Enhanced light trapping in Ge-on-Si-on-insulator photodetector by guided mode resonance effect

We propose a thin-film Ge-on-Si-on-insulator (Ge-on-SOI) photodetector with enhanced performance by exploiting induced guided mode resonance (GMR) employing Ge/SiO2 grating on Si-on-insulator (SOI). Numerically calculated results and theoretical analysis demonstrate that normal-incidence light can be coupled to the GMR and partly be converted into the spatial resonance mode which propagates along the whole properly designed grating structure. A notable absorption efficiency of higher than 70% is obtained in the photodetector with only 280 nm-thick Ge/SiO2 grating, which is about 35 times larger than that of the counterpart without the designed grating structure. Remarkable enhanced light absorption can be achieved in the device with very few grating periods, which significantly promotes a theoretical 3-dB bandwidth-efficiency product of ∼66 GHz. The result is promising for a compact Ge-on-Si photodetector design with low dark current, high-bandwidth, and high-responsivity.