[Paper Review] Hyper-doped silicon nanoantennas and metasurfaces for tunable infrared plasmonics

Jean‐Marie Poumirol, Clément Majorel+12 more|arXiv (Cornell University)|Nov 16, 2020

Plasmonic and Surface Plasmon Research43 references20 citations

TL;DR

This paper demonstrates all-silicon plasmonic metasurfaces based on hyper-doped silicon nanodisks (Si-NDs) with tunable localized surface plasmon resonance (LSPR) in the mid-infrared (2–5 μm). By using pulsed laser thermal annealing to achieve carrier concentrations up to 10²¹ cm⁻³ in 100 nm diameter, 23 nm tall Si-NDs, the authors achieve strong infrared absorption and reflectance modulation, with simulations confirming near-field coupling and lattice periodicity effects that enable independent control of absorptance and reflectance.

ABSTRACT

We present the experimental realization of ordered arrays of hyper-doped silicon nanodisks, which exhibit a localized surface plasmon resonance. The plasmon is widely tunable in a spectral window between 2 and 5 $\\mu$m by adjusting the free carrier concentration between 10$^{20}$ and 10$^{21}$ cm$^{-3}$. We show that strong infrared light absorption can be achieved with all-silicon plasmonic metasurfaces employing nano-structures with dimensions as low as 100\\,nm in diameter and 23 nm in height. Our numerical simulations show an excellent agreement with the experimental data and provide physical insights on the impact of the nanostructure shape as well as of near-field effects on the optical properties of the metasurface. Our results open highly promising perspectives for integrated all-silicon-based plasmonic devices for instance for chemical or biological sensing or for thermal imaging.

Motivation & Objective

• To develop all-silicon plasmonic metasurfaces with tunable localized surface plasmon resonance (LSPR) in the mid-infrared (MIR) range.
• To overcome limitations of noble metals and high-index dielectrics in MIR plasmonics by using hyper-doped silicon nanostructures with high free carrier concentration.
• To achieve precise, homogeneous doping of silicon nanodisks via pulsed laser thermal annealing (LTA) for scalable, CMOS-compatible fabrication.
• To experimentally demonstrate strong infrared light absorption and tunable LSPR across 2–5 μm by controlling carrier density in Si-NDs.
• To investigate and quantify near-field coupling and collective effects in dense metasurfaces using numerical simulations and experimental validation.

Proposed method

• Fabrication of silicon nanodisks (Si-NDs) using a top-down approach on silicon-on-insulator (SOI) substrates with a 23 ± 2 nm Si overlayer and 20 nm buried oxide (BOX).
• Implantation of phosphorus (P) at low energy (4 keV) with four increasing doses to tune carrier concentration across 10²⁰–10²¹ cm⁻³.
• Application of pulsed laser thermal annealing (LTA) to achieve hyper-doping beyond solid solubility limits while preserving single-crystalline structure.
• Use of the Green Dyadic Method (GDM) with effective polarizability approximation for truncated cones to simulate optical response of the metasurface.
• Incorporation of near-field coupling effects in simulations by comparing cases with and without dipolar interactions between Si-NDs.
• Lattice periodicity (gap between Si-NDs) systematically varied from 50 nm to 500 nm to study coherent scattering and interference effects on reflectance and absorptance.

Experimental results

Research questions

• RQ1 Can hyper-doped silicon nanodisks support tunable localized surface plasmon resonance (LSPR) in the mid-infrared (2–5 μm) range?
• RQ2 To what extent does pulsed laser thermal annealing enable homogeneous, high-concentration doping in silicon nanostructures without degrading crystallinity?
• RQ3 How do near-field coupling and collective scattering effects influence the reflectance and absorptance of dense Si-ND metasurfaces?
• RQ4 Can lattice periodicity be used as an independent control parameter to tune reflectance while maintaining constant absorptance?
• RQ5 What is the role of 3D nanodisk shape and optical near-field interactions in determining the LSPR response of all-silicon metasurfaces?

Key findings

• The Si-ND metasurface exhibits a tunable LSPR peak across 2.5–5 μm by adjusting free carrier concentration from 10²⁰ to 10²¹ cm⁻³.
• A 10% drop in transmittance is observed at the LSPR frequency, indicating strong infrared light interaction despite the subwavelength size (100 nm diameter) relative to the 2–5 μm wavelength.
• Near-field coupling between Si-NDs increases reflectance by approximately 20% and causes a slight redshift in the resonance peak compared to isolated disks.
• Reflectance per unit area increases by more than 10-fold when the gap between Si-NDs decreases from 500 nm to 50 nm, due to coherent scattering and constructive interference.
• Absorptance per covered area remains nearly constant across different lattice spacings, indicating that near-field coupling primarily enhances reflectance, not absorption.
• Numerical simulations using the Green Dyadic Method (GDM) with effective polarizability show excellent quantitative agreement with experimental reflectance and transmittance spectra.