Plasmonic Cloaking Hides PhotodetectorCategory: Science & Technology
Posted: May 22, 2012 09:45AM
In myth and legend, invisibility is achieved by way of magical objects and spells. In reality though, invisibility is accomplished by redirecting light around an area, using metamaterials, or by destructive interference, using plasmonics. Researchers at the Stanford School of Engineering have created an invisible photodetector using plasmonics.
Light is an electromagnetic phenomenon, which means the electromagnetic properties of a material affect how it interacts with light. In this case the researchers used silicon and gold to drop the reflective scattering of light from the photodetector by a factor of 100. The silicon is the actual photodetector, because light striking it creates an electric current, which is why it is used in solar panels. The gold is added to create a dipole, which means that it has the opposite charge to the silicon. When these two opposite charges interact, they cancel out, which causes the light that would normally scatter off of the materials to also cancel out. The key is to make sure the gold and silicon are in tune with each other, to actually cause the destructive interference.
Some of you may be wondering about how much this affects the silicon's ability to absorb light. After all, the gold is in a coating around the silicon nanowires. Even though gold is a reflective material, and the silicon is invisible, the light absorbed is only a forth of what it would be with the silicon being completely visible. That is a small enough drop to not affect the function of the photodetector.
What use is an invisible photodetector? This approach could be used to make digital cameras sharper, by reducing the crosstalk between neighboring pixels. Even without invisibility, this is a valuable discovery because it shows that metal-semiconductor pairings can be tuned to manipulate how they interact with light, which can affect solar cells, chip-scale lasers, and more.