Photodetector Identifies Miniscule Differences in Wavelengths

A novel technology that combines nanophotonics and thermoelectrics has the potential to detect different wavelengths of light, including visible and IR, at high resolution. The detector operates about 10 to 100 times faster than comparable thermoelectric devices and can detect light across a broader range of the spectrum than traditional photodetectors.

Researchers at California Institute of Technology (Caltech) combined resonant absorption and thermoelectric junctions within a single suspended membrane nanostructure, creating a bandgap-independent photodetection mechanism. The team showed that such structures are tunable and capable of wavelength-specific detection, with an input power responsivity of up to 38 V W^–1 and bandwidth of nearly 3 kHz.

The team tested and reported on both bismuth telluride/antimony telluride and chromel/alumel structures, as examples of a potentially broader class of resonant nanophotonic-thermoelectric materials for optoelectronic applications such as nonbandgap-limited hyperspectral and broadband photodetectors.

This is an artist's representation of a conceptual design for the color detector, which uses thermoelectric structures with arrays of nanoscale wires that absorb different wavelengths of light based on their width. Courtesy of Harry Atwater and Kelly Mauser/Caltech.

The detectors were fabricated in the Kavli Nanoscience Institute cleanroom at Caltech, where the team used a combination of vapor deposition and electron beam lithography to create the subwavelength structures. While the structures were created from alloys with well-known thermoelectric properties, according to the team, the research could be applied to a wide range of materials.

“In nanophotonics, we study the way light interacts with structures that are much smaller than the optical wavelength itself, which results in extreme confinement of light. In this work, we have combined this attribute with the power conversion characteristics of thermoelectrics to enable a new type of optoelectronic device,” said Harry Atwater, Howard Hughes Professor of Applied Physics and Materials Science in the Division of Engineering and Applied Science at Caltech.

There are several potential applications for the detector. It could be used in satellites that study changing vegetation and landscape, and in medical imagers that differentiate between healthy and cancerous cells based on color variations. Because the detector is potentially capable of capturing IR wavelengths of sunlight and heat, which cannot be collected efficiently with conventional solar materials, the technology could be used to improve solar cells and imaging devices.

“This research is a bridge between two research fields, nanophotonics and thermoelectrics, that don’t often interact, and creates an avenue for collaboration,” said researcher Kelly Mauser. “There is a plethora of unexplored and exciting application and research opportunities at the junction of these two fields.”

The research was published in Nature Nanotechnology (doi: 10.1038/nnano.2017.87).