An extending broadband near-infrared absorption of Si-based deep-trench microstructures

We design and investigate numerically a Si-based deep-trench microstructure covered with continuous thin gold (Au) films. It breaks through the absorption limitation of Si material and greatly extends the near-infrared (NIR) absorption range to 1500 nm. By the simulated distributions of electric-field intensity, we observe clearly the excitation of surface plasmon polaritons and the standing wave resonance of plasmon cavity formed inside the deep trench, by which we explain the extending broadband NIR absorption well. We further discuss the influence of trench depth on the cavity mode and NIR absorption in detail. By combination of the proposed microstructures, it is a promising approach to realize an extending broadband and high NIR photoresponse in Si-based detectors.