Infrared surface plasmons on heavily doped silicon

Abstract

Conductors with infrared plasma frequencies are potentially useful hosts of surface plasmon polaritons (SPP) with sub-wavelength mode confinement for sensing applications. A challenge is to identify such a conductor that also has sharp SPP excitation resonances and the capability to be functionalized for biosensor applications. In this paper we present experimental and theoretical investigations of IR SPPs on doped silicon and their excitation resonances on doped-silicon gratings. The measured complex permittivity spectra for p-type silicon with carrier concentration 6Â10 19 and 1Â10 20 cm À3 show that these materials should support SPPs beyond 11 and 6 lm wavelengths, respectively. The permittivity spectra were used to calculate SPP mode heights above the silicon surface and SPP propagation lengths. Reasonable merit criteria applied to these quantities suggest that only the heaviest doped material has sensor potential, and then mainly within the wavelength range 6 to 10 lm. Photon-to-plasmon coupling resonances, a necessary condition for sensing, were demonstrated near 10 lm wavelength for this material. The shape and position of these resonances agree well with simple analytic calculations based on the theory of Hessel and Oliner (1965). V

Mapping the electromagnetic field confinement in the gap of germanium nanoantennas with plasma wavelength of 4.5 micrometers

“…The observed nanoantenna resonance was at k > 10 lm; however, a large portion of the mid-IR molecular fingerprint region was excluded. Group-IV semiconductors such as Si and Ge have the potential for direct integration in microelectronic platforms, 16,17 also allowing for fast optical switching. 18,19 In n-Ge, given a conductivity effective mass m* ¼ 0.12 m e and a screening constant e m;1 ¼ 16, k p ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi m à e 0 e m;1 =q e 2 n e p < 5 lm is expected if very high free electron concentrations n e in excess of 10 20 cm À3 are achieved (here m e and q e are the electron mass and charge, respectively).…”

Tunability of the dielectric function of heavily doped germanium thin films for mid-infrared plasmonics

“…It has been proposed that, in order to obtain tunable values of ǫ ′ in the entire IR range 11,12 , heavily doped semiconductors [13][14][15][16][17][18][19] and conducting oxides 20 may be used because their free carrier density can be set by selecting the doping level and further tuned by electrostatic gating 16 or optical excitation 21,22 .…”

Review of mid-infrared plasmonic materials

“…In particular, doped semiconductors have been shown to exhibit plasmonic properties from the THz to mid-IR frequencies. [29][30][31][32] The advantages of doped semiconductors as mid-IR plasmonic materials are many. First, these materials can be grown epitaxially, offering singlecrystal materials with high mobility and accurate doping concentration control, as well as the potential for integration with semiconductor optoelectronic structures.…”