Performance of long-wave infrared band of microstructured heavily doped InAsSb on type II superlattice layer part 1: the photonic study.

This article deals with the optical study of nanostructured components which absorb light across the entire long-wave infrared (LWIR) spectral band. The components are made of type-II superlattice (T2SL) absorber and highly doped InAsSb, the latter being nanostructured to ensure multiple resonances. We studied two components: in the first one, the T2SL has a thickness of 1.6 µm, and in the second its thickness is 300 nm. The calculated absorption spectra were shown and the components revealed high absorption thanks to optical resonance and high angular acceptance. A fabrication process has been developed, and optical measurements have confirmed the reliability of the model.

THz time-domain spectroscopy modulated with semiconductor plasmonic perfect absorbers.

Terahertz time-domain spectroscopy (THz-TDS) at room temperature and standard atmosphere pressure remains so far the backbone of THz photonics in numerous applications for civil and defense levels. Plasmonic microstructures and metasurfaces are particularly promising for improving THz spectroscopy techniques and developing biomedical and environmental sensors. Highly doped semiconductors are suitable for replacing the traditional plasmonic noble metals in the THz range. We present a perfect absorber structure based on semiconductor III-Sb epitaxial layers. The insulator layer is GaSb while the metal-like layers are Si doped InAsSb (∼ 5·1019 cm-3). The doping is optically measured in the IR with polaritonic effects at the Brewster angle mode. Theoretically, the surface can be engineered in frequency selective absorption array areas of an extensive THz region from 1.0 to 6.0 THz. The technological process is based on a single resist layer used as hard mask in dry etching defined by electron beam lithography. A wide 1350 GHz cumulative bandwidth experimental absorption is measured in THz-TDS between 1.0 and 2.5 THz, only limited by the air-exposed reflectance configuration. These results pave the way to implement finely tuned selective surfaces based on semiconductors to enhance light-matter interaction in the THz region.

All-semiconductor plasmonic gratings for biosensing applications in the mid-infrared spectral range.

We propose 1D periodic, highly doped InAsSb gratings on GaSb substrates as biosensing platforms applicable for surface plasmon resonance and surface enhanced infrared absorption spectroscopies. Based on finite-difference time-domain simulations, the electric field enhancement and the sensitivity on refractive index variations are investigated for different grating geometries. The proposed, optimized system achieves sensitivities of 900 nm RIU-1. A clear red shift of the plasmon resonance as well as the enhancement of an absorption line are presented for 2 nm thin adlayers in simulations. We experimentally confirm the high sensitivity of the InAsSb grating by measurements of the wavelength shift induced by a 200 nm thin polymethylmethacrylate layer and demonstrate an enhancement of vibrational signals. A comparison to a gold grating with equivalent optical properties in the mid-infrared is performed. Our simulations and experimental results underline the interest in the alternative plasmonic material InAsSb for highly sensitive biosensors for the mid-infrared spectral range.

Fano-like resonances sustained by Si doped InAsSb plasmonic resonators integrated in GaSb matrix.

By using metal-free plasmonics, we report on the excitation of Fano-like resonances in the mid-infrared where the Fano asymmetric parameter, q, varies when the dielectric environment of the plasmonic resonator changes. We use silicon doped InAsSb alloy deposited by molecular beam epitaxy on GaSb substrate to realize the plasmonic resonators exclusively based on semiconductors. We first demonstrate the possibility to realize high quality samples of embedded InAsSb plasmonic resonators into GaSb host using regrowth technique. The high crystalline quality of the deposited structure is confirmed by scanning transmission electron microscopy (STEM) observation. Second, we report Fano-like resonances associated to localized surface plasmons in both cases: uncovered and covered plasmonic resonators, demonstrating a strong line shape modification. The optical properties of the embedded structures correspond to those modeled by finite-difference time-domain (FDTD) method and by a model based on Fano-like line shape. Our results show that all-semiconductor plasmonics gives the opportunity to build new plasmonic structures with embedded resonators of highly doped semiconductor in a matrix of un-doped semiconductor for mid-IR applications.