Influence of Dielectric Anisotropy on the Absorption Properties of Localized Surface Plasmon Resonances Embedded in Si Nanowires

Abstract

We utilize discrete dipole approximation simulations to provide a detailed picture of the scattering behavior of mid-infrared localized surface plasmon resonances (LSPRs) in selectively doped (i.e., i–n++–i) Si nanowires. Our simulations, and their quantitative comparison to recent experimental results, show that the large refractive indices (n ≈ 3–4) of undoped semiconductors in the infrared and the anisotropic dielectric environment inherent in the nanowire geometry strongly enhance/depress absorption by the longitudinal/transverse LSPR. An examination of “cladding” materials other than Si (e.g., GaAs, Ge, etc.) reveals that this behavior scales with refractive index and that absorption enhancements of at least 35× are possible relative to an isotropic vacuum. We also show how scattering and absorption contribute to the overall extinction and extract a value for the carrier density of Si-based resonators synthesized via the vapor–liquid–solid (VLS) mechanism. Our findings establish a framework for rationally engineering LSPR spectral response in semiconductor nanowires and highlight the promise of the VLS technique for this purpose.