Laser doping method could enable new infrared imaging systems.
Researchers have tried a variety of methods to develop detectors that are responsive to a broad range of infrared light — which could form imaging arrays for security systems, or solar cells that harness a broader range of sunlight’s energy — but these methods have all faced limitations. Now, a new system developed by researchers at five institutions, including MIT, could eliminate many of those limitations.
The new approach is described in a paper published in the journal Nature Communications by MIT graduate student Jonathan Mailoa, associate professor of mechanical engineering Tonio Buonassisi, and 11 others.
Silicon, which forms the basis of most semiconductor and solar-cell technology, normally lets most infrared light pass right through. This is because the material’s bandgap — a fundamental electronic property — requires an energy level greater than that carried by photons of infrared light. “Silicon usually has very little interaction with infrared light,” Buonassisi says.
Various treatments of silicon can mitigate this behavior, usually by creating a waveguide with structural defects or doping it with certain other elements. The problem is that most such methods have significant negative effects on silicon’s electrical performance; only work at very low temperatures; or only make silicon responsive to a very narrow band of infrared wavelengths.
The new system works at room temperature and provides a broad infrared response, Buonassisi says. It incorporates atoms of gold into the surface of silicon’s crystal structure in a way that maintains the material’s original structure. Additionally, it has the advantage of using silicon, a common semiconductor that is relatively low-cost, easy to process, and abundant.