Influence of Metal Type and Layer Thickness on Absorption of Optical Radiation by Profiled Si3N4/Me/Si3N4 Structures

Abstract

The effect of the structural layer thickness on the absorption peak intensity and bandwidth in optical absorption spectra of Si₃N₄/Me/Si₃N₄ structures calculated by the finite differences in time domain method was found. The absorption increased by ~20% and the absorption band with an intensity of >90% broadened from 0.8 to 1.6 μm if the total thickness of the upper and lower layers of Si₃N₄ was reduced from 400 to 100 nm. It was shown that the width of the absorption band with an intensity of >90% was 4.3 μm in the absorption spectrum of an Si₃N₄/Ti/Si₃N₄ structure with a thickness of 50 nm for each layer. The maximum absorption decreased insignificantly from 99 to 96% if the thickness of the profiled Ti layer was reduced from 130 to 50 nm. It was shown that the absorption band broadening was associated with the effect of the Si₃N₄ thickness on interference processes in the Si₃N₄/Ti/Si₃N₄ structures. It was established that the absorption level in the range 8.3–13 μm depended on the metal type because of the dependence of the free-electron concentration on the metal type.