We have recently demonstrated subwavelength thermoelectric nanostructures designed for resonant spectrally selective absorption, which creates large localized temperature gradients even with unfocused, spatially-uniform illumination to generate easily measureable thermoelectric voltages. We have shown that such structures are tunable and are capable of highly wavelength - specific detection, with an input power responsivity of up to 38 V/W, referenced to incident illumination, and bandwidth of nearly 3 kHz, by combining resonant absorption and thermoelectric junctions within a single membrane-suspended nanostructure, 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.
Probing thermal states in such nanophotonic systems has traditionally come with the caveat that the measurement technique itself alters the thermal state of the system. For example, AFM thermal probes, which come within nanometers of the surface, may radiatively alter the system and are also limited by thermocouple error. Platinum RTD thermometers, with wires comparable to the size and thickness of the nanophotonic device itself, alter the thermal profile of the system. Non-contact, far-field techniques such as Fourier transform infrared spectroscopy, are limited in collection area by the thermal wavelength which is often larger than the nanophotonic device being measured. Additionally, it is not possible to obtain sub-Kelvin temperature resolution by collecting thermal radiation.
We have developed a non-invasive measurement technique which uses the nanophotonic materials themselves as thermometers. We combine noise thermometery, which measures the absolute temperature of the electrons within the nanophotonic material, with thermoelectric measurements of the nanophotonic devices, which allow us to observe the temperature rise in a nanophotonic wire array with probes as far as 100 microns away from the center of light absorption in a nanophotonic thermoelectric device. We predict a temperature rise of several Kelvin within the nanophotonic structures, and test these predictions using room temperature, kHz noise thermometry to get better than 0.5 Kelvin error in temperature.
 Mauser, K. M., et al, “Resonant Thermoelectric Nanophotonics”, Nature Nanotechnol., 2017, 12, 770-775.