  Aluminum, as a metallic material for plasmonics, is of great interest because
it extends the applications of surface plasmon resonance into the ultraviolet
(UV) region and excels noble metals in the natural abundance, cost and
compatibility with modern semiconductor fabrication process. Here, we present
UV to near-infrared (NIR) plasmonic resonance of single-crystalline aluminum
nanoslits and nanoholes. The high-definition nanostructures are fabricated with
focused ion-beam (FIB) milling into an ultrasmooth single-crystalline aluminum
film grown on a semiconducting GaAs substrate with molecular beam epitaxy (MBE)
method. The single-crystalline aluminum film shows improved reflectivity and
reduced two-photon photoluminescence (TPPL) due to the ultrasmooth surface.
Both linear scattering and non-linear TPPL are studied in detail. The nanoslit
arrays show clear Fano-like resonance and the nanoholes are found to support
both photonic modes and localized surface plasmonic resonance. We also found
that TPPL generation is more efficient when the excitation polarization is
parallel rather than perpendicular to the edge of the aluminum film. Such
counter-intuitive phenomenon is attributed to the high refractive index of the
GaAs substrate. We show that the polarization of TPPL from aluminum well
preserves the excitation polarization and is independent of the crystal
orientation of the film or substrate. Our study gains insight into the optical
property of aluminum nanostructures on high-index semiconducting GaAs substrate
and illustrates a practical route to implement plasmonic devices onto
semiconductors for future hybrid nanodevices.
