Metasurface-Enabled Circular Light Propagation for Ultra-fast and Efficient Photodetection

We present a novel photodetector concept that involves the metasurface-induced scattering of a vertically incident photon beam wave front toward desired direction, facilitating guided light propagation, and resulting in enhanced detection efficiency in an ultra-thin photo absorption layer. The higher absorption efficiency is enabled by an enhanced photon density of states while substantially reducing the optical group velocity of light and extending the photon material interaction time compared to the traditional semiconductor photodetectors without an integrated metasurface. We have demonstrated a surface-illuminated Si PIN photodiode (PD) structure with a metasurface composed of etched isosceles triangle pillars using Finite Difference time Domain numerical simulation that can enable photon beam steering and guided light propagation. This increases the absorption efficiency in devices with very small diameter (<10µm), surpassing the capabilities of conventional omnidirectional scattering diffraction patterns. Our results show a 3.5-fold increase in internal quantum efficiency over wavelengths above 900 nm compared to the structure without metasurface. The absorption enhancement brought about by directional scattering is not limited to thin i-layers; it can potentially improve a wide range of photodiode geometries and structures.