Enhanced Absorption of a Patterned Thin Germanium Layer as a High-Contrast Grating

Absorbers such as photonic crystals, metasurfaces, and nanowires have been demonstrated to have important applications in solar cells, detectors, etc. The application of thin-layer-based absorbers to photodetectors is beneficial to simultaneously improve responsivity and 3 dB bandwidth. In this work, we propose a high-contrast-gratings-like absorber to achieve ultra-high absorption based on a thin Germanium layer. High absorption approximately 95% at wavelength 1310 nm is reached for TE-polarized incidence due to the interference of two guided modes, which is 4 times compared to the planar film with the same thickness. The high absorption of the absorber is also experimentally demonstrated. This work shows a new method for enhanced absorption with thin Germanium layer, indicating a promising prospect for high-efficiency photodetection.