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6CCVD Research

Numerical Study of an Ultra-Broadband All-Silicon Terahertz Absorber

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2020-01-07
JournalApplied Sciences
AuthorsJinfeng Wang, Tingting Lang, Tingting Shen, Changyu Shen, Zhi Hong
InstitutionsChina Jiliang University
Citations30
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This analysis focuses on a numerical study proposing an ultra-broadband, all-silicon terahertz (THz) absorber, designed for high-efficiency absorption without the limitations of traditional metal-based structures.

  • Core Design: The absorber consists solely of silicon, featuring a single-layer periodic array of diamond metamaterial placed on a cubic silicon substrate.
  • Performance: Achieves nearly perfect absorption (up to 99.7%) at 1 THz and maintains an absorption efficiency greater than 90% across a wide 1.3 THz bandwidth.
  • Mechanism: Perfect broadband absorption is driven by coupled electric and magnetic resonances excited within the silicon layer, ensuring effective impedance matching with free space.
  • Robustness: The highly symmetric structure provides polarization independence and maintains high absorption efficiency under large incident angles (up to 70° for Transverse Electric (TE) polarization).
  • Material Advantage: Utilizing all-silicon avoids the disadvantages of metal-dielectric-metal absorbers, such as high ohmic losses, low melting points, and high thermal conductivity, ensuring suitability for high-power or high-temperature optical applications.
  • Fabrication Potential: The use of common semiconductor material (silicon) promises easy integration and low manufacturing cost compared to complex multilayered metal structures.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Absorption Bandwidth (>90%)1.3THzAchieved for TE polarization
Peak Absorption (f = 1 THz)99.7%Normal Incidence
Second Peak Absorption (f = 1.72 THz)97.8%Normal Incidence
Operating Frequency Range0.2 to 2THzSimulated range
Angular Stability (TE)Up to 70°Absorption efficiency >90% maintained
Angular Stability (TM)Up to 40°Absorption efficiency >90% maintained
Metamaterial Period (p)170”mOptimized structural parameter
Substrate Height (h)250”mOptimized structural parameter
Metamaterial Layer Thickness (t)60”mOptimized structural parameter
Silicon Intrinsic Permittivity (Δ∞)11.68N/ADrude response model constant
Silicon Carrier Mobility (”)386cm2 V-1 S-1Empirical parameter
Silicon Carrier Density (N)0.03 x 1018cm-3Derived from conductivity

Key Methodologies

Section titled “Key Methodologies”

The study was conducted numerically using the Finite Difference Time Domain (FDTD) method to simulate electromagnetic wave interaction with the subwavelength structure.

  1. Simulation Environment: Commercial software Lumerical FDTD Solutions was used to obtain the reflectance (R) and transmittance (T) spectra.
  2. Absorption Calculation: The absorption (A) was derived directly from the simulated R and T values using the formula: A = 1 - R - T.
  3. Material Modeling: The silicon material was modeled using the Drude response model, incorporating optimized parameters for intrinsic permittivity, carrier mobility, and carrier density.
  4. Resonance Analysis: The absorption mechanism was verified by analyzing the distribution of electric (E) and magnetic (H) fields at the two primary resonant peaks (1 THz and 1.72 THz).
  5. Impedance Matching Verification: Effective Medium Theory (EMT) and S-parameters (S11, S21) were used to calculate the effective impedance (Z) of the absorber, confirming that Z approaches the free-space impedance (Z0 = 1) at the working frequencies.
  6. Polarization and Angle Testing: Absorption spectra were simulated for both Transverse Electric (TE) and Transverse Magnetic (TM) polarizations across incident angles ranging from 0° to 70°.

Commercial Applications

Section titled “Commercial Applications”

This all-silicon THz absorber technology is highly relevant for fields requiring robust, high-efficiency THz components, particularly those benefiting from silicon integration and thermal stability.

  • THz Sensing and Imaging:
    • High-resolution THz imaging systems.
    • Explosives and chemical detection devices.
    • Non-destructive testing and quality control (e.g., food inspection).
  • Optoelectronics and Communication:
    • Integrated THz sensors and modulators.
    • Photoelectric detection devices operating in the THz gap.
    • High-speed THz wireless communication components.
  • Semiconductor Manufacturing:
    • Applications requiring CMOS-compatible fabrication processes due to the exclusive use of silicon.
    • Devices demanding high thermal stability, as the design avoids low-melting-point metals.
View Original Abstract

In this article we present and numerically investigate a broadband all-silicon terahertz (THz) absorber which consists of a single-layer periodic array of a diamond metamaterial layer placed on a silicon substrate. We simulated the absorption spectra of the absorber under different structural parameters using the commercial software Lumerical FDTD solutions, and analyzed the absorption mechanism from the distribution of the electromagnetic fields. Finally, the absorption for both transverse electric (TE) and transverse magnetic (TM) polarizations under different incident angles from 0 to 70° were investigated. Herein, electric and magnetic resonances are proposed that result in perfect broadband absorption. When the absorber meets the impedance matching principle in accordance with the loss mechanism, it can achieve a nearly perfect absorption response. The diamond absorber exhibits an absorption of ~100% at 1 THz and achieves an absorption efficiency >90% within a bandwidth of 1.3 THz. In addition, owing to the highly structural symmetry, the absorber has a polarization-independent characteristic. Compared with previous metal-dielectric-metal sandwiched absorbers, the all-silicon metamaterial absorbers can avoid the disadvantages of high ohmic losses, low melting points, and high thermal conductivity of the metal, which ensure a promising future for optical applications, including sensors, modulators, and photoelectric detection devices.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2016 - Experimental realization of perfect terahertz plasmonic absorbers using highly doped silicon substrate and COMS-compatible techniques [Crossref]
  2. 1996 - Extremely low frequency plasmons in mentallic mesostructures [Crossref]
  3. 2003 - Security applications of terahertz technology [Crossref]
  4. 2013 - Graphene metamaterials based tunable terahertz absorber: Effective surface conductivity approach [Crossref]
  5. 2010 - Review of terahertz and subterahertz wireless communications [Crossref]
  6. 2007 - Cutting-edge terahertz technology [Crossref]
  7. 2007 - Optical negative-index metamaterials [Crossref]
  8. 2012 - From metamaterials to metadevices
  9. 2011 - A terahertz polarization insensitive dual band metamaterials absorber [Crossref]
  10. 2008 - A metamaterial absorber for the terahertz regime: Design, fabrication and characterization [Crossref]

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