Nat. Nanotech. (2017)


Heat generation in resonant subwavelength nanostructures is creating new opportunities for photodetector design. Now, Kelly Mauser and colleagues from the California Institute of Technology, USA have exploited resonant light absorption and the thermoelectric effect within a single suspended membrane nanostructure to realize a wavelength-tunable photodetector. The nanostructure consists of a guided mode resonance wire array on a thin, suspended, electrically insulated substrate. Made of established thermoelectric materials, bismuth telluride/antimony telluride (Bi2Te3/Sb2Te3), the wires are 40 nm × 100 nm × 50 μm and spaced 488 nm apart. Owing to the spatially localized absorption in resonant nanophotonic structures, localized heating of the thermoelectric material occurs, leading to large thermal gradients between the centre and the edge of the nanostructure even under unfocused optical excitation. The team have observed that the small heat capacity enables a temporal response of 337 μs, which is 10–100 times faster than conventional thermoelectric detectors. They also show that their detectors are tunable from the visible to the mid-infrared and are capable of wavelength-specific detection, with an input power responsivity of up to 38 V W−1 and a frequency bandwidth of nearly 3 kHz.