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

Theoretically calculated IR absorption spectra of Ti/SiO₂/Si₃N4/n⁺-Si structures with an island surface layer were used to show that the absorption maximum broadened and shifted to longer wavelength as the n⁺-Si island size increased with a constant period of their placement on the surface. This peak was probably associated with excitation of plasmon oscillations in the surface island layer. A structure with an island size of 3 μm and a period of 6 μm was shown to absorb ~99% of the incident radiation at a wavelength practically equal to the period (6.2 μm). Other absorption bands at ~4 μm and 9.0–9.5 μm arose regardless of the island size and were associated with absorption in the SiO₂ layer. A layer of undoped silicon of thickness up to 200 nm located between the Ti substrate and SiO₂ layer slightly reduced the intensity and half-width of the plasmon absorption maximum.