Broadband light management using low-Q whispering gallery modes in spherical nanoshells


Y. Yao, Yao, J., Narasimhan, V. K., Ruan, Z., Xie, C., Fan, S., and Cui, Y., “Broadband light management using low-Q whispering gallery modes in spherical nanoshells,” Nature Communications, vol. 3, pp. 664, 2012.


Light trapping across a wide band of frequencies is important for applications such as solar cells and photodetectors. Here, we demonstrate a new approach to light management by forming whispering-gallery resonant modes inside a spherical nanoshell structure. The geometry of the structure gives rise to a low quality-factor, facilitating the coupling of light into the resonant modes and substantial enhancement of the light path in the active material, thus dramatically improving absorption. Using nanocrystalline silicon (nc-Si) as a model system, we observe broadband absorption enhancement across a large range of incident angles. The absorption of a single layer of 50-nm-thick spherical nanoshells is equivalent to a 1-μm-thick planar nc-Si film. This light-trapping structure could enable the manufacturing of high-throughput ultra-thin film absorbers in a variety of material systems that demand shorter deposition time, less material usage and transferability to flexible substrates.


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