Broadband Quantum Efficiency Enhancement of Al0.3InAsSb p–i–n Photodiodes with All-Dielectric Amorphous Germanium Metasurfaces

Transparent amorphous germanium (a-Ge) has emerged as a promising material for engineering nanostructures and metasurfaces, offering significant potential for enhancing the performance of photonic devices in the short-wavelength infrared (SWIR) spectrum. Herein, the successful application of a-Ge metasurfaces with a truncated pyramid profile to enhance the external quantum efficiency (EQE) of a digital alloy Al_0.3InAsSb p–i–n photodiode across a broad-wavelength range in the SWIR is presented. The experimental findings demonstrate a broadband enhancement in EQE. Two metasurface samples are designed to emphasize different-wavelength ranges. Notably, 51% improvement in EQE at 1550 nm and 125% enhancement at 2000 nm is achieved. Finite-difference time domain simulations show that the observed EQE improvement originates from the reduction of reflection and electromagnetic field enhancement. This study underscores the promising role of a-Ge metasurfaces in advancing the capabilities of SWIR photodetectors. It lays the groundwork for further exploration in optoelectronic device enhancements.