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

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 approximate to 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 35X 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.