All-Semiconductor Plasmonic Nanoantennas for Infrared Sensing

Abstract

Infrared absorption spectroscopy of vibro-rotational molecular resonances provides a powerful method for investigation of a wide range of molecules and molecular compounds. However, the wavelength of light required to excite these resonances is often orders of magnitude larger than the absorption cross sections of the molecules under investigation. This mismatch makes infrared detection and identification of nanoscale volumes of material challenging. Here we demonstrate a new type of infrared plasmonic antenna for long-wavelength nanoscale enhanced sensing. The plasmonic materials utilized are epitaxially grown semiconductor engineered metals, which results in high-quality, low-loss infrared plasmonic metals with tunable optical properties. Nanoantennas are fabricated using nanosphere lithography, allowing for cost-effective and large-area fabrication of nanoscale structures. Antenna arrays are optically characterized as a function of both the antenna geometry and the optical properties of the plasmonic semiconductor metals. Thin, weakly absorbing polymer layers are deposited upon the antenna arrays, and we are able to observe very weak molecular absorption signatures when these signatures are in spectral proximity to the antenna resonance. Experimental results are supported with finite element modeling with strong agreement.

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

“…In Ref. 15, the nInAs material system epitaxially grown on the GaAs wafers was employed. The observed nanoantenna resonance was at k > 10 lm; however, a large portion of the mid-IR molecular fingerprint region was excluded.…”

Highly doped semiconductor plasmonic nanoantenna arrays for polarization selective broadband surface-enhanced infrared absorption spectroscopy of vanillin

“…While numerous studies have been carried out on metallic nanoantennas, either as individual objects [12][13][14][15][16][17], or organized in arrays [1,10,[18][19][20][21], semiconductor plasmonic nanoantenna surfaces have rarely been investigated [22], especially in ordered array arrangements [23][24][25]. Highly doped semiconductors (HDSC) have been introduced as engineered metals or "designed metals" for plasmonics [22,23] as they offer the possibility of tuning the plasma frequency, an intrinsic parameter for traditional metals, via the doping level.…”

“…Highly doped semiconductors (HDSC) have been introduced as engineered metals or "designed metals" for plasmonics [22,23] as they offer the possibility of tuning the plasma frequency, an intrinsic parameter for traditional metals, via the doping level. Doping densities of several 10 19 cm −3 have been reported for InAs [23], and densities up to 10 20 cm −3 have been predicted [26].…”

Group-IV midinfrared plasmonics

“…Indeed, a few seminal works have already outlined the very interesting possibilities that will be opened by the use of such materials for mid-IR plasmonics. [14][15][16] The idea of turning attention to semiconductors as "metals" in the mid-IR comes from the dependence of the plasma frequency (marking the onset of conducting behavior) on the carrier density n, according to the relation ω p ∝ ffiffiffiffiffiffiffiffiffiffiffi n∕m à p , where m à represents the effective mass of the free carriers involved in the plasma oscillations.…”