Influence of the thickness of the n-Si substrate and its doping level on the absorbing properties of silicon plasmon structures in the infrared range

Abstract

The absorption spectra of Si/SiO₂/Si₃N₄/Si⁺ and Si/SiO₂/Si⁺ structures with an island surface layer are calculated using the finite difference time domain method. The absorption spectra were modeled depending on the thickness of the substrate and its doping level. It was found that the thickness of the i-Si substrate does not affect the overall absorption of the structure. At the same time, an increase in the thickness of the n-Si substrate leads to an expansion of the absorption band with an intensity of more than 70%. It is established that the doping level of the substrate affects the absorption value of the structures and bandwidth with an absorption value above 80%. It is shown that a wide absorption band with intensity of more than 80% occurs at the doping level of the substrate in the range of 2 × 10¹⁹—5 × 10¹⁹ cm^–3 . Dispersion relations in the Si⁺/SiO2/Si⁺ structure with an unstructured surface layer are obtained. These dispersion relations may indicate the existence of plasmon oscillations in the system. It is established that a violation of the phase synchronization of the modes at both Si/dielectric interfaces at a significant difference between the doping levels of the substrate and the surface layer can lead to a decrease in the absorption.