A sub-wavelength plasmonic Au–Ge grating was used to enhance the responsivity of Ge-based metal–semiconductor–metal photodetectors at infrared communication wavelengths. Furthermore, a finite-difference time-domain simulation was performed to optimize absorption of light by the detectors. Characterizations of the photoelectronic properties of the optimized device revealed high-performance photodetection with a responsivity of 0.38 A/W and an external quantum efficiency of 30% for 1.55 μm wavelength incident light. Moreover, an enhancement peak across three infrared telecommunication bands (C-band, L-band, and U-band) was achieved in the plasmon-enhanced photodetector. According to the simulation results of the optical absorption spectra, the distributions of electric field, and absorbed power, the enhancements of responsivity and quantum efficiency could be ascribed to the surface plasmons at the Au/Ge interface. These plasmons boosted inter-band transition and internal photoemission effect simultaneously, enabling high efficient photodetection around the C-band. The results of the fabricated devices demonstrated the potential of this approach for achieving high-performance Ge-based photodetectors.
