Paper NS-WeA11
Localized Surface Plasmon Resonances in Silicon

Wednesday, October 31, 2012, 5:20 pm, Room 12

Localized surface plasmon resonances (LSPRs) in semiconductors offer new opportunities to engineer the interaction of electromagnetic radiation with solid-state materials. Importantly, the carrier density of semiconductors, and thus LSPR frequency, can be modulated via doping and/or electric field. In addition to realizing novel plasmonic devices, the direct integration of plasmonic and excitonic behavior also promises fundamentally distinct functionality. Here, we demonstrate and systematically control LSPRs in nanoscale Si for the first time. More specifically, Si nanowires are synthesized via the vapor-liquid-solid (VLS) technique with a combination of Si₂H₆ and PCl₃ precursors. PCl₃ simultaneously introduces P atoms to the nanowire core and delivers Cl atoms to the sidewall so as to minimize radial dopant incorporation. This chemistry enables growth sufficiently far from equilibrium such that dopant concentrations can exceed thermodynamic limits. Electron microscopy reveals that these nanowires are single crystalline and <111> oriented with very few lattice defects. Polarization dependent in-situ infrared spectroscopy measurements show intense mid-IR absorption bands only for the P-doped nanowires, which we assign to longitudinal LSPRs. A significantly weaker transverse mode is occasionally observed as well. The LSPR frequency can be readily adjusted by varying nanowire length. Mie-Gans theory supports our experimental results and indicates that electrically active dopant concentrations exceed 10²⁰ cm^-3.