How to decorate graphene film into silicon nanowires array for maximizing long-wave infrared photodetection?

As an exciting material with excellent electrical and optical properties, graphene is widely used in optoelectronics, especially for its absorption band into Terahertz region, therefore it can be used for long-wave infrared (LWIR) photodetectors based on silicon nanowires (Si-NWs) array. How to design the Si-NWs array to maximize the absorption for long-wave infrared (i.e. 8-14 μm) photodetection? To answer this question, in this work, the absorption for LWIR light by Si-NWs array, where both graphene and Au films are filled in its interstitial spaces within Si-NWs array as the active layers, is firstly simulated with finite-difference time-domain (FDTD) method by considering the anisotropic properties of graphene, and then experiments are done to confirm our simulation results. The effective area of graphene on the Si-NWs increases with the height of graphene film filled in the interstitial spaces of Si-NWs, thus to enhance the absorption of LWIR light. A perfect bimodal absorption-peak is obtained in the LWIR region from structure Si-NW/graphene/Au, and our simulation on photodetector Si-NWs/graphene/Au shows a responsivity R of 1.79 mA/W with a specific detectivity (D∗) of 8.41 × 10⁸ Jones under 25 mW/cm² 10 μm illumination. Also, a specific detectivity of 1.1571 × 10⁸ Jones is obtained from our photodetector Ag/Si-NWs/rGO/Au at room temperature, obviously, it is in agreement with our simulation results since some defects are introduced into both Si-NWs array and rGO during their actual manufacturing process. Thus, this work provides a groundwork for graphene-based long-wave infrared optoelectronic devices.