Room-Temperature Hole Plasmons and Plasmon-Phonon Interactions in Epitaxial p-Type Scandium Nitride

The plasmon resonance represents collective oscillations of free electrons, enabling subwavelength light confinement and local field enhancement in conductive media. While electron-based plasmons in metals and n-type semiconductors have been widely explored, their hole-based counterparts in p-type semiconductors remain largely underexplored due to low hole densities and large effective masses that push plasmon response to the far-infrared with strong damping. Here, we present conclusive experimental evidence of low-loss, room-temperature hole plasmons in the mid-infrared regime, realized in epitaxial p-type scandium nitride thin films. Enabled by a high hole concentration of ∼1.4 × 1020 cm-3 and mobility of ∼21 cm2 V-1 s-1, these hole plasmons exhibit strong confinement with moderate damping. Furthermore, by tuning hole concentrations to spectrally overlap the plasmonic resonance with surface phonon polaritons, we demonstrate a mixed hole-plasmon-LO-phonon interaction giving rise to broadband hybrid absorption response. These results establish robust hole plasmonics in p-type semiconductors for infrared nanophotonic devices.