Absorption spectra of AlGaN/GaN grating-gate plasmonic crystals with a period from 1 µm to 2.5 µm were studied experimentally at T = 70 K using Fourier-transform infrared spectrometry. The plasmonic crystals exhibit distinct absorption lines of various plasmon harmonics across the 0.5 to 6 THz frequency range, tunable by gate voltage. Cumbersome and time-consuming electromagnetic simulations are usually needed to interpret or predict the grating-gate crystal spectra. In this work, we examine an analytical model and show that it can successfully describe the majority of existing experimental results. In this way, we demonstrate a new analytical platform for designing plasmonic crystals for THz filters, detectors, and amplifiers.
Keywords: AlGaN/GaN; THz Fourier spectroscopy; grating gate; plasmonic crystal.