Ultrathin Si-PD design with enhanced guided-mode resonance through slanted surface-relief gratings

We propose a new, to the best of our knowledge, surface-illuminated Si photodetector (PD) structure with slanted surface-relief grating that solves issues of low sensitivity to near-infrared (NIR) light and a trade-off between absorption layer thickness and high-speed response. The slanted grating, composed of tilted Si and SiO₂ arrays, efficiently deflects normally incident photons. When coupled with the lateral quasi-propagating mode in the absorption layer with a circular resonator shape, the photon lifetime is dramatically extended, resulting in increased absorption of NIR photons. Simulations have confirmed that even an absorption layer as thin as 300 nm can achieve an extremely high absorption of 29.2% at a wavelength of 1012 nm. We believe this innovative design can play a crucial role in the design of thin and high-speed PDs.