Modified rigorous coupled-wave analysis for grating-based plasmonic structures with delta-thin conductive channel. Far- and near-field study

The modified rigorous coupled-wave analysis technique is developed to describe the optical characteristics of the plasmonic structures with the grating-gated delta-thin conductive channel in the far- and near-field zones of electromagnetic waves. The technique was applied for analysis of the resonant properties of AlGaN/GaN heterostructures combined with deeply-subwavelength metallic grating which facilitates the excitation of the two-dimensional plasmons in the THz frequency range. The convergence of the calculations at the frequencies near the plasmon resonances is discussed. The impact of the grating's parameters, including filling factor and thickness of the grating, on resonant absorption of the structure was investigated in details. The spatial distributions of electromagnetic field in a near-field zone were used for the evaluation of total absorption of the plasmonic structures separating contributions of the grating-gated two-dimensional electron gas and the grating coupler.