Hot-Carrier Enhancement in Silicon-Based Mid-Infrared Photodetectors via Periodic Inverted Pyramid Structures

The rapid advancement of technology has driven a growing demand for mid-infrared (MIR) photodetection. Although compound semiconductors are commonly used as sensing materials due to their excellent performance, they are costly and incompatible with standard complementary metal–oxide–semiconductor (CMOS) processes. This study presents a silicon-based photodetector incorporating inverted pyramid structures (IPSs) with varying sizes to induce strong localized surface plasmon resonance (LSPR), thereby enhancing hot-carrier generation and utilization. Experimental results reveal that applying a reverse bias of 1 V significantly improves the photoresponse. Moreover, by employing linear regression to analyze the instantaneous slope of a triangular-wave input, the originally slow-response waveform can be transformed into a fast-switching square wave, enabling quicker and more accurate detection of signal variations. Under illumination at a wavelength of 3.46μm, the IPS with a 14μm achieved a responsivity of 348.947 mA/sW, approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\times $</tex-math> </inline-formula> higher than that of the 8-4μm device (231.237 mA/sW), indicating that the structure size of the device plays a critical role in determining MIR response performance. COMSOL Multiphysics simulations further confirm that the 14-μm IPS exhibits an electric field intensity enhancement approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.4\times $</tex-math> </inline-formula> greater than the 8-μm structure and nearly <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20\times $</tex-math> </inline-formula> higher light intensity, outperforming the 10- and 12-μm counterparts. These findings confirm that a large IPS structure effectively enhances plasmonic resonance, thereby improving the overall photodetector responsivity.