A team of researchers from Pohang University of Science and Technology have developed near-infrared (NIR) photodiodes from silicon that are approximately one-third more sensitive than existing photodiodes. Existing NIR photodiodes are typically made of chemical materials that require separate cooling devices and are difficult to integrate. The researchers, led by professor Chang-Ki Baek, used hourglass-shaped silicon nanowires to increase silicon’s absorption of NIR light. Courtesy of Pohang University of Science and Technology. The upper inverted nanocone of the nanowires increases absorption probability by extending the dwell time of NIR-SWIR photons via the generation of whispering-gallery-mode resonances, whereas the lower nanocone with its low reflectance reabsorbs the light incident from surrounding nanowires. The nanowires showed 29% increased NIR photoresponse at a wavelength of 1000 nm in comparison to existing silicon photodiodes with flat panel. The newly developed photodiode was applied to a mobile heart-rate measurement system for demonstration. The photodiode demonstrated greater sensitivity and less than 1% error rate compared to existing photodiodes. The silicon used to create the photodiodes can be manufactured at low cost en masse, Baek said. Potential applications include lidar for autonomous vehicles, medical lasers, night vision, image sensors, and more. The research was published in Nature Electronics (www.dx.doi.org/10.1038/s41928-019-0317-z).