A new photodetector mimics living organisms’ ability to sense colors, enhancing color filtering and selectivity. The biomimetic color photodetector, developed at Rice University’s Laboratory for Nanophotonics (LANP), uses an aluminum grating and is CMOS compatible. The new device responds directly to red, green and blue light, similar to the human eye. “Today’s color filtering mechanisms often involve materials that are not CMOS compatible, but this new approach has advantages beyond on-chip integration,” said LANP Director Dr. Naomi Halas. “It’s also more compact and simple, and more closely mimics the way living organisms ‘see’ colors.” A new biomimetic photodetector uses aluminum gratings like the one in an image from a scanning electron microscope. The light-filtering slits in the grating are about 100 nm wide. Images courtesy of Bob Zheng/Rice University. The researchers based their device in part on work done by a team from the Marine Biological Laboratory in Woods Hole, Mass., and the University of Maryland that studied cephalopods, which are color blind but thought to detect color through the skin. The new device uses a combination of band engineering and plasmonic aluminum gratings. With electron beam evaporation, a thin layer of aluminum was deposited onto a silicon photodetector and topped with an ultrathin oxide coating. Color selection through the detector is realized through interference effects between the plasmonic grating and the photodetector’s surface. Specifically, the device accumulates charge in an energy well, which, according to the study, “results in photocurrent gain and a plasmonic aluminum grating for photocurrent enhancement and red-green-blue color selectivity.” “With plasmonic gratings, not only do you get color tunability, you can also enhance near fields,” said LANP graduate researcher Bob Zheng. “The near-field interaction increases the absorption cross section, which means that the grating sort of acts as its own lens. You get this funneling of light into a concentrated area.” A diagram of the photodetector. Carefully tuning the oxide thickness, as well as the width and spacing of the slits allowed the researchers to either preferentially direct different colors into the silicon photodetector or reflect it back into free space. “Not only are we using the photodetector as an amplifier, we’re also using the plasmonic color filter as a way to increase the amount of light that goes into the detector,” Zheng said. The study notes that this work “provides a more intelligent way to design imaging sensors by integrating amplifiers and color filters directly into pixels.” The research was published in Advanced Materials (doi: 10.1002/adma.201401168). For more information, visit www.lanp.rice.edu.