title: Observation of strongly enhanced photoluminescence from inverted cone-shaped silicon nanostructures. [corrected].
abstract: Silicon nanowires (SiNWs) attached to a wafer substrate are converted to inversely tapered silicon nanocones (SiNCs). After excitation with visible light, individual SiNCs show a 200-fold enhanced integral band-to-band luminescence as compared to a straight SiNW reference. Furthermore, the reverse taper is responsible for multifold emission peaks in addition to the relatively broad near-infrared (NIR) luminescence spectrum. A thorough numerical mode analysis reveals that unlike a SiNW the inverted SiNC sustains a multitude of leaky whispering gallery modes. The modes are unique to this geometry and they are characterized by a relatively high quality factor (Q ~ 1300) and a low mode volume (0.2 < (λ/n eff)(3) < 4). In addition they show a vertical out coupling of the optically excited NIR luminescence with a numerical aperture as low as 0.22. Estimated Purcell factors Fp ∝ Q/Vm of these modes can explain the enhanced luminescence in individual emission peaks as compared to the SiNW reference. Investigating the relation between the SiNC geometry and the mode formation leads to simple design rules that permit to control the number and wavelength of the hosted modes and therefore the luminescent emission peaks.
authors.affiliation: Max Planck Institute for the Science of Light, Photonic Nanostructures, Günther-Scharowsky-Str. 1, 91058 Erlangen/Germany Helmholtz-Zentrum Berlin für Materialien und Energie, Institute Nanoarchitectures for Energy Conversion, Hahn-Meitner-Platz 1, 14109 Berlin/Germany.
authors.forename: Sebastian W
authors.initials: SW
authors.lastname: Schmitt
authors.affiliation: Max Planck Institute for the Science of Light, Photonic Nanostructures, Günther-Scharowsky-Str. 1, 91058 Erlangen/Germany Helmholtz-Zentrum Berlin für Materialien und Energie, Institute Nanoarchitectures for Energy Conversion, Hahn-Meitner-Platz 1, 14109 Berlin/Germany.
authors.forename: George
authors.initials: G
authors.lastname: Sarau
authors.affiliation: Max Planck Institute for the Science of Light, Photonic Nanostructures, Günther-Scharowsky-Str. 1, 91058 Erlangen/Germany Helmholtz-Zentrum Berlin für Materialien und Energie, Institute Nanoarchitectures for Energy Conversion, Hahn-Meitner-Platz 1, 14109 Berlin/Germany.
authors.forename: Silke
authors.initials: S
authors.lastname: Christiansen