN

Aluminum nitride (AlN)-based optoelectronics have demonstrated great promises in application scenarios such as waveguides, beam splitters, directional couplers and interferometers. Yet, existing studies primarily focus on its photonic applications in the UV-Vis spectrum, with limited exploration in the mid and long IR spectrum. With its strong polarity, AlN can host the surface phonon polaritons (SPhPs) and modulate radiative properties via inducing localized resonances in metasurface. Herein, we fully investigate propagating and localized SPhPs and infrared radiative properties of AlN nanoresonators by combining spectroscopic ellipsometry measurements and multiscale simulations, and further explore their dependence on temperature and structural morphology. Elevated temperatures enhance anharmonic phonon scattering of AlN, thus weakening their ability to support SPhPs. The absorption spectra of anisotropic AlN nanoresonators are dominated by two peaks, with the height playing a key role in tuning them due to the effect on the polaritonic field disturbance. This work provides physical insights into temperature-induced spectral tuning of AlN nanoresonators and facilitates the development of photonics applications under high-temperature conditions.