Highly Enhanced Near-Infrared Photodiode With Asymmetric Wave-Shaped Silicon Nanopillars

Silicon nanopillars (SiNPs) have attracted considerable interest due to their improved optical characteristics in the near-infrared (NIR) range. However, their high selectivity restricts their practical applications. In this study, we investigate how asymmetric wave-shaped sidewall SiNPs (WS SiNPs) can improve and broaden the spectral photoresponse by forming low-Q whispering gallery resonant modes. Tapered wave-shaped (T-WS) and symmetric WS (S-WS) SiNP structures were fabricated using a precise etching control process. The wavelength with peak responsivity shifts from 865 nm for S-WS SiNPs to 840 nm for T-WS SiNPs, indicating that the resonant frequency is influenced by the gradual change in diameter of the WS SiNPs. Furthermore, the asymmetric design supports multiple resonant wavelengths, resulting in a broader photoresponse compared to the symmetric design. Consequently, the S-WS SiNP photodetector (PD) achieves the highest average external quantum efficiency (EQE) of 90.1% within the narrow range of 860–865 nm, whereas the T-WS SiNP PD reaches 89.3% over a wider range from 720 to 840 nm. These findings are supported by 3-D numerical simulations. This research not only provides valuable foundational elements for light-trapping structures but also opens avenues for the design of silicon-based optoelectronic devices.