Highly Doped Semiconductor Plasmonics for Mid-IR Applications

GaSb-based material could be the building block for all-semiconductor mid-infrared plasmonic devices. The metal is a highly doped InAsSb layer deposited by molecular beam epitaxy on GaSb substrate. Electrical and optical characterizations have demonstrated the possibility to control the plasma frequency in the mid-infrared range by adjusting the doping level. Sub-wavelength periodic arrays are fabricated in the InAsSb layer and localized surface plasmon resonances are observed in reflectance experiments. A perfect control of the doping level and of the geometry of the periodic arrays allows adjusting the frequency of the plasmonic resonances. By covering the InAsSb periodic arrays, it is possible to drastically modify the plasmonic resonances and observe Fano-like resonances.

Surface plasmon polaritons result of the strong coupling between an electromagnetic wave and the collective oscillation of free electrons of a metal. They are generated at the interface between a metal and a dielectric. They present actually a great interest because of their potential applications in the fields of metamaterial or metasurfaces, enhanced photonic devices properties, nanophotonics integrated circuits and nano-bio-photonics. All these applications rely on the use of gold resonators. Because of the need to integrate plasmonic functionalities to semiconductor devices and to keep high field exaltation at the metal/dielectric interface for mid-IR application, it is really attractive to use highly doped semiconductors. The plasma frequency as the magnitude of the permittivity of the highly doped semiconductor can be controlled via its doping level. The proposed experimental study is based on stripe arrays of doped and encapsulated in un-doped semiconductors. The samples consist of a layer of 100 nm of lattice-matched InAsSb grown by Molecular Beam Epitaxy (MBE) on a GaSb substrate. The highly doped InAsSb arrays are realized by holography and wet or dry etching. The typical grating period is 540 nm. The encapsulating layer of GaSb is performed by MBE on the InAsSb grating. Angular dependent reflectance experiments with polarized light allowed identifying Fano-like resonance due to localized surface plasmon.

thierry.taliercio@univ-montp2.fr