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 380nm. The optical simulation results show that the light field can be perfectly localized in the 210nm IAL, and the absorptivity is as high as 99.45% at 1550nm, 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 mu m, while the responsivity of the photodetector is close to 1 A/W at -1V bias voltage, which is nearly 23 times that of a bulk device with the same thickness, and the 3dB bandwidth is up to 40GHz, 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.