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 (similar to 5 center dot 10(19) 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. (c) 2023 Optica Publishing Group

Automated summary

Terahertz time-domain spectroscopy is an important technology in terahertz photonics, with extensive applications in civil and defense fields. Plasmonic microstructures and metasurfaces show promise in improving terahertz spectroscopy techniques and developing biomedical and environmental sensors. Highly doped semiconductors are being used to replace traditional noble metals for plasmonics in the terahertz range. By using semiconductor materials with specific structures, selective absorption of terahertz waves can be achieved.