Influence of n-Si Substrate Thickness and Doping Level on the Absorbing Properties of Silicon Plasmon Structures in the Infrared Range

Absorption spectra of Si/SiO₂/Si₃N₄/Si⁺ and Si/SiO₂/Si⁺ structures with an island surface layer were calculated as a function of the substrate thickness and doping level using the finite difference time-domain method. It was found that the thickness of the i-Si substrate did not affect the overall absorption of the structures. At the same time, the absorption band expanded with an intensity >70% if the thickness of the n-Si substrate increased. It was established that absorption of the structures and the bandwidth with absorption >80% was affected by the substrate doping level. It was shown that a broad absorption band of intensity >80% persisted at a substrate doping level in the range 2·10¹⁹–5·10¹⁹ cm^–3. Dispersion relations of vibrations in the Si⁺/SiO₂/Si⁺ structure with an unstructured surface layer were analyzed to prove the existence of plasmon effects. It was established that a violation of the phase synchronization of the modes at both Si/dielectric interfaces with a significant difference between the doping levels of the substrate and surface layer could lead to decreased absorption.