IR-Absorption in Ti/(Si)/SiO2/Si3N4/n+-Si Structures with an Island Surface Layer of Various Horizontal Geometries

Abstract

Absorption spectra of Ti/SiO₂/Si₃N₄/n⁺-Si structures with an island surface layer were calculated. It is shown that with increasing islands size, the absorption peak with maximum intensity shifts to a longer wavelength region and its width increases. This peak is probably associated with the excitation of plasmon oscillations in the surface island layer. It is shown that a structure with an island size of 3 μm and period of 6 μm absorbs 99% of the incident radiation at a wavelength of 6.2 μm. It is found that other absorption bands at 4 μm and 9.0–9.5 μm do not depend on islands sizes and are associated with vibrations of bonds  in the dielectric layer. An additional layer of undoped silicon with thickness up to 200 nm located between the Ti substrate and the SiO₂ layer slightly reduces the intensity and semi-width of the plasmonic absorption peak.