In this work a detailed analysis of the scattering cross-section of silicon Nano-particles with high number of excess carriers in the near and Mid Infrared (MIR) is provided. The effect of different radii of the nanoparticles on the resonance peaks is studied using Mie theory and verified using FDTD. The effect of the level of excess carrier generated on the scattering cross section also analyzed. The study reveals many useful characteristics for such particles which behaves as plasmonic particles in the MIR. Using this study, different particles are designed as scatters in the MIR based on specific dimensions and excess carriers level. These particles can be utilized for infrared spectroscopy of different application such as gas and biomedical sensing in the MIR.
Localized Surface Plasmon Resonance (LSPR) that occur in plasmonic nanoparticles due to interaction with electromagnetic waves at wavelengths larger than the nanoparticles themselves has been exploited in many application like solar cells, cancer treatment and spectroscopy due to the enhanced scattering and absorption cross sections that LSPR provides. Being able to control the resonance peaks of scattering in real time using light can be a valuable tool for sensing-related applications as well especially if it happens in the near and Mid-IR spectrum where most of the biological molecules can be sensed as such spectrum contains strong characteristic vibrational transitions of many important molecules . In this work presented here, we used silicon nanoparticles and increased the concentration of free excess carriers in the nanoparticles by light generation until the free carrier concentration was large enough to cause LSPR similar to what we get with nanoparticles made of Noble metals. The LSPR generated by Si nanoparticles with high concentration of free carriers caused the resonance peak to happen in near and mid IR. Depending on the level of carrier concentration which can be changed dynamically in real time, we can control the scattering resonance peak characteristics and position as shown in our work. Successful fabrication of the Silicon nanosphere is demonstrated as well.