Shells absorb light from all directions

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Improving the sensitivity of light sensors or the efficiency of solar cells requires fine-tuning of light capturing. KAUST researchers have used complex geometry to develop tiny shell-shaped coverings that can increase the efficiency and speed of photodetectors.

Many optical-cavity designs have been investigated to seek efficiencies of light: either by trapping the electromagnetic wave or by confining light to the active region of the device to increase absorption. Most employ simple micrometer- or nanometer-scale spheres in which the light propagates around in circles on the inside of the surface, known as a whispering gallery mode.

Former KAUST scientist Der-Hsien Lien, now a postdoctoral researcher at the University of California, Berkeley, and his colleagues from China, Australia and the U.S. demonstrate that a more complex geometry comprising convex nanoscale shells improves the performance of photodetectors by increasing the speed at which they operate and enabling them to detect light from all directions.

Surface effects play an important role in the operation of some devices, explains KAUST principal investigator, Jr-Hau He. Nanomaterials offer a way to improve performance because of their high surface-to-volume ratio. “However, although nanomaterials have greater sensitivity in light detection compared to the bulk, the light–matter interactions are weaker because they are thinner,” describes He. “To improve this, we design structures for trapping light.”

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