The plasmonic behavior of dimers of touching semiconductor disks is studied experimentally in the difficult‐to‐realize regime where the disks are only marginally overlapping. Previous theoretical studies have shown that this geometry exhibits a highly efficient broadband response that may be very promising for light harvesting and sensing applications. By taking advantage of the plasmonic character of InSb in the terahertz regime, we experimentally confirm this broadband response and describe the associated strong field enhancement and sub‐micrometer field confinement between the disks.

Research on terahertz (THz) electromagnetic radiation has been booming in the past two decades in view of its unique properties and important applications in sensing, imaging, and spectroscopy. [1][2][3] The recent advancement of plasmonics and metamaterials has brought new approaches for manipulating THz waves. Signifi cant progress has been achieved in THz component development, such as ultra-high refractive index THz metamaterials, [ 4 ] beam collimated THz quantum cascade laser, [ 5 ] high effi ciency THz photomixer, [ 6 ] near fi eld on-chip THz detector, [ 7 ] THz modulators, [8][9][10][11][12] high extinction ratio THz polarizer [ 13 ] and THz spoof surface plasmon waveguides. [14][15][16] The electromagnetic response of plasmonic and metamaterial structures arise from the combined contributions of subwavelength structuring and the dielectric materials properties. As the properties of metals can hardly be tuned, THz metamaterial and plasmonic devices based on metallic subwavelength structures are normally tuned or modulated only through adjusting the properties of ambient or active dielectric elements. On the other hand, low-bandgap semiconductors, such as InSb, are excellent candidates for plasmonic materials in the THz range, owing to their small band gap, high electron mobility, small effective mass and low electron density. More importantly, the properties of semiconductors can be easily tuned by thermal, electrical or optical ways. Very recently, broadband THz plasmonic absorption in InSb touching disks was demonstrated, which showed consistency with the theoretical predictions of transformation optics for gold nanostructures at visible frequencies. [ 17 ] InSb was also used as the material to study coherent interference induced THz transparency tuned via an external magnetic fi eld. [ 18 ] By taking advantage of the fast response time of optical processes, semiconductor-based optically tunable THz active plasmonics is a very suitable concept for high-speed THz modulation. In this paper, we report the direct optical tuning of the THz plasmonic response of InSb subwavelength gratings. The potential modulation speed was characterized through carrier lifetime study by optical-pump THz-probe (OPTP) spectroscopy. Theoretical calculations of the subwavelength grating plasmonic structure show full-scale operation agility in modulation frequency and depth.In THz frequency range InSb can be modeled as a classic solid-state plasma, with its permittivity given by g InSb (T) = g ∞ [1 − T 2 p / T 2 + iT( ] and plasma frequency T p = ne 2 / g 0 g ∞ m * , where n is the carrier concentration. [ 19 ] At room temperature, the plasma frequency of InSb lies within the THz frequency range and its permittivity resembles that of noble metals in the optical frequencies, enabling plasmonic resonances of subwavelength structures with incident THz waves. [ 20,21 ] As indicated by the above equations, the permittivity of InSb depends strongly on carrier concentration, which allows the permittivity and consequently plasmonic res...

We report the growth of InSbN on a lattice-mismatched GaAs substrate using radio frequency nitrogen plasma-assisted molecular beam epitaxy. The effects of a two-step thin InSb buffer layer grown at 330 and 380 °C and substrate temperature (270–380 °C) on the properties of the InSbN are studied. The crystalline quality of the InSbN is significantly improved by the two-step buffer layer due to defect suppression. The shifting in the absorption edge of the InSbN from ∼5 to 8 µm following an increase in the substrate temperature is correlated with the reduction in free carrier concentration from ∼1018 to 1016 cm−3 and increase in concentration of N substituting Sb from ∼0.2 to 1%. These results will be beneficial to those working on the pseudo-monolithic integration of InSbN detectors on a GaAs platform.