  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, 35nm 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 1.08eV
to 1.58eV when decreasing the triangle size from 170nm to 100nm on GaAs, we
observed a global redshift by 0.25 +- 0.05eV 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 8x 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.
