Terahertz volume plasmon-polariton modulation in all-dielectric hyperbolic metamaterials

TL;DR

This work addresses the challenge of achieving terahertz plasmonics with low-loss, tunable platforms by proposing all-dielectric hyperbolic metamaterials built from doped III-V semiconductors. A multiscale framework—combining atomistic DFT+$U$ calculations to obtain dielectric functions, effective medium theory for anisotropic homogenization, scattering-matrix methods for finite stacks with grating couplers, and photonic-band-structure analysis—is used to predict and engineer volume plasmon-polariton modes. The study demonstrates that Si:InAs/AlSb multilayers support tunable Type-I and Type-II hyperbolic dispersion in the THz to mid-IR range and host multiple VPPs whose energies are controllable via doping and grating geometry, with the SMM and PBS analyses providing practical design guidance. The results pave the way for semiconductor-based THz devices, enabling on-chip modulators, sensors, and thermal-emission control with improved epitaxial compatibility and reduced losses.

Abstract

The development of plasmonics and related applications in the terahertz range faces limitations due to the intrinsic high electron density of standard metals. All-dielectric systems are profitable alternatives, which allows for customized modulation of the optical response upon doping. Here we focus on plasmon-based hyperbolic metamaterials realized stacking doped III-V semiconductors that have been shown to be optically active in the terahertz spectral region. By using a multi-physics multi-scale theoretical approach, we unravel the role of doping and geometrical characteristics (e.g., thickness, composition, grating) in the modulation of high-k plasmon-polariton modes across the metamaterial.

Figures (21)

• Figure 1: (a) Schematic representation of a finite stacked metamaterial composed of alternating metallic ($m$) and dielectric ($d$) layers, each characterized by its dielectric function $\varepsilon_j$ and thickness $d_j$, where $j=\{m,d\}$. Gray regions indicate the embedding media for reflection and transmission, also characterized by the respective dielectric functions $\varepsilon_{in}$ and $\varepsilon_{out}$. The optical axis is aligned along the z direction. (b) Scattering matrix formulation for a single layer. Forward $(c_1^+, c_2^+)$ and backward $(c_1^-, c_2^-)$ propagating wave amplitudes are related through the elements $S_{ij}$ of the scattering matrix.
• Figure 2: a) Atomic structure of Si:InAs supercell. b) Total (black line) and Si-projected (red line) density of states (DOS) of Si:InAs (model 2). c) Real and d) imaginary parts of the dielectric function of Si:InAs as a function of Si concentration.
• Figure 3: Real (solid lines) and imaginary (dashed lines) parts of the parallel (red lines) and perpendicular (blue lines) dielectric functions of Si:InAs/AlSb multilayer ($c_{\bf 2}=3.12\%$ and $f_m$ = 0.5). Top bar indicates spectral optical character of the multilayer -- namely Type-I (orange) and Type-II (blue) hyperbolic, and dielectric (gray). Vertical dashed lines mark characteristics energies discussed in the text.
• Figure 4: Spectral optical character -- namely Type-I (orange) and Type-II (blue) hyperbolic, and dielectric (gray) -- of HMMs composed of: a) III-V semiconductors/Si:InAs ($c_{\bf 2}=3.12\%$, $f_m=0.5$) as a function of the dielectric component; b) Si:InAs/AlSb ($f_m=0.5$) as a function of Si doping concentration; c) Si:InAs/AlSb ($c_{\bf 2}=3.12\%$) as a function of the filling factor $f_m$ in the range (0.05 -- 0.95)%.
• Figure 5: a) Real part of the angular dielectric function ($\varepsilon_\varphi$, top panel) and allowed conic angles ($\Theta$, bottom panel) of excited VPPs with respect to optical axis for Si:InAs/AlSb multilayer ($c_{\bf 2}=3.12\%$, $f_m=0.5$) corresponding to the energies $E_1$, $E_2$, and $E_3$ shown in Figure \ref{['fig:fig3']}; b) 2D projected $k$-dispersions for Si:InAs/AlSb (straight lines) corresponding to $E_1$ (Type-I, red lines) and $E_2$ (Type-II, blue lines). Dashed lines correspond to hyperboloid asymptotes whose slopes correspond to critical angles $\varphi_{c}$ marked in panel a.