Satellites that study the earth’s changing vegetation and landscape, medical imagery that can distinguish healthy cells from cancerous ones, and a variety of other applications employ light detectors that can tell the difference between different colors of light or heat.
Traditional light detectors employ a semiconductor to absorb photons of light, exciting electrons to produce an electric current that can be measured and quantified as a signal. Infrared light, made up of lower-energy photons than visible light, is difficult to capture with these types of systems.
By combining the disparate technologies of nanophotonics and thermoelectrics, engineers at Caltech have developed a light detector that can distinguish between different colors of light at high resolution – including both visible and infrared wavelengths.
The researchers created nanostructures smaller than the wavelengths of light that represent the visible spectrum, which ranges from about 400 to 700 nanometers. By employing a variety of widths to absorb different wavelengths, the nanostructures generate signals that correspond to the color absorbed.
As described in Nature Nanotechnology, the new detector is capable of detecting light across a wider range of the electromagnetic spectrum than traditional light detectors, and operates about 10 to 100 times faster than current comparable thermoelectric devices. The technology could lead to better solar cells and imaging devices.
"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," says Harry Atwater, an applied physics and materials sciences professor at Caltech and corresponding author of the study. Atwater is the director of the Joint Center for Artificial Photosynthesis (JCAP), a DoE Energy Innovation Hub focused on developing a cost-effective method of turning sunlight, water and carbon dioxide into fuel.
"This research is a bridge between two research fields, nanophotonics and thermoelectrics, that don't often interact, and creates an avenue for collaboration," says graduate student Kelly Mauser lead author of the study. "There is a plethora of unexplored and exciting application and research opportunities at the junction of these two fields."