Enhanced optical absorption utilizing Ni gratings over germanium

This work investigates the optical response of a nickel (Ni) grating structure on germanium (Ge) substrate for near infrared (NIR) photodetection applications. A one-dimensional (1D) periodic Ni grating was analyzed using rigorous coupled-wave analysis (RCWA) implemented in MATLAB. The simulation results reveal that introducing uni-periodic Ni grating on a thin ~2 nm Ni film deposited on Ge, significantly enhances optical absorption. This enhanced absorption attributes to efficient light trapping and excitation of surface plasmon resonances at the Ni/Ge interface. Notably, the structure exhibited maximum absorption of 92.55% at 1600 nm for TM-polarized light, while TE polarization has very low absorption (~19%), confirming the strong polarization dependence of plasmonic coupling. These findings demonstrate that Ni gratings provide a promising route to enhance infrared absorption and hold potential for improving the efficiency of Ni-based optoelectronic and photonic devices, particularly infrared sensors and photodetectors.