Light scattering into silicon-on-insulator waveguide modes by random and periodic gold nanodot arrays

Experimental characterization and finite-element numerical simulations of the electromagnetic interaction between random or periodic Au nanodot arrays patterned atop a silicon-on-insulator (SOI) photodetector and incident electromagnetic plane waves have been performed at wavelengths of 400–1100nm. The presence of the Au nanodots is found to lead to increased electromagnetic field amplitude within the semiconductor and, consequently, increased photocurrent response for both cases. Random arrays tend to exhibit broad increases in photocurrent over wavelength, whereas periodic arrays demonstrate sharp resonance peaks in the photocurrent absorption spectrum. Such features are due to the coupling of normally incident light into waveguide modes that satisfy the Bragg diffraction condition. Analysis of the dispersion relation of the waveguide modes allows for accurate prediction of the resonance peaks in the photocurrent absorption spectrum of the SOI photodetectors patterned with periodic nanodot arrays.