| We report the development of a compact frequency sensitive THz detector using gated gratings on a 2-dimensional electron gas (2DEG) structure. The method is based on the resonant absorption of the 2-dimensional plasmon dependence on system dimension and the tunability of that dimension by depletion gating. The structure is based on earlier 1D gratings, but has the added advantages of polarization independence, low cost and high sensitivity. We realize the large area gated grid plasmonic structure on 2DEG material by using nanosphere self-assembly lithography. This fabrication method has not been widely developed for III-V processing but allows us to achieve large area sensitive detectors with tunability in the 1-4 THz range. We report on the protocols for fabricated large area nanosphere monolayers on GaAs, and subsequent processing for tunable aperture size. The device show strong plasmonic absorption with up to the 5th harmonic being observed. We examine how the plasmon absorption is dependent on grid periodicity versus duty cycle. Measurements at 80K show a transmission change of 25%, a large enhancement change compared to previous measurements of plasmonic absorption using 1-D grids on 2DEG systems. We also confirmed a magneto plasmon dispersion for this device. Our measurements and calculations find the surprising result that, the radiative damping frequency dependence enhances absorption at the higher harmonics such that they are comparable or larger than the absorption at the fundamental. We also demonstrate for the first time that self-assembled nanosphere devices can be used as low cost inductive grid filters in the infrared. |
