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

At a Glance

Metadata	Details
Publication Date	2020-01-07
Journal	Applied Sciences
Authors	Jinfeng Wang, Tingting Lang, Tingting Shen, Changyu Shen, Zhi Hong
Institutions	China Jiliang University
Citations	30
Analysis	Full AI Review Included

Technical Documentation & Analysis: Ultra-Broadband All-Silicon Terahertz Absorber

Executive Summary

This documentation analyzes a numerical study detailing an ultra-broadband, all-dielectric Terahertz (THz) absorber. While the research utilizes silicon, the structural requirements (high symmetry, precise micron-scale patterning, and low-loss dielectric performance) directly align with the superior capabilities of 6CCVD’s MPCVD diamond materials.

Core Achievement: Demonstrated a simulated all-silicon THz absorber exhibiting nearly perfect absorption (up to 99.7%) across a wide bandwidth.
Performance Metrics: Achieved an absorption efficiency >90% over a 1.3 THz bandwidth (0.42 THz to 1.72 THz).
Mechanism: Absorption is driven by coupled electric and magnetic resonances excited within the periodic diamond-shaped metamaterial layer.
Key Advantage: The all-dielectric design successfully avoids the high ohmic losses, low melting points, and poor thermal management associated with traditional metal-dielectric-metal THz absorbers.
Polarization & Angle: The highly symmetric structure ensures polarization independence and maintains high absorption efficiency up to 70° for Transverse Electric (TE) polarization.
6CCVD Value Proposition: To advance this research beyond doped silicon, 6CCVD offers high-purity, low-loss Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) wafers, providing significantly lower intrinsic loss tangent and superior thermal conductivity for next-generation, high-power THz applications.

Technical Specifications

The following hard data points were extracted from the numerical study of the optimized all-silicon diamond absorber structure:

Parameter	Value	Unit	Context
Peak Absorption (P1)	99.7	%	At 1.0 THz (TE/TM polarization)
Peak Absorption (P2)	97.8	%	At 1.72 THz (TE/TM polarization)
Absorption Bandwidth (>90%)	1.3	THz	Range from 0.42 THz to 1.72 THz
Operating Frequency Range	0.2 - 2	THz	Range investigated in the study
Angular Stability (TE)	Up to 70	°	Absorption >90% maintained
Angular Stability (TM)	Up to 40	°	Absorption efficiency weakens above this angle
Unit Cell Period (p)	170	µm	Optimized structural parameter
Substrate Thickness (h)	250	µm	Optimized structural parameter (Silicon)
Metamaterial Layer Thickness (t)	60	µm	Optimized structural parameter (Silicon)
Diamond Side Length (a)	75 * 2^1/2 (approx. 106.07)	µm	Optimized structural parameter
Silicon Intrinsic Permittivity (ε_∞)	11.68	N/A	Drude model parameter for Si
Silicon Carrier Density (N)	0.03 * 10¹⁸	cm^-3	Used for Drude model calculation

Key Methodologies

The research relied on advanced numerical modeling and optimization techniques to achieve the ultra-broadband absorption characteristics:

Simulation Platform: The Finite Difference Time Domain (FDTD) method was employed using the commercial software Lumerical FDTD Solutions to analyze the interaction between electromagnetic waves and the subwavelength structures.
Material Modeling: The silicon used in the simulation was modeled using the Drude response model. This model incorporates the intrinsic permittivity (ε_∞ = 11.68), plasma frequency (W_p), and damping rate (γ) derived from the free carrier concentration (N) and mobility (µ) of the doped silicon substrate.
Absorption Calculation: Absorption (A) was calculated directly from the simulated reflectance (R) and transmittance (T) using the fundamental equation: A = 1 - R - T.
Resonance Analysis: The working principle was explained using Effective Medium Theory (EMT). Perfect absorption was achieved when the effective impedance (Z) of the absorber matched the free-space impedance (Z₀ = 1).
Structural Optimization: A systematic parametric study was performed, varying the thickness of the metamaterial layer (t), the length of the diamond diagonal (a), the periodic length (p), and the substrate thickness (h) to maximize the absorption bandwidth and efficiency in the THz region.

6CCVD Solutions & Capabilities

The successful demonstration of an all-dielectric THz absorber highlights the critical need for materials with low intrinsic loss and high thermal stability. 6CCVD’s MPCVD diamond is the ideal material platform to replicate and significantly enhance this research, offering performance far exceeding doped silicon.

Research Requirement/Challenge	6CCVD MPCVD Diamond Solution	Specific Capability Match
Need for Lowest Intrinsic Loss	The paper seeks to eliminate ohmic losses. High-purity diamond exhibits the lowest loss tangent of any known material in the THz and microwave regimes.	Optical Grade SCD/PCD: We provide SCD and PCD wafers optimized for low absorption and high transparency in the THz band, ensuring maximum energy coupling and minimal parasitic heating.
Superior Thermal Management	The authors note the thermal limitations of traditional materials.	High Thermal Conductivity Substrates: CVD diamond boasts the highest thermal conductivity (up to 2200 W/mK). 6CCVD offers diamond substrates up to 10mm thick, crucial for high-power THz applications (e.g., THz imaging, high-speed modulators).
Precise Metamaterial Dimensions	The design requires micron-scale thickness (60 µm) and lateral patterning (170 µm period).	Custom Thickness and Dimensions: 6CCVD specializes in custom SCD and PCD wafers with precise thickness control from 0.1 µm up to 500 µm, perfectly matching the required metamaterial layer dimensions. We supply plates/wafers up to 125mm (PCD).
High-Quality Surface for Etching	Fabrication of the diamond-shaped metamaterial requires an ultra-smooth surface for high-resolution lithography and etching processes.	Advanced Polishing Services: We guarantee industry-leading surface quality: Ra < 1nm for SCD and Ra < 5nm for inch-size PCD, ensuring optimal conditions for patterning complex subwavelength structures.
Integration with Active Devices	Future THz devices often require integrated metal contacts or active layers.	Custom Metalization: 6CCVD offers internal metalization capabilities, including deposition of Au, Pt, Pd, Ti, W, and Cu, allowing researchers to integrate contact pads or complex multilayer stacks directly onto the diamond substrate.

Applicable Materials

To replicate or extend this ultra-broadband THz absorber research using a superior dielectric platform, 6CCVD recommends:

Optical Grade Single Crystal Diamond (SCD): For applications requiring the absolute lowest loss, highest purity, and best thermal performance. Ideal for high-fidelity THz sensing and imaging.
Optical Grade Polycrystalline Diamond (PCD): Cost-effective solution for large-area THz metamaterials (up to 125mm diameter) where the grain boundaries do not significantly impact THz performance.

Engineering Support

6CCVD’s in-house PhD engineering team possesses deep expertise in the electromagnetic properties of diamond. We can assist researchers in translating FDTD/Drude model parameters from silicon to diamond, optimizing material selection (e.g., nitrogen concentration, doping levels) to achieve specific THz absorption or transmission profiles for similar THz imaging, sensing, or detection projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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

Original Source

DOI: https://doi.org/10.3390/app10020436

References

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