Thin InSb layers with metallic gratings: a novel platform for spectrally-selective THz plasmonic sensing

TL;DR

This study computationally explores thin InSb layers with metallic gratings for terahertz plasmonic sensing, revealing sensitive surface plasmon modes that can detect analytes and vibrational fingerprints.

Contribution

It introduces a novel InSb-based plasmonic structure with strong, tunable resonances for highly sensitive terahertz sensing applications.

Findings

Two strong absorption resonances identified as standing surface plasmon modes.

Sensor sensitivity of 7200 nm per refractive index unit.

Surface plasmon-vibrational mode interaction enables vibrational fingerprint detection.

Abstract

We present a computational study of terahertz optical properties of a grating-coupled plasmonic structure based on micrometer-thin InSb layers. We find two strong absorption resonances that we interpret as standing surface plasmon modes and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The observed surface plasmon modes are well described by a simple theory of the air/InSb/air trilayer. The plasmonic response of the grating/InSb structure is highly sensitive to the dielectric environment and the presence of an analyte (e.g., lactose) at the InSb interface, which is promising for terahertz plasmonic sensor applications. We determine the sensor sensitivity to be 7200 nm per refractive index unit (or 0.06 THz per refractive index unit). The lower surface plasmon mode also exhibits a splitting when tuned in resonance with the vibrational mode of lactose at 1.37 THz. We propose that such interaction between surface plasmon and vibrational modes can be used as the basis for a new sensing modality that allows the detection of terahertz vibrational fingerprints of an analyte.