Surface plasmon enhanced exciton transitions, cavity resonance effects, and exciton-/polariton-LO phonon interactions in ZnO nanowires

Optical properties of single-subwavelength ZnO nanowires are highly improved by the Al₂O₃ layer/rough Ag film plasmonic structure as a substrate, owing to the exciton-surface plasmon (SP) interactions. The ZnO nanowire luminescence efficiency was enhanced on the Al₂O₃ layer/rough Ag film as compared with the SiO₂/Si substrate. The exciton transitions can be highly enhanced with narrow linewidth and distinguished clearly above 80 K. Typically, three different bound exciton transitions originating from different impurities as trap centers can be identified at 80 K and traced clearly before thermal dissociation. Meanwhile, the strong local electromagnetic field induced by SP can enhance the whispering-gallery-mode (WGM) resonance and the exciton-/exciton-polariton (polariton for short)-longitudinal optical (LO) phonon interaction. The formation of WGM polaritons with energy in the region of first-order LO phonon replica is efficiently promoted by polariton-LO phonon scattering relaxation. These findings provide an effective method for designing novel semiconductor-nanostructure luminescence or lasing devices in future.