Optical properties and interparticle coupling of plasmonic bowtie nanoantennas on a semiconducting substrate

Abstract

We present the simulation, fabrication and optical characterization of plasmonic gold bowtie nanoantennas on a semiconducting GaAs substrate as geometrical parameters such as size, feed gap, height and polarization of the incident light are varied. The surface plasmon resonance was probed using white light reflectivity on an array of nominally identical, 35 nm thick Au antennas. To elucidate the influence of the semiconducting, high refractive index substrate, all experiments were compared using nominally identical structures on glass. Besides a linear shift of the surface plasmon resonance from 1.08 eV to 1.58 eV when decreasing the triangle size from 170 nm to 100 nm on GaAs, we observed a global redshift by 0.25 ± 0.05 eV with respect to nominally identical structures on glass. By performing polarization resolved measurements and comparing results with finite difference time domain simulations, we determined the near field coupling between the two triangles composing the bowtie antenna to be ∼8× stronger when the antenna is on a glass substrate compared to when it is on a GaAs substrate. The results obtained are of strong relevance for the integration of lithographically defined plasmonic nanoantennas on semiconducting substrates and, therefore, for the development of novel optically active plasmonic-semiconducting nanostructures.

Linear and non-linear response of lithographically defined plasmonic nanoantennas

“…Furthermore, the interparticle coupling redshifts and broadens the resonance to E SP R, = 1.55 eV and ∆E SP R, = 0.327 eV, respectively. 28 In summary, our simulations illustrate how the peak energy and the width of the surface plasmon resonance strongly depend on the shape of the particle as already discussed in the literature. 8,11 The bowtie-geometry provides a high scattering cross section and a moderate damping.…”

“…We note that the offset in photon energies and the increased linewidth is related to the higher refractive index of GaAs compared to glass and the difference in size as recently discussed. 28 From our findings we conclude that in non-linear optics experiments an adhesion layer should be avoided whenever possible to ensure the lowest damping and highest field enhancements.…”

Emission redistribution from a quantum dot-bowtie nanoantenna

“…We obtain for the decay length [ = 11.3 ± 0.5 , which we attribute to the strong localization of the electromagnetic field at the feed-gap of the bowtie nanoantenna. This hypothesis is supported by complementary simulations of the electromagnetic field enhancement = … / [ … , where and [ denote the field with and without the bowtie, respectively [29]. A typical simulation of for a bowtie nanoantenna with [ = 110 and [ = 30 is shown in the lower inset of Figure 3(a).…”

“…In strong contrast to so far mostly used chemically synthesized semiconductor nanocrystals [45], self-assembled InGaAs quantum dots grown by molecular beam epitaxy offer a couple of advantages; (i) They are embedded in a threedimensional semiconductor matrix and, thus, do not suffer from blinking and bleaching [5], exhibiting already short exciton lifetimes on the order of 1 and internal quantum efficiencies close to unity at cryogenic temperatures [46]. (ii) Moreover, since the quantum dots are directly grown on a semiconductor substrate, such as GaAs [46] and even Si [47], they are structurally stable and one can easily integrate them into photonic [3] and plasmonic nanostructures [29] [33]. (iii) In addition to their spectrally broadband response [28], plasmonic cavities are intrinsically capable to exploit the employed metal also as local electrical contacts [48] and, thus, allows for electrical tunability [41].…”

Monolithically integrated single quantum dots coupled to bowtie nanoantennas

“…As such it represents the most promising route to interface state-of-the-art electronics with true nano-photonic devices on the same chip [7]. To this end, the study, optimisation and integration of nano-scale plasmonic components, such as antennas [14] and waveguides [4], on highquality semiconductor substrates [15] is essential in order to prove their applicability in real-world applications. Monolithically integrated, self-assembled quantum dots [1] exhibit outstanding electrical and optical properties, they do not suffer from bleaching or blinking and have near-unity internal quantum efficiencies.…”