Porous Si loaded with Ag nanoparticles for ultra-broadband infrared absorption and detection

Abstract

With the rapid development of semiconductor technology, silicon based infrared detector chips have been greatly optimized with the help of MEMS process. The infrared absorber, as the core part of thermal detector, requires infrared absorption characteristics such as wide spectrum and high absorption. In this paper, two kinds of porous silicon materials loaded with Ag nanoparticles (Si@AgNPs), honeycomb-like and forest-like, were constructed by chemical etching method. The experimental results and corresponding analyses illustrated that micro- and nano-porous structures of silicon with arbitrary sizes and random spatial positions can have a great guiding effect on the light waves, providing multiple reflections and scattering, allowing increased light propagation paths and generating light trapping effect, leading to enhanced infrared absorption in a wide spectral range. AgNPs are loaded, and the collective oscillation of free electrons resonates with incident photons, thereby exciting plasmon resonance effect, which can further improve the infrared absorption properties of the material. Benefiting from the synergistic effect of light trapping and plasmon resonance, the porous Si@AgNPs with honeycomb-like or forest-like structure both exhibited high absorption properties at 2.5–20 μm. Moreover, the honeycomb-like Si@AgNPs also possessed optical interference effect, which can further enhance the absorption, compared with the forest-like Si@AgNPs.