Spectral Tunability of Plasmonic Scattering by Silver Nanodiscs near a Reflector

The scattering properties of a plasmonic array can be reinforced by placing the array near a planar reflector. Finite-Difference-Time-Domain (FDTD) simulations have been used to demonstrate the key design challenge of modulating the electric field that drives the plasmonic scattering, by varying the distance of a single Ag nanodisc from a Ag reflector. We show that the thickness of the dielectric separation layer plays a critical role in determining the spectral characteristics and the intensity of the power scattered by a Ag nanodisc near a reflector. A possible application of the designed structure as a plasmonic light-trap for thin Si solar cells is also experimentally demonstrated. Electron-beam lithography has been used to fabricate a pseudo-random array of 150nm plasmonic Ag nanodiscs on SiO2 on a Ag reflector substrate. The plasmonic reflector shows a high diffuse reflectance of similar to 54% in the near-infrared, near-bandgap 600-900nm wavelength region for thin Si solar cells, with a low broadband absorption loss of similar to 18%. Wavelength-angle resolved scattering measurements indicate an angular scattering range between 20 degrees to 80 degrees with maximum intensity of the scattered power in the 20 degrees to 60 degrees angular range.