High Efficiency Ultra-Thin Normal-Incidence Ge-On-Si Photodetector Based on Optical Metasurface

The much thicker intrinsic absorption layer (IAL) in normal-incidence Ge-on-Si photodetectors (NIPD) usually causes a contradiction between responsivity and bandwidth. In response to this issue, here, we simulate the design of an NIPD with geranium (Ge) layers based on a “fishnet” metasurface, leading to a reduced device thickness as thin as 380[Formula: see text]nm. The optical simulation results show that the light field can be perfectly localized in the 210[Formula: see text]nm IAL, and the absorptivity is as high as 99.45% at 1550[Formula: see text]nm, which is even better than bulk materials. Moreover, the electrical simulation results suggest that the horizontal size of the photosensitive region can be reduced to 11.2 [Formula: see text]m, while the responsivity of the photodetector is close to 1 A/W at −1[Formula: see text]V bias voltage, which is nearly 23 times that of a bulk device with the same thickness, and the 3dB bandwidth is up to 40[Formula: see text]GHz, which can be compared with waveguide photodetectors. Besides, this device also demonstrates a high signal-to-noise ratio with a low dark current of 28.68 nA, making it an excellent PD for opto-electrical communication.