Plasmonic-based photodetectors are receiving increased attention because simple structural changes can make the photodetectors spectrally sensitive. In this study, asymmetric gold nanostructures are used as simple structures for photodetection via the photothermoelectric response. These single metal photodetectors use localized optical absorption from plasmon resonances of gold nanowires at desired wavelengths to generate temperature gradients. Combined with a geometry-dependent Seebeck coefficient, the result is a net electrical signal when the whole geometry is illuminated, with spectral sensitivity and polarization dependence from the plasmon resonances. We show experimental results and simulations of single-wavelength photodetectors at two wavelengths in the near IR range: 785 and 1060 nm. Based on simulation results and a model for the geometry-dependent Seebeck response, we demonstrate a photodetector structure that generates polarization-sensitive responses of opposite signs for the two wavelengths. The experimental photothermoelectric results are combined with simulations to infer the geometry dependence of the Seebeck response. These results can be used to increase the responsivity of these photodetectors further.
Keywords: Seebeck coefficient; gold nanowire; photodetector; photothermoelectric effect; plasmons.