Abstract

Near infrared (NIR) light in the wavelength range longer than 1.4 μm has been increasingly important because of the high safety for eyes, and there have been strong demands to extend the detection range of a Si-based photodetector to that wavelength. Among several approaches, we have been developing a metasurface that strongly enhances small sub-band gap absorption of Si by optical resonances. We demonstrated that a hexagonal array of low-aspect-ratio Si nanodisks formed on a Si thin film holds anapole-like states arising from the interference between the toroidal dipole (TD) and electric dipole modes, and exhibit narrowband photocurrent enhancement in the sub-band gap range [1,2]. The highest absorptance predicted from simulation reaches ~45% in the wavelength range where the extinction coefficient of Si is very small.

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