  Photodetectors are typically based on photocurrent generation from
electron-hole pairs in semiconductor structures and on bolometry for
wavelengths that are below bandgap absorption. In both cases, resonant
plasmonic and nanophotonic structures have been successfully used to enhance
performance. In this work, we demonstrate subwavelength thermoelectric
nanostructures designed for resonant spectrally selective absorption, which
creates large enough localized temperature gradients to generate easily
measureable thermoelectric voltages. We show that such structures are tunable
and are capable of highly wavelength specific detection, with an input power
responsivity of up to 119 V/W (referenced to incident illumination), and
response times of nearly 3 kHz, by combining resonant absorption and
thermoelectric junctions within a single structure, yielding a
bandgap-independent photodetection mechanism. We report results for both
resonant nanophotonic bismuth telluride-antimony telluride structures and
chromel-alumel structures as examples of a broad class of nanophotonic
thermoelectric structures useful for fast, low-cost and robust optoelectronic
applications such as non-bandgap-limited hyperspectral and broad-band
photodetectors.
